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Biol 121 Community Ecology.docx

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BIOL 121
Carol Pollock

Biol 121 225 Freeman 1196-1209 (Ch. 53) Jan. 13, 2010 Define community -interacting species living within a defined area How can species interact in -species in a community interact constantly general? -members of different spp (species) eat one another, pollinate each other, exchange nutrients, compete for resources, and provide habitats for each other -therefore, fate of a population may be tightly linked to other species that share its habitat Define fitness and describe how -to study species interactions, biologists focus on analyzing effects on the fitness of biologists focus on it to study the individuals involved species interactions. -fitness is the ability to survive and produce offspring -does the relationship b/t two species provide a fitness benefit to members of one species? Four categories of interaction -/- means competition +/- consumption and parasitism +/+ mutualism +/0 commensalism – birds feeding on insects that ants drive out What do species interactions -species interactions may affect the distribution and abundance of a particular affect? species -e.g. predation, disease, competition -changes in species interactions often explain short-term changes in population size/distribution What does species interactions -species act as agents of natural selection when they interact – for e.g. deer are fast have to do with natural in response to natural selection exerted by their major predators like wolves, which selection? then favours fast wolves with good sense of smell and eyesight -in biology, a coevolutionary (species influence each others’ evolution) arms race occurs b/t predators and prey, parasites and hosts, etc. How can the type of interaction -outcome of interactions among species is dynamic and conditional change? -e.g. in commensal relationship b/t birds and ants, if bird attacks force some insects into path of ants, then becomes mutual -if birds begin to take prey that would otherwise be taken by ants, then parasitism -outcome of interaction may depend on number and types of prey, bird, and ants present, and may change over time Competition -/- interaction that occurs when diff. individuals use same resources and when those resources are limiting -related to theory of evoluation by natural selection -individuals that are more successful in competition leave more offspring than others – they are fitter -if traits that lead to success are heritable, then fq of alleles in pop changes Intraspecific vs interspecific -competition b/t members of same species is intraspecific, vice versa competition Types of competition (6) -consumptive – individuals consume same resources like trees consuming water -pre-emptive – one species makes space unavailable to other species -overgrowth – one species grows above another (plant taking sunlight) -chemical – one species produces toxins -territorial – mobile species protects feeding/breeding territory -encounter – two species interfere directly for specific resources (hyena vs vulture) Niche -niche is the range of resources that the species is able to use or the range of conditions it can tolerate -interspecific competition occurs when the niches of two species overlap Competitive exclusion principle -hypothesis that species with the same niche cannot coexist -asymmetric competition – one species suffers a much greater fitness decline than Biol 121 225 Freeman 1196-1209 (Ch. 53) Jan. 13, 2010 the other species (eventual elimination) -symmetric – each of the interacting species experiences a roughly equal decrease in fitness -basically, the stronger competitor drives out the weaker one to extinction IF their niches overlap completely -if not complete, then weaker one can retreat to an area of non-overlap Fundamental vs realized niche -fundamental niche is combo of resources of areas used or conditions tolerated in the absence of competitors, and its realized niche, which is the portion of resources or areas used or conditions tolerated when competition occurs Asymmetric vs symmetric In asymmetric competition, one species suffers much greater fitness decline than competition the other species. In symmetric competition, both experience roughly equal fitness decrease If two species have completely -the stronger competitor will dominate the weaker competitor (asymmetric overlapping niches... competition) and the weaker one will be driven to extinction – there is no refuge for the weaker competitor If niches of two species do not -then in asymmetric competition, the stronger one will dominate and be closer to its overlap completely... fundamental niche while the weaker will be forced to ‘retreat’ and use non- overlapping resources Fitness trade-off -ability to compete for a particular resource is only one aspect of an organism’s niche -if individuals are extremely good at competing for a particular resource, probably less goo
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