Interactions within a Community The five main types are: Predation Competition Parasitism Mutualism Commensalism
PREDATION In predation, one individual, the predator, captures, kills, and consumes another individual, the prey.
Predators, Prey, and Natural Selection Natural Selection favors adaptations that improve a predator‘s efficiency at finding, capturing, and consuming prey. These adaptations include a shark’s jaws, a scorpion’s claws and stinger, and a spider’s web and fangs
Prey Adaptation Some animals are very fast and can escape capture simply due to their speed Other prey animals depend on camouflage, hoping to avoid detection Some organisms are poisonous and use bright colors (often yellow and black) to warn other organisms of their toxicity
Mimicry In mimicry, a harmless species resembles a poisonous or distasteful species. The harmless species is protected because it is often mistaken for the dangerous look-alike
The cycles of increase and decrease reflects a predator –prey intercation e.g lions feeding on impalas, lynx feeding on rabbits Prey population reaches higher density than predator population Portion A = geometric phase- rapid increas of prey, predator pop too low to hinder increase More prey means more food for predators and the population increases More predators = increase in mortality of prey Less prey could cause predators to emigrate / die, hence prey population can increase again Graph interpretation
Competition Competition occurs when organisms in the same community seek the same limiting resource. This resource may be prey, water, light, nutrients, nest sites, etc. Competition among members of the same species is intraspecific. Competition among individuals of different species is interspecific.
Intraspecific Competition Competition between organisms of the same species
Interspecific Competition Panthera leo Crocuta crocuta Competition between organisms of the same species
Outcomes of Competition Niches of similar species may overlap. Two species cannot compete for the same limiting resource for long. eventually one species outcompetes the other One species survive, other emigrates OR dies out Even a minute reproductive advantage leads to the replacement of one species by the other. This is called the COMPETITIVE EXCLUSION PRINCIPAL.
Evidence for Competitive Exclusion the Russian ecologist, G.F. Gausse demonstrated that Paramecium aurellia outcompetes and displaces Paramecium caudatum in mixed laboratory cultures, apparently confirming the principle.
Resource Partitioning When two or more similar species coexist, such as these varieties of warbler, each species only uses part of the available resources. This is called resource partitioning. (species sharing resources)
PARASITISM Parasitism is a species interaction that resembles predation in that one individual is harmed while the other benefits. However, in parasitism, the parasite feeds on the host individual. This does not result in the immediate death of the host. Rather, the parasite may feed on the host for a long time instead of killing it.
Endoparasites Endoparasites are internal parasites, and live inside the host’s body Endoparasites include bacteria and other micro- organisms, and many worms
Mutualism Mutualism is a symbiotic relationship in which both members of the association benefit. Often help organisms obtain food or avoid predation. Bacteria in human intestinal tact. Need not be equally beneficial to both species. Cleaning Symbiosis