Chapter 28

Community Interactions

Why Are Interactions in Communities Important?

• Community • Interactions limit population size

– Balance between resources and # of individuals

– Exotic species may upset balance

• Interactions influence evolutionary change– Coevolution

Interspecific Competition

• Each species has a unique place in its ecosystem– Ecological niche

• Niches of species never overlap completely– Competitive exclusion

• Competitive exclusion may help determine population distribution– Fundamental niche vs. Realized niche

• Species may evolve to reduce competition– Resource partitioning

What are the Effects of Predator-Prey Interactions

• Coevolution

• Predators consume prey

• Parasites feeding off host but may not kill the host– Herbivores

• Camouflage– Hiding in plain site

Blending in

resemble specific objects

Camouflage assists predators

Camouflage can be beneficial to predators as well

• Bright colors or chemical defenses may warn off predators

Warning coloration

Startle coloration

Warning mimicry

Visual and behavioral mimicry

Chemical Warfare

• Plants have defenses against herbivores – Chemicals

– Tough outer parts

• Symbiosis

– Communalistic • + / neutral

– Mutualistic• + / +

– Parasitic• + / -

Mutualism

Keystone species

How do Communities Change Over Time

• Succession– Pioneers– Climax community

Primary Succession

Secondary Succession