Ecology Part 1 Chapter 2 – Principles of Ecology Ecosystems and the Biosphere

Energy Transfer Autotrophs – organisms that can make their own foodAutotrophs – organisms that can make their own food Because autotrophs capture energy and use it to make organic molecules, they are called producers.Because autotrophs capture energy and use it to make organic molecules, they are called producers. Most are photosyntheticMost are photosynthetic Chemosynthetic organisms do not use sunlight as an energy source. They use inorganic molecules to produce carbohydrates.Chemosynthetic organisms do not use sunlight as an energy source. They use inorganic molecules to produce carbohydrates.

In terrestrial ecosystems, plants are the major producers.In terrestrial ecosystems, plants are the major producers. In aquatic ecosystems, photosynthetic protists and bacteria are the major producers.In aquatic ecosystems, photosynthetic protists and bacteria are the major producers. Gross primary productivity is the rate at which producers capture energy.Gross primary productivity is the rate at which producers capture energy. Organic material in an ecosystem is known as biomass.Organic material in an ecosystem is known as biomass. Producers add biomass to an ecosystem by making organic molecules.Producers add biomass to an ecosystem by making organic molecules.

Net primary productivity is the rate at which biomass accumulatesNet primary productivity is the rate at which biomass accumulates Usually expressed in units of energy per year (kcal/m 2 /yr) or in units of mass per unit area per year (g/m 2 /yr)Usually expressed in units of energy per year (kcal/m 2 /yr) or in units of mass per unit area per year (g/m 2 /yr) Equals the gross primary productivity minus the rate of respiration in producers.Equals the gross primary productivity minus the rate of respiration in producers. In terrestrial ecosystems, productivity is determined by light, temperature, and precipitation.In terrestrial ecosystems, productivity is determined by light, temperature, and precipitation. In aquatic ecosystems, productivity is determined by light and the availability of nutrients.In aquatic ecosystems, productivity is determined by light and the availability of nutrients.

Consumers Organisms that cannot manufacture their own food are called heterotrophsOrganisms that cannot manufacture their own food are called heterotrophs Heterotrophs obtain energy by consuming organic molecules made by other organisms. They are know as consumers.Heterotrophs obtain energy by consuming organic molecules made by other organisms. They are know as consumers. Herbivores eat producersHerbivores eat producers Carnivores eat other consumersCarnivores eat other consumers Omnivores eat both producers and consumersOmnivores eat both producers and consumers Detritivores are consumers that feed on dead and decaying matter.Detritivores are consumers that feed on dead and decaying matter. Decomposers are a type of detritivore. They cause decay by breaking down complex molecules in dead tissue into simpler molecules that can be recycled.Decomposers are a type of detritivore. They cause decay by breaking down complex molecules in dead tissue into simpler molecules that can be recycled.

Energy Flow In an ecosystem, energy flows in one direction only, from producers to consumers.In an ecosystem, energy flows in one direction only, from producers to consumers. An organism’s trophic level shows the organism’s position in the sequence of energy transfersAn organism’s trophic level shows the organism’s position in the sequence of energy transfers

All producers belong to the first trophic level.All producers belong to the first trophic level. Herbivores belong to the second trophic levelHerbivores belong to the second trophic level Predators of herbivores belong to the third trophic level.Predators of herbivores belong to the third trophic level. Most ecosystems contain only three or four trophic levels.Most ecosystems contain only three or four trophic levels. A food chain is a single pathway of feeding relationships in an ecosystem that results in energy transfer.A food chain is a single pathway of feeding relationships in an ecosystem that results in energy transfer.

Most food chains interlink.Most food chains interlink. A food web shows the interrelated food chains in an ecosystem.A food web shows the interrelated food chains in an ecosystem.

Quantity of Energy Transfer Roughly 10% of the total energy in one trophic level is available to the organisms in the next levelRoughly 10% of the total energy in one trophic level is available to the organisms in the next level The rest of the energy is used for metabolism and is lost as heat.The rest of the energy is used for metabolism and is lost as heat.

Since the rate of energy transfer between trophic levels is so low, ecosystems rarely contain more than a few trophic levels.Since the rate of energy transfer between trophic levels is so low, ecosystems rarely contain more than a few trophic levels. It takes many more producers to support first, second, and third order consumers.It takes many more producers to support first, second, and third order consumers. If the first trophic level contained 50,000 kcal of energy, how much would be available to the:If the first trophic level contained 50,000 kcal of energy, how much would be available to the: First-order consumers?First-order consumers? Second-order consumers?Second-order consumers? Third-order consumers?Third-order consumers?

Ecosystem Recycling Remember, energy flows through an ecosystem (one direction only)Remember, energy flows through an ecosystem (one direction only) Water and minerals like carbon, nitrogen, calcium, and phosphorus are recycled and reused.Water and minerals like carbon, nitrogen, calcium, and phosphorus are recycled and reused. Biogeochemical cycles move substances from the abiotic (non-living) part of the environment, into living things, and back again.Biogeochemical cycles move substances from the abiotic (non-living) part of the environment, into living things, and back again. We will look at the water cycle, carbon cycle, and nitrogen cycle.We will look at the water cycle, carbon cycle, and nitrogen cycle.

The Water Cycle

The Carbon Cycle

The Nitrogen Cycle

Nitrogen gas, N 2, is readily available in the atmosphere.Nitrogen gas, N 2, is readily available in the atmosphere. Most plants can use nitrogen only in the form of nitrate.Most plants can use nitrogen only in the form of nitrate. The process of converting nitrogen gas into nitrate is called nitrogen fixation.The process of converting nitrogen gas into nitrate is called nitrogen fixation. Nitrogen-fixing bacteria convert nitrogen gas into ammonia, then nitrite, and then nitrate, which plants can use.Nitrogen-fixing bacteria convert nitrogen gas into ammonia, then nitrite, and then nitrate, which plants can use.

Nitrogen-fixing bacteria live in the soil and in the roots of some kinds of plants, like beans, peas, clover, and alfalfa (a mutualistic relationship)Nitrogen-fixing bacteria live in the soil and in the roots of some kinds of plants, like beans, peas, clover, and alfalfa (a mutualistic relationship) Decaying organisms release nitrogen as ammonia in a process called ammonificationDecaying organisms release nitrogen as ammonia in a process called ammonification Bacteria in the soil take up ammonia and oxidize it into nitrates and nitrites in a process called nitrification.Bacteria in the soil take up ammonia and oxidize it into nitrates and nitrites in a process called nitrification. Plants use nitrates to form amino acids.Plants use nitrates to form amino acids. Nitrogen is returned to the atmosphere through denitrification, which occurs when anaerobic bacteria break down nitrates and release nitrogen gas back into the atmosphere.Nitrogen is returned to the atmosphere through denitrification, which occurs when anaerobic bacteria break down nitrates and release nitrogen gas back into the atmosphere.

Plants can absorb nitrates from the soil, but animals cannot.Plants can absorb nitrates from the soil, but animals cannot. How can animals get nitrogen?How can animals get nitrogen? Animals get nitrogen the same way they get energy – by eating plants and other organisms and then digesting the proteins and amino acids to get nitrogen.Animals get nitrogen the same way they get energy – by eating plants and other organisms and then digesting the proteins and amino acids to get nitrogen.

The Phosphorus Cycle

Phosphorus Cycle Unlike carbon, oxygen, and nitrogen, phosphorus does not enter the atmosphere.Unlike carbon, oxygen, and nitrogen, phosphorus does not enter the atmosphere. Phosphorus remains mostly on land in rock and soil minerals, and in ocean sediments.Phosphorus remains mostly on land in rock and soil minerals, and in ocean sediments. Phosphorus exists in the form of inorganic phosphatePhosphorus exists in the form of inorganic phosphate As the rocks and sediments gradually wear down, phosphate is released.As the rocks and sediments gradually wear down, phosphate is released.

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