Community Ecology Differences within a Community Community an

Community Ecology

Differences within a Community • Community - an assemblage of species living close enough for the potential of interaction – Species richness - number of species within a community. – Relative abundance - the number of common species as compared to rare species. – Species diversity - species richness+relative abundance

Interspecific Interactions between Populations of Different Species • The adaptation of one species to the presence of another may lead to coevolution (a change in one species acts as a selective force on another). • Example – predator/prey – mutualism – commensalism

Predation/Parasitism • Predation - a predator eats a prey • Parasitism - parasites live in or on a host, usually killing them outright. • Parasitoidism - small insects such as wasps lay eggs on hosts; the larvae feed within the body of the host, killing it. • Herbivory - animals eat plants

Plant Defenses Against Herbivores • Thorns/hooks/spines in or on leaves and stems • chemicals that produce distasteful foliage such as strychnine, morphine, nicotine • production of analogous (same in appearance not function) hormones that causes abnormal insect development when eaten

Animal Defenses Against Predators • Hiding, fleeing, alarm calls, distraction displays, escaping, combat tactics. • Cryptic coloration - passive defense that makes potential prey difficult to see (camouflage) • Batesian mimicry - palatable prey resembles the appearance of a harmful or unpalatable species

Predation • Parasitism - one organisms derives nourishment from another – Endoparasites - live within the host tissue or cavities (tapeworms) – Ectoparasites - attach or briefly feed on external surfaces ( mosquitoes)

Interspecific Competitions • Competitive Exclusion Principle - two similar species in the same area with similar resources can not coexist.

Ecological Niche • What is your niche? • Ecological niche - how an organisms fits in to its environment by using biotic and abiotic resources • Two species can not coexist if they have identical niches.

Evidence for Competition • The weaker individual will become extinct. • One of the species will evolve to the point of using a different set of resources. – Resource partitioning

Commensalism • Symbiotic relationship where one organism benefits without significantly affecting another; unlike parasitism. – Cattle egrets • Difficult to find a true commensalistic relationship when most relationships will benefit both species to some degree.

Mutualism • Symbiotic relationship where both organisms benefit. – Nitrogen fixing bacteria and legumes.

Community Structure - Food Webs Secondary Consumers Primary Producers

Disturbance and Nonequilibrium • Disturbance - anything that disrupts a community – change in resource availability allowing for disappearance or emergence of new species – natural disasters – human intervention • • clear cutting logging pollution grassland destruction

Succession • Succession - transition of species composition over time – Primary succession - succession of barren areas due to lack of soil formation, rubble, or barren rock (colonization of new lands) • pioneering species - species that will first colonize areas in primary succession (mosses, algae)

Succession (con’t) • Secondary succession - occurs when an existing community has been cleared by some disturbance that leaves the soil intact which will be recolonized by a fugitive species (weeds).