Community Ecology Interactions between Populations of different species Interspecific Interactions and Community Structure Disturbances and Nonequilibrium Community Ecology and Biogeography
Interactions between Populations of Different Species • Role of coevolution (passion flower, Passiflora, and butterfly, Heliconius) • Predation, parasitism, parasatoidism, and herbivory • Competitive exclusion principle • Ecological niche • Symbiosis: commensalism and mutualism
APEX PREDATORS • Apex predators (also alpha predators, superpredators, or top-level predators) are predators that, as adults, are not normally preyed upon in the wild in significant parts of their range by creatures not of their own species and are not obliged to enter places in which they might be preyed upon. As top killers they often shape the ecology through their predation and rarely have cause for fear of being killed as prey in large parts of their range and alter the behavior of prey species.
Keystone Predator (species) • Keystone Predator • A keystone predator is an animal that is important for maintaining species richness (number of species) in a community. Keystone predators feed on different species that normally would compete with each other. Competitive exclusion of a species does not occur because the densities of competitors are kept reduced by a common predator. • A good example of a keystone predator is Piaster, a sea star, that reduces the populations of a mussel, Mytilus. If Piaster is experimentally removed from the community, the species richness of the community decreased from 15 to 8 species. The reason for this decline is because Mytilus propogated and outnumbered other species found in the community.
Disturbances • Events that disrupt communities • Succession-the transition in species composition over ecological time • Primary succession-begins in areas barren of life • Secondary succession-existing community has been destroyed by fire, abandoned agricultural field, etc.
Competitive Exclusion Principle • sometimes referred to as Gause'sLaw of competitive exclusion • theory which states that two speciescompeting for the same resources cannot stably coexist, if the ecological factors are constant. • Either of the two competitors will always take over the other which leads to either the extinction of one of the competitors or its evolutionary or behavioral shift towards a different ecological niche.