Community Ecology

Community = all the populations of organisms inhabiting a common environment and interacting with one another

Interactions Between Populations of Different Species Interspecific interactions—occur between populations of different species Coevolution—a change in one species acts as a selective force on another species Symbiosis— For at least part of the life cycle, individuals of two or more species interact with neutral, positive. Or negative effects on each other

The Niche A niche is a way of life, or a role in an ecosystem. an organism’s role in the environment (its profession, not its address) Includes the habitat, food sources, other resources that are necessary to the survival of the organism. Two Types Fundamental Realized

Fundamental vs. Realized Niche Fundamental niche - determined by the physiological limits of the organism Realized niche - the portion of the fundamental niche actually utilized due to interactions with other species e.g., Chthamalus and Balanus barnacles

Interspecific Interactions 1) Interspecific Competition (–/–) Competition occurs when 2 or more populations overlap in their niches Limiting resources Food Space

Interspecific Interactions Two possible outcomes: Weaker competitor becomes extinct One or both species may evolve enough to use a different set of resources Competition cannot operate for long periods of time

Interspecific Interactions: Resource Partitioning Resource partitioning—The subdividing of some category of similar resources that lets competing species coexist.

Interactions Between Populations of Different Species 2) Predation (+/–) consumption of one organism by another Predator eats prey

Symbiotic Relationships 3) Parasitism (+/–)—specialized predator (parasite) lives on/in its host, not killed immediately Endoparasitism—live inside host (tapeworms/viruses) Ectoparasitism—live on surface of host (mosquitoes/aphids)

Symbiotic Relationships 4) Commensalism (+/0)—one partner benefits while not harming the other

Symbiotic Relationships 5) Mutualism (+/+)—both partners benefit. Lichens-association between fungus and algae Nitrogen-fixing bacteria and legumes

Evolutionary Arms Race Populations of other species are part of any organism’s environment, and the ones that interact as predators and prey exert selection pressure on each other. One must defend itself and the other must overcome the defenses. This is the basis of an evolutionary arms race that has resulted in amazing adaptations.

Camouflage Some prey species gain protection from camouflage, they hide in the open. Such species have adaptations in their form, patterning, color, and behavior that help them blend with the surroundings and escape detection.

Warning Coloration Many prey species taste bad, are toxic, or inflict pain on attackers. Toxic types often have warning coloration, or conspicuous patterns and colors that predators learn to recognize and avoid. Aposematic coloration: Red/black; yellow/black

Mimicry Mimicry—prey resembles species that cannot be eaten. Batesian mimicry: Imitate color patterns or appearance of more dangerous organisms

Mimicry Müllerian mimicry describes a situation where two or more species have very similar warning or aposematic signals and both share genuine anti-predation attributes.

Moment of Truth Defenses Prey that are cornered or under attack may turn on a last chance trick to avoid predation. Dung beetle scent and noise Sea cucumber fights with guts Baboon baring teeth