Lecture 10

Community Ecology

Today’s topics

• What is community ecology?• Interspecific relationships• Community Structure and Function• Exam 1 review

Community Ecology

• Community – assemblage of multiple species populations that live in the same place at the same time.

• The interaction among species and the effect those interactions have on both living and nonliving features of their environment.

Interspecific relationships

• All the interactions that exist between organisms of different species in an ecosystem fall in the category of symbiosis meaning “to live together”.– Competition (-/-)– Predation (parasitism) (+/-)– Commensalism (+/0)– Mutualism (+/+)

Mechanisms of Competition

• Species can compete directly by fighting to gain access to resources (interference competition) http://www.youtube.com/watch?v=EOB5S5IXCFg&feature=related

Mechanisms of CompetitionOr compete indirectly by consuming the same

resource (exploitative competition)

Competitive Exclusion Principle

Two species competing for the exact same limited resource cannot stably coexist.

If two competing species coexist in a stable environment, they do so as a result of differentiation of their niche.

The Ecological Niche

• Distributional component - A habitat a species occupies as a function of its physiological and behavioral attributes.

• Functional component – A species role in the community in terms of its trophic level

• Most ecologists include both in the definition an consider a niche to be all adaptations of a species to a particular environment

Two types of niche

• 1. Fundamental niche – all the potential resources that a species can use in its environment. – Requires the absence of competition

Two types of niche

• 2. Realized niche – some habitats and resources are not available because competitors occupy them. – This is what the species actually uses

Tamias alpinus

Tamias speciosus

Tamias amoenus

Tamias minimus

Pretend this is a mountain

Fundamental niches

Realized niches

Character Displacement

• 2 sympatric species differ more than 2 allopatric– Sympatric = ranges overlap– Allopatric = ranges do not overlap

Predation • Parasitism is a similar form of this symbiotic relationship, but

the host may only be weakened.• As we discussed in the previous lecture, predation has

negative immediate consequences, but can have positive long-term.

• For instance, thinning out the weak or sick.

Predators may play a significant role in structuring communities

• Important concepts:• Trophic cascade –predators depress

populations of herbivores to the point that plant biomass increases (Dr. Murphy will talk more about this later)

• Keystone Predators• Guilds

Keystone predators – exert a controlling force over community

structure and function

Guilds – more than one species occupying the same trophic level and exploited a common resource

• Keystone Guilds – more than one species plays a keystone role in the same community

Mutualism

• Both species benefit• http://www.youtube.com/watch?v=Qqa0OPbdvjw&feature=related

Commensalism• One species benefits while the other neither

benefits nor is harmed

Community Function

• Evaluating energy flow and food webs are comment ways to understand how a community functions.

Energy flow through trophic levels

Mammals typically do not account for a large proportion of total energy flow in communities, but total effect on energy flow can be significant

Food webs