Community Ecology

Species Interactions the effects of one species on another may be negative, positive, or neutral five kinds of interactions: POPULATION APOPULATION B COMPETITION PREDATION PARASITISM COMMENSALISM MUTUALISM

Intraspecific Competition Intraspecific Competition – members of the SAME species compete for resources

Interspecific Competition Interspecific Competition – two or more DIFFERENT species use the same limited resource (food, space, etc.) and adversely affect each other – / – niche overlap Ex: fire ants & native ants in North America

High Low Relative population density Days Each species grown alone Paramecium aurelia Paramecium caudatum No Competition

High Low Relative population density Days Both species grown together Paramecium aurelia Paramecium caudatum Interspecific Competition

Resource Partitioning Species with similar resource requirements can coexist because they use limited resources: at different times in different ways in different places © Brooks/Cole Publishing Company / ITP

Resource Partitioning

Competitive exclusion principle - no two species can occupy the same niche at the same time Dividing resources can be a “truce” in the competition for resources

Parasitism One organism (parasite) lives in or on part of another organism (host) + / – Ex: flea living on a dog © Brooks/Cole Publishing Company / ITP

Mutualism Two species interact in a way that benefits both + / + Ex: lichens (algae & fungi) Ex: clownfish & anemones Ex: ants & acacias © Brooks/Cole Publishing Company / ITP

Commensalism One organism benefits from another, but neither helps nor harms the other organism + / 0 Ex: elephants and cattle egrets

Keystone Species Keystone Species: species that play a critical role in an ecosystem Ex: sea otters are keystone species because they prevent sea urchins from depleting kelp beds Ex: flying foxes are keystone species because they pollinate & disperse tropical trees such as durian

Keystone Species Increase Biodiversity

Primary Succession Primary succession – occurs on surfaces that are initially devoid of soil

Pioneer Species – Lichens and Moss

Secondary Succession Secondary succession – occurs in areas that have been disturbed, but have not lost their soil

The Secondary Succession Cycle