Ecology of the Biosphere BIO 44 by Owen Borville September 23, 2025
Ecology is the study of interactions of living organisms with their environment and understanding scientifically the distribution and abundance of living things in the physical environment. Ecologists are concerned with factors that influence the survival of endangered species and sometimes use mathematical models to predict their survival with conservation methods. Conservation management of ecology requires accurate data collection of current population size, factors affecting reproduction such as physiology and behavior, habitat requirements such as plants and soils, and human influences. Levels of ecology study that often overlap include organisms, populations, communities, ecosystems, and the biosphere of Earth.
Organismal ecology involves the study of abilities that allow individuals to live in specific habitats, including morphological, physiological, and behavioral abilities, and symbiotic relationships between two different organisms that depend on each other.
Population ecology involves a population or a group of interbreeding organisms that are members of the same species living in the same area at the same time. Organisms of the same species are also called conspecifics. A population is identified by where it lives and its area of population may have natural or artificial boundaries. Natural boundaries might be rivers, mountains, or deserts, while artificial boundaries may be mowed grass, manmade structures, or roads. The study of population ecology focuses on the number of individuals in an area and how and why population size changes over time.
The ecology of biological communities consists of the different species within an area, typically three-dimensional space, and the interactions within and among these species. Community ecologists are focused on the processes driving these interactions and their consequences. Questions about conspecific interactions often focus on competition among members of the same species for a limited resource. Ecologists also study interactions between various species, and members of different species are called heterospecifics. Examples of heterospecific interactions include predation, parasitism, herbivory, competition, and pollination, These interactions can have regulating effects on population sizes and can impact ecological processes and diversity
Mutualism is a form of long-term relationship between two species from which each species benefits. For mutualism to exist between individual organisms, each species must receive some benefit from the other as a consequence of the relationship. The Karner blue butterfly larvae have a mutualistic relationship with ants, where the ants protect the larvae from predators while the larvae secrete ant-like pheromones and a carbohydrate-rich substance that is an energy source for the ants.
Ecosystem ecology is related to and a part of organismal, population, and community ecology. The ecosystem is composed of all of the biotic components (living things) in an area along with the abiotic components (nonliving things) of that area. Abiotic components include air, water, and soil. Ecosystem biologists focus on how nutrients and energy are stored and how they move among organisms and through the surrounding atmosphere, soil, and water.
The biosphere includes all of the parts of the Earth inhabited by life. The biosphere extends into the atmosphere and into the depths of the oceans. Many abiotic forces influence where life can exist and the types of organisms found in different parts of the biosphere. The abiotic factors that influence the distribution of biomes are large areas of land with similar climate, flora, and fauna.
Biogeography is the study of the geographic distribution of living things and the abiotic factors that affect their distribution. Abiotic factors include temperature and rainfall and these are based on location and elevation. As these variables change, the type of plant and animal communities change as one travels across the earth. Warmer and moister environments produce different living things than colder and dryer environments. Ecologists and biogeographers study patterns of species distribution. There are no biospecies that exist everywhere or in every environment. Endemic species are species that are only found in specific geographic areas of specific size. Generalist species can live in a wide variety of geographic environments.
Species distribution patterns are based on biotic and abiotic factors. Species distribution patterns can also be identified in their absence, where certain species of animals are not found. Species can become extinct in certain locations because of changing environmental conditions. Like animals, plants can also be endemic or generalist species. Endemic plants are only found in specific regions of the Earth, while generalist species are found in many regions. Isolated land masses such as Australia, Hawaii, and Madagascar often have large numbers of endemic plant species, and some of these are endangered due to human activity.
Energy sources from the sun are captured by green plants, algae, cyanobacteria, and photosynthetic protists as they convert solar energy into chemical energy needed by all living things. Therefore light availability is an important force in energy sources. Plants have adaptations or designed abilities that allow their flowers to bloom during the times of the year when the sun is more available.
In aquatic ecosystems, sunlight may be partially or fully blocked by water, plants, particles, or microorganisms, particularly at deeper depths. Photosynthesis cannot take place if the sunlight is blocked, so there must be another way that aquatic plants can receive sunlight. Aquatic plants have photosynthetic parts on or near the surface of the water where sunlight can be absorbed, such as the water lily. In the deep sea surface, some bacteria can extract energy from inorganic chemicals in hydrothermal vent environments in the absence of light for photosynthesis.
Ocean upwelling allows deep ocean waters to rise by way of prevailing winds blown along surface waters near a coastline. The ocean upwelling allows energy and nutrients in dead organisms on the ocean bottom to be lifted up and recycled to the top of the ocean surface to be used by living
organisms in the ocean waters.
In freshwater lakes, nutrients are recycled in response to air temperature and wind changes. The nutrients at the bottom of lakes are recycled twice each year during the spring and fall turnover. The spring and fall turnover are seasonal processes that recycle nutrients and oxygen from the bottom of a freshwater lake to the top of the lake. These turnovers are caused by the formation of a thermocline, layers of water with temperatures that are significantly different from those above and below it.
Many northern lakes’ surface freezes in the winter, but the underlying water is warmer and denser at the deepest layer at 4 degrees C. In the spring, the air temperature increases and the surface ice melts. When the surface water reaches 4 degrees, it becomes denser, heavier, and sinks toward the bottom. The water at the bottom of the lake is then displaced by heavier and denser surface water and rises to the top. The water rises and brings sediments and nutrients with it. This is called spring turnover. In the summer, the warmest water is at the lake surface. In the fall, as air temperatures drop, the temperature of the lake water cools to 4 degrees and this causes fall turnover as the heavy cold water sinks and displaces the water at the bottom. The oxygen rich water at the surface of the lake then moves to the bottom of the lake, while the nutrients at the bottom of the lake rise to the surface. During the winter, the oxygen at the bottom of the lake is used by decomposers and other organisms requiring oxygen, such as fish. Ice transparency allows some light to penetrate the surface for photosynthesis, particularly for algae.
Temperature affects the physiology of organisms as well as the density and state of water. Few living things can survive at temperatures below zero degrees Celsius or above 45 degrees Celsius due to metabolic functions of the body. Enzymes can only function within specific temperature ranges, so that the body must maintain a certain temperature or the environment must stay at a certain temperature for the organism to survive to allow metabolic function. Living things sometimes have particular protections against extreme temperature through dormant states of hibernation or reptilian torpor. Some bacteria called extremophiles can withstand extremely hot temperatures in geysers.
The temperature of water and air can limit the distribution of living things. When temperature fluctuates, animals can respond by migration, or moving to a more suitable environment. Migration is practiced by many animals, including those who live in seasonally cold environments. Migration helps animals survive extreme temperatures, locate food, and find mates. Migratory birds such as the arctic tern are a good example, along with monarch butterflies, and mammals such as reindeer. Some animals lack or have limited migratory skills like amphibians and reptiles. There are also risks in migration and large energy consumption, so some animals choose not to migrate.
Some animals hibernate or estivate to survive extreme temperatures. Hibernation enables animals to survive extreme cold temperatures, and estivation allows animals to survive extremely hot and dry temperatures. Animals that hibernate or estivate enter a state known as a torpor, a condition in which their metabolic rate is significantly reduced, allowing the animal to wait until the environment is more suitable for survival. Some amphibians have chemicals in their cells that prevent them from freezing or bursting, therefore preserving their integrity.
Water is required by all living things because it is critical for cellular processes. Terrestrial organisms lose water to the environment, so they must have methods of retaining water. Plants have leaf hairs and a waxy cuticle that helps prevent water loss from transpiration and convection. Freshwater organisms have abilities to maintain solute concentrations in their bodies by excreting dilute urine. Marine organisms have the ability to regulate solute concentration in their bodies to retain water and release solutes into the environment.
Inorganic nutrients such as nitrogen and phosphorus are important in determining the distribution and abundance of living things. Plants obtain inorganic nutrients from the soil when water moves into the plant through the roots. Soil structure and particle size of soil, soil pH, and soil nutrient content together all play an important role in the distribution of plants. Animals obtain inorganic nutrients from the food they consume, particularly plants and other animals. Animal distributions are related to the distribution of the food they eat, as some animals follow their food resource as it moves through the environment.
Terrestrial animals obtain oxygen from the air they breathe, but oxygen availability can be limited at high elevations. In aquatic systems, the concentration of dissolved oxygen is related to water temperature and the speed at which water moves, as cold water has more dissolved oxygen than warmer water. Salinity, currents, and tidal changes can be important abiotic factors in aquatic ecosystems.
Wind can be an important abiotic factor because it influences the rate of evaporation, transpiration, and convective heat loss from the surface of all organisms. The physical force of wind is also important because it can move soil, water, or other abiotic factors, as well as an ecosystem’s organisms.
Fire is another terrestrial factor that can be an important agent of disturbance in terrestrial ecosystems. Some organisms have the ability to survive fire and require high heat associated with fire to complete a part of their life cycle, such as pine trees and cones.
Abiotic factors of plant growth include temperature, moisture, and available organic matter. Net primary productivity is an estimation of all of the organic matter available as food and it is calculated as the total amount of carbon fixed per year minus the amount that is oxidized during cellular respiration. In terrestrial environments, net primary productivity is estimated by measuring the above-ground biomass per unit area, which is the total mass of living plants, excluding roots (whose mass is difficult to measure). Net primary productivity is an important variable when considering differences in biomes.
Annual biomass production is directly related to the abiotic components of the environment. Environments with the greatest amount of biomass produce conditions in which photosynthesis, plant growth, and the resulting net primary productivity are optimized. These environments are warm, wet, and photosynthesis can occur at a high rate, enzymes can work most efficiently, and stomata can remain open without excessive transpiration. Therefore, carbon dioxide intake is maximized and high biomass is produced. The above-ground biomass provides habitat and food for other living organisms. In contrast, dry and cold environments have lower rates of photosynthesis and less biomass, affecting the ability of animals and plants to live there.
Biomes of the Earth are divided into two major groups: terrestrial and aquatic. Terrestrial biomes are based on land, while aquatic biomes include both ocean and freshwater biomes. Terrestrial biomes are distinguished by characteristic temperatures and precipitation amounts to determine the abiotic factors of each biome. The same biome can occur in geographically distinct areas with similar climates.
Tropical wet forests or tropical rainforests are found in equatorial regions where the vegetation is made of plants with broad leaves that fall and are replaced throughout the year. Unlike the trees of deciduous forests, the trees in this biome do not have seasonal loss of leaves associated with variations in temperature and sunlight. These forests are evergreen year-round.
Temperature in tropical wet forests range from 20 to 34 degrees Celsius, which is a relatively small margin and allows year-round plant growth instead of seasonal growth as in other biomes. There is also a constant amount of daily sunlight throughout the year, which provides more solar radiation and plant growth.
The annual rainfall in tropical wet forests ranges from 125 to 660 cm (50-200 in) with some variation in wet months and dry months. Tropical wet forests have high net primary productivity because the annual temperatures and precipitation values in these areas are ideal for plant growth. The high productivity leads to large biomass and large species diversity. There are more tree species than any other biome, up to several hundred species.
There are horizontal layers within the tropical wet forest biome. On the forest floor is a sparse layer of plants and decaying plant matter. Above that is an understory of short shrubby foliage. A layer of trees rises above this understory and is topped by a closed upper canopy, the uppermost overhead layer of branches and leaves. Within these layers are diverse complex habitats of plants, fungi, animals, and other organisms in the tropical wet forests.
Epiphytes are plants that grow on other plants and are usually not harmed. Epiphytes are found in tropical wet forest biomes. Many species of animals use the variety of plants and the complex structure of the wet forests for food and shelter, both on the ground and above ground within the trees.
Savannas are grasslands with scattered trees and are located in Africa, South America, and northern Australia. Savannas are commonly hot, tropical areas with temperatures averaging from 24 to 29 degrees C (75-84 F) and annual rainfall of 10 cm to 40 cm (4-16 in). Savannas have an extensive dry season and forest trees do not grow as well as they do in the tropical wet forest. Savannas have grasses and forbs (herbaceous flowering plants) and few trees. Fires are common in grasslands, however plants have the ability to quickly regrow after a fire.
Subtropical deserts exist between 15 and 30 degrees north and south latitude along the Tropics of Cancer and Capricorn (Sahara-Arabian Deserts, Mexican and southwest USA deserts, Australia’s Great Simpson Desert and Great Victoria Desert, Namib Desert, Central Asian deserts, and the Atacama Desert and Patagonia of South America. This biome is very dry and sometimes evaporation exceeds precipitation. Subtropical hot deserts can have daytime soil surface temperatures above 60 degrees C (140 F) and nighttime temperatures at 0 C (32 F). This large temperature variation is due to the lack of atmospheric water. Cold deserts can range from 25 C and -30 C. Subtropical deserts commonly have annual precipitation less than 30 cm (12 in).
The vegetation and low animal diversity in this biome is a result of low and unpredictable precipitation. Many plants in this biome are annual that grow and reproduce quickly during precipitation and die when precipitation disappears. Many plants in this biome can conserve water with deep roots, reduced foliage, and water-storing stems. Seed plants in the desert produce seeds that can be in dormancy for extended periods during rains. Desert animals stay active at night when it is cooler and burrow in the ground.
The chaparral (scrub forest) is found in California, the Mediterranean Sea, and along the southern coast of Australia. The annual rainfall in this biome is 65 cm to 75 cm (25-29 in), and the majority of the rain falls in the winter. Summers are very dry and many chaparral plants are dormant during the summertime. The chaparral vegetation is dominated by shrubs that can endure fires, the ashes of which are rich in nutrients like nitrogen that fertilize the soil and promote plant growth.
Temperate grasslands (called prairies) are found throughout central North America, and Eurasia (called steppes). Temperate grasslands have hot summers and cold winters. The annual temperature variation produces specific growing seasons for plants, where plant growth is possible when temperatures are warm enough and enough water is available. This growing season occurs during the spring, summer, and fall. During the winter, temperatures are low, and water in the form of ice is not available for plant growth.
Annual precipitation ranges from 25 cm to 75 cm (10-30 in). Because of relatively lower annual precipitation in temperate grasslands, there are few trees except for those found growing along rivers or streams. The dominant vegetation is grasses dense enough to sustain populations of grazing animals. The vegetation is very dense and the soils are fertile because the subsurface of the soil is packed with the roots and rhizomes (underground stems) of these grasses. The roots and rhizomes act to anchor plants into the ground and replenish the organic material (humus) in the soil when they die and decay.
Fires in temperate grasslands are caused by natural lightning. When the fires end, vegetation is converted to scrub and dense forests with drought-tolerant tree species. Conservation management in temperate grasslands often uses controlled burns to limit tree growth in favor of grasses.
Temperate forests are the most common biome in eastern North America, Western Europe, Eastern Asia, Chile, and New Zealand. This biome is found through the mid-latitude regions. Temperatures range from -30 C to 30 C (-22 F to 86 F) and drop to below freezing periodically during cold winters. Temperate forests have growing seasons during the spring, summer, and early fall. Precipitation is constant at 75 cm to 150 cm (29-59 in) annually.
Because of the moderate annual rainfall and temperatures, deciduous trees are the dominant plant in this biome. Deciduous trees lose their leaves each fall and remain leafless in the winter. Thus, no photosynthesis occurs in the deciduous trees during the dormant winter period. Each spring, new leaves appear as the temperature increases. Because of the dormant period, the net primary productivity of temperate forests is less than that of tropical wet forests. In addition, temperate forests show less diversity of tree species than tropical wet forest biomes.
The trees of temperate forests leaf out and shade much of the ground, but this biome is more open than tropical wet forests because most trees in the temperate forests do not grow as tall as the trees in tropical wet forests. The soils of temperate forests are rich in inorganic and organic nutrients. This is due to the thick layer of leaf litter on the forest floors, which does not develop in tropical rainforests. As this leaf litter decays, nutrients are returned to the soil. The leaf litter also protects soil from erosion, insulates the ground, and provides habitats for invertebrates and their predators.
Boreal forest (taiga or coniferous forest) is found south of the Arctic Circle and across most of Canada, Alaska, Russia, and northern Europe. This biome has cold, dry winters and short, cool, wet summers. The annual precipitation is from 40 cm to 100 cm (15-39 in) and usually takes the form of snow. Little evaporation occurs because of the cold temperatures.
The long and cold winters in the boreal forest have led to the predominance of cold-tolerant cone-bearing (coniferous) plants. These are evergreen coniferous trees like pines, spruce, and fir, which retain their needle-shaped leaves year-round. Evergreen trees can photosynthesize earlier in the spring than deciduous trees because less energy from the sun is required to warm a needle-like leaf than a broad leaf. This benefits evergreen trees, which grow faster than deciduous trees in the boreal forest. In addition, soils in the boreal forest tend to be acidic with little available nitrogen. Leaves are a nitrogen-rich structure and deciduous trees must produce a new set of these nitrogen-rich structures each year. Therefore, coniferous trees that retain nitrogen-rich needles may have a competitive advantage over the broad-leafed deciduous trees.
The net primary productivity of boreal forests is lower than that of temperate forests and tropical wet forests. The above-ground biomass of boreal forests is high because these slow-growing tree species are long-lived and accumulate a large standing biomass over time. Plant species diversity is less than that seen in temperate forests and tropical wet forests. Boreal forests lack the pronounced elements of the layered forest structure seen in tropical wet forests. The structure of a boreal forest is often only a tree layer and a ground layer. When conifer needles are dropped, they decompose more slowly than broad leaves, therefore, fewer nutrients are returned to the soil to fuel plant growth.
The Arctic tundra is north of the subarctic boreal forest and is located throughout the Arctic regions of the northern hemisphere. The average winter temperature is -34 C (-29 F) and the average summer temperature is from 3 C to 12 C (37 F to 52 F). Plants in the arctic tundra have a very short growing season of about 10 to 12 weeks.
However, during this time, there are almost 24 hours of daylight and plant growth is rapid. The annual precipitation of the Arctic tundra is very low with little annual variation in precipitation. And as in the boreal forests, there is little evaporation due to the cold temperatures.
Plants in the Arctic tundra are generally low to the ground. There is little species diversity, low net primary productivity, and low above-ground biomass. The soils of the Arctic tundra may remain in a perennially frozen state referred to as permafrost. The permafrost makes it impossible for roots to penetrate deep into the soil and slows the decay of organic matter, which inhibits the release of nutrients from organic matter. During the growing season, the ground of the Arctic tundra can be completely covered with plants or lichens.
The oceans in aquatic biomes are divided into several different zones. The entire ocean’s open water is called the pelagic realm (or zone). The benthic realm or zone extends along the ocean bottom from the shoreline to the deepest parts of the ocean floor. Within the pelagic realm is the photic zone, which is the portion of the ocean that light can penetrate (200m/650ft). At depths greater than 200 meters, light cannot penetrate, and this zone is referred to as the aphotic zone. The majority of the ocean is aphotic and lacks sufficient light for photosynthesis. The deepest part of the ocean is the Challenger Deep in the Mariana Trench, western Pacific Ocean (11,000 m/ 6.8 miles deep). Below the aphotic zone is the abyssal zone, the deep ocean region between 3,000 and 6,500 meters (9,842 to 21,325 feet) deep, characterized by complete darkness, freezing temperatures (around 2-6°C), and immense hydrostatic pressure.
The ocean is the largest marine biome. The ocean is a single body of salty water relatively uniform in chemical composition of a weak solution of mineral salts and decayed biological matter. Within the ocean, coral reefs are a second type of marine biome. Estuaries that are found in coastal areas where salt water and fresh water mix, are a third unique marine biome.
The ocean has physical diversity and a significant influence on plants, animals, and other organisms. The ocean is divided into different zones. The intertidal zone is between high and low tide and is the closest region to land. This zone can be sandy, rocky, or muddy. The intertidal zone is an extremely variable environment because of action of tidal ebb and flow. Organisms are exposed to air and sunlight at low tide and are underwater most of the time, especially during high tide. Living things in the intertidal zone can be dry for long periods of time. The shore of the intertidal zone may also be repeatedly struck by waves, and the organisms found there can withstand damage from their pounding action. The exoskeletons of shoreline crustaceans such as the shore crab are tough and protect them from desiccation (drying out) and wave damage. Another consequence of pounding waves is that few algae and plants establish themselves in the constantly moving rocks, sand, or mud.
The neritic zone extends from the intertidal zone to depths of 200 m (650 ft) at the edge of the continental shelf underwater. Since light can penetrate this depth, photosynthesis can still occur in the neritic zone. The water here contains silt and is well-oxygenated, low in pressure, and stable in temperature. Phytoplankton and floating Sargassum (seaweed) provide a habitat for some sea life found in the neritic zone. Zooplankton, protists, small fishes, and shrimp are found in the neritic zone and are the base of the food chain.
Beyond the neritic zone is the open ocean area known as the pelagic or open oceanic zone. Within this zone is thermal stratification where warm and cold waters mix because of ocean currents. Abundant plankton serve as the base of the food chain for larger animals such as whales and dolphins. Nutrients are scarce and this is a relatively less productive part of the marine biome. When photosynthetic organisms and the protists and animals that feed on them die, their bodies fall to the bottom of the ocean, where they remain. Unlike freshwater lakes, most of the open ocean lacks a process for bringing the organic nutrients back up to the surface (although there are some ocean upwellings). The majority of organisms in the aphotic zone include sea cucumbers (Echinodermata) and other organisms that survive on the nutrients contained in the dead bodies of organisms in the photic zone.
Beneath the pelagic zone is the benthic realm, the water region beyond the continental shelf that starts at the shoreline and extends to the deepest regions of the ocean. The bottom of the benthic realm is composed of sand, silt, and dead organisms. Temperature decreases, remaining above freezing, as water depth increases. This is a nutrient-rich portion of the ocean because of the dead organisms that fall from the upper layers of the ocean. Because of this high level of nutrients, a diversity of fungi, sponges, sea anemones, marine worms, sea stars, fishes, and bacteria exist.
The deepest part of the open ocean is the abyssal zone (4,000 m or greater). The abyssal zone is very cold and has very high pressure, very low or no oxygen content, and high nutrient content as the dead and decomposing material drifts down from the layers above. There are a variety of invertebrates and fishes found in this zone, but the abyssal zone does not have plants because of the lack of light. Hydrothermal vents are found primarily in the abyssal zone. Chemosynthetic bacteria utilize the hydrogen sulfide and other minerals emitted from the vents to produce biomass. These chemosynthetic bacteria use various molecules as an energy source and serve as the base of the food chain found in the abyssal zone.
Coral reefs are ocean ridges formed by marine invertebrates, comprising mostly of cnidarians and mollusks living in warm shallow waters within the photic zone of the ocean. They are found within 30 degrees north and south of the equator. The Great Barrier Reef is the best known and largest reef system in the world (it is visible from space). This massive and ancient reef is located several miles off the northeastern coast of Australia. Other coral reef systems are fringing islands, which are directly adjacent to land, or atolls, which are circular reef systems surrounding a former landmass that is now underwater. The coral organisms (Cnidaria) are colonies of saltwater polyps that secrete a calcium carbonate skeleton. These calcium-rich skeletons slowly accumulate, forming the underwater reef. Corals found in shallower waters (60 m/ 200 ft) have a mutualistic relationship with photosynthetic unicellular algae. The relationship provides corals with the majority of the nutrition and the energy they require. The waters in which these corals live are nutritionally poor and, without this mutualism, it would not be possible for large corals to grow. Some corals living in deeper and colder water do not have a mutualistic relationship with algae. These corals attain energy and nutrients using stinging cells called cnidocytes on their tentacles to capture prey.
It is estimated that more than 4,000 fish species inhibit coral reefs. These fishes can feed on coral, the cryptofauna invertebrates found within the calcium carbonate substrate of the coral reefs, or the seaweed and algae that are associated with the coral. In addition, some fish species inhabit the boundaries of a coral reef. These species include predators, herbivores, and planktivores, which consume planktonic organisms such as bacteria, archaea, algae, and protists floating in the pelagic zones.
Estuaries are biomes that occur where a source of fresh water, such as a river, meets the ocean. Therefore, both fresh water and salt water are found in the same area. Mixing results in a diluted, brackish saltwater. Estuaries form protected areas where many of the young offspring of crustaceans, mollusks, and fish begin their lives, which also creates important breeding grounds for other animals. Salinity is a very important factor that influences the organisms and the adaptations of the organisms found in estuaries. The salinity of estuaries varies considerably and is based on the rate of flow of its freshwater sources, which may depend on the seasonal rainfall. Once or twice a day, high tides bring salt water into the estuary. Low tides occurring at the same frequency reverse the current of salt water.
Many estuarine plant species are halophytes, or plants that can tolerate salt conditions. In some halophytes, filters in the roots remove the salt from the water that the plant absorbs. Other plants are able to pump oxygen into their roots. Animals such as mussels and clams have abilities to deal with saline waters. When these animals are exposed to low salinity, they stop feeding, close their shells, and switch from aerobic respiration (gills for oxygen) to anaerobic respiration (does not require oxygen and takes place inside the animals cells). When high tide returns to the estuary, the salinity and oxygen content of the water increases, and these animals open their shells, begin feeding, and return to aerobic respiration.
Freshwater biomes include lakes and ponds of standing water as well as rivers and streams of flowing water. They also include wetlands. Humans rely on freshwater biomes to provide ecosystem benefits, which are sources of drinking water, crop irrigation, sanitation, and industry. Lakes and ponds are connected with abiotic and biotic factors influencing their terrestrial biomes.
Lakes and ponds can be a few square meters to thousands of square kilometers in area. Temperature is an important abiotic factor affecting living things found in lakes and ponds. In the summer, as we have seen, thermal stratification of lakes and ponds occurs when the upper layer of water is warmed by the sun and does not mix with the deeper, cooler water. Light can penetrate within the photic zone of the lake or pond. Phytoplankton (algae or cyanobacteria) are found here and carry out photosynthesis, providing the base of the food web of lakes and bonds. Zooplankton, such as rotifers and larvae and adult crustaceans, consume these phytoplankton. At the bottom of lakes and ponds, bacteria in the aphotic zone break down dead organisms that sink to the bottom.
Nitrogen and phosphorus are important limiting nutrients in lakes and ponds and are therefore determining factors in the amount of phytoplankton growth that takes place in lakes and ponds. When there is a large input of nitrogen and phosphorus (from sewage and runoff from fertilized lawns and farms) the growth of algae increases dramatically, resulting in a large accumulation of algae called an algal bloom. Algal blooms can become so extensive that they reduce the light penetration in water. They may also release toxic byproducts into the water, contaminating any drinking water taken from that source. In addition, the lake or pond becomes aphotic, and photosynthetic plants cannot survive. When algae die and decompose, severe oxygen depletion of the water occurs. Fishes and other organisms that require oxygen are then more likely to die, resulting in a dead zone. Lake Erie and the Gulf of Mexico represent freshwater and marine habitats where phosphorous control and storm water runoff pose significant environmental challenges.
Rivers and streams are continuously moving bodies of water that carry large amounts of water from the source, or headwater, to a lake or ocean. The largest rivers include the Nile River in Africa, the Amazon River in South America, and the Mississippi River in North America. Abiotic features of rivers and streams vary along the length of the river or stream. Streams begin at a point of origin referred to as source water. The source water is usually cold, low in nutrients, and clear. The channel (stream width) is narrower than at any other place along the length of the river or stream. Because of this, the current is often faster here than at any other point of the river or stream.
The fast-moving water results in minimal silt accumulation at the bottom of the river or stream. Therefore, water is usually clear and free of debris. Photosynthesis here is mostly attributed to algae that are growing on rocks. The swift current inhibits the growth of phytoplankton. An additional input of energy can come from leaves or other organic material that fall downstream into the river or stream, as well as from trees and other plants that border the water. When the leaves decompose, the organic material and nutrients in the leaves are returned to the water. Plants and animals have features that allow them to survive the fast-moving water. Some species have flat bodies and clawed legs that allow them to attach to submerged rocks in the stream.
Downstream, the river or stream widens and the current slows because of a gradient decrease and volume increase as tributaries combine and sedimentation increases. Phytoplankton can also be suspended in slow-moving water and the water will be less clear. The water is also warmer downstream. Worms and insects can be found burrowing into the mud. Predator vertebrates include waterfowl, frogs, and fishes, who use these slow moving waters to find prey using their senses of taste or chemical sensing instead of vision.
Wetlands are environments in which the soil is either permanently or periodically saturated with water. Wetlands are different from lakes because wetlands are shallow bodies of water whereas lakes vary in depth. Emergent vegetation consists of wetland plants that are rooted in the soil but have portions of leaves, stems, and flowers, extending above the water’s surface. There are several types of wetlands including marshes, swamps, bogs, mudflats, and salt marshes. The three shared characteristics among these types of wetlands are their hydrology, hydrophytic vegetation, and hydric soils.
Freshwater marshes and swamps are characterized by slow and steady water flow. Bogs, however, develop in depressions where water flow is low or non-existent. Bogs usually occur in areas where there is a clay bottom with poor percolation of water. Percolation is the movement of water through the pores in the soil or rocks. The water found in a bog is stagnant and oxygen-depleted because the oxygen used during the decomposition of organic matter is not readily replaced. As the oxygen in the water is depleted, decomposition slows. This leads to a buildup of acids and a lower water pH. The Lower pH creates challenges for plants because it limits the available nitrogen. As a result, some bog plants capture insects in order to extract the nitrogen from their bodies. Bogs have low net primary productivity because the water found in bogs has low levels of nitrogen and oxygen.
Climate and Its Effects on Biomes and Climate Change: All biomes are affected by global conditions such as climate. Global climate change is the term used to describe the altered global weather patterns, especially a worldwide increase in temperature and resulting changes in the climate, due to rising levels of atmospheric carbon dioxide.
Climate refers to the long-term predictable atmospheric conditions of a specific area. The climate of a biome is characterized by having consistent seasonal temperature and rainfall ranges. Weather refers to the conditions of the atmosphere during a short period of time, such as one to two days. Longer-range weather forecasts are usually unreliable.
Global climate change is focused on (1) evidence of current and past global climate change (2) drivers of global climate change (3) documented results of climate change.
Evidence for past global climate change includes vertical ice core samples from Antarctica, the South Polar ice cap. Ice core samples are drilled thousands of meters deep. Air bubbles and other biological evidence in the core samples can reveal information about temperature and carbon dioxide levels in the past. Evidence from the core samples shows evidence of fluctuating or varying temperature in the past.
In addition to ice core samples, boreholes in the ground, tree rings, glacier lengths, pollen remains, and ocean sediments have been used to determine past climate change patterns.
Variations in the sun's intensity can also affect climate change. Solar intensity is the the amount of solar power or energy the sun emits in a given amount of time. There is a direct correlation relationship between solar intensity and temperature.
Volcanic eruptions are another factor in climate change. The solids and gases released from a volcanic eruption can influence climate over a period of a few years. These solids and gases released by a volcanic eruption include carbon dioxide, water vapor, sulfur dioxide, hydrogen sulfide, hydrogen, and carbon monoxide. Volcanic eruptions commonly cool the climate as volcanic material in the atmosphere blocks the sun.
Greenhouse gases are major drivers of the climate. Greenhouse gases affect the climate when heat energy from the sun strikes the Earth, and greenhouse gases trap the heat in the atmosphere just like the glass walls of a greenhouse. Greenhouse gases that affect the Earth include carbon dioxide, methane, water vapor, nitrous oxide, and ozone. About half of the radiation from the sun passes through these gases and strikes the Earth. This radiation is converted into thermal or infrared radiation on the Earth's surface, and then a portion of that energy is re-radiated back into the atmosphere. Greenhouse gases reflect most of the thermal energy back to the Earth's surface. The more greenhouse gases there are in the atmosphere, the more thermal energy is reflected back to Earth's surface, causing the temperature to rise on the surface and the above atmosphere. The greenhouse effect is the warming of the Earth due to carbon dioxide and other greenhouse gases in the atmosphere. Evidence of greenhouse gasses and temperature increase comes from measurements of carbon dioxide levels in the atmosphere, and measurements of other greenhouse gases, which shows rising carbon dioxide concentrations in the atmosphere. However, life on earth would not survive with out the warmth from greenhouse gases. Human activity including the burning of fossil fuels and other activities releases carbon dioxide and methane into the atmosphere, two of the main greenhouse gases.
Ecology is the study of interactions of living organisms with their environment and understanding scientifically the distribution and abundance of living things in the physical environment. Ecologists are concerned with factors that influence the survival of endangered species and sometimes use mathematical models to predict their survival with conservation methods. Conservation management of ecology requires accurate data collection of current population size, factors affecting reproduction such as physiology and behavior, habitat requirements such as plants and soils, and human influences. Levels of ecology study that often overlap include organisms, populations, communities, ecosystems, and the biosphere of Earth.
Organismal ecology involves the study of abilities that allow individuals to live in specific habitats, including morphological, physiological, and behavioral abilities, and symbiotic relationships between two different organisms that depend on each other.
Population ecology involves a population or a group of interbreeding organisms that are members of the same species living in the same area at the same time. Organisms of the same species are also called conspecifics. A population is identified by where it lives and its area of population may have natural or artificial boundaries. Natural boundaries might be rivers, mountains, or deserts, while artificial boundaries may be mowed grass, manmade structures, or roads. The study of population ecology focuses on the number of individuals in an area and how and why population size changes over time.
The ecology of biological communities consists of the different species within an area, typically three-dimensional space, and the interactions within and among these species. Community ecologists are focused on the processes driving these interactions and their consequences. Questions about conspecific interactions often focus on competition among members of the same species for a limited resource. Ecologists also study interactions between various species, and members of different species are called heterospecifics. Examples of heterospecific interactions include predation, parasitism, herbivory, competition, and pollination, These interactions can have regulating effects on population sizes and can impact ecological processes and diversity
Mutualism is a form of long-term relationship between two species from which each species benefits. For mutualism to exist between individual organisms, each species must receive some benefit from the other as a consequence of the relationship. The Karner blue butterfly larvae have a mutualistic relationship with ants, where the ants protect the larvae from predators while the larvae secrete ant-like pheromones and a carbohydrate-rich substance that is an energy source for the ants.
Ecosystem ecology is related to and a part of organismal, population, and community ecology. The ecosystem is composed of all of the biotic components (living things) in an area along with the abiotic components (nonliving things) of that area. Abiotic components include air, water, and soil. Ecosystem biologists focus on how nutrients and energy are stored and how they move among organisms and through the surrounding atmosphere, soil, and water.
The biosphere includes all of the parts of the Earth inhabited by life. The biosphere extends into the atmosphere and into the depths of the oceans. Many abiotic forces influence where life can exist and the types of organisms found in different parts of the biosphere. The abiotic factors that influence the distribution of biomes are large areas of land with similar climate, flora, and fauna.
Biogeography is the study of the geographic distribution of living things and the abiotic factors that affect their distribution. Abiotic factors include temperature and rainfall and these are based on location and elevation. As these variables change, the type of plant and animal communities change as one travels across the earth. Warmer and moister environments produce different living things than colder and dryer environments. Ecologists and biogeographers study patterns of species distribution. There are no biospecies that exist everywhere or in every environment. Endemic species are species that are only found in specific geographic areas of specific size. Generalist species can live in a wide variety of geographic environments.
Species distribution patterns are based on biotic and abiotic factors. Species distribution patterns can also be identified in their absence, where certain species of animals are not found. Species can become extinct in certain locations because of changing environmental conditions. Like animals, plants can also be endemic or generalist species. Endemic plants are only found in specific regions of the Earth, while generalist species are found in many regions. Isolated land masses such as Australia, Hawaii, and Madagascar often have large numbers of endemic plant species, and some of these are endangered due to human activity.
Energy sources from the sun are captured by green plants, algae, cyanobacteria, and photosynthetic protists as they convert solar energy into chemical energy needed by all living things. Therefore light availability is an important force in energy sources. Plants have adaptations or designed abilities that allow their flowers to bloom during the times of the year when the sun is more available.
In aquatic ecosystems, sunlight may be partially or fully blocked by water, plants, particles, or microorganisms, particularly at deeper depths. Photosynthesis cannot take place if the sunlight is blocked, so there must be another way that aquatic plants can receive sunlight. Aquatic plants have photosynthetic parts on or near the surface of the water where sunlight can be absorbed, such as the water lily. In the deep sea surface, some bacteria can extract energy from inorganic chemicals in hydrothermal vent environments in the absence of light for photosynthesis.
Ocean upwelling allows deep ocean waters to rise by way of prevailing winds blown along surface waters near a coastline. The ocean upwelling allows energy and nutrients in dead organisms on the ocean bottom to be lifted up and recycled to the top of the ocean surface to be used by living
organisms in the ocean waters.
In freshwater lakes, nutrients are recycled in response to air temperature and wind changes. The nutrients at the bottom of lakes are recycled twice each year during the spring and fall turnover. The spring and fall turnover are seasonal processes that recycle nutrients and oxygen from the bottom of a freshwater lake to the top of the lake. These turnovers are caused by the formation of a thermocline, layers of water with temperatures that are significantly different from those above and below it.
Many northern lakes’ surface freezes in the winter, but the underlying water is warmer and denser at the deepest layer at 4 degrees C. In the spring, the air temperature increases and the surface ice melts. When the surface water reaches 4 degrees, it becomes denser, heavier, and sinks toward the bottom. The water at the bottom of the lake is then displaced by heavier and denser surface water and rises to the top. The water rises and brings sediments and nutrients with it. This is called spring turnover. In the summer, the warmest water is at the lake surface. In the fall, as air temperatures drop, the temperature of the lake water cools to 4 degrees and this causes fall turnover as the heavy cold water sinks and displaces the water at the bottom. The oxygen rich water at the surface of the lake then moves to the bottom of the lake, while the nutrients at the bottom of the lake rise to the surface. During the winter, the oxygen at the bottom of the lake is used by decomposers and other organisms requiring oxygen, such as fish. Ice transparency allows some light to penetrate the surface for photosynthesis, particularly for algae.
Temperature affects the physiology of organisms as well as the density and state of water. Few living things can survive at temperatures below zero degrees Celsius or above 45 degrees Celsius due to metabolic functions of the body. Enzymes can only function within specific temperature ranges, so that the body must maintain a certain temperature or the environment must stay at a certain temperature for the organism to survive to allow metabolic function. Living things sometimes have particular protections against extreme temperature through dormant states of hibernation or reptilian torpor. Some bacteria called extremophiles can withstand extremely hot temperatures in geysers.
The temperature of water and air can limit the distribution of living things. When temperature fluctuates, animals can respond by migration, or moving to a more suitable environment. Migration is practiced by many animals, including those who live in seasonally cold environments. Migration helps animals survive extreme temperatures, locate food, and find mates. Migratory birds such as the arctic tern are a good example, along with monarch butterflies, and mammals such as reindeer. Some animals lack or have limited migratory skills like amphibians and reptiles. There are also risks in migration and large energy consumption, so some animals choose not to migrate.
Some animals hibernate or estivate to survive extreme temperatures. Hibernation enables animals to survive extreme cold temperatures, and estivation allows animals to survive extremely hot and dry temperatures. Animals that hibernate or estivate enter a state known as a torpor, a condition in which their metabolic rate is significantly reduced, allowing the animal to wait until the environment is more suitable for survival. Some amphibians have chemicals in their cells that prevent them from freezing or bursting, therefore preserving their integrity.
Water is required by all living things because it is critical for cellular processes. Terrestrial organisms lose water to the environment, so they must have methods of retaining water. Plants have leaf hairs and a waxy cuticle that helps prevent water loss from transpiration and convection. Freshwater organisms have abilities to maintain solute concentrations in their bodies by excreting dilute urine. Marine organisms have the ability to regulate solute concentration in their bodies to retain water and release solutes into the environment.
Inorganic nutrients such as nitrogen and phosphorus are important in determining the distribution and abundance of living things. Plants obtain inorganic nutrients from the soil when water moves into the plant through the roots. Soil structure and particle size of soil, soil pH, and soil nutrient content together all play an important role in the distribution of plants. Animals obtain inorganic nutrients from the food they consume, particularly plants and other animals. Animal distributions are related to the distribution of the food they eat, as some animals follow their food resource as it moves through the environment.
Terrestrial animals obtain oxygen from the air they breathe, but oxygen availability can be limited at high elevations. In aquatic systems, the concentration of dissolved oxygen is related to water temperature and the speed at which water moves, as cold water has more dissolved oxygen than warmer water. Salinity, currents, and tidal changes can be important abiotic factors in aquatic ecosystems.
Wind can be an important abiotic factor because it influences the rate of evaporation, transpiration, and convective heat loss from the surface of all organisms. The physical force of wind is also important because it can move soil, water, or other abiotic factors, as well as an ecosystem’s organisms.
Fire is another terrestrial factor that can be an important agent of disturbance in terrestrial ecosystems. Some organisms have the ability to survive fire and require high heat associated with fire to complete a part of their life cycle, such as pine trees and cones.
Abiotic factors of plant growth include temperature, moisture, and available organic matter. Net primary productivity is an estimation of all of the organic matter available as food and it is calculated as the total amount of carbon fixed per year minus the amount that is oxidized during cellular respiration. In terrestrial environments, net primary productivity is estimated by measuring the above-ground biomass per unit area, which is the total mass of living plants, excluding roots (whose mass is difficult to measure). Net primary productivity is an important variable when considering differences in biomes.
Annual biomass production is directly related to the abiotic components of the environment. Environments with the greatest amount of biomass produce conditions in which photosynthesis, plant growth, and the resulting net primary productivity are optimized. These environments are warm, wet, and photosynthesis can occur at a high rate, enzymes can work most efficiently, and stomata can remain open without excessive transpiration. Therefore, carbon dioxide intake is maximized and high biomass is produced. The above-ground biomass provides habitat and food for other living organisms. In contrast, dry and cold environments have lower rates of photosynthesis and less biomass, affecting the ability of animals and plants to live there.
Biomes of the Earth are divided into two major groups: terrestrial and aquatic. Terrestrial biomes are based on land, while aquatic biomes include both ocean and freshwater biomes. Terrestrial biomes are distinguished by characteristic temperatures and precipitation amounts to determine the abiotic factors of each biome. The same biome can occur in geographically distinct areas with similar climates.
Tropical wet forests or tropical rainforests are found in equatorial regions where the vegetation is made of plants with broad leaves that fall and are replaced throughout the year. Unlike the trees of deciduous forests, the trees in this biome do not have seasonal loss of leaves associated with variations in temperature and sunlight. These forests are evergreen year-round.
Temperature in tropical wet forests range from 20 to 34 degrees Celsius, which is a relatively small margin and allows year-round plant growth instead of seasonal growth as in other biomes. There is also a constant amount of daily sunlight throughout the year, which provides more solar radiation and plant growth.
The annual rainfall in tropical wet forests ranges from 125 to 660 cm (50-200 in) with some variation in wet months and dry months. Tropical wet forests have high net primary productivity because the annual temperatures and precipitation values in these areas are ideal for plant growth. The high productivity leads to large biomass and large species diversity. There are more tree species than any other biome, up to several hundred species.
There are horizontal layers within the tropical wet forest biome. On the forest floor is a sparse layer of plants and decaying plant matter. Above that is an understory of short shrubby foliage. A layer of trees rises above this understory and is topped by a closed upper canopy, the uppermost overhead layer of branches and leaves. Within these layers are diverse complex habitats of plants, fungi, animals, and other organisms in the tropical wet forests.
Epiphytes are plants that grow on other plants and are usually not harmed. Epiphytes are found in tropical wet forest biomes. Many species of animals use the variety of plants and the complex structure of the wet forests for food and shelter, both on the ground and above ground within the trees.
Savannas are grasslands with scattered trees and are located in Africa, South America, and northern Australia. Savannas are commonly hot, tropical areas with temperatures averaging from 24 to 29 degrees C (75-84 F) and annual rainfall of 10 cm to 40 cm (4-16 in). Savannas have an extensive dry season and forest trees do not grow as well as they do in the tropical wet forest. Savannas have grasses and forbs (herbaceous flowering plants) and few trees. Fires are common in grasslands, however plants have the ability to quickly regrow after a fire.
Subtropical deserts exist between 15 and 30 degrees north and south latitude along the Tropics of Cancer and Capricorn (Sahara-Arabian Deserts, Mexican and southwest USA deserts, Australia’s Great Simpson Desert and Great Victoria Desert, Namib Desert, Central Asian deserts, and the Atacama Desert and Patagonia of South America. This biome is very dry and sometimes evaporation exceeds precipitation. Subtropical hot deserts can have daytime soil surface temperatures above 60 degrees C (140 F) and nighttime temperatures at 0 C (32 F). This large temperature variation is due to the lack of atmospheric water. Cold deserts can range from 25 C and -30 C. Subtropical deserts commonly have annual precipitation less than 30 cm (12 in).
The vegetation and low animal diversity in this biome is a result of low and unpredictable precipitation. Many plants in this biome are annual that grow and reproduce quickly during precipitation and die when precipitation disappears. Many plants in this biome can conserve water with deep roots, reduced foliage, and water-storing stems. Seed plants in the desert produce seeds that can be in dormancy for extended periods during rains. Desert animals stay active at night when it is cooler and burrow in the ground.
The chaparral (scrub forest) is found in California, the Mediterranean Sea, and along the southern coast of Australia. The annual rainfall in this biome is 65 cm to 75 cm (25-29 in), and the majority of the rain falls in the winter. Summers are very dry and many chaparral plants are dormant during the summertime. The chaparral vegetation is dominated by shrubs that can endure fires, the ashes of which are rich in nutrients like nitrogen that fertilize the soil and promote plant growth.
Temperate grasslands (called prairies) are found throughout central North America, and Eurasia (called steppes). Temperate grasslands have hot summers and cold winters. The annual temperature variation produces specific growing seasons for plants, where plant growth is possible when temperatures are warm enough and enough water is available. This growing season occurs during the spring, summer, and fall. During the winter, temperatures are low, and water in the form of ice is not available for plant growth.
Annual precipitation ranges from 25 cm to 75 cm (10-30 in). Because of relatively lower annual precipitation in temperate grasslands, there are few trees except for those found growing along rivers or streams. The dominant vegetation is grasses dense enough to sustain populations of grazing animals. The vegetation is very dense and the soils are fertile because the subsurface of the soil is packed with the roots and rhizomes (underground stems) of these grasses. The roots and rhizomes act to anchor plants into the ground and replenish the organic material (humus) in the soil when they die and decay.
Fires in temperate grasslands are caused by natural lightning. When the fires end, vegetation is converted to scrub and dense forests with drought-tolerant tree species. Conservation management in temperate grasslands often uses controlled burns to limit tree growth in favor of grasses.
Temperate forests are the most common biome in eastern North America, Western Europe, Eastern Asia, Chile, and New Zealand. This biome is found through the mid-latitude regions. Temperatures range from -30 C to 30 C (-22 F to 86 F) and drop to below freezing periodically during cold winters. Temperate forests have growing seasons during the spring, summer, and early fall. Precipitation is constant at 75 cm to 150 cm (29-59 in) annually.
Because of the moderate annual rainfall and temperatures, deciduous trees are the dominant plant in this biome. Deciduous trees lose their leaves each fall and remain leafless in the winter. Thus, no photosynthesis occurs in the deciduous trees during the dormant winter period. Each spring, new leaves appear as the temperature increases. Because of the dormant period, the net primary productivity of temperate forests is less than that of tropical wet forests. In addition, temperate forests show less diversity of tree species than tropical wet forest biomes.
The trees of temperate forests leaf out and shade much of the ground, but this biome is more open than tropical wet forests because most trees in the temperate forests do not grow as tall as the trees in tropical wet forests. The soils of temperate forests are rich in inorganic and organic nutrients. This is due to the thick layer of leaf litter on the forest floors, which does not develop in tropical rainforests. As this leaf litter decays, nutrients are returned to the soil. The leaf litter also protects soil from erosion, insulates the ground, and provides habitats for invertebrates and their predators.
Boreal forest (taiga or coniferous forest) is found south of the Arctic Circle and across most of Canada, Alaska, Russia, and northern Europe. This biome has cold, dry winters and short, cool, wet summers. The annual precipitation is from 40 cm to 100 cm (15-39 in) and usually takes the form of snow. Little evaporation occurs because of the cold temperatures.
The long and cold winters in the boreal forest have led to the predominance of cold-tolerant cone-bearing (coniferous) plants. These are evergreen coniferous trees like pines, spruce, and fir, which retain their needle-shaped leaves year-round. Evergreen trees can photosynthesize earlier in the spring than deciduous trees because less energy from the sun is required to warm a needle-like leaf than a broad leaf. This benefits evergreen trees, which grow faster than deciduous trees in the boreal forest. In addition, soils in the boreal forest tend to be acidic with little available nitrogen. Leaves are a nitrogen-rich structure and deciduous trees must produce a new set of these nitrogen-rich structures each year. Therefore, coniferous trees that retain nitrogen-rich needles may have a competitive advantage over the broad-leafed deciduous trees.
The net primary productivity of boreal forests is lower than that of temperate forests and tropical wet forests. The above-ground biomass of boreal forests is high because these slow-growing tree species are long-lived and accumulate a large standing biomass over time. Plant species diversity is less than that seen in temperate forests and tropical wet forests. Boreal forests lack the pronounced elements of the layered forest structure seen in tropical wet forests. The structure of a boreal forest is often only a tree layer and a ground layer. When conifer needles are dropped, they decompose more slowly than broad leaves, therefore, fewer nutrients are returned to the soil to fuel plant growth.
The Arctic tundra is north of the subarctic boreal forest and is located throughout the Arctic regions of the northern hemisphere. The average winter temperature is -34 C (-29 F) and the average summer temperature is from 3 C to 12 C (37 F to 52 F). Plants in the arctic tundra have a very short growing season of about 10 to 12 weeks.
However, during this time, there are almost 24 hours of daylight and plant growth is rapid. The annual precipitation of the Arctic tundra is very low with little annual variation in precipitation. And as in the boreal forests, there is little evaporation due to the cold temperatures.
Plants in the Arctic tundra are generally low to the ground. There is little species diversity, low net primary productivity, and low above-ground biomass. The soils of the Arctic tundra may remain in a perennially frozen state referred to as permafrost. The permafrost makes it impossible for roots to penetrate deep into the soil and slows the decay of organic matter, which inhibits the release of nutrients from organic matter. During the growing season, the ground of the Arctic tundra can be completely covered with plants or lichens.
The oceans in aquatic biomes are divided into several different zones. The entire ocean’s open water is called the pelagic realm (or zone). The benthic realm or zone extends along the ocean bottom from the shoreline to the deepest parts of the ocean floor. Within the pelagic realm is the photic zone, which is the portion of the ocean that light can penetrate (200m/650ft). At depths greater than 200 meters, light cannot penetrate, and this zone is referred to as the aphotic zone. The majority of the ocean is aphotic and lacks sufficient light for photosynthesis. The deepest part of the ocean is the Challenger Deep in the Mariana Trench, western Pacific Ocean (11,000 m/ 6.8 miles deep). Below the aphotic zone is the abyssal zone, the deep ocean region between 3,000 and 6,500 meters (9,842 to 21,325 feet) deep, characterized by complete darkness, freezing temperatures (around 2-6°C), and immense hydrostatic pressure.
The ocean is the largest marine biome. The ocean is a single body of salty water relatively uniform in chemical composition of a weak solution of mineral salts and decayed biological matter. Within the ocean, coral reefs are a second type of marine biome. Estuaries that are found in coastal areas where salt water and fresh water mix, are a third unique marine biome.
The ocean has physical diversity and a significant influence on plants, animals, and other organisms. The ocean is divided into different zones. The intertidal zone is between high and low tide and is the closest region to land. This zone can be sandy, rocky, or muddy. The intertidal zone is an extremely variable environment because of action of tidal ebb and flow. Organisms are exposed to air and sunlight at low tide and are underwater most of the time, especially during high tide. Living things in the intertidal zone can be dry for long periods of time. The shore of the intertidal zone may also be repeatedly struck by waves, and the organisms found there can withstand damage from their pounding action. The exoskeletons of shoreline crustaceans such as the shore crab are tough and protect them from desiccation (drying out) and wave damage. Another consequence of pounding waves is that few algae and plants establish themselves in the constantly moving rocks, sand, or mud.
The neritic zone extends from the intertidal zone to depths of 200 m (650 ft) at the edge of the continental shelf underwater. Since light can penetrate this depth, photosynthesis can still occur in the neritic zone. The water here contains silt and is well-oxygenated, low in pressure, and stable in temperature. Phytoplankton and floating Sargassum (seaweed) provide a habitat for some sea life found in the neritic zone. Zooplankton, protists, small fishes, and shrimp are found in the neritic zone and are the base of the food chain.
Beyond the neritic zone is the open ocean area known as the pelagic or open oceanic zone. Within this zone is thermal stratification where warm and cold waters mix because of ocean currents. Abundant plankton serve as the base of the food chain for larger animals such as whales and dolphins. Nutrients are scarce and this is a relatively less productive part of the marine biome. When photosynthetic organisms and the protists and animals that feed on them die, their bodies fall to the bottom of the ocean, where they remain. Unlike freshwater lakes, most of the open ocean lacks a process for bringing the organic nutrients back up to the surface (although there are some ocean upwellings). The majority of organisms in the aphotic zone include sea cucumbers (Echinodermata) and other organisms that survive on the nutrients contained in the dead bodies of organisms in the photic zone.
Beneath the pelagic zone is the benthic realm, the water region beyond the continental shelf that starts at the shoreline and extends to the deepest regions of the ocean. The bottom of the benthic realm is composed of sand, silt, and dead organisms. Temperature decreases, remaining above freezing, as water depth increases. This is a nutrient-rich portion of the ocean because of the dead organisms that fall from the upper layers of the ocean. Because of this high level of nutrients, a diversity of fungi, sponges, sea anemones, marine worms, sea stars, fishes, and bacteria exist.
The deepest part of the open ocean is the abyssal zone (4,000 m or greater). The abyssal zone is very cold and has very high pressure, very low or no oxygen content, and high nutrient content as the dead and decomposing material drifts down from the layers above. There are a variety of invertebrates and fishes found in this zone, but the abyssal zone does not have plants because of the lack of light. Hydrothermal vents are found primarily in the abyssal zone. Chemosynthetic bacteria utilize the hydrogen sulfide and other minerals emitted from the vents to produce biomass. These chemosynthetic bacteria use various molecules as an energy source and serve as the base of the food chain found in the abyssal zone.
Coral reefs are ocean ridges formed by marine invertebrates, comprising mostly of cnidarians and mollusks living in warm shallow waters within the photic zone of the ocean. They are found within 30 degrees north and south of the equator. The Great Barrier Reef is the best known and largest reef system in the world (it is visible from space). This massive and ancient reef is located several miles off the northeastern coast of Australia. Other coral reef systems are fringing islands, which are directly adjacent to land, or atolls, which are circular reef systems surrounding a former landmass that is now underwater. The coral organisms (Cnidaria) are colonies of saltwater polyps that secrete a calcium carbonate skeleton. These calcium-rich skeletons slowly accumulate, forming the underwater reef. Corals found in shallower waters (60 m/ 200 ft) have a mutualistic relationship with photosynthetic unicellular algae. The relationship provides corals with the majority of the nutrition and the energy they require. The waters in which these corals live are nutritionally poor and, without this mutualism, it would not be possible for large corals to grow. Some corals living in deeper and colder water do not have a mutualistic relationship with algae. These corals attain energy and nutrients using stinging cells called cnidocytes on their tentacles to capture prey.
It is estimated that more than 4,000 fish species inhibit coral reefs. These fishes can feed on coral, the cryptofauna invertebrates found within the calcium carbonate substrate of the coral reefs, or the seaweed and algae that are associated with the coral. In addition, some fish species inhabit the boundaries of a coral reef. These species include predators, herbivores, and planktivores, which consume planktonic organisms such as bacteria, archaea, algae, and protists floating in the pelagic zones.
Estuaries are biomes that occur where a source of fresh water, such as a river, meets the ocean. Therefore, both fresh water and salt water are found in the same area. Mixing results in a diluted, brackish saltwater. Estuaries form protected areas where many of the young offspring of crustaceans, mollusks, and fish begin their lives, which also creates important breeding grounds for other animals. Salinity is a very important factor that influences the organisms and the adaptations of the organisms found in estuaries. The salinity of estuaries varies considerably and is based on the rate of flow of its freshwater sources, which may depend on the seasonal rainfall. Once or twice a day, high tides bring salt water into the estuary. Low tides occurring at the same frequency reverse the current of salt water.
Many estuarine plant species are halophytes, or plants that can tolerate salt conditions. In some halophytes, filters in the roots remove the salt from the water that the plant absorbs. Other plants are able to pump oxygen into their roots. Animals such as mussels and clams have abilities to deal with saline waters. When these animals are exposed to low salinity, they stop feeding, close their shells, and switch from aerobic respiration (gills for oxygen) to anaerobic respiration (does not require oxygen and takes place inside the animals cells). When high tide returns to the estuary, the salinity and oxygen content of the water increases, and these animals open their shells, begin feeding, and return to aerobic respiration.
Freshwater biomes include lakes and ponds of standing water as well as rivers and streams of flowing water. They also include wetlands. Humans rely on freshwater biomes to provide ecosystem benefits, which are sources of drinking water, crop irrigation, sanitation, and industry. Lakes and ponds are connected with abiotic and biotic factors influencing their terrestrial biomes.
Lakes and ponds can be a few square meters to thousands of square kilometers in area. Temperature is an important abiotic factor affecting living things found in lakes and ponds. In the summer, as we have seen, thermal stratification of lakes and ponds occurs when the upper layer of water is warmed by the sun and does not mix with the deeper, cooler water. Light can penetrate within the photic zone of the lake or pond. Phytoplankton (algae or cyanobacteria) are found here and carry out photosynthesis, providing the base of the food web of lakes and bonds. Zooplankton, such as rotifers and larvae and adult crustaceans, consume these phytoplankton. At the bottom of lakes and ponds, bacteria in the aphotic zone break down dead organisms that sink to the bottom.
Nitrogen and phosphorus are important limiting nutrients in lakes and ponds and are therefore determining factors in the amount of phytoplankton growth that takes place in lakes and ponds. When there is a large input of nitrogen and phosphorus (from sewage and runoff from fertilized lawns and farms) the growth of algae increases dramatically, resulting in a large accumulation of algae called an algal bloom. Algal blooms can become so extensive that they reduce the light penetration in water. They may also release toxic byproducts into the water, contaminating any drinking water taken from that source. In addition, the lake or pond becomes aphotic, and photosynthetic plants cannot survive. When algae die and decompose, severe oxygen depletion of the water occurs. Fishes and other organisms that require oxygen are then more likely to die, resulting in a dead zone. Lake Erie and the Gulf of Mexico represent freshwater and marine habitats where phosphorous control and storm water runoff pose significant environmental challenges.
Rivers and streams are continuously moving bodies of water that carry large amounts of water from the source, or headwater, to a lake or ocean. The largest rivers include the Nile River in Africa, the Amazon River in South America, and the Mississippi River in North America. Abiotic features of rivers and streams vary along the length of the river or stream. Streams begin at a point of origin referred to as source water. The source water is usually cold, low in nutrients, and clear. The channel (stream width) is narrower than at any other place along the length of the river or stream. Because of this, the current is often faster here than at any other point of the river or stream.
The fast-moving water results in minimal silt accumulation at the bottom of the river or stream. Therefore, water is usually clear and free of debris. Photosynthesis here is mostly attributed to algae that are growing on rocks. The swift current inhibits the growth of phytoplankton. An additional input of energy can come from leaves or other organic material that fall downstream into the river or stream, as well as from trees and other plants that border the water. When the leaves decompose, the organic material and nutrients in the leaves are returned to the water. Plants and animals have features that allow them to survive the fast-moving water. Some species have flat bodies and clawed legs that allow them to attach to submerged rocks in the stream.
Downstream, the river or stream widens and the current slows because of a gradient decrease and volume increase as tributaries combine and sedimentation increases. Phytoplankton can also be suspended in slow-moving water and the water will be less clear. The water is also warmer downstream. Worms and insects can be found burrowing into the mud. Predator vertebrates include waterfowl, frogs, and fishes, who use these slow moving waters to find prey using their senses of taste or chemical sensing instead of vision.
Wetlands are environments in which the soil is either permanently or periodically saturated with water. Wetlands are different from lakes because wetlands are shallow bodies of water whereas lakes vary in depth. Emergent vegetation consists of wetland plants that are rooted in the soil but have portions of leaves, stems, and flowers, extending above the water’s surface. There are several types of wetlands including marshes, swamps, bogs, mudflats, and salt marshes. The three shared characteristics among these types of wetlands are their hydrology, hydrophytic vegetation, and hydric soils.
Freshwater marshes and swamps are characterized by slow and steady water flow. Bogs, however, develop in depressions where water flow is low or non-existent. Bogs usually occur in areas where there is a clay bottom with poor percolation of water. Percolation is the movement of water through the pores in the soil or rocks. The water found in a bog is stagnant and oxygen-depleted because the oxygen used during the decomposition of organic matter is not readily replaced. As the oxygen in the water is depleted, decomposition slows. This leads to a buildup of acids and a lower water pH. The Lower pH creates challenges for plants because it limits the available nitrogen. As a result, some bog plants capture insects in order to extract the nitrogen from their bodies. Bogs have low net primary productivity because the water found in bogs has low levels of nitrogen and oxygen.
Climate and Its Effects on Biomes and Climate Change: All biomes are affected by global conditions such as climate. Global climate change is the term used to describe the altered global weather patterns, especially a worldwide increase in temperature and resulting changes in the climate, due to rising levels of atmospheric carbon dioxide.
Climate refers to the long-term predictable atmospheric conditions of a specific area. The climate of a biome is characterized by having consistent seasonal temperature and rainfall ranges. Weather refers to the conditions of the atmosphere during a short period of time, such as one to two days. Longer-range weather forecasts are usually unreliable.
Global climate change is focused on (1) evidence of current and past global climate change (2) drivers of global climate change (3) documented results of climate change.
Evidence for past global climate change includes vertical ice core samples from Antarctica, the South Polar ice cap. Ice core samples are drilled thousands of meters deep. Air bubbles and other biological evidence in the core samples can reveal information about temperature and carbon dioxide levels in the past. Evidence from the core samples shows evidence of fluctuating or varying temperature in the past.
In addition to ice core samples, boreholes in the ground, tree rings, glacier lengths, pollen remains, and ocean sediments have been used to determine past climate change patterns.
Variations in the sun's intensity can also affect climate change. Solar intensity is the the amount of solar power or energy the sun emits in a given amount of time. There is a direct correlation relationship between solar intensity and temperature.
Volcanic eruptions are another factor in climate change. The solids and gases released from a volcanic eruption can influence climate over a period of a few years. These solids and gases released by a volcanic eruption include carbon dioxide, water vapor, sulfur dioxide, hydrogen sulfide, hydrogen, and carbon monoxide. Volcanic eruptions commonly cool the climate as volcanic material in the atmosphere blocks the sun.
Greenhouse gases are major drivers of the climate. Greenhouse gases affect the climate when heat energy from the sun strikes the Earth, and greenhouse gases trap the heat in the atmosphere just like the glass walls of a greenhouse. Greenhouse gases that affect the Earth include carbon dioxide, methane, water vapor, nitrous oxide, and ozone. About half of the radiation from the sun passes through these gases and strikes the Earth. This radiation is converted into thermal or infrared radiation on the Earth's surface, and then a portion of that energy is re-radiated back into the atmosphere. Greenhouse gases reflect most of the thermal energy back to the Earth's surface. The more greenhouse gases there are in the atmosphere, the more thermal energy is reflected back to Earth's surface, causing the temperature to rise on the surface and the above atmosphere. The greenhouse effect is the warming of the Earth due to carbon dioxide and other greenhouse gases in the atmosphere. Evidence of greenhouse gasses and temperature increase comes from measurements of carbon dioxide levels in the atmosphere, and measurements of other greenhouse gases, which shows rising carbon dioxide concentrations in the atmosphere. However, life on earth would not survive with out the warmth from greenhouse gases. Human activity including the burning of fossil fuels and other activities releases carbon dioxide and methane into the atmosphere, two of the main greenhouse gases.