24 Energy flow in Food Webs

Persistent Organic Pollutants (POPs)

Remain in the environment for a long time, originate from from industrial and agricultural activities.

POPs remain in … for many decades

arctic snow and ice

Omnivores

Organisms that feed at multiple trophic levels

Allochthonous Inputs

External energy inputs into aquatic ecosystems (plant leaves, stems, wood, dissolved organic matter)

Autochthonous Energy

Energy produced by autotrophs

Allochthonous inputs are more important in…

streams and rivers

Allochthonous energy is often of…

Lower quality

Autochthonous energy inputs are more important in … of a river

the middle

Cumulative available energy … with each trophic level

decreases

What represents the energy transferred and lost between trophic levels

the trophic pyramid

Biomass pyramid

Represents the mass of organisms at each tropic levels.

Biomass pyramid in Aquatic system

In aquatic ecosystems the biomass pyramid is inverted compared to the energy pyramid because of high consumption rates and relatively short lifespans of primary producers

Energy efficiency

The output of energy per unit of energy input

Trophic efficiency

The amount of energy at one trophic level divided by the amount of energy at the trophic level immediately below it.

Consumption efficiency

The proportion of available energy that is consumed

Assimilation efficiency

The proportion of ingested food that is assimilated by the consumer

Production efficiency

The proportion of assimilated food that goes into producing new consumer biomass

Consumption efficiency is typically … in aquatic ecosystems than in terrestrial ecosystems.

Higher

Assimilation efficiency is determined by…

The quality of the food and physiology of the consumer

Quality of food available to herbivores and detritovores is generally… than that of the food available to carnivores.

Lower because complex carbon compounds are not easily digested

Endotherms digest food … than ectotherms

more completely (have higher assimilation efficiency)

Endotherms have … production efficiency than ectotherms.

Lower

How does body size control production efficiency?

Smaller = more heat lost = lower production efficiency

Bottom up Control

The resources that limit NPP determine energy flow through an ecosystem.

Top Down Control

Energy flow is governed by rates of consumption at the highest trophic levels.

Trophic Cascade

Changes at one trophic level affect multiple levels of the food web, typically top down.

What buffers the effects of trophic cascades

Omnivory

Factors affecting the number of trophic levels in an ecosystem

• Energy entering an ecosystem

• Disturbances

• Ecosystem area

Assimilation efficiency

The proportion of the ingested food that is assimilated

Production Efficiency

The proportion of the assimilated food that is

used to produce new consumer biomass

Endotherms tend to digest food … than ectotherms

More completely due to

• Higher thermal stability

• Tendency to have a more developed digestive system

• Higher assimilation efficiency

Interaction Strength

a measure of the effect of the population of one species on

the population size of another species

Keystone Species Concept

implies that

protecting such species may be critical for protection of the many other species

that depend on them

Portfolio affect

variation in the population of one species cancels out variation in another such that overall abundance in the community remains the same.

Bioaccumulation

Chemical compounds taken up by organisms are not metabolized or excreted so they become progressively more concentrated in the body over the organism’s lifetime

Biomagnification

Bioaccumulation can lead to increasing tissue concentrations of these compounds in animals at successively higher trophic levels as animals at each trophic level consume prey with higher concentrations of the compounds.