INTERACTIONS WITHIN COMMUNITIES Community: Populations of different species living in the same area.

INTERACTIONS WITHIN COMMUNITIES Ecological niche: The role an organism fills within a community (what it does, eats, its pattern of living)

INTERACTIONS WITHIN COMMUNITIES Interspecific competition: competition for resources among members of two or more different species. Hyenas battle with a lioness and win the day. Photo by Brittany Gunther, 2008

Types of Niches: Fundamental niche: the role the organism would fill under ideal enviromental conditions (if there was no interspecific competition).

Realized niche: the portion of the fundamental niche the organism actually fills (due to competition).

A. Symbiosis Interactions in which members of two (or more) species maintain a close association. There are 3 main types:

1. Parasitism The interaction is beneficial to one species and harmful (but not fatal) to the other species. Parasites can be both micro- and macroscopic as well as ecto- and endoparasites.

Social parasites mimic the behaviour of another species in order to complete their lifecycle (i.e. cowbirds).

2. Mutualism The interaction is beneficial to both species. Ex. Bees and flowers Obligatory mutualism is when neither species can survive without the other (gut bacteria in herbivores, oxpecker birds).

3. Commensalism The interaction is beneficial to one species while the other is unaffected. Remoras and sharks are a possible example.

B. Types of Interspecific Competition: 1.Interference Competition: two species are actually fighting over the resources (birds over birdhouses, lion vs. hyena).

B. Types of Interspecific Competition: 2.Exploitative Competition: two species are using a common resource and one species is more efficient at obtaining it ex. arctic foxes and snowy owls eating arctic hares, canopy trees in rainforest.

Gause's Principle/ Principle of Competitive Exclusion: if the resources are limited, no two species can remain in competition for exactly the same niche indefinitely. One species will always out compete the other.

Resource Partitioning The avoidance of, or reduction in, competition for similar resources by individuals of different species that do not occupy the same niche

Resource Partitioning i.e. Plant root systems, lizards/insects/birds in different parts of the tree.

C. Predation Predator-prey relationships are an important interaction in a community.

C. Predation When the prey population increases, the predator population will increase shortly thereafter. Predator-prey populations follow a cyclical pattern.

C. Predation Predator-prey interactions have caused prey to evolve diverse defence mechanisms in order not to be eaten. Predators are evolving to bypass these defences (Evolutionary Arms Race).

D. Defense Mechanisms Plants use morphological defenses such as thorns, hooks, needles, spines and chemical defenses such as toxins, hormones, and other chemicals to deter herbivores from eating them.

D. Defense Mechanisms Animals use passive defences such as hiding / being poisonous or active defences such as fleeing/ fighting/ producing venom.

D. Defense Mechanisms Some animals use mimicry, which is one species appearing very similar to another species.

D. Defense Mechanisms Batesian mimicry: a harmless species mimics a harmful one (ie. An edible butterfly mimics a toxic species so it won't get eaten)

D. Defense Mechanisms Mullerian mimicry: dangerous species all appear similar which causes predators to learn quickly to avoid them.