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Chapter 53

Biology Chapter 53.docx

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McMaster University
Jon Stone

1Biology Chapter 53 Community EcologySpecies InteractionA biological community consists of interacting species usually living within a defined areaTo study species interaction biologists focus on analyzing the effects on the fitness of individuals involvedFour categories of interactiono relationship known as competitiono relationship known as consumption and parasitismo relationship termed mutualismo0 relationship termed commensalismEx Birds that follow moving army ants in the tropicsAs ants march along forest they hunt insects and small vertebratesAs they do birds follow and pick off prey species that fly or jump out of the way of the antsThe birds are commensals that benefit from the associationbut have no measurable impact on the ants 0Section focuses on three key themesoSpecies interaction may affect the distribution and abundance of a particular speciesChanges in species interactions often explain shortterm changes in population size and distributionoSpecies act as agents of natural selection when they interactDeer are fast and agile in response to natural selection exerted by major predatorsSpeed and agility of deer in turn promote natural selection that favours wolves and cougars that are fast and have superior eyesight and senses of smellChanges in species interactions lead to longterm changes in characteristics of populations a phenomenon called coevolution in addition to having shortterm impacts on population size2oOutcome of interactions among species is dynamic and conditionalConsider relationship between army ants and bids that follow them which is usually commensalIf bird attacks start to force other insects into path of ants then both benefit and relationship becomes mutualisticIf birds begin to steal prey that would otherwise be taken by ants relationship becomes parasitic CompetitionoCompetition is ainteraction that occurs when different individuals use the same resources and when those resources are limitingoCompetition that occurs between members of same species is called intraspecific competitionIntraspecific competition for space sunlight food and other resources intensifies as populations density increases A major cause of densitydependent growthoInterspecific competition arises when individuals from different species use the same limiting resourcesoThere are many types if interspecific competitionConsumptive competition occurs when individuals consume the same resources ex trees competing for same water and nutrientsPreemptive consumption exists when one species makes space unavailable to other species Overgrowth competition happens when one species grows above another ex large fern overgrown other individuals and is shading themChemical competition takes place when one species produces toxins that negatively affect another speciesTerritorial competition arises when a mobile species protects its feeding or breeding territory against other species ex grizzly bears drive off black bearsEncounter competition occurs when two species interfere directly for access to specific resources ex spotted hyenas and vultures fight over kill
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