Ch. 53

Communities

Assembly of species living close enough together for possible interaction

Differ in species richness

Coevolution

• describes interactions involving reciprocal evolutionary adaptations in 2 species

Table 53.1 Interspecific Interactions

Interspecific Interactions

• Occur between populations of different species living together within a community

• Predation

• Parasitism

Interspecific Interactions - Predation

Community interactions where one species eats another species

Plant defenses

• whole plant is rarely consumed

• mechanical (thorns, hooks, spines)

• chemical (bad taste, produce abnormal development in insects that feed upon them)

Interspecific Interactions - Predation

Animal defenses• passive

– hiding

• active– escaping, fleeing, self-defense,

mobbing, alarm calls

• chemical– toxins (skunk, poisonous toads)

Figure 53.5 Camouflage: Poor-will (left), lizard (right)

Figure 53.6 Aposematic (warning) coloration in a poisonous blue frog

Interspecific Interactions - Predation

Animal defenses

Adaptive coloration

• cryptic (camouflage)

• aposematic (bright; coloring acts as a warning of another physical or chemical defense)

Figure 53.x1 Deceptive coloration: moth with "eyeballs"

Figure 53.7 Batesian mimicry

Figure 53.8 Müllerian mimicry: Cuckoo bee (left), yellow jacket (right)

Interspecific Interactions - PredationMimicry• bears a superficial resemblance to another

species• batesian: a palatable species mimics a bad

tasting model• mullerian: 2 or more unpalatable species,

aposematically colored species resemble each other

• luring prey– tongue of snapping turtle looks like a worm

Interspecific Interactions - Parasitism

Host is harmed in some way

Endoparasites

• live within host’s tissues or body cavities

• tapeworms, Ascaris

Ectoparasites

• attach or briefly feed on the external surface of the host

• mosquito, aphid

Interspecific Competitions

Occurs when 2 or more species in a community rely on similar limiting resources

2 ways competition occurs

• interference (actual fighting over resources)

• exploitative (consumption or use of similar resources)

Interspecific Competitions

Competitive exclusion principle

• predicts that 2 species competing for the same limiting resources cannot coexist in the same community

• one uses resources more efficiently so it reproduces faster

Interspecific Competitions

Ecological niches

• sum of the total of an organism’s use of biotic and abiotic resources in its environment

• how an organism “fits” into its environment

Interspecific CompetitionsFundamental niche• resources a population is theoretically

capable of using under ideal conditionsRealized niche• resources a population actually uses• biological constraints

– competition, predation, resource limitation

Interspecific Competitions

• If niches are identical for 2 species, cannot coexist

• Ecologically similar species can coexist

Interspecific Competitions

Evidence for competition• should be rare if competitive exclusion

principle applies• weaker competitor becomes extinct• one of the species will evolve to use

another set of resources• huge impact on shaping niches

Interspecific Competitions

Speciation• Sympatric• Allopatric

Interspecific CompetitionsCharacter displacement• tendency for characteristics to be more

divergent in sympatric populations of 2 species than in allopatric populations of the same species

Figure 53.x3 Commensalism between a bird and mammal

SymbiosisForm of interspecific interaction in which a

host species and a symbiont maintain a close association

Commensalism• symbiont benefits/host unaffected

• cowbirds and cattle egrets

This shows the symbiotic relationship commensalism, the bird getsfood from the back of the cow but the cow is not affected

SymbiosisMutualism

• a change in the symbiont affects the host

• root nodules of legumes

• Ants and acacia trees

(video clip)

When coyotes and badgers team up, the pairs track small, burrowing animals such as prairie dogs and ground squirrels. If the prey is above ground, the coyote usually chases it down, and the badger takes over the hunt if the prey descends underground. And not only do they find food together, but coyotes also have more success in this partnership than if they go it alone.

SymbiosisParasitism

• host is

harmed

Disturbance & NonequilibriumDisturbances

• events that disrupt communities

• humans (most widespread agent)

Succession

• process of change that results from disturbances in communities

• ecological

• primary

• secondary

SuccessionEcological• transition in species composition over timePrimary• begins in areas eventually barren of life

due to lack of formed soil or on rubbleSecondary• if an existing community has been created

by some disturbance that leaves the soil in tact

Disturbance and Nonequilibrium

Recruitment

• colonization by species from distant areas not directly associated with the disturbed patch or its immediate vicinity