Honors Biology Chapter 37 The Nature of Ecosystems

Concise review of ecosystem components, energy flow, ecological pyramids, biogeochemical cycles, and human impacts based on the Chapter 37 class notes.

Ecosystem

A system containing abiotic nonliving components and biotic living components.

Abiotic components

Nonliving parts of an ecosystem, such as the atmosphere, water, and soil.

Biotic components

The living parts of an ecosystem.

Autotrophs or producers

Organisms that use inorganic nutrients and an outside energy source to make organic nutrients.

Heterotrophs or consumers

Organisms that obtain organic nutrients from other organisms for energy.

Photosynthetic producers

Producers that use light energy; mainly algae in water and green plants on land.

Chemoautotrophs

Bacteria that obtain energy by oxidizing inorganic compounds.

Where are chemoautotrophs found?

Hydrothermal vents and caves.

Herbivores

Primary consumers that eat plants.

Carnivores

Consumers that eat animals; secondary consumers eat herbivores.

Tertiary consumers

Carnivores that eat other carnivores that ate herbivores.

Omnivores

Consumers that eat both plants and animals.

Decomposers

Fungi and bacteria that use enzymes to break down dead organic material.

Detritivores

Decomposers that eat decaying material called detritus; examples include worms and crabs.

Energy flow

Energy moves from the Sun to autotrophs and then consumers, eventually dissipating as heat.

Chemical cycling

Inorganic nutrients enter producers and are recycled for repeated use in ecosystems.

Food chain

A single path of energy flow through an ecosystem.

Food web

Multiple interconnected paths of energy flow that show complex feeding relationships.

Grazing food web

A food web that begins with leaves, stems, and seeds eaten by herbivores.

Detrital food web

A food web that begins with decaying matter and often contains the largest energy store.

How are grazing and detrital food webs connected?

Organisms can link them; for example, birds feed on worms.

Trophic level

A feeding position in a food chain or food web.

First trophic level

Primary producers.

Second trophic level

Primary consumers, or herbivores.

Third trophic level

Secondary consumers, or carnivores.

10 percent rule

On average, only about 10% of one trophic level's energy is incorporated into the next.

Why are food chains usually short?

Limited energy transfer usually supports only three or four trophic links.

Limitation of ecological pyramids

They do not provide a clear place for decomposers.

Pyramid of numbers

Shows the number of organisms at each trophic level, usually decreasing upward.

Pyramid of biomass

Shows total weight at each trophic level, usually decreasing upward.

Pyramid of energy

Shows energy content at each trophic level; energy decreases upward and this is the best model.

Biogeochemical cycle

The movement and recycling of chemicals through living organisms and the nonliving environment.

Reservoir

A storehouse for a chemical in a biogeochemical cycle.

Exchange pool

The part of a biogeochemical cycle where autotrophs access a chemical.

Biotic community role in chemical cycles

Chemicals move through the community along food chains.

Primarily gaseous cycles

The carbon and nitrogen cycles.

Primarily sedimentary cycle

The phosphorus cycle.

Water cycle

The cycling of water through processes including evaporation and precipitation.

Transpiration

Evaporation of water from plants through leaf openings called stomata.

Aquifer

An underground store of freshwater.

How much of Earth's water is freshwater?

About 3%.

Groundwater mining

Aquifer withdrawal that exceeds replenishment and can cause sinkholes.

Phosphorus cycle reservoir

Rocks, which release phosphorus through weathering.

Limiting nutrient

A scarce nutrient, often phosphorus, that autotrophs quickly incorporate before it moves to heterotrophs.

Human impacts on the phosphorus cycle

Mining, fertilizers, and waste runoff add large amounts of phosphorus to ecosystems.

Eutrophication

Nutrient over-enrichment causes algal blooms, more decomposition, oxygen loss, and possible massive fish kills.

Nitrogen cycle reservoir

The atmosphere, which is about 78% nitrogen gas.

Nitrogen fixation

Conversion of nitrogen gas into usable nitrogen compounds.

Bacterial nitrogen fixation

Bacteria convert N2 into NH3.

Atmospheric nitrogen fixation

Lightning converts N2 into nitrate.

Nitrification

Bacteria convert NH3 into nitrite and then nitrate.

Nitrogen movement through organisms

Plants incorporate nitrate into tissues, animals consume it, and decomposers return ammonia to soil.

Denitrification

Bacteria convert nitrate back into N2 gas; it is the opposite of nitrogen fixation.

Human impacts on the nitrogen cycle

Fertilizers and fossil-fuel burning produce nitrous oxides.

Effects of excess nitrous oxides

They contribute to acid rain, photochemical smog, and thermal inversions.

Carbon cycle reservoir

Living and dead organisms.

Carbon cycle exchange pool

The atmosphere; photosynthesis and cellular respiration exchange carbon dioxide.

Carbon in water

Carbon dioxide in water becomes bicarbonate.

Human impacts on the carbon cycle

Fossil-fuel burning and forest destruction release more CO2 than ecosystems remove.

Greenhouse effect

Excess atmospheric gases trap heat, raising global mean temperature and contributing to global warming.