Community Ecology II: Species Interactions

Ecological communities: Assemblages of two or more species living and interacting in the same area. Species interactions: the ways different organisms affect each other and how they have adapted to each other’s presence.

FOUR main kinds of species interactions; all play a role in the formation of community structure... Competition (-,-) Predation, parasitism (+,-) Mutualism (+,+) Commensalism (+,0)

Interspecific Competition: Use or defense of a resource by one species that reduces availability of that resource to a different species. exploitative competition interference competition

Competition in Paramecium

Competitive Exclusion: A result of competition between species for a limiting resource, in which one species completely eliminates the other.

Ecological Niche: a species’ ecological ‘role’ all the environmental factors that influence the growth, survival, and reproduction of a species an n-dimensional hypervolume within which a species’ population growth is positive

3-dimensional niche

Fundamental Niche vs Realized Niche Fundamental Niche: the niche that a species potentially could occupy, in the absence of competitors. Realized Niche: the niche to which a species is restricted in the presence of competitors.

Competition in Barnacles

Competitive Release: Expansion of a species’ ecological niche when a competitor is removed (usually in a removal experiment).

Q: How do similar species coexist? A1: Resource Partitioning

Species using similar resources can coexist when the habitat is spatially and temporally complex, thus allowing for resource partitioning.

Anolis spp.

Number of different Anole species on different islands

VIDEO CLIP

A2: Character Displacement Q: How do similar species coexist?

Character Displacement The tendency for physical characteristics to be more different in sympatric populations of two closely related species than in allopatric populations of the same two species. Allopatric Sympatric

FOUR main kinds of species interactions; all play a role in the formation of community structure... Competition (-,-) Predation, parasitism (+,-) Mutualism (+,+) Commensalism (+,0)

True Predators - prey is killed immediately upon successful attack Great White Shark, Siberian Tiger, Fox Squirrel

Partial Predators - prey usually not killed but many prey organisms affected during predators lifetime - grazers, browsers Giraffe, Bison, Monarch Caterpillar

Parasitoids - lay eggs on or in prey and then eggs hatch and developing offspring consume the prey Parasitoid wasp attacking moth caterpillar

Predators can influence species within communities by selecting for anti-predator adaptations in prey…

Behavioral Defenses

Morphological Defenses

Crypsis - matching background Cryptic coloration Flexible crypsis

Aposematic or Warning Coloration Monarch Butterfly and Caterpillar Morphological & Physiological Defenses

Blue jay eats monarch, but vomits due to cardiac glycoside from milkweed

Mimicry Batesian mimicry in which a palatable species mimics a harmful “model” species Müllerian mimicry in which two or more harmful species come to resemble each other

Batesian mimicry – several fly species mimicking bees and wasps

Batesian mimicry – coral and king snakes Arizona Coral Snake Central American coral snakes and king snake mimic – coral snake on left or in middle

Müllerian Mimicry MonarchViceroy

Complex of Batesian and Müllerian Mimics

e.g. Wolves and Moose on Isle Royale Predators can also influence the numbers and distribution of their prey.

Parasites can affect host populations by reducing their survival, reproduction and density.

Ticks (ectoparasites) suck blood and cause irritation Lead to weakened moose, which are more susceptible to predation by wolves and death from starvation. Parasitic effects on host species can be indirect or direct.

Parasites can also affect the behavior of the hosts, making them more likely to pass the parasite from one host to another. e.g. endoparasites in sticklebacks cause them to approach water surface more often and increase predation risk.