Ecology of Ecosystems BIO 46 by Owen Borville September 29, 2025
Ecosystem dynamics are about competition for limited resources, including organic material, sunlight, and minerals along with the habitat's latitude, amount of rainfall, topography, and available species.
An ecosystem is a community of living organisms and their interaction with their abiotic (nonliving environment). Ecosystems can vary in size, from a small pond to an entire rainforest.
Three categories ecosystems are freshwater, ocean water, and terrestrial ecosystems.
Ocean ecosystems are the most abundant, as they make up over 70 percent of the Earth's surface and have three types: shallow ocean, deep ocean, and deep ocean surfaces. The shallow ocean ecosystems include extremely biodiverse coral reef ecosystems, and the deep ocean surface is known for its large numbers of plankton and marine animals (crustaceans). These two environments are very important to aerobic respirators worldwide as the phytoplankton perform 40 percent of all photosynthesis on Earth. Although not as diverse as the other two, deep ocean ecosystems contain a wide variety of marine organisms. Such ecosystems exist even at the bottom of the ocean where light is unable to penetrate through the water.
Freshwater ecosystems are the rarest ecosystem, making up only about 1.8 percent of the Earth's surface. Lakes, rivers, streams, and springs comprise these ecosystems that are very diverse and support a variety of fish, amphibians, reptiles, insects, phytoplankton, fungi, and bacteria.
Terrestrial ecosystems are also known for their diversity and are grouped into large categories called biomes such as tropical rain forests, savannas, deserts, coniferous forests, deciduous forests, and tundra. There is also great diversity within these categories.
Ecosystems are very complex and are affected by changes and disturbances in the environment including yearly variation in rainfall, temperature, and natural forest fires, and the effects of human activities.
Equilibrium is the steady state of an ecosystem where all organisms are in balance with their environment and with each other. Resistance is the ability of an ecosystem to remain at equilibrium in spite of disturbances. Resilience is the speed at which an ecosystem recovers equilibrium after being disturbed. Human impact is a big factor in equilibrium resistance and resilience. If there are too many disturbances, the ecosystem could be permanently destroyed despite resistance and resilience.
Food chains are linear sequences of organisms through which nutrients and energy pass. Primary producers, primary consumers, and higher-level consumers are used to describe the ecosystem structure and dynamics. There is a single path through the chain and each organism in the food chain occupies a trophic level where depending on their role as producers or consumers, species or groups of species can be assigned to various trophic levels.
Primary producers are photosynthetic organisms (plants or phytoplankton) at the bottom of the food chain. Primary consumers are herbivore organisms that consume the primary producers. Secondary consumers are usually carnivores that eat the primary consumers. Tertiary consumers are carnivores that eat other carnivores. Apex consumers are organisms at the top of the food chain.
Energy is the major factor that limits the length of the food chain, as energy is lost as heat between each trophic level due to the second law of thermodynamics. Therefore, after a limited number of trophic energy transfers, the amount of energy remaining in the food chain may not be great enough to support populations at a higher trophic level. Most of the energy is available at the lowest trophic level, the primary producers and energy is lost at each higher trophic level so that at the apex, the least amount of energy is available.
A major problem when using food chains to describe ecosystems is that even when all organisms are grouped at appropriate trophic levels, some of these organisms can feed on species from more than one trophic level and some of these organisms can be eaten by species from multiple trophic levels. Therefore, the linear food chain model of ecosystems is not completely linear and a linear model cannot completely describe an ecosystem. A holistic model which accounts for all the interactions between different species and their complex interconnected relationships with each other and with the environment is a more accurate and descriptive model for ecosystems. A food web is a graphic representation of a holistic, nonlinear web of primary producers, primary consumers, and higher-level consumers used to describe ecosystem structure and dynamics.
A comparison of the two types of structural ecosystem models shows that each model has strength. Food chains are more flexible for analytic modeling and are easier to understand and experiment with while food web models more accurately represent ecosystem dynamics and its data are more accurate for modeling.
Types of food webs that often exist within a single ecosystem include a grazing food web that has plants or other photosynthetic organisms at its base, followed by herbivores and carnivores. A detrital food web consists of a base of organisms that feed on decaying organic matter or dead organisms called decomposers. These organisms are usually bacteria or fungi that recycle organic material back into the biotic part of the ecosystem as they themselves are consumed by other organisms.
Ecosystem dynamics is study of the changes in ecosystem structure caused by changes in the environment (disturbances) or internal forces. Research in ecosystems include both controlled experiments along with researching ecosystems in their natural state.
A holistic ecosystem model attempts to quantify the composition, interaction, and dynamics of entire ecosystems and is the most representative of the ecosystem in its natural state. A food web is an example of a holistic ecosystem model. However, research using this model is time consuming, expensive, unfeasible, and unethical on large natural ecosystems. Quantifying all different species and dynamics for large habitats is difficult.
Therefore, researchers usually study ecosystems under more controlled conditions: A mesocosm is a part of a natural ecosystem that is partitioned and used for experiments. A microcosm is a recreation of an ecosystem entirely in an indoor or outdoor laboratory environment. However, the downside to using these methods is that altering a natural ecosystem may change the dynamics of the ecosystem.
Researchers use data from these experiments to develop ecosystem models that demonstrate the structural dynamics of ecosystems. One ecosystem model is a conceptual model that contains flow charts to show interactions of different compartments of the living and the nonliving components of the ecosystem structure and dynamics, and how disturbances affect the ecosystem. An analytical model is an ecosystem model that is created using simple mathematical formulas to predict the effects of environmental disturbances on the ecosystem. A simulation model is an ecosystem model that is created using complex computer algorithms to holistically model ecosystems and to predict the effects of environmental disturbances on the ecosystem.
Conceptual models are useful for describing ecosystem structure and dynamics and for demonstrating the relationships between different organisms in a community and their environment, most commonly depicted graphically as flow charts showing the relationship and transfer of energy or nutrients between them, and the flow of energy through a particular ecosystem. However, conceptual models are limited by their inability to predict the consequences of a changes in ecosystem species and environment. Ecosystems altered from their initial equilibrium state can often recover from natural or human disturbances.
Analytical models often use simple, linear components of ecosystems, such as food chains, and are mathematically complex. Therefore, analytical models are limited by their mathematical complexity. However, simulation models that use computer programs are more capable to handle the mathematical complexity of ecosystems. Recently supercomputers have been used to create simulations of ecosystems that account for the behavior of individual organisms.
Energy flows through ecosystems as all living things require energy for most metabolic pathways and assembling macromolecules like proteins, lipids, nucleic acids, and carbohydrates. Food webs illustrate how energy flows directionally through ecosystems.
Energy is acquired by living things in three ways: photosynthesis, chemosynthesis, and the consumption and digestion of other living or dead living organisms by heterotrophs.
Photosynthetic and chemosynthetic organisms are both classified as autotrophs: organisms capable of synthesizing their own food. Photosynthetic autotrophs use sunlight as an energy source, whereas chemosynthetic autotrophs use inorganic molecules as an energy source. Autotrophs are important for all ecosystems because these organisms produce energy for other living organisms to make life possible.
Photoautotrophs such as plants, algae, and photosynthetic bacteria serve as the energy source for a majority of the world's ecosystems, which are described by grazing food webs. Photoautotrophs use solar energy of the sun and convert it to chemical energy in the form of ATP, which is used to make organic molecules like glucose.
Chemoautotrophs are mainly bacterial that are found in rare ecosystems where sunlight is not available, such as caves or hydrothermal vents at the ocean bottom. Many chemoautotrophs in hydrothermal vents use hydrogen sulfide released from the vents as a source of chemical energy to make organic molecules like glucose for their energy and also supply energy to the ecosystem.
Productivity in an ecosystem is the percentage of energy of entering the ecosystem incorporated into biomass in a particular trophic level. Biomass is the total mass (living or dead) in a unit area at the time of measurement at the trophic level. The productivity of the primary producers is important in the ecosystem because these organisms bring energy to other living organisms by photoautotrophy or chemoautotrophy. The rate at which photosynthetic primary producers incorporate energy from the sun is called gross primary productivity.
All organisms need some energy for their own body functions. Net primary productivity of an ecosystem is the energy that remains in the primary producers after accounting for the organisms' respiration and heat loss. The net productivity is then available to the primary consumers at the next trophic level.
Energy flow is lost from primary producers in the ecosystem through the trophic levels, and the ecosystem loses large amounts of energy. The measurement of energy transfer efficiency between two successive trophic levels is the trophic level transfer efficiency (TLTE) and has the formula:
TLTE = (production at the present trophic level)/(production at the previous trophic level) x 100
Net production efficiency (NPE) allows ecologists to quantify how efficiently organisms of a particular trophic level incorporate the energy they receive into biomass to fuel the next trophic level:
NPE = (net consumer productivity)/(assimilation) x 100
Net consumer productivity is the energy content available to the organisms of the next trophic level. Assimilation is the biomass (energy content generated per unit area) of the present trophic level after accounting for the energy lost due to incomplete ingestion of food, energy used for respiration, and energy lost as waste. Some consumers eat only part of their food (and leave the bone), and this is called incomplete ingestion.
Ecological pyramids show the relative amounts of various parameters (number of organisms, energy, biomass) across trophic levels in the ecosystem. Pyramids of numbers can be either upright or inverted, depending on the ecosystem. Pyramids of biomass measure the amount of energy converted into living tissue at the different trophic levels. Pyramid ecosystem modeling can also be used to show energy flow through the trophic levels. Pyramids of energy are among the most consistent and representative models of ecosystem structure.
Biomagnification is the increasing concentration of persistent, toxic substances in organisms at each trophic level and is of environmental concern. Examples of toxic substances of concern in biomagnification are the pesticide (DDT), the coolant chemical (PCB), and heavy metals in seafood like mercury and cadmium.
Biogeochemical cycles are the recycling of inorganic matter between living organisms and their environment. Geologic processes of weathering, erosion, water drainage, and the subduction of the tectonic plates all contribute to the recycling of materials. As energy flows through the ecosystem from sunlight and leaving as heat, biomass is conserved and recycled through the most common elements of organic molecules: carbon, nitrogen, hydrogen, oxygen, phosphorus, and sulfur in the atmosphere, land, water, or subsurface.
The hydrosphere is the total amount of water (H2O) on Earth in all forms of solid, liquid, and gas: rivers, lakes, oceans, groundwater, polar ice caps, and glaciers, along with water vapor. Carbon is found in all organic macromolecules and fossil fuels. Nitrogen is a major component of our nucleic acids and proteins and it is very important to human agriculture. Phosphorous is a major component of nucleic acid along with nitrogen and is a main ingredient of artificial fertilizers used in agriculture and impact surface water. Sulfur is very important to the protein folding process. These element cycles are interconnected and depend on each other.
The Water Cycle: Only one percent of freshwater on earth is accessible from lakes and rivers. The rest of the water (99 percent) is either underground or frozen as ice. Many living things depend on freshwater. Most of the water on Earth is stored for long periods in the oceans, underground, and as ice. Residence time is a measure of the average time an individual water molecule stays in a particular reservoir.
Water cycle processes and stages include evaporation and sublimation, condensation and precipitation, subsurface water flow, surface runoff and snowmelt, and streamflow. The sun's energy leads to evaporation or liquid surface water to water vapor and the sublimation (ice to water vapor to atmosphere) of frozen water. Water vapor condenses into clouds as liquid or frozen droplets, followed by precipitation in the form of rain or snow to the Earth's surface. Rain or snow water permeates the ground, flows beneath the surface, enters surface water, or is stored for a long time. Water runoff from rain or melting ice enters streams and lakes that connect to oceans or directly to the ocean from runoff to complete the cycle. Rain and surface water runoff causes minerals from land to water. These minerals contain carbon, nitrogen, phosphorous, and sulfur.
The Carbon Cycle: Carbon is the second most abundant element in living organisms. Carbon is present in all organic molecules, and its role in the structure of macromolecules is very important to living organisms. The carbon cycle has two main sub-cycles: one involving the rapid carbon exchange among living organisms and the other involving the long-term cycling of carbon through geologic processes.
In the carbon cycle, carbon dioxide gas in the atmosphere dissolves in water. Photosynthesis converts carbon dioxide gas to organic carbon, and respiration cycles the organic carbon back into carbon dioxide gas. Long term storage of organic carbon occurs when matter from living organisms is buried deep underground and becomes fossilized. Volcanic activity and human emissions bring this stored carbon back into the carbon cycle.
Photosynthetic organisms convert atmospheric carbon dioxide into oxygen for the atmosphere that humans and animals breathe. Heterotrophs acquire the high-energy carbon compounds from autotrophs by consuming them and breaking them down by respiration to obtain cellular energy including ATP. There is constant exchange of oxygen and carbon dioxide between the autotrophs (plants and food producers) which need carbon and heterotrophs (animals and food consumers) which need oxygen. Gas exchange through the atmosphere and water allows the carbon cycle to connect all living things on Earth.
The biogeochemical cycle through land, water, and air is complex and occurs over longer periods of time. Carbon is stored in carbon reservoirs like the atmosphere, oceans and water bodies, ocean sediment, soil, land sediments, fossil fuels, and the interior of the Earth. Carbon dioxide from the atmosphere dissolves in water and combines with water molecules to form carbonic acid, and then it ionizes to carbonate and bicarbonate ions.
More than 90 percent of carbon in the ocean is bicarbonate ions. Some of these ions combine with seawater calcium to form calcium carbonate and marine organism shells. These organisms become part of the seafloor and forms limestone, the largest carbon reservoir on Earth.
On land, carbon is stored in soil from decomposition of living organisms or from weathering of rocks and minerals. This carbon can be leached into the water reservoirs by runoff. Also deeper underground are fossil fuels made of decomposed organic material. Carbon can also enter the atmosphere from volcanic eruptions and other geothermal systems and hydrothermal vents on the ocean floor.
Humans produce atmospheric carbon from burning fossil fuels and other materials. In addition, human civilization has cause the growth of farm animals that feed the world's humans also produces more atmospheric carbon.
The Nitrogen Cycle: Nitrogen enters the living world from the atmosphere through nitrogen-fixing bacteria. This nitrogen and nitrogenous waste from animals is then processed back into gaseous nitrogen by soil bacteria, which also supply terrestrial food webs with the organic nitrogen they need. Human activity can release nitrogen into the environment from the combustion of fossil fuels and the use of artificial fertilizers in agriculture, which is then moved into lakes, streams, and rivers by surface runoff. Atmospheric nitrogen produces acid rain and greenhouse gas. Agricultural fertilizer runoff also cause eutrophication, when nitrogen runoff cause the excess growth of microorganisms, which in turn deplete dissolved oxygen levels and kill living organisms. In the marine nitrogen cycle, ammonification, nitrification, and denitrification processes are performed by marine bacteria.
The Phosphorous Cycle: Phosphorous is a major component of nucleic acid and phospholipids, along with calcium phosphate in bones. Phosphorous is a nutrient in aquatic ecosystems. Phosphate runoff occurs from human activity and natural surface rock weathering, volcanic activity into the soil, water, and air. Phosphate enters the oceans from surface runoff, groundwater flow, and river flow. Phosphate dissolved in ocean water cycles into marine food webs. Some phosphate from the marine food webs falls to the ocean floor sediment. Fertilizer runoff produces excess phosphorous, causing excessive growth of microorganisms and depletes the dissolved oxygen, leading to the death of living organisms in oceans, rivers, and lakes.
A dead zone is an area within a freshwater or marine ecosystem where large areas are depleted of their normal flora and fauna caused by eutrophication, oil spills, toxic chemical dumping, and other human activities.
The Sulfur Cycle: Sulfur is an element in macromolecules of living things, the amino acid cysteine. Sulfur is part of the protein folding process. Sulfur enters the atmosphere from decomposition of organic molecules, volcanic activity, geothermal vents, and from the burning of fossil fuels by humans. Sulfur on land is deposited by precipitation, directly from the atmosphere (fallout), rock weathering, and geothermal vents. Sulfur enters the ocean from land runoff, atmospheric fallout, and from marine geothermal vents. Fossil fuels release sulfur into the atmosphere when burned. Acid rain takes sulfur to the ground surface and soil, causes building damage, and harms lake fauna.
Ecosystem dynamics are about competition for limited resources, including organic material, sunlight, and minerals along with the habitat's latitude, amount of rainfall, topography, and available species.
An ecosystem is a community of living organisms and their interaction with their abiotic (nonliving environment). Ecosystems can vary in size, from a small pond to an entire rainforest.
Three categories ecosystems are freshwater, ocean water, and terrestrial ecosystems.
Ocean ecosystems are the most abundant, as they make up over 70 percent of the Earth's surface and have three types: shallow ocean, deep ocean, and deep ocean surfaces. The shallow ocean ecosystems include extremely biodiverse coral reef ecosystems, and the deep ocean surface is known for its large numbers of plankton and marine animals (crustaceans). These two environments are very important to aerobic respirators worldwide as the phytoplankton perform 40 percent of all photosynthesis on Earth. Although not as diverse as the other two, deep ocean ecosystems contain a wide variety of marine organisms. Such ecosystems exist even at the bottom of the ocean where light is unable to penetrate through the water.
Freshwater ecosystems are the rarest ecosystem, making up only about 1.8 percent of the Earth's surface. Lakes, rivers, streams, and springs comprise these ecosystems that are very diverse and support a variety of fish, amphibians, reptiles, insects, phytoplankton, fungi, and bacteria.
Terrestrial ecosystems are also known for their diversity and are grouped into large categories called biomes such as tropical rain forests, savannas, deserts, coniferous forests, deciduous forests, and tundra. There is also great diversity within these categories.
Ecosystems are very complex and are affected by changes and disturbances in the environment including yearly variation in rainfall, temperature, and natural forest fires, and the effects of human activities.
Equilibrium is the steady state of an ecosystem where all organisms are in balance with their environment and with each other. Resistance is the ability of an ecosystem to remain at equilibrium in spite of disturbances. Resilience is the speed at which an ecosystem recovers equilibrium after being disturbed. Human impact is a big factor in equilibrium resistance and resilience. If there are too many disturbances, the ecosystem could be permanently destroyed despite resistance and resilience.
Food chains are linear sequences of organisms through which nutrients and energy pass. Primary producers, primary consumers, and higher-level consumers are used to describe the ecosystem structure and dynamics. There is a single path through the chain and each organism in the food chain occupies a trophic level where depending on their role as producers or consumers, species or groups of species can be assigned to various trophic levels.
Primary producers are photosynthetic organisms (plants or phytoplankton) at the bottom of the food chain. Primary consumers are herbivore organisms that consume the primary producers. Secondary consumers are usually carnivores that eat the primary consumers. Tertiary consumers are carnivores that eat other carnivores. Apex consumers are organisms at the top of the food chain.
Energy is the major factor that limits the length of the food chain, as energy is lost as heat between each trophic level due to the second law of thermodynamics. Therefore, after a limited number of trophic energy transfers, the amount of energy remaining in the food chain may not be great enough to support populations at a higher trophic level. Most of the energy is available at the lowest trophic level, the primary producers and energy is lost at each higher trophic level so that at the apex, the least amount of energy is available.
A major problem when using food chains to describe ecosystems is that even when all organisms are grouped at appropriate trophic levels, some of these organisms can feed on species from more than one trophic level and some of these organisms can be eaten by species from multiple trophic levels. Therefore, the linear food chain model of ecosystems is not completely linear and a linear model cannot completely describe an ecosystem. A holistic model which accounts for all the interactions between different species and their complex interconnected relationships with each other and with the environment is a more accurate and descriptive model for ecosystems. A food web is a graphic representation of a holistic, nonlinear web of primary producers, primary consumers, and higher-level consumers used to describe ecosystem structure and dynamics.
A comparison of the two types of structural ecosystem models shows that each model has strength. Food chains are more flexible for analytic modeling and are easier to understand and experiment with while food web models more accurately represent ecosystem dynamics and its data are more accurate for modeling.
Types of food webs that often exist within a single ecosystem include a grazing food web that has plants or other photosynthetic organisms at its base, followed by herbivores and carnivores. A detrital food web consists of a base of organisms that feed on decaying organic matter or dead organisms called decomposers. These organisms are usually bacteria or fungi that recycle organic material back into the biotic part of the ecosystem as they themselves are consumed by other organisms.
Ecosystem dynamics is study of the changes in ecosystem structure caused by changes in the environment (disturbances) or internal forces. Research in ecosystems include both controlled experiments along with researching ecosystems in their natural state.
A holistic ecosystem model attempts to quantify the composition, interaction, and dynamics of entire ecosystems and is the most representative of the ecosystem in its natural state. A food web is an example of a holistic ecosystem model. However, research using this model is time consuming, expensive, unfeasible, and unethical on large natural ecosystems. Quantifying all different species and dynamics for large habitats is difficult.
Therefore, researchers usually study ecosystems under more controlled conditions: A mesocosm is a part of a natural ecosystem that is partitioned and used for experiments. A microcosm is a recreation of an ecosystem entirely in an indoor or outdoor laboratory environment. However, the downside to using these methods is that altering a natural ecosystem may change the dynamics of the ecosystem.
Researchers use data from these experiments to develop ecosystem models that demonstrate the structural dynamics of ecosystems. One ecosystem model is a conceptual model that contains flow charts to show interactions of different compartments of the living and the nonliving components of the ecosystem structure and dynamics, and how disturbances affect the ecosystem. An analytical model is an ecosystem model that is created using simple mathematical formulas to predict the effects of environmental disturbances on the ecosystem. A simulation model is an ecosystem model that is created using complex computer algorithms to holistically model ecosystems and to predict the effects of environmental disturbances on the ecosystem.
Conceptual models are useful for describing ecosystem structure and dynamics and for demonstrating the relationships between different organisms in a community and their environment, most commonly depicted graphically as flow charts showing the relationship and transfer of energy or nutrients between them, and the flow of energy through a particular ecosystem. However, conceptual models are limited by their inability to predict the consequences of a changes in ecosystem species and environment. Ecosystems altered from their initial equilibrium state can often recover from natural or human disturbances.
Analytical models often use simple, linear components of ecosystems, such as food chains, and are mathematically complex. Therefore, analytical models are limited by their mathematical complexity. However, simulation models that use computer programs are more capable to handle the mathematical complexity of ecosystems. Recently supercomputers have been used to create simulations of ecosystems that account for the behavior of individual organisms.
Energy flows through ecosystems as all living things require energy for most metabolic pathways and assembling macromolecules like proteins, lipids, nucleic acids, and carbohydrates. Food webs illustrate how energy flows directionally through ecosystems.
Energy is acquired by living things in three ways: photosynthesis, chemosynthesis, and the consumption and digestion of other living or dead living organisms by heterotrophs.
Photosynthetic and chemosynthetic organisms are both classified as autotrophs: organisms capable of synthesizing their own food. Photosynthetic autotrophs use sunlight as an energy source, whereas chemosynthetic autotrophs use inorganic molecules as an energy source. Autotrophs are important for all ecosystems because these organisms produce energy for other living organisms to make life possible.
Photoautotrophs such as plants, algae, and photosynthetic bacteria serve as the energy source for a majority of the world's ecosystems, which are described by grazing food webs. Photoautotrophs use solar energy of the sun and convert it to chemical energy in the form of ATP, which is used to make organic molecules like glucose.
Chemoautotrophs are mainly bacterial that are found in rare ecosystems where sunlight is not available, such as caves or hydrothermal vents at the ocean bottom. Many chemoautotrophs in hydrothermal vents use hydrogen sulfide released from the vents as a source of chemical energy to make organic molecules like glucose for their energy and also supply energy to the ecosystem.
Productivity in an ecosystem is the percentage of energy of entering the ecosystem incorporated into biomass in a particular trophic level. Biomass is the total mass (living or dead) in a unit area at the time of measurement at the trophic level. The productivity of the primary producers is important in the ecosystem because these organisms bring energy to other living organisms by photoautotrophy or chemoautotrophy. The rate at which photosynthetic primary producers incorporate energy from the sun is called gross primary productivity.
All organisms need some energy for their own body functions. Net primary productivity of an ecosystem is the energy that remains in the primary producers after accounting for the organisms' respiration and heat loss. The net productivity is then available to the primary consumers at the next trophic level.
Energy flow is lost from primary producers in the ecosystem through the trophic levels, and the ecosystem loses large amounts of energy. The measurement of energy transfer efficiency between two successive trophic levels is the trophic level transfer efficiency (TLTE) and has the formula:
TLTE = (production at the present trophic level)/(production at the previous trophic level) x 100
Net production efficiency (NPE) allows ecologists to quantify how efficiently organisms of a particular trophic level incorporate the energy they receive into biomass to fuel the next trophic level:
NPE = (net consumer productivity)/(assimilation) x 100
Net consumer productivity is the energy content available to the organisms of the next trophic level. Assimilation is the biomass (energy content generated per unit area) of the present trophic level after accounting for the energy lost due to incomplete ingestion of food, energy used for respiration, and energy lost as waste. Some consumers eat only part of their food (and leave the bone), and this is called incomplete ingestion.
Ecological pyramids show the relative amounts of various parameters (number of organisms, energy, biomass) across trophic levels in the ecosystem. Pyramids of numbers can be either upright or inverted, depending on the ecosystem. Pyramids of biomass measure the amount of energy converted into living tissue at the different trophic levels. Pyramid ecosystem modeling can also be used to show energy flow through the trophic levels. Pyramids of energy are among the most consistent and representative models of ecosystem structure.
Biomagnification is the increasing concentration of persistent, toxic substances in organisms at each trophic level and is of environmental concern. Examples of toxic substances of concern in biomagnification are the pesticide (DDT), the coolant chemical (PCB), and heavy metals in seafood like mercury and cadmium.
Biogeochemical cycles are the recycling of inorganic matter between living organisms and their environment. Geologic processes of weathering, erosion, water drainage, and the subduction of the tectonic plates all contribute to the recycling of materials. As energy flows through the ecosystem from sunlight and leaving as heat, biomass is conserved and recycled through the most common elements of organic molecules: carbon, nitrogen, hydrogen, oxygen, phosphorus, and sulfur in the atmosphere, land, water, or subsurface.
The hydrosphere is the total amount of water (H2O) on Earth in all forms of solid, liquid, and gas: rivers, lakes, oceans, groundwater, polar ice caps, and glaciers, along with water vapor. Carbon is found in all organic macromolecules and fossil fuels. Nitrogen is a major component of our nucleic acids and proteins and it is very important to human agriculture. Phosphorous is a major component of nucleic acid along with nitrogen and is a main ingredient of artificial fertilizers used in agriculture and impact surface water. Sulfur is very important to the protein folding process. These element cycles are interconnected and depend on each other.
The Water Cycle: Only one percent of freshwater on earth is accessible from lakes and rivers. The rest of the water (99 percent) is either underground or frozen as ice. Many living things depend on freshwater. Most of the water on Earth is stored for long periods in the oceans, underground, and as ice. Residence time is a measure of the average time an individual water molecule stays in a particular reservoir.
Water cycle processes and stages include evaporation and sublimation, condensation and precipitation, subsurface water flow, surface runoff and snowmelt, and streamflow. The sun's energy leads to evaporation or liquid surface water to water vapor and the sublimation (ice to water vapor to atmosphere) of frozen water. Water vapor condenses into clouds as liquid or frozen droplets, followed by precipitation in the form of rain or snow to the Earth's surface. Rain or snow water permeates the ground, flows beneath the surface, enters surface water, or is stored for a long time. Water runoff from rain or melting ice enters streams and lakes that connect to oceans or directly to the ocean from runoff to complete the cycle. Rain and surface water runoff causes minerals from land to water. These minerals contain carbon, nitrogen, phosphorous, and sulfur.
The Carbon Cycle: Carbon is the second most abundant element in living organisms. Carbon is present in all organic molecules, and its role in the structure of macromolecules is very important to living organisms. The carbon cycle has two main sub-cycles: one involving the rapid carbon exchange among living organisms and the other involving the long-term cycling of carbon through geologic processes.
In the carbon cycle, carbon dioxide gas in the atmosphere dissolves in water. Photosynthesis converts carbon dioxide gas to organic carbon, and respiration cycles the organic carbon back into carbon dioxide gas. Long term storage of organic carbon occurs when matter from living organisms is buried deep underground and becomes fossilized. Volcanic activity and human emissions bring this stored carbon back into the carbon cycle.
Photosynthetic organisms convert atmospheric carbon dioxide into oxygen for the atmosphere that humans and animals breathe. Heterotrophs acquire the high-energy carbon compounds from autotrophs by consuming them and breaking them down by respiration to obtain cellular energy including ATP. There is constant exchange of oxygen and carbon dioxide between the autotrophs (plants and food producers) which need carbon and heterotrophs (animals and food consumers) which need oxygen. Gas exchange through the atmosphere and water allows the carbon cycle to connect all living things on Earth.
The biogeochemical cycle through land, water, and air is complex and occurs over longer periods of time. Carbon is stored in carbon reservoirs like the atmosphere, oceans and water bodies, ocean sediment, soil, land sediments, fossil fuels, and the interior of the Earth. Carbon dioxide from the atmosphere dissolves in water and combines with water molecules to form carbonic acid, and then it ionizes to carbonate and bicarbonate ions.
More than 90 percent of carbon in the ocean is bicarbonate ions. Some of these ions combine with seawater calcium to form calcium carbonate and marine organism shells. These organisms become part of the seafloor and forms limestone, the largest carbon reservoir on Earth.
On land, carbon is stored in soil from decomposition of living organisms or from weathering of rocks and minerals. This carbon can be leached into the water reservoirs by runoff. Also deeper underground are fossil fuels made of decomposed organic material. Carbon can also enter the atmosphere from volcanic eruptions and other geothermal systems and hydrothermal vents on the ocean floor.
Humans produce atmospheric carbon from burning fossil fuels and other materials. In addition, human civilization has cause the growth of farm animals that feed the world's humans also produces more atmospheric carbon.
The Nitrogen Cycle: Nitrogen enters the living world from the atmosphere through nitrogen-fixing bacteria. This nitrogen and nitrogenous waste from animals is then processed back into gaseous nitrogen by soil bacteria, which also supply terrestrial food webs with the organic nitrogen they need. Human activity can release nitrogen into the environment from the combustion of fossil fuels and the use of artificial fertilizers in agriculture, which is then moved into lakes, streams, and rivers by surface runoff. Atmospheric nitrogen produces acid rain and greenhouse gas. Agricultural fertilizer runoff also cause eutrophication, when nitrogen runoff cause the excess growth of microorganisms, which in turn deplete dissolved oxygen levels and kill living organisms. In the marine nitrogen cycle, ammonification, nitrification, and denitrification processes are performed by marine bacteria.
The Phosphorous Cycle: Phosphorous is a major component of nucleic acid and phospholipids, along with calcium phosphate in bones. Phosphorous is a nutrient in aquatic ecosystems. Phosphate runoff occurs from human activity and natural surface rock weathering, volcanic activity into the soil, water, and air. Phosphate enters the oceans from surface runoff, groundwater flow, and river flow. Phosphate dissolved in ocean water cycles into marine food webs. Some phosphate from the marine food webs falls to the ocean floor sediment. Fertilizer runoff produces excess phosphorous, causing excessive growth of microorganisms and depletes the dissolved oxygen, leading to the death of living organisms in oceans, rivers, and lakes.
A dead zone is an area within a freshwater or marine ecosystem where large areas are depleted of their normal flora and fauna caused by eutrophication, oil spills, toxic chemical dumping, and other human activities.
The Sulfur Cycle: Sulfur is an element in macromolecules of living things, the amino acid cysteine. Sulfur is part of the protein folding process. Sulfur enters the atmosphere from decomposition of organic molecules, volcanic activity, geothermal vents, and from the burning of fossil fuels by humans. Sulfur on land is deposited by precipitation, directly from the atmosphere (fallout), rock weathering, and geothermal vents. Sulfur enters the ocean from land runoff, atmospheric fallout, and from marine geothermal vents. Fossil fuels release sulfur into the atmosphere when burned. Acid rain takes sulfur to the ground surface and soil, causes building damage, and harms lake fauna.