BISC 121 - Ecosystem Ecology Part 1 - Midterm 4

What does an ecosystem consist of?

All the organisms living in a community, as well as the abiotic factors with which they interact.

What do ecosystems range from?

A microcosm, such as an aquarium, to a large area such as a lake or forest.

What two main processes do ecosystem dynamics involve?

Energy flow and chemical cycling.

What does energy do in ecosystems?

Flows through ecosystems.

What does matter do in ecosystems?

Cycles within them.

What do physical laws govern?

Energy flow and chemical cycling in ecosystems.

What do ecologists study within their system?

The transformations of energy and matter.

To what does the conservation of energy apply?

Ecosystems, particularly energy flow.

What does the first law of thermodynamics state?

Energy cannot be created or destroyed, only transformed.

How does energy enter an ecosystem?

As solar radiation.

What happens to energy in an ecosystem?

It is conserved and is lost from organisms as heat.

What does the second law of thermodynamics state?

Every exchange of energy increases the entropy of the universe.

What is true about energy conversions in ecosystems?

They are not completely efficient, and some energy is always lost as heat.

What does the law of conservation of mass state?

Matter cannot be created or destroyed.

What happens to chemical elements within ecosystems?

They are continually recycled.

How do most nutrients enter a forest ecosystem?

As dust or solutes in rain.

How are most nutrients carried away in a forest ecosystem?

In water.

What does it mean that ecosystems are open systems?

They absorb energy and mass and release heat and waste products.

What do autotrophs do?

Build molecules themselves using photosynthesis or chemosynthesis as an energy source.

What do heterotrophs depend on?

The biosynthetic output of other organisms.

What do energy and nutrients pass from and to?

From primary producers (autotrophs) to primary consumers (herbivores) to secondary consumers (carnivores) to tertiary consumers (carnivores that feed on other carnivores).

What are detritivores or decomposers?

Consumers that derive their energy from detritus.

What is detritus?

Nonliving organic matter.

What groups are important detritivores?

Prokaryotes and fungi.

What does decomposition connect?

All trophic levels.

What is primary production in an ecosystem?

The amount of light energy* converted to chemical energy by autotrophs during a given time period.

What does photosynthetic production set for an ecosystem’s energy budget?

The spending limit for an ecosystem’s energy budget.

What does the asterisk next to “light energy” indicate?

Some ecosystems are based locally on chemoautotrophy, not only light energy (e.g. hydrothermal vents).

What limits photosynthetic output of ecosystems on a global scale?

The amount of solar radiation reaching the Earth’s surface.

How much solar energy actually strikes photosynthetic organisms?

Only a small fraction.

How much of the solar energy that strikes photosynthetic organisms is usable?

Even less is of a usable wavelength.

What is gross primary production (GPP)?

Total primary production.

What is net primary production (NPP)?

GPP minus energy used by primary producers for respiration.

What is available to consumers, GPP or NPP?

NPP.

What do ecosystems vary greatly in regarding production?

NPP and contribution to the total NPP on Earth.

What is standing crop?

The total biomass of photosynthetic autotrophs at a given time.

What technique is used for satellite analysis of productivity?

Chlorophyll and light measurements.

What does satellite analysis supplement?

Ground-based data.

What advantage does satellite analysis provide?

Views huge areas at once.

What ecosystems are among the most productive per unit area?

Tropical rain forests, estuaries, and coral reefs.

What is true about marine ecosystems per unit area?

They are relatively unproductive.

Why do marine ecosystems contribute much to global net primary production?

Because of their volume.

What do different ecosystems differ greatly in?

Their production and their contribution to the total production of the Earth.

What controls primary production in marine and freshwater ecosystems?

Both light and nutrients.

What does depth of light penetration affect?

Primary production in the photic zone of an ocean or lake.

What is the first variable to control primary production in oceans?

Light.

Why is light the first variable to control primary production in oceans?

Solar radiation can only penetrate to a certain depth (photic zone).

What is the absolute maximum depth listed for light penetration?

200m.

Why is the usual light penetration depth much shallower, such as 50m?

Absorption of light by phytoplankton and other particles.

What are nitrogen and phosphate levels usually like in the open ocean photic zone?

Very low.

Why are nitrogen and phosphate levels low in the photic zone?

Due to uptake by phytoplankton.

Where are nitrogen and phosphate levels high?

In deeper water where light does not penetrate and nutrients are regenerated by heterotrophs.

What prevents mixing between deep nutrient-rich water and the photic zone?

Stratification.

What usually limits primary production in the photic zone of oceans and lakes?

Nutrients.

What is a limiting nutrient?

The element that must be added for production to increase in an area.

What nutrients typically most often limit marine production?

Nitrogen and phosphorous.

What nutrient sometimes limits production in some central ocean basins?

Iron.

What did nutrient enrichment experiments off Long Island, New York confirm?

That nitrogen was limiting phytoplankton growth.

What did experiments in the Sargasso Sea show?

That iron limited primary production.

What does upwelling contribute to?

Regions of high primary production and major fisheries.

What causes upwelling?

Wind patterns.

What are important upwelling regions?

Equatorial upwelling (divergent currents) and some temperate or tropical west coasts where prevailing winds blow surface water offshore.

What partly controls primary production in freshwater lakes?

Solar radiation and temperature.

What else is important in controlling freshwater primary production?

Nutrients.

What shifted many U.S. lakes in the 1970s toward green algae–dominated communities?

Sewage and fertilizer pollution adding significant nutrients.

What is this process called?

Eutrophication.

What are undesirable impacts of eutrophication?

Murky water, often locally anaerobic and smelly.

What helps control eutrophication?

Controlling pollution.

What did whole-lake experiments show as the limiting factor?

P is the limiting factor.

What reduced eutrophication?

Reduction of P in home detergents.

What affects primary production on a large scale in terrestrial ecosystems?

Temperature and moisture.

What types of places are the most productive?

Rainy warm places.

What does actual evapotranspiration represent?

The contrast between wet and dry climates.

What is actual evapotranspiration?

The water annually transpired by plants and evaporated from a landscape.

What is actual evapotranspiration related to?

Net primary production.

On a more local scale, what often limits primary production?

A soil nutrient.

In the experiment with various nutrient combinations added to soil, what factor limits production early?

N limits early.

In the same experiment, what happens after extra N is added?

Extra N leads to P limitation.

What is secondary production of an ecosystem?

The amount of chemical energy in food converted to new biomass during a given period of time.

When a caterpillar feeds on a leaf, how much of the leaf’s energy is used for secondary production?

Only about one-sixth.

What is an organism’s production efficiency?

The fraction of energy stored in food that is not used for respiration.

What is trophic efficiency?

The percentage of production transferred from one trophic level to the next.

What is the usual range of trophic efficiency?

5% to 20%.

What happens to trophic efficiency over the length of a food chain?

It is multiplied.

Approximately what percentage of chemical energy fixed by photosynthesis reaches a tertiary consumer?

0.1%.

What does a pyramid of net production represent?

The loss of energy with each transfer in a food chain.

In a biomass pyramid, what does each tier represent?

The dry weight of all organisms in one trophic level.

What do most biomass pyramids show?

A sharp decrease at successively higher trophic levels.

Why can some aquatic ecosystems have inverted biomass pyramids?

Producers (phytoplankton) are consumed so quickly that they are outweighed by primary consumers.

What is turnover time?

A ratio of the standing crop biomass to production.

What must an inverted biomass pyramid be supported by?

More rapid turnover at lower trophic levels.

What implication does the efficiency of energy flow have for humans?

Eating meat is a relatively inefficient way of tapping photosynthetic production.

What could worldwide agriculture theoretically do if humans ate only plant material?

Feed more people.

What does this idea support?

The rationale of some vegetarians.

What complicates the issue of dietary energy efficiency?

Animal feed (grain or grass), sustainability, ecosystem stability, use of animal waste as fertilizer, and other variables.

Why can humans not eat grass?

Humans are naturally omnivores and cannot eat grass.

What question does the green world hypothesis address?

Why aren’t the plants all eaten?

What does the green world hypothesis propose?

Several factors that keep herbivores in check.

What factors keep herbivores in check according to the green world hypothesis?

Plant defenses.

What other interactions keep herbivores in check?

Interspecific interactions (including predation!).