Ecology 2

Ecology 2 - Ecology 2 Concepts: 54.2 54.3 (1211-1212) 55.3...

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1 Concepts: 54.2 54.3 (1211-1212) 55.3 55.5 (1237-1241) Community structure and disturbance events Ecology 2 Concept 54.2: Dominant and keystone species exert strong controls on community structure In general, a few species in a community exert strong control on that community‟s structure Two fundamental features of community structure are species diversity and feeding relationships Species Diversity Species diversity of a community is the variety of organisms that make up the community Species richness is the total number of different species in the community Relative abundance is the proportion each species represents of the total individuals in the community Fig. 54-9 Community 1 A: 25% B: 25% C: 25% D: 25% Community 2 A: 80% B: 5% C: 5% D: 10% A B C D Two communities can have the same species richness but a different relative abundance Diversity can be compared using a diversity index Shannon diversity index ( H ): H = –[( p A ln p A ) + ( p B ln p B ) + ( p C ln p C ) + …] Community 1, H=1.39 Community 2, H=0.71 Trophic Structure Trophic structure is the feeding relationships between organisms in a community Food chains link trophic levels from producers to top carnivores A food web is a branching food chain with complex trophic interactions Humans Smal er toothed whales Baleen whales Sperm whales Elephant seals Leopard seals Crab-eater seals Birds Fishes Squids Carnivorous plankton Copepods Euphausids (kril ) Phyto- plankton Quaternary consumers Tertiary consumers Secondary consumers Primary consumers Primary producers Marine food chain Phytoplankton Zooplankton Carnivore Carnivore Carnivore Marine food web
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2 Limits on Food Chain Length Each food chain in a food web is usually only a few links long The energetic hypothesis suggests that length is limited by inefficient energy transfer The dynamic stability hypothesis proposes that long food chains are less stable than short ones Most data support the energetic hypothesis Fig. 54-14 Productivity Number of trophic links 0 1 2 3 4 5 High (control): natural rate of litter fall Medium: 1 / 10 natural rate Low: 1 / 100 natural rate Number of trophic links falls if reduce the amount of leaf litter input in a treehole community, ie. greater food supply at producer level supports longer food chains Energy transfers between trophic levels is ~ 10% efficient When a caterpillar feeds on a leaf, only about one-sixth (17%) of the leaf‟s energy is used for secondary production Cellular respiration 100 J Growth (new biomass) Feces 200 J 33 J 67 J Plant material eaten by caterpillar 33% is the production efficiency of caterpillar the fraction of energy stored in food that is not used for respiration Trophic efficiency is the percentage of production transferred from one trophic level to the next (typically 5-20%) Fig. 55-10 Primary producers 100 J 1,000,000 J of sunlight 10 J 1,000 J 10,000 J Primary consumers Secondary consumers Tertiary consumers A pyramid of net production represents the loss
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This note was uploaded on 03/22/2010 for the course BISC 120 taught by Professor Webb,wetzer,? during the Fall '07 term at USC.

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Ecology 2 - Ecology 2 Concepts: 54.2 54.3 (1211-1212) 55.3...

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