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BIOL 103 Lecture Notes Mar 25

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Queen's University
BIOL 103

th Week of March 25 Community Ecology -studies how groups of species interact and form functional communities  Communities consist of interacting species living within a defined area  Communities lie between special scales of a biome and a population  Species distribute according to ‘tolerance ranges’ due to genetic, physiological, and lifecycle characteristics, and interactions with other species o Characteristic species in different habitats are due to unique traits  There are sharp changes in biotic/abiotic environment, therefore community composition may change abruptly – an ecotone is an area where distinct communities meet  There is a broad overlap of species populations along environmental gradients; communities continuously “grade” into each other – rather than forming distinct groups, this makes community definition unclear Community change along a gradient Note many overlaps between species and conditions Ecological Niche -lifestyle and role of an organism in its community  Accounts of abiotic and biotic factors  An organism’s habitat is used to describe its niche Fundamental Niche -potential niche for organism in absence of predators and competing species Realized Niche -niche an organism actually occupies Abiotic Factors provide a fundamental niche, but biotic factors limit them to realized niches: (In real situations, you will be dealing with more than two parameters) Competition: Two or more individuals attempting to use the same resource (eg. Food) or space o Intraspecific Competition: among individuals within a population – sexual selection: (males of species competing for female access for breeding); thinning: acorns on ground surrounding mother tree which all cannot grow into trees (competition for resources in order to sprout and grow to reasonable size) o Interspecific competition: between different species – eg. Different species of tree roots competing for moisture o Interference competition – allelopathy; animals physically fighting  Plants of different or same species can compete (eg. Different species of tree roots competing for moisture) by active warfare (for example: allelopathy, figure 51.3 in text.)  Lab experiments by Gause shows interspecific competition between protozoan species (fig 54.6); P. Aurelia fed on suspended particles near top and P. bursaria fed on bottom layers  By looking at graph, it can be seen that P. caudatum is the weak competitor o Experiment done where P. caudatum was put into container of water with glass wool in which they had the opportunity to hide from competitors and still be fed, and they did not go extinct.  Work by Joseph Connell on barnacles: predictions of this experiment - C. stellatus are abselnt from lower intertidal zone because: o Unstable abiotic environment (too deep)? o Competition from B. Balanoides?  Tide lines on shores in PEI etc. represent different banacles and levels on which they’d existed  Sessile: stable, stationary o Controlled experiments like these are needed to prove that competitive interactions are significant o Remember: small banacles (Chthamalus) on top and the bigger (Balanus) on the bottom  Large boulders, and take them lower into the tidal zone and subjected them with treatments (put coverage around rock to allow food in and out but make it difficult for balanus to get in and out); all treatments predicted that Chthamalus would survive without presence of Balanus, which was true o Final conclusion: Balanus is excluding Chthamalus from lower zone o Interference competition was occuring, seen through a long study Competitiove Exclusion Principal: two species cannot occupy the same space in the same community for an indefinite period; one species in excluded by the other as a result of competition  Complete competitors cannot exist. –Garret Hardin Types of competitive interactions: Competiton (-/-) – both species have their fitness reduced (not neccessaritly equally) Predation/paratism (+/-) – beneficail for predator, reduction of fitness for prey  Predation is when predator is lrger than prey (predator kills prey); parsitism is when parasite is smaller than host (does not kill host, at least not immediately – most likely through disease) Mutualism (+/+) – coevolutionary arms race; can start off by parasite-host interaction where the relationship grows over many many years by which both partners inrease their fitness  Symbyosis is when 2 species live very
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