Interactions Within Communities December 1, 2010 Text p
Mortality (a) and growth (b) in steelhead trout (Keeley et al. 2001)
Species Interactions Populations do not live in isolation Interact with other species in the community Individual interactions within populations can shape communities One type of interaction: symbiosis
Symbiosis Relationship where individuals of two different species live in close (usually physical) contact At least ONE organism benefits 3 categories of symbiosis: 1.Mutualism 2.Commensalism 3.Parasitism
Mutualism Both organisms benefit, neither are harmed A (+/+) relationship Lichens
2 Main Types of Mutualisms Obligatory – Neither organism could grow or reproduce without the other Facultative – One or both organisms can grow or reproduce without the other
Obligatory Mutualism
Facultative Mutualisms
Ecological Classifications of Mutualism 1.Trophic partnerships – To obtain energy and nutrients 2.Defensive partnerships – Provides protection against herbivores, predators or parasites 3.Dispersive partnerships – Disperse pollen or seeds, generally for food reward
Trophic Partnership
Defensive Partnerships
Dispersive Partnerships
Mutualistic relationships do not have to be symmetric – One organism may be obligated to the mutualism, while the other can live without its mutualistic partner
Commensalism A symbiotic relationship where one organism benefits and the other is unaffected A (+/0) relationship Is there really such a thing? Not well understood, and difficult to classify
Commensalism
Parasitism One organism benefits at the expense of another organism (the host) The other organism is usually never killed but is often harmed A (+/-) relationship Come from almost all taxonomic groups
4 Types of Parasitism 1.Microparasites 2.Macroparasites 3.Endoparasites 4.Ectoparasites
Microparasite Microscopic, rapid reproduction rate Blood protozoans Often requires a vector Plasmodium Trypanosoma
Macroparasites Larger parasites that are readily visible
Endoparasites Live and feed within the host’s body
Ectoparasites Live and feed on the outside of the host
Social Parasites Complete their life cycle by manipulating the social behaviour of their hosts
Effects on Host May kill Reduce fitness Sterilize Alter the phenotype – E.g. alter behaviour of host to benefit parasite but at host’s expense
Herbivory The eating or consumption of plants (primary producers) by animals known as primary consumers – Heterotrophs – Autotrophs Like parasitism & predation, is a (+/-) interaction Herbivory is important because plants are the ultimate source of energy for food webs in most environments.
Are all herbivores equal? Feeding Specialization n Specialists: u Koalas u Monarch caterpillars n Generalists: u Deer u Cows u Leaf-cutter ants
Herbivory Alters species dominance patterns
Control of Herbivores? Predators and parasites control herbivore abundance Plants defend themselves (particularly terrestrial plants)
Amensalism One species is hurt, but the other does not benefit A (-/0) relationship
Species Interactions Interactions can be complex and varied Next class... Predators, prey, cycles, defense mechanisms