Interactions within Communities

Grade 9/10 Review Individuals of the same species living in the same area make up a population. Populations of different species living in the same area form a community.

Niche Definitions Ecological niche: the role an organism fills within a community (includes what it does, eats, basically anything that describes its pattern of living) Fundamental niche: has the biological characteristics of the organism plus the set of resources it is capable of using under ideal conditions (no interspecific competition exists). Realized niche: the portion of the fundamental niche the organism actually fills.

Competition Intraspecific competition: competition for resources between members of the same species.

Competition Interspecific competition: competition for resources among members of two or more different species.

Interspecific Competition Competition between two species can be interference competition in which the two species are actually fighting over the resources (i.e. birds fighting over birdhouses). Exploitative competition is where the two species are using a common resource (i.e. arctic foxes and snowy owls eating arctic hares).

Interspecific Competition 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 species and drive the other to extinction.

Gause’s Principle

Resource partitioning Resource partitioning: the avoidance of, or reduction in, competition for similar resources by individuals of different species that do no occupy the same niche (i.e. plants in the same area will have different root structures so each species is able to get nutrients and water from the soil and not compete with the other species).

Symbiosis Symbiosis: interactions in which members of two (or more) species maintain a close association. The following slides are types of symbiosis.

Parasitism Parasitism: the interaction is beneficial to one species and harmful (not fatal) to the other species. Parasites can be both micro- and macro- as well as ecto- and endo-. Social parasites mimic the behaviour of another species in order to complete their lifecycle (i.e. cowbirds)

Ecto-parasites and Endo-parasites

Mutualism Mutualism: the interaction is beneficial to both species. Obligatory mutualism is when neither species can survive without the other such as with lichens (fungi and algae/cyanobacteria).

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

Commensalism or Mutualism?

Predator-Prey Relationships Predator-prey relationships are an important interspecific interaction in a community. When the prey population increases, the predator population will increase shortly thereafter. Predator-prey populations follow cyclical pattern.

Stuff you know already! Predator-prey interactions have caused prey to evolve diverse defense mechanisms in order not to be eaten. Predators are evolving to bypass these defenses (Evolutionary Arms Race!)

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

Animals Animals use passive defenses such as hiding or active defenses such as fleeing.

Mimicry Some animals use mimicry, which is one species appearing very similar to another species. There are two types of mimicry: Batesian mimicry: a harmless species mimics a harmful one (i.e. edible butterfly species mimics a toxic species so it won’t get eaten). 2) Mullerian mimicry: where two or more dangerous species appear similar which causes their common predators to learn quicker to avoid them (i.e. poisonous butterflies all look similar)

Mimicry