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 bottom- up 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

Individualistic Hypothesis Why do plant communities have different species assemblages? 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 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 = x, P < 0.035, R 2 = 0.345) and b, elevation (y = x, P < 0.014, R 2 = 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. Frequency-dependent Batesian mimicry David W. Pfennig, William R. Harcombe and Karin S. Pfennig Nature 410, 323(15 March 2001) doi: / Frequency-dependent Batesian mimicry David W. Pfennig, William R. Harcombe and Karin S. Pfennig Nature 410, 323(15 March 2001) doi: / Frequency-dependent Batesian mimicry: David W. Pfennig, William R. Harcombe and Karin S. Pfennig Nature 410, 323(15 March 2001)

Müllerian mimicry –Two or more unpalatable species resemble each other (a) Cuckoo bee (b) Yellow jacket 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.

Interspecific Interaction: Herbivory The process in which an herbivore eats parts of a plant

Mutualism

Figure 53.9 Mutualism

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" Species "B"

Species "A" + Parasitism Predation Herbivory Commensalism Mutualism Neutralism Commensalism Competition Parasitism Predation Herbivory Species "B" No interaction

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 bottom- up and top-down control mechanisms