Food Webs & Factors (Class 17)

Food Chain

is a representation of feeding relationships within a community

What are these diagrams following the flow of?

Energy

what direction do the arrows go

Prey to Predator

Links

the arrows from the consumed to consumer

basal species

usually autotrophs and/or organisms that do not feed on others but is eaten (ex: grass)

What tis the base of all food webs?

Primary Producers or autotrophs

Intermediate species

Herbivores, Carnivores, or Omnivores- organisms that feed on other species (ex: squirrel)

Top Predator

Feed on Intermediate and sometime basal species

3 Metrics used to compare food webs

• connectance

• linkage density

• chain length

S

species richness (count the list/species)

L

number of links (count the arrows)

connectance

C = L / S²

Linkage Density

LD = L / S

Chain Length

mean chain Length

limitation of food webs

rarely reflects where energy actually is and community dynamics do not involve indirect effects that happens in a community

Realized niche

set of conditions actually used by given animal (pop, species), after interactions with other species (predation and especially competition) have been taken into account.

fundamental niche

the entire set of conditions under which an animal (population, species) can survive and reproduce itself.

how does a niche influence and determine community structure?

environmental conditions change causing a change in distribution and abundance shifting community structure

zonation

refers to spatital changes in community structure

what drives zonation?

tolerance and interactions

• low resources → more competition (upper boundary)

• high resources → who is better adapted (lower boundary)

diffuse competition

describes the total competitive effects of a number of interspecific competitors (predation and mututalism can also be so)