Community Concept An assemblage of populations interacting with one another within the same environment Composition is a listing of various species in the community Diversity includes both species richness and species diversity

Community Structure Competition When two species compete, the abundance of both species is negatively impacted Predation (or parasitism) Expected to increase the abundance of the predator (or parasite) And reduce the abundance of the prey (or host)

Habitat and Ecological Niche The area an organism lives and reproduces in Ecological niche The role a species plays in its community Includes its habitat, and Its interactions with other organisms

Feeding niches for Wading Birds

Competition Between Populations Interspecific competition Members of different species require the same resource The supply of the resource is limited Competitive Exclusion Principle No two species can occupy the same niche at the same time Resource Partitioning decreases competition

Competition Between Two Laboratory Populations of Paramecium

Predator-Prey Interactions Predation One living organism, the predator, feeds on another, the prey Predator is larger Predator has lower reproductive rate Presence of predators can decrease prey densities, and vice-versa

Predator-prey Interaction Between a Lynx and a Snowshoe Hare

Prey Defenses Prey defenses Mechanisms that thwart the possibility of being eaten by a predator Spines Tough Epidermis Poisonous Chemicals Camouflage Bright Coloration

Mimicry Mimicry One species resembles another species Mimicked species possesses an overt antipredator defense Batesian Mimicry - Mimic lacks defense of the organism it resembles Müllerian Mimicry - Mimic shares same protective defense

Mimicry Among Insects

Symbiotic Relationships Symbiosis Interactions in which there is a close relationship between members of two species Parasitism Parasite derives nourishment from a host, and may use host as habitat and mode of transmission

Mutualism Symbiosis, cont. Mutualism A symbiotic relationship in which both members of the association benefit Often help each other obtain food or avoid predation Bacteria in human intestinal tract

Commensalism Symbiosis, cont. Commensalism A symbiotic relationship in which one species benefits and the other is indifferent Many supposed examples may turn out to be mutualism or parasitism

Predation, Competition, and Biodiversity Predation by a particular species may reduce competition and increases diversity Such predators are referred to as keystone predators Exotic species May lead to unbridled competition Resultant reduction in biodiversity