mcdb20lec13su09

mcdb20lec13su09 - Lecture 13 Biological communities Species...

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Lecture 13 Biological communities Species interactions Ecosystems Biomes Energy Flows Nutrients Cycle Ecosystem stability Biological communities Populations (of different species) living together in a habitat Type of habitat shapes a community’s structure Species Interactions Most interactions are neutral; they have no effect on either species Interspecific competition has a negative effect on both species Three Major Types of Interactions Competition: -/- where both species are harmed Exploitation: +/- where one species benefits, while the other is harmed Mutualism: +/+ where both species benefit When Populations Compete, Both are Harmed Competitive exclusion principle Two species cannot coexist while exploiting the same resources. ! Populations with completely overlapping niches cannot coexist forever. ! Competition for resources occurs until one or both species evolve in ways that reduce the competition, through character displacement, or until one becomes extinct in that location. Interacting species evolve together.
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Predation produces adaptation in both predators and their prey. Predation ! One of the most important forces shaping the composition and abundance of species in a community Why do exotic species often flourish when released into novel habitats, even though natural selection has not adapted them to this new environment? Prey Adaptations for Reducing Predation ! There are two broad categories of defenses against predators: • Physical • Behavioral Physical Defenses Include Mechanical, Chemical, Warning Coloration, and Camouflage Mechanisms 1) Mechanical Defenses 2) Chemical Defenses 3) Warning Coloration 4) Camouflage
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Behavioral Defenses Include both seemingly passive and active behaviors: hiding or escaping, or alarm calling or fighting back Predator adaptations for enhancing predation Why don’t predators become so efficient at capturing prey that they drive the prey to extinction? The “Life-dinner Hypothesis” ! Predators and their prey are in an evolutionary arms race. ! As physical and behavioral features evolve in prey species to reduce their predation risk, predators develop more effective and efficient methods of predation. ! The coevolutionary process can result in brightly colored organisms, alarm calling, and many types of mimicry. Parasitism is a form of predation. ! Parasitism is a symbiotic relationship in which one organism benefits while the other is harmed. ! Parasites face some unusual challenges relative to other predators, particularly how to get from one individual host to another, and some complex parasite life cycles have evolved.
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Parasite Predators ! Parasites have some unique features and face some unusual challenges: The parasite generally is much smaller than its host and stays in contact with the host for extended periods of time. Complicated life cycles as means of getting from
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mcdb20lec13su09 - Lecture 13 Biological communities Species...

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