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Major Objectives 1. Understand basic community ecology definitions and processes 2. Know the two main hypotheses for why plant communities have different species assemblages 3. Know the 5 potential interspecific interactions between species 4. Know the difference between bottomup and top-down control mechanisms What is a Community? A collection of all the populations of different species that inhabit a particular area. Communities differ in SPECIES RICHNESS and RELATIVE ABUNDANCE Beaver (Castor canadensis) Ecosystem Engineer Beaver Lodges Ecosystem Engineer keystone species Pisaster spp. is a keystone species Competitive Exclusion Hypothesis Two species competing for same limited resource can not exist Why do plant communities have different species assemblages? Individualistic Hypothesis A community is the result of chance because of species having similar abiotic requirements Interactive or "Organismic" Hypothesis A community is the result of closely linked species locked in by mandatory biotic interactions Species Interactions Parasitism Interspecific Interaction: Predation • Cryptic coloration, or camouflage Figure 53.5 • Aposematic coloration – Warns predators to stay away from prey Batesian Mimicry – A palatable or harmless species mimics an unpalatable or harmful model Frequency-dependent Batesian mimicry: David W. Pfennig, William R. Harcombe and Karin S. Pfennig Nature 410, 323(15 March 2001) The proportion of carnivore attacks on ringed replicas of scarlet kingsnakes (top left; a mimic of eastern coral snakes) and sonoran mountain kingsnakes (top right; a mimic of western coral snakes) increased with a, latitude (y = - 13.314 + 0.391 x , P < 0.035, R2 = 0.345) and b, elevation (y = - 0.329 + 0.00032 x, P < 0.014, R2 = 0.310). Horizontal dashed line: proportion of attacks on ringed replicas expected under randomness. Vertical dashed line: maximum latitude and elevation for coral snakes in North Carolina and Arizona, respectively. Müllerian mimicry – Two or more unpalatable species resemble each other (a) Cuckoo bee Figure 53.8a, b The viceroy (Limenitis sp.; right) and monarch (Danaus sp.) butterflies look very similar but may differ in their palatability to avian predators. (b) Yellow jacket Interspecific Interaction: Herbivory • The process in which an herbivore eats parts of a plant Mutualism Mutualism Figure 53.9 Commensalism Competition Life in the shade Plants can tell the difference between the shade of an inanimate object and the shade of another plant. When a plant detects competition from neighboring plants, it initiates a set of responses, called collectively the shade avoidance syndrome, that alter its growth and physiology. A rapid and transient increase of newly synthesized auxin via a newly discovered auxin synthesis pathway allows plants to elongate and grow toward the sun. Image: Courtesy of Dr. Jean-Luc Ferrer, Salk Institute for Biological Studies Nuetralism + Species "A" 0 - 0 Species "B" + + Parasitism Predation Herbivory Commensalism Mutualism Species "A" 0 - Neutralism Commensalism Competition No interaction Parasitism Predation Herbivory - 0 No interaction Species "B" + Bottom-Up Control Top-Down Control Trophic Structure Feeding relationship between organisms Major Objectives 1. Understand basic community ecology definitions and processes 2. Know the two main hypotheses for why plant communities have different species assemblages 3. Know the 5 potential interspecific interactions between species 4. Know the difference between bottomup and top-down control mechanisms