Chapter 54.1-2 Community Ecology: The Interactions of Different Populations

I. What is a Community?- An assemblage of species living close enough together for potential interaction.

- A competition for resources between individuals of two or more species when resources are in short supply; detrimental to both species (-/-)

II. Interspecific Interactions!

A. Competition ( - / - )

B. Competitive Exclusion PrincipleTwo species with similar needs for same limiting resources cannot coexist in the same place. Example - Paramecium

What forms the community structure?

- Interaction detrimental to both species

C. Ecological Niche

-The Competitive Exclusion Principle can be restated to say that two species cannot coexist in a community if their niches are identical.

-Sum total of an organism’s use of abiotic/biotic resources in the environment.

1. Fundamental Niche

2. Realized Niche

-Niche that is possible for the organism due to abiotic conditions

- Niche that results due to biotic interactions

-differentiation of niches that enables two similar species to coexist in a community.

D. Resource Partitioning

An organism’s role in the environment.

E. Character Displacement-the tendency for characteristics to be more divergent in sympatric populations of 2 species than allopatric populations of same 2 species

Character Displacement(don’t focus on too much, will see again in evolution unit)

-Allopatric means geographically separate; sympatric means geographically overlapping

-both birds eat similarly sized seeds on Los Hermanos and Daphne islands.

-Difference in beak morphology show adaptations that favor eating different-sized seeds

F. Predation Types

1) “Standard” ( + / - ) predator eats prey that is immediately consumed

2) Herbivory (+ / - ) animal eats plant

3) Parasitism predators live on (ectoparasite) /or in (endoparasite) a host and depend on the host for nutrition

(+ / - )

4) Parasitoidism (+ / - ) special type of parasitism where the parasite eventually kills the host

G. Prey Defenses1) Cryptic Coloration

2) Aposematic Coloration

3) Batesian Mimicry

4) Mullerian Mimicry

camouflage including deceptive markings.

warning colors, that is sometimes associated with other defenses (toxins).

harmless species mimics a harmful one

two or more unpalatable species resemble each other

( + / - )

Vocab Quiz

H. Symbiosistwo species benefit from their interaction

one species benefits from the interaction, but other is not affected.

1) Mutualism ( + / + )

2) Commensalism

( + / 0 )

http://www.youtube.com/watch?v=Df_iGe_JSzI

III. Species Diversity – 2 components

A. Species Richness -the number of different species in the community

B. Relative Abundance -the proportion each species represents of all individuals in the community

-the variety of different kinds of organisms that make up the community

C. Measure using Shannon diversity (H) -the higher the value H, the more diverse community

H=1.39

H=0.71

D. Diversity & Community Stability -more resistant to invasive species (organism established outside native area), more resistant to disturbance/stress (drought, fire, flood), and are more productive (more biomass, meaning total mass of all organisms in a habitat)

IV. Trophic Structure

A. Food Chains

determines the feeding relationships between organisms

transfer of food energy from its source in photosynthetic organisms through herbivores and carnivores

All trophic relationships diagrammed in a community; interconnecting food chains

B. Food Webs

C. Dominant Species-have the highest abundance or highest biomass (the sum weight of all individuals in a population)

D. Keystone Species

-exert an important regulating effect on other species in a community

Nellie the otter

E. Ecosystem Engineers-an organism that influences community structure by causing physical changes to the environment

V. How is Community Structure controlled?

A. Bottom-up model -unidirectional influence from lower to higher trophic levels

B. Top-down model -predation controls community organization because predators limit herbivore numbers, which in turn control plant/phytoplankton numbers, which in turn control nutrient levels (aka trophic cascade model)

N = minerals/nutrients V = vegetation H = herbivores P = predators

N V H P

N V H P

Slide 3

Pygmy Seahorses

Slide 3

Slide 3

Predator Interaction

B:

G

F:

H:

E:D:

C:A:

Which community relationship is demonstrated by each of the pictures below?

Commensalism Parasitoidism Mutualism

Cryptic ColorationBatesian Mimicry

Aposematic Coloration

Mullerian Mimicry

Herbivory Batesian MimicryI: Slide 3

Gause’s experiment that led to idea of Competitive Exclusion

Slide 1