Community Interactions Chapter 47

Community Interactions Habitat is a place where an organism lives and it is characterized by distinctive physical and chemical features, as well as the array of species living in it. Community is an association of the populations of all species that occupy the same habitat Population - all individuals of the same species that are occupying a specific area Niche - sum total of all activities and relationships in which individuals of a species engage as they secure and use the resources requires to survive and reproduce Habitat - place where an organisms or species lives; characterized by its physical and chemical features and its species Community - all populations in a habitat. Also, a group of organisms with similar life-styles. Ecosystem - array of organisms, together with their environment, interacting through a flow of energy and a cycling of materials Biosphere - all regions of the earth’s waters, curst and atomosphere in which organisms live

Niche - the sum of all activities and relationships in which its individuals engage as they secure and use the resources required for their survival and reproduction. The fundamental (potential) niche is the one that could prevail in the absence of competition The realized niche result from shifts in large and small ways over time, as individuals of the species respond to changes

Categories of Species Interactions Interactions can occur b/w any two species in a community Several types of species interactions - (1) Commensalism - one species benefits and the other is not affected (ex. Bird’s nest in a tree) (2) Mutualism - a symbiotic relationship where both species benefit (plants and their pollinators) (3) Parasitism - one species (parasite) benefits while the other (host) is harmed. (4) Competition - both species are harmed by the interaction (5) Predation

Competitive Exclusion Competitive Exclusion suggests that complete competitors cannot coexist indefinitely. - When competitor’s niches do not overlap as much, the coexistence is more probable - Differences in adaptive traits will give certain species the competitive edge.

Resource Partitioning Resource Partitioning - similar species share the same resources in different ways. Arises in 2 ways: (1) Ecological differences b/w established & competing populations may increase through natural selection (2) only species that are dissimilar from established ones can succeed in joining an existing community Bristly foxtail Resource partitioning - the subdividing of some category of similar resources that lets competing species coexist. Each species is adapted to exploiting a different portion of the habitat Drought-tolerant foxtail grasses have shallow roots fibrous roots that quickly abosrb rainwater. They grow where moisture in the soil varies from day to day. Mallow plants, with a taproot system, grow in deeper soil that is moist early in the growing season but drier later. Smartweed's taproot system branches in topsoil and soil below the roots of the other species. It grows where soil is continuously moist Indian mallow Smartweed

Predation

Predation Predation vs. Parasitism : Predators get their food from prey, but they do not take up residence on or in the prey, typically their prey are killed outright or mutilated. Parasites get their food from host, and they live on or in the host for a good part of their life cycle; they may or may not kill the host. Many of the adaptations of predators and their victims arose through coevolution - the joint evolution of two or more species that exert selection pressure on each other as an outcome of close ecological interaction.

Adaptations that arise as a result of Predator-Prey Interactions … Coevolution

Camouflage - any adaptation in form, color, patterning, or behavior that allows a prey or predator to blend with its surroundings Desert plant, Lithops, resembles a small rock. Only during a brief rainy season does Lithops flower. This is when other plants grow profusely and divert herbivores from Lithops - and when free water instead of juicy plant tissues are available to quench an animals thirst.

Warning Coloration - Toxic prey offer bright colors or bold patterns that serve as a warning to predators Mimicry - Prey not equipped with defenses may escape predation by resembling toxic prey Monarch butterfly Mimic Yellow Jacket Taste bad Highly toxic - often have warning coloration or conspicuous patterns Inflict pain on attackers Mimic Mimic

Moment-of-truth Defense - allow prey animals to defend themselves by startling or intimidating the predator with display behavior Predator Response to Prey — adaptations used by predators to counter prey defenses

Forces Contributing to Community Stability Succession model Ecological succession - is the predictable developmental sequence of species in a community Pioneer species - first to colonize an area Climax community - most persistent array of species that results after some lapse of time Primary succession - happens in an area that was devoid of life and begins with a pioneer species (ex. new volcanic island or land exposed when a glacier retreats) Secondary succession - is when a community re-establishes itself to a climax state after a disturbance (abandoned fields, burned forest)

Community Instability Keystone species - a dominant species that can dictate community structure

Exotic species - Australia & Rabbits / Kudzu

Caulerpa taxifolia suffocating a marine ecosystem

Mainland and Marine Patterns Tropics - Greatest number of coexisting species Resource availability is greatest b/c more rainfall & sunlight Species diversity might be self-reinforcing Rates of speciation in the tropics have exceeded those of background extinction

Island Patterns

Larger island supports more species Island Patterns Distance Effect islands distant from source areas receive fewer colonizing species Area Effect Larger island supports more species