Major Objectives 1. Understand basic community ecology definitions and processes 2. Know the two main hypotheses for why plant communities have different.

Major Objectives1. 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 HypothesisTwo 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 = - 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.

Frequency-dependent Batesian mimicryDavid W. Pfennig, William R. Harcombe and Karin S. PfennigNature 410 , 323(15 March 2001)doi:10.1038/35066628

Frequency-dependent Batesian mimicryDavid W. Pfennig, William R. Harcombe and Karin S. PfennigNature 410 , 323(15 March 2001)doi:10.1038/35066628

Frequency-dependent Batesian mimicry: David W. Pfennig, William R. Harcombe and Karin S. PfennigNature 410, 323(15 March 2001)

Müllerian mimicry– Two or more unpalatable species resemble each

other

(a) Cuckoo bee

(b) Yellow jacketFigure 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 shadePlants 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"

Species "A"

+ParasitismPredationHerbivory

Commensalism Mutualism

  Neutralism Commensalism

Competition   ParasitismPredationHerbivory

0

-

  -   0   +

Species "B"

No interaction

No interaction

Bottom-Up Control

Top-Down Control

Trophic

Structure

Feeding relationship between organisms

Major Objectives1. 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