ecology: the study of how organisms interact with each other and the environment

Copyright © 2005 Brooks/Cole — Thomson Learning

Biology, Seventh Edition CHAPTER 52 Community Ecology


Biology, Seventh Edition Solomon • Berg • Martin

Ecology: Ecology: The study The study of how organisms of how organisms

interact with each other interact with each other and the environment.and the environment.



Ecology Definitions:• Habitat: The space or environment

when an organism lives• Niche: role of an organism in a

community• Biotic Factors: All the living things

within an environment• Abiotic Factors: All the physical

(non-living) things in an environment



Connections to the size of the acorn crop



Limiting Resources• Environmental factors that restrict

the growth of populations.



Effect of competition on an organism’s realized niche



• Competition• Two or more individuals attempting

to use the same resource• Intraspecific competition

–Among individuals within a population

• Interspecific competition–Between different species



Interspecific competition



Competitive exclusion principle• Two species cannot occupy the

same niche in the same community for an indefinite period

• One species is excluded by another as a result of competition



• Some species reduce competition by resource partitioning

• Competition among species is reduced by character displacement• Structural ecological and

behavioral characteristics diverge where ranges overlap



Resource partitioning



Predation• Consumption of one species (the

prey) by another (the predator)

Co-evolution• Predator and prey both evolve

more efficient ways to interact



Ecological interactions among species



Defenses• Mechanical defenses• Associating in groups• Cryptic coloration• Warning coloration• Müllerian mimicry



Cryptic coloration



Symbiosis• Mutualism

–Both partners benefit

• Commensalism–One partner benefits and the other is

unaffected

• Parasitism –One partner benefits while the other is

harmed



Mutualism between flowering plants & pollinators



Mutualism between clown fish Mutualism between clown fish & & sea anemone sea anemone



Commensalism:

Spanish moss & trees



Parasitism: Ticks and Mammals Parasitism: Ticks and Mammals



Parasitism



• Keynote species• Present in small numbers but are

crucial in determining the species composition and ecosystem functioning

• Dominant species• Affect the community because they

are so common



• Species richness• Number of species within a

community

• Species diversity• Relative importance of each

species within a community



Effect of community complexity on species richness



Ecological Succession• Primary succession

–Occurs in an area not previously inhabited

• Secondary succession–Occurs where there is a pre-existing

community and well-formed soil



Ecological SuccessionEcological SuccessionPioneer SpeciesPioneer Species= annual plants/grasses= annual plants/grassesSecondary SpeciesSecondary Species= shrubs= shrubsClimax SpeciesClimax Species= trees= trees



• Intermediate disturbance hypothesis• Disturbance affects succession and

species richness• Species richness is greatest at

moderate levels of disturbance



Intermediate disturbance hypothesis



• The nature of communities• Organismic model

–Views a community as a superorganism that goes through stages of development (succession)

• Individualistic model–Abiotic environmental factors are

primary determinants of species composition

–Organisms are independent

ecology: the study of how organisms interact with each other and the environment

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