chapter 41 - species interactions

Community

Group of populations of different species living close enough to interact called a biological community

6 interspecific interations

1. Competition

2. Predation

3. Herbivory

4. Parasitism

5. Mutualism

6. Commensalism

What are community interactions classified by

Whether they help, harm, or have no effects on the species involved

• interspecific interactions can affect the survival and reproduction of each species and the effects can be summarized as positive, negative or no effect

Competition (-/-)

Interspecific competition is a -/- interaction that occurs when individuals of different species compete for a resource that limits the survival and reproduction of each species

Ex. Weed growing in a garden compete with garden plants for nutrients and water

Competitive exclusion

Caused by strong competition and local elimination of competing species

Competitive exclusion principle

2 species competing for the same limiting resources cannot co exist in the same place

Ecological niche

Total use of a species biotic and abiotic resources

• can also be an organisims ecological role

• Ecologically similar species can coexist in a community if there are one or more significant differences in their niches

Resource partitioning

Differentiation of ecological niches, enabling similar species to co exist in a community

• as a result of competition, a species fundamental niche may differ from its realized niche

Ex. Chthamalus spread into a region formerly occupied by balanus

Character displacement

Tendency for characteristics to be more divergent in Sympatric populations of two species than in Allopatric populations of the same two species

Ex. Variation in beak size between populations of two species in Galapagos finches

Exploitation

All photosynthetic organisms must eat and all organisms are at risk of being eaten

3 types of Exploitative interactions

1. Predation (+/-) - predator and prey relationship

2. Herbivory (+/-) - herbivore eats parts of plant or algae, leads to evolution of plant mechanical and chemical defences and adaptations by herbivores

3. Parasitism (+/-) - parasite derives nourishment from a host that gets harmed in the process

Feeding adaptations of predators

Claws, teeth, fangs, stingers and poison

Forms of prey defence

• hiding

• Fleeing

• Forming herds or schools

• Self defence

• Alarm calls

• Cryptic colouration/ camouflage

Aposematic colouration

Animals with effective chemical defence exhibiting bright warning colouration

• predators are particularly cautious with prey that have such colouration

Bayesian mimicry and deceptive mimicry

B - unpalatable or harmless species mimics an unpalatable or harmful model

Ex. Monarch and viceroy butterflies

D- predators using mimicry to lure in prey

Endoparasites

Parasites that on the external surface of a host

Social parasites

Take advantage of social interactions of host species such as feeding offspring or incubation

Ex. Cowbirds, beetles and cuckoo catfish

How are cowbirds and common cuckoos social parasites

• Cowbirds are raised alongside the host nestlings

• Common cuckoos are ejector species that removes the host eggs and nestlings, leaving brood parasite as the only remaining chicken

6 Adaptations of avian brood parasites

1. Host selection - choose host species suitable for brood parasite nestling

2. Synchronize egg laying with hosts

3. Short incubation periods - hatch before host nestlings

4. Removal of some or all of host clutch or brood - reduce nestling competition

5. Exaggerated begging displays

6. In ejector species mimicry of host eggs and nestlings

Positive interactions

One or both parties benefit and neither is harmed

• includes mutualism (+/+) and commensalism (+/0)