Community Ecology

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Slide 21

Trophic Structure = a key factor in community dynamics

Trophic structure is the feeding relationships between organisms in a community.

Food chains link trophic levels from producers to top carnivores.

A food web is a branching food chain with complex trophic interactions.

Species may play a role at more than one trophic level.

Food chains in a food web are usually only a few links long. WHY?

Slide 22

Terrestrial and Marine Food Chains

Carnivore

Carnivore

Carnivore

Herbivore

Plant

A terrestrial food chain

Quaternary

consumers

Tertiary

consumers

Secondary

consumers

Primary

consumers

Primary

producers

A marine food chain

Phytoplankton

Zooplankton

Carnivore

Carnivore

Carnivore

Slide 23

An Antarctic Marine Food Web

Humans

Smaller

toothed

whales

Baleen

whales

Sperm

whales

Elephant

seals

Leopard

seals

Crab-eater

seals

Birds

Fishes

Squids

Carnivorous

plankton

Copepods

Euphausids

(krill)

Phyto-

plankton

Slide 24

Limits on Food Chain Length

Food chains in food webs are usually only a few links long.

Two hypotheses attempt to explain food chain length: the energetic hypothesis and the dynamic stability hypothesis.

The energetic hypothesis suggests that length is limited by inefficient energy transfer.

The dynamic stability hypothesis proposes that long food chains are less stable than short ones.

Most data support the energetic hypothesis.

Slide 25

Species with a Large Impact

Certain species have a very large impact on community structure. Such species are highly abundant OR play a pivotal role in community dynamics.

Dominant species = those that are most abundant or have the highest biomass.

Biomass is the total mass of all individuals in a population. Dominant species exert powerful control over the occurrence and distribution of other species.

Slide 26

Invasive species, typically introduced to a new environment by humans, often lack predators or disease pathogens. Invasive species disrupt ecosystem dynamics. They frequently out-compete / displace native populations.

Slide 27

Keystone Species

Keystone species exert strong control on a community by their ecological roles, or niches.