BIOL202 - Lectures 5-7

BIOL202 Lectures - LECTURE 5 INTERSPECIFIC COMPETITION II OUTCOMES OF COMPETITION Two possible outcomes of competition(in the short-term a stable

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Unformatted text preview: LECTURE 5: INTERSPECIFIC COMPETITION II - OUTCOMES OF COMPETITION Two possible outcomes of competition (in the short-term) a) stable coexistence : populations of both species coexist but at do so at lower densities than expected if the other species was not present b) competitive exclusion : population of one species ("weaker" competitor) is driven to extinction in areas where the two species are found-------------------------------------------------------------------------------------------- G.F. Gause's experiments on competition between different species of Paramecium Three different species grown in test tubes alone: Outcomes when two species are grown together: Competitive exclusion in species of scalesuckers Scale insects on citrus Scales are a specialized type of phytophagous insect Scalesuckers are tiny wasps that are parasitoids of scales Until late 1950s: Golden-naveled scalesucker ( Aphytis chrysomphali ) is the only scalesucker in southern CA citrus groves. 1957: Lingnan scalesucker ( A. lingnanensis ) introduced from China. Result: What determines whether or not two ecologically similar species can coexist in the same community? In theory, two things: 1. Extent of overlap in the niches of the two species 2. How abundant the "stronger" competitor can become Niche overlap and potential for coexistence : Imagine have two similar species of animal, each feeds on 10 different kinds of food. Imagine Species 1 is the stronger competitor. Situation I: Slight Niche Overlap Food types Species 1: A B C D E F G H I Species 2: G H I J K L M N O P In this situation:-------------------------------------------------------------------------------------------- Situation II: Extensive Niche Overlap Food types Species 1: A B C D E F G H I J Species 2: B C D E F G H I J K In this situation : A second look at Gause's paramecia Key result: Key result: Feeding niches of Gause's three Paramecium spp.: P . caudatum : P. aurelia : P. bursaria : Take home message: Competitive Exclusion Principle : Abundance of stronger competitor and potential for coexistence First: What is a “strong competitor”, i.e., what makes a particular species the “stronger competitor”? In interference competition : the species that can overpower the other, get the most resources, and hence produce the most offspring In exploitative competition : the species that outreproduces the other species because... ...it consumes more of the resource and/or ...it is more efficient at converting resources into offspring In either case.... Strong competitor produces more offspring than the weaker competitor each generation So each generation, the weaker competitor species will get less resources overall and produce less offspring because of this Eventually, weaker competitor’s numbers drop to zero: extinction Suppose you have two tree species in same forest environment: Tree Species X Tree Species Y Taller, captures more sunlight Shorter, gets less sunlight Individual trees produce Individual trees produce...
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This note was uploaded on 04/18/2008 for the course BIOL 201 taught by Professor Mechling during the Spring '07 term at Towson.

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BIOL202 Lectures - LECTURE 5 INTERSPECIFIC COMPETITION II OUTCOMES OF COMPETITION Two possible outcomes of competition(in the short-term a stable

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