Ecology - Community Energetics Final 2 Flashcards
Give an example of a study where the community of all herbivores showed greater stability with increasing plant diversity.
Insect and spider communities were studied in experimental prairie plots with different plant species diversity over the course of 11 years
What is the “The Portfolio Effect’”
a phrase that ecologists use to describe why it is that more diverse systems seem to be more stable
how does the Portfolio Effect cause natural systems to be more stable when they are more diverse?
the fact that there are a lot of similarities between the human economy and how ecosystems work!
What are compensatory interactions and how do causes natural systems to be more stable?
When one species’ abundance declines, another species is freed from competition with that species, and the population size of that species can increase
Give some examples of some organisms do not conveniently fit into trophic levels.
Omnivores that eat anything and everything like a coyote
In terrestrial ecosystems, only a small portion of the biomass is actually consumed; what happens to the rest of it?
most of the energy flow passes through as detritus
What is meant by trophic efficiency?
refers to the way in which energy is passed around the levels of a food web
Give three reasons why is so much energy, biomass, or number of individuals lost in going from one trophic level to the next?
(1) much of what is produced dies without being grazed, supporting a decomposer community of bacteria, fungi and detritivores
(2) Not all of the biomass ingested is assimilated, and some of it is lost in feces, which also becomes available to decomposers
(3) The Second Law of Thermodynamics dictates that some energy will inevitably be lost during all energy transfers!
What are transfer efficiencies?
proportion of primary productivity flowing along each of the possible energy pathways
depends on the way energy is used and passed on from one trophic level to the next!
What is meant by consumption efficiency
percentage of total productivity available at one trophic level that is actually consumed
why is consumption efficiency typically low for most communities?
much of what is out there is not good to eat, as well as the fact that herbivore densities are low in many habitats
Are consumption efficiencies higher in aquatic ecosystems than in terrestrial ecosystems?
Consumption efficiency is higher in aquatic ecosystems than in terrestrial ecosystems.
are consumption efficiencies higher for carnivores than herbivores
higher for carnivores than for herbivores
What is meant by assimilation efficiency?
Assimilation efficiency refers to the percentage of food taken in the guts of consumers that is assimilated across the gut wall
How does food quality affect assimilation efficiencies?
Food quality of plants and detritus is low because of complex compounds such as cellulose, lignins and humic acids, which are not easily digested and low concentrations of nutrients such as nitrogen and phosphorus
How do some herbivores have higher assimilation efficiencies than expected when so much of their diet includes cellulose?
Endotherms need to digest food more completely than ectotherms and thus have higher assimilation efficiencies - some herbivores have mutualistic symbionts that help them digest cellulose
What is meant by production efficiencies?
Production efficiency refers to the percentage of assimilated energy that is incorporated into new biomass
Why are production efficiencies so low for endotherms?
A small endotherm (e.g., a shrew), loses a greater proportion of its heat across its body surface
How does body size affect production efficiencies in endotherms? Why?
Smaller body size, the lower the product efficiency
How might the number of trophic levels change in a community?
Change in food quantity or quality impacts trophic efficiency and can determine consumer population size
What kind of factors may control the number of trophic levels in a community?
Amount of energy entering via primary production:
* More production should allow more trophic level
* This appears to be important in resource-poor ecosystems
Nutritional content of autotrophs, detritus and prey and the efficiency of energy transfers
* Herbivores on land consume a much lower proportion of autotroph biomass than herbivores in most aquatic ecosystems
What kind of evidence suggests that herbivore production is limited by the amount of food available?
positive relationship between net primary production and amount of biomass consumed by herbivores
Provide three reasons why terrestrial herbivores don’t consume more of the available biomass?
(1) Herbivores are constrained by predators and never reach carrying capacity
(2) Autotrophs have defenses against herbivory, such as secondary compounds, spines, etc.
(3) Autotrophs have defenses against herbivory, such as secondary compounds, spines, etc.
How might the frequency of disturbance affect the number of trophic levels in a community?
Higher trophic levels depend on lower levels and take time to re-establish after disturbance
* If disturbance is too frequent, higher levels may never become established