Lecture 8: Energy flows and food webs Flashcards
Food web data connects
species to their food resources and predators
Food web
depicts energy flow through an ecological community
Decomposition
Breakdown of detritus by detritivores
Bacteria, Archaea, Fungi
Critical in many element cycles
Omnivores are effectively in between
trophic levels (able to eat both plants and animals)
Arrows in food webs denote
direction of flow of energy and nutrients
Trophic pyramids portray
relative amounts of energy or biomass in each trophic level
In terrestrial ecosystems, energy and biomass pyramids are
similar since biomass is closely associated with energy production
In aquatic ecosystems energy and biomass pyramids are
not closely associated so biomass pyramids may be inverted
___ is not always good indicator of energy flows through food chains
Biomass (since lots of it is lost)
Factors affecting energy flow
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
Trophic efficiency
Amount of energy at one trophic level divided by amount of energy at the next lowest trophic level.
Consumption efficieny
proportion of available energy ingested
Consumption efficiency is seen higher in
Higher in aquatic ecosystems than in terrestrial
Higher in carnivores
Assimilation efficiency
proportion of food ingested that is assimilated
depends on food quality and consumer physiology
Production efficiency
proportion of assimilated food that produces new biomass
relates to thermal physiology and consumer size
Why is consumption efficiency from autotrophic to herbivores greater in aquatic than terrestrial systems?
Population growth of herbivores less constrained in aquatic systems
Organisms in aquatic are shorter lived, less economics of defense
Bottom up control of food chains
focuses on the lower trophic levels of a food chain
nutrients, light, or water
Top down control of food chains
when populations of organisms in lower trophic levels are controlled by organisms at the top
Factors controlling number of trophic levels
amount of energy entering via primary production
ecosystem size
frequency of disturbance
Trophic cascade
series of trophic interactions that result in change in biomass and species composition
tend to be stronger and more common in aquatic systems
