Ecology -Communities (Part 2)-

Communities - Processes between Populations + = beneficial to a species = detrimental to a species 0 = species is unaffected Kinds of Interactions Interaction Species 1 Species 2 Competition - Predation + Herbivory Parasitism Disease Mutualism Commensalism

Communities - Processes between Populations Competition A (+, -) interaction between members of the same species (Intraspecific) or between members of different species (Interspecific) for resources that are in short supply Resources can be food, water, mates, nesting sites etc.

Communities - Processes between Populations Competition 1934 - Gause - Experiments with Paramecium Paramecium aurelia Paramecium caudatum

Communities - Processes between Populations Competition 1934 - Gause - Experiments with Paramecium P. aurelia alone P. caudatum alone previous P. aurelia P. aurelia P. caudatum Grown together

Communities - Processes between Populations Competition From Gause’s Paramecium experiments Competitive exclusion principle When two species compete for the same limited resource, one species will eventually eliminate the other.

Communities - Processes between Populations Competition Ecological niche The total of species’ use of biotic and abiotic resources in its environment Eugene Odum - the habitat is a species address, the niche is its “profession”.

= dN (K - N) dt rN K Remember equation for logistic population growth Two new terms: α = effect* of species 2 on species 1 β = effect* of species 1 on species 2 *‘effect’ means how much the growth of a population is decreased

= = dN1 (K1 – N1- α N2) dt r1N1 K1 dN2 (K2 – N2- β N1) dt r2N2 K2 Logistic population growth and competition dN1 dt (K1 – N1- α N2) K1 = r1N1 Effect of species 2 on species 1 depends on the degree of the effect (α) and the numbers of species 2 dN2 dt (K2 – N2- β N1) K2 = r2N2 Effect of species 1 on species 2 depends on the degree of the effect (β) and the numbers of species 1

Logistic population growth and competition P. aurelia if alone α P. aurelia in competition P. caudatum if alone β P. caudatum in competition P. aurelia is species 1 Effect of aurelia on caudatum is β P. caudatum is species 2 Effect of caudatum on aurelia is α

Communities - Processes between Populations Competition How do species respond to competition? Character displacement Geographical distribution of species B Geographical distribution of species A Area of Sympatry (and competition)

Communities - Processes between Populations Competition How do species respond to competition? Character displacement Geospiza fuliginosa Geospiza fortis

Communities - Processes between Populations Competition How do species respond to competition? Character displacement Beak depth (and therefore the kind of food eaten) changes in sympatric area

Communities - Processes between Populations Competition How do species respond to competition? 2. Resource Partitioning -differentiation of ecological niches that allows two species to coexist

Communities - Processes between Populations Myrtle warbler Bay breasted warbler Cape May warbler All eat the same food (insects) and live in the same trees

Communities - Processes between Populations Competition 2. Resource Partitioning Cape May warbler Bay breasted warbler Myrtle warbler

Communities - Processes between Populations Competition 2. Resource Partitioning

Communities - Processes between Populations Mutualism Any interaction between members of two species that is beneficial to both

Communities - Processes between Populations Mutualism - Corals and Algae Mesoglea Gastrodermis Ectodermis • • • • • zooxanthellae •

Communities - Processes between Populations Mutualism - Corals and Algae Sugars to polyp Nitrogen to zooxanthella

Communities - Processes between Populations Predation A (+, -) interaction between members of two species in which one species kills and eats members of the other

Communities - Processes between Populations Predation Predator and prey have co-evolved in response to one another Predator evolves some mechanism to be a better predator Prey evolves some reponse to avoid the predator Prey evolves some reponse to avoid the predator

Communities - Processes between Populations Predation Some mechanisms for making predators more efficient Incisor teeth (molars) for piercing and holding prey Carnassial teeth (molars) for shearing meat

Communities - Processes between Populations Predation Some mechanisms for making predators more efficient Spine acts as a spring to give extra thrust when running

Communities - Processes between Populations Predation How to avoid being prey Mimicry Either look like something distasteful Have a number of distateful animals resemble one another or Viceroy Monarch Batesian Mimicry Mullerian Mimicry

Communities - Processes between Populations Predation How to avoid being prey Mimicry of other objects

Communities - Processes between Populations Predation How to avoid being prey Evoke startle response

Communities - Processes between Populations Predation Populations of predators and prey cycle slightly out of phase with one another.

Communities - Processes between Populations Predation

Communities - Processes between Populations Predation Holling’s Disk Equation

Top down vs bottom up controls Two views on how community structure is controlled Top-down mechanism Bottom-up mechanism

Numbers of a prey species Top-down control Predator species controls Numbers of a prey species controls Numbers of a plant species

- Already seen an example of this Top-down control - Already seen an example of this - after hunting of sea otters

Numbers of a plant species controls Bottom-up control Numbers of a plant species controls Nutrients Numbers of a prey species controls Predator species

Bottom-up control Quantity and quality of grass Number of grasshoppers Nitrogen, phosphorus