Ecology - Community Energetics Final 2

Question 1

Give an example of a study where the community of all herbivores showed greater stability with increasing plant diversity.

Answer 1

Insect and spider communities were studied in experimental prairie plots with different plant species diversity over the course of 11 years

Question 2

What is the “The Portfolio Effect’”

Answer 2

a phrase that ecologists use to describe why it is that more diverse systems seem to be more stable

Question 3

how does the Portfolio Effect cause natural systems to be more stable when they are more diverse?

Answer 3

the fact that there are a lot of similarities between the human economy and how ecosystems work!

Question 4

What are compensatory interactions and how do causes natural systems to be more stable?

Answer 4

When one species’ abundance declines, another species is freed from competition with that species, and the population size of that species can increase

Question 5

Give some examples of some organisms do not conveniently fit into trophic levels.

Answer 5

Omnivores that eat anything and everything like a coyote

Question 6

In terrestrial ecosystems, only a small portion of the biomass is actually consumed; what happens to the rest of it?

Answer 6

most of the energy flow passes through as detritus

Question 7

What is meant by trophic efficiency?

Answer 7

refers to the way in which energy is passed around the levels of a food web

Question 8

Give three reasons why is so much energy, biomass, or number of individuals lost in going from one trophic level to the next?

Answer 8

(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!

Question 9

What are transfer efficiencies?

Answer 9

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!

Question 10

What is meant by consumption efficiency

Answer 10

percentage of total productivity available at one trophic level that is actually consumed

Question 11

why is consumption efficiency typically low for most communities?

Answer 11

much of what is out there is not good to eat, as well as the fact that herbivore densities are low in many habitats

Question 12

Are consumption efficiencies higher in aquatic ecosystems than in terrestrial ecosystems?

Answer 12

Consumption efficiency is higher in aquatic ecosystems than in terrestrial ecosystems.

Question 13

are consumption efficiencies higher for carnivores than herbivores

Answer 13

higher for carnivores than for herbivores

Question 14

What is meant by assimilation efficiency?

Answer 14

Assimilation efficiency refers to the percentage of food taken in the guts of consumers that is assimilated across the gut wall

Question 15

How does food quality affect assimilation efficiencies?

Answer 15

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

Question 16

How do some herbivores have higher assimilation efficiencies than expected when so much of their diet includes cellulose?

Answer 16

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

Question 17

What is meant by production efficiencies?

Answer 17

Production efficiency refers to the percentage of assimilated energy that is incorporated into new biomass

Question 18

Why are production efficiencies so low for endotherms?

Answer 18

A small endotherm (e.g., a shrew), loses a greater proportion of its heat across its body surface

Question 19

How does body size affect production efficiencies in endotherms? Why?

Answer 19

Smaller body size, the lower the product efficiency

Question 20

How might the number of trophic levels change in a community?

Answer 20

Change in food quantity or quality impacts trophic efficiency and can determine consumer population size

Question 21

What kind of factors may control the number of trophic levels in a community?

Answer 21

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

Question 22

What kind of evidence suggests that herbivore production is limited by the amount of food available?

Answer 22

positive relationship between net primary production and amount of biomass consumed by herbivores

Question 23

Provide three reasons why terrestrial herbivores don’t consume more of the available biomass?

Answer 23

(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.

Question 24

How might the frequency of disturbance affect the number of trophic levels in a community?

Answer 24

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

Question 25

How might ecosystem size affect the species diversity of a community?

Answer 25

Larger ecosystems support larger populations, have more habitat heterogeneity and have higher species diversity

Question 26

Cite a study that demonstrated that larger sized ecosystems have higher species diversity

Answer 26

6 islands in the Bahamas found that island size was correlated with number of trophic levels (Takimoto et al. 2008)

Question 27

What are “ecological pyramids” and what causes them?

Answer 27

loss of energy (about 90%) that occurs at each trophic level usually results in what Elton (1927) called ecological pyramids

Question 28

What is biomagnification and why does it occur?

Answer 28

the concentration of persistent toxins (i.e., ones that are not broken down or metabolized) in the bodies of organisms occupying higher trophic levels

Question 29

Give an example of the effects of biomagnification

Answer 29

On humans: DDT in some mother’s milk is found in levels higher than that allowed by EPA for cow’s milk!

Question 30

What is bioaccumulation and how does it differ from biomagnification?

Answer 30

here is another term that relates to the concentration of toxins in the bodies of living organisms within a trophic level

Question 31

Give an example of bioaccumulation and its effects on humans.

Answer 31

DDT in mother milk

Question 32

Who was Rachel Carson and what was the title of the book she wrote?

Answer 32

Silent Spring (1962)
* She described the devastating effects of pesticides, especially DDT, on nontarget bird and mammal species

Question 33

How did this book contribute to the conservation movement and eventual ban on DDT in the United States?

Answer 33

documentation and ability to communicate with the public led to increased scrutiny of chemical pesticides and eventually a ban on manufacture and use of DDT in the United States