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Lecture 14

Lecture 14 Nature of communities.docx

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Biological Sciences

Lecture 14 Winter 2012 and Chapter 15 The Nature of communities Ecologists define communities as groups of interacting species that occur together at the same place and time Interactions among multiple species are synergistic which means that they make communities into something more than the sum of their parts For example we all know that the human body made up of various limbs and organs assumes true structure and function only when all the parts interact These interactions can be negative positive direct or indirectA community may be defined by the physical characteristics of its environment for example a physically defined community might encompass all the species in a sand dune a mountain stream or a desert Similarly a biologically defined community might include all the species associated with a kelp forest a freshwater bog or a coral reefEcologists may use subsets of species to define communities One common way of subdividing a community is based on taxonomic affinity FigA For example a study of a forest community might be limited to all the bird species within that community Another useful subset of a community is a guild a group of species that use the same resources even though they might be taxonomically distant FigB For example some birds bees and bats feed on flower pollen thus forming a guild of polleneating animals Finally a functional group is a subset of a community that includes species that function in similar ways but do not necessarily use the same resources FigC For example mosquitoes and aphids both have stylet mouthparts although one feeds on mammalian blood and the other feeds on plant phloem Food Webs and Interaction WebsFigA Food webs describe trophic interactions among speciesFigB Interaction webs include both trophic interactions vertical arrows and nontrophic horizontal interactions such as competition and positive mutualism interactions
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