Lecture 8: Energy flows and food webs

Question 1

Food web data connects

Answer 1

species to their food resources and predators

Question 1

Food web

Answer 1

depicts energy flow through an ecological community

Question 2

Decomposition

Answer 2

Breakdown of detritus by detritivores
Bacteria, Archaea, Fungi
Critical in many element cycles

Question 3

Omnivores are effectively in between

Answer 3

trophic levels (able to eat both plants and animals)

Question 4

Arrows in food webs denote

Answer 4

direction of flow of energy and nutrients

Question 5

Trophic pyramids portray

Answer 5

relative amounts of energy or biomass in each trophic level

Question 6

In terrestrial ecosystems, energy and biomass pyramids are

Answer 6

similar since biomass is closely associated with energy production

Question 7

In aquatic ecosystems energy and biomass pyramids are

Answer 7

not closely associated so biomass pyramids may be inverted

Question 8

___ is not always good indicator of energy flows through food chains

Answer 8

Biomass (since lots of it is lost)

Question 9

Factors affecting energy flow

Answer 9

Amount of NPP at base of food web
Proportion of each trophic level consumed by one above it
Nutritional content of autotrophs, detritus, and prey
Efficiency of energy transfers

Question 10

Trophic efficiency

Answer 10

Amount of energy at one trophic level divided by amount of energy at the next lowest trophic level.

Question 11

Consumption efficieny

Answer 11

proportion of available energy ingested

Question 12

Consumption efficiency is seen higher in

Answer 12

Higher in aquatic ecosystems than in terrestrial
Higher in carnivores

Question 13

Assimilation efficiency

Answer 13

proportion of food ingested that is assimilated
depends on food quality and consumer physiology

Question 14

Production efficiency

Answer 14

proportion of assimilated food that produces new biomass
relates to thermal physiology and consumer size

Question 15

Why is consumption efficiency from autotrophic to herbivores greater in aquatic than terrestrial systems?

Answer 15

Population growth of herbivores less constrained in aquatic systems
Organisms in aquatic are shorter lived, less economics of defense

Question 16

Bottom up control of food chains

Answer 16

focuses on the lower trophic levels of a food chain

nutrients, light, or water

Question 17

Top down control of food chains

Answer 17

when populations of organisms in lower trophic levels are controlled by organisms at the top

Question 18

Factors controlling number of trophic levels

Answer 18

amount of energy entering via primary production
ecosystem size
frequency of disturbance

Question 19

Trophic cascade

Answer 19

series of trophic interactions that result in change in biomass and species composition

tend to be stronger and more common in aquatic systems