Chap. 53 Community Ecology AP Biology Mr. Orndorff May 2005

What is community structure? Species composition: species present Species diversity: variety of species present –Species richness: number of different species –Relative abundance: number of individuals of each species

How does species diversity vary? Latitude gradient: species diversity gets less going from the equator to the poles. Depth gradient: species diversity increases with depth to 3000 meters and then decreases; very high on deep sea bottom. Pollution gradient: species diversity gets less as pollution increases.

Species Interactions Predation and Parasitism (+/-) Interspecific Competition (-/-) –Competitive exclusion principle –Resource partitioning –Character displacement

Interspecific Competition (53.10)

Resource partitioning in Anolis lizards at La Palma in the Dominican Republic (Fig )

Character displacement: circumstantial evidence for competition in nature (Fig )

Experimental evidence for competition in nature (Fig )

Keystone species Species believed to play a more important role in maintaining ecosystem processes than their abundance or biomass suggests. Example: In intertidal pools, Pisaster (starfish) acts as a keystone species by feeding on Mytilus (mussel). This allows other species to compete with Mytilus for attachment space on rocks.

Symbiosis Parasitism (+/-) –Tapeworms, pathogenic microorganisms Commensalism (+/0) –Epiphytes, cowbirds on grazing herbivores Mutualism (+/+) –Lichens, termites and hindgut microbes

Ecosystem disturbances Storms, fire, drought, flood, overgrazing and human activities that damage communities. Most ecosystems are kept in a state of nonequilibrium by some amount of disturbance.

Ecological succession Transition of species composition over time in response to ecological disturbances. Primary succession = process in which lifeless area without soil (e.g. new volcanic island, glacial morraine) develops a living community. Secondary succession = process in which a disturbance to an existing community leaves the soil intact so that the early stages of primary succession are not necessary.

Stages of succession Pioneer species = hardy species such as lichens and mosses able to colonize bare rock and begin the soil making process. Early successional species = often r-selected species able to tolerate extremes of abiotic conditions. Midsuccessional species and late successional species = often K-selected species which can inhibit, facilitate, or tolerate other species producing unique combinations of species in the community.

Diversity of life and periods of mass extinction

Continental drift and natural barriers (deserts, mountains) create biogeographical realms

Factors influencing range of species Species may never have dispersed beyond current boundaries. Pioneers which did spread beyond observed range died. Species may have retracted from a once larger range to present boundaries.

Hypothesis of island biogeography (Fig )

Species richness and island size (Fig )