HUMAN POPULATION I NTERACTIONS IN A C OMMUNITY A.R. Farmer 13 July 2011

Community Ecology

 Community  Producers, Consumers, Decomposers  Predation  Competition  Intraspecific; Interspecific; Competitive exclusion;  Symbioses - 3 types  parasitism  mutualism  commensalism IMPORTANT CONCEPTS

Community A group of populations occuring in a particular area, e.g. zebras, hyenas, giraffes in the Kruger National Park

Trophic levels: Produces(mainly plants) Consumers  Primary (herbivores)  Secondary (carnivores)  Tersiary (Carnivores) Decomposers(bacteria and fungi - saprophytes

Feeding levels in a community

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

Other Predatory Adaptations

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

Examples of mimicry

Prey-predation interaction A

 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)

Resource partitioning

Resource Partitioning

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.

Ectoparasites  Ectoparasites are external parasites.  They live on their hosts body, but do not enter it.  Examples include ticks, fleas, lice, lampreys, leeches and mosquitoes

Ectoparasites

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

Cleaning Symbiosis

Pollination  Pollination is the most important of the mutualistic relationships.  The plant provides food for the pollinators, which in turn carries the pollen to another flower

COMMENSALISM Is a relationship in which one species benefits and the other is not affected

INTERACTION IN A COMMUNITY