CHAPTER 53 – CHAPTER 53 – COMMUNITY ECOLOGYCOMMUNITY ECOLOGY

Themes:•Interaction with the environment•Regulation•Scientific Inquiry•Evolution

Objectives:Rivet vs. Redundancy ModelsPopulations are linked by competition, predation, mutualism, and commensalismTrophic structure is key in community dynamicsDominant and keystone species exert strong controls on a communityBottom-up (nutrients) vs. Top-down (predation)Most communities are in a state of nonequilibrium due to disturbances (Humans the typical agent)Species Richness – related to communities geographic sizeCommunity biodiversity – measures the # of species and their relative abundance

Root WordsCrypto –Ecto – Endo – Herb – - voraHetero – Inter – Mutu –

Community – all organisms that live in a particular area; many populations (different species) living close enough to have potential interaction.

Coevolution – Reciprocal evolutionary adaptations in 2 species.

(1) Example: Flowers and their pollinators (insects, birds).

(a) Change in one species – new selective force for another species

Cryptic Coloration (camouflage); 3 types of mimicry; aposematic (Warning) coloration

CamouflageDeception coloration

(E) Species richness- the number of species that a community contains.

1). This increases as you travel north from the South pole.

(F) All of the following act to increase species diversity:

1). Keystone predators; patchy environments; moderate disturbances and migration of a population.

(G) Herbivory – The consumption of plant material by a herbivore.

(H) Creatures can defend themselves by such things as cryptic coloration; mobbing; hiding or fleeing.

Redundancy Model – Most of the species in a community are not tightly associated with each other, and the web of life is very loose. Thus, the increase or decrease of ones species in the community has little effect on the other species.

1. Example: If one predator disappears and then another predatory species will usually take its place.

Rivet Model – that says that most species in a community are associated tightly with other species in a web. Thus increasing or decreasing one species in a community affects many other species.

Community Models

Mimicry Systems depend on Defensive Mimicry Systems depend on Defensive Behavior:Behavior:

a. The model is noxious or disagreeable, and easily recognized.

b. The mimic is less common than their models.c. The ability of prey to “learn” characteristics of their predator.

Mullerian mimicry – is when 2 dangerous organisms resemble each other. (like 2 poisonous snakes that resemble each other).

Ecologists consider STABILITY to be a measure of the ability of a community to either resist change or to recover its original state after change.

Trophic structure of a community describes the feeding relationships within a community.

Many plant species in communities seem to independently distributed.

(I.) Niche

1). Ecological niche – sum total of an organism’s use of biotic and abiotic resources in the environment.

2). Fundamental niche – resources a population theoretically is capable of using under ideal conditions.

(a) Physiological limits of tolerance.

(b) Absence of interaction with other organisms.3). Realized Niche – Portion of the fundamental niche the organism actually uses.

*(NOTE): Competition between species makes the difference between # 2 & 3.*

4). Need to know definitions and comparisons: parasitism, commensalism and mutualism

Fig. 53.3 – Resource Partitioning in a group of sympatric Fig. 53.3 – Resource Partitioning in a group of sympatric lizardslizards

Slight variations in a niche allow closely related species to coexist.

4 ?’s. on Fig. 50.4 Biogeographical Realms4 ?’s. on Fig. 50.4 Biogeographical Realms

(J) Competitive Exclusion Principle – 2 species cannot coexist in a community if their ecological niches are identical.

Competition in Laboratory Populations of Paramecium.

This is especially true if one species has a reproductive advantage over the other.

(K) Keystone Predator – exerts an important regulating effect on other species in a community.

(1) Helps maintain higher species diversity (reduces strong competitors).

(L) Species Equitability – The relative number of individuals in each species.

Ecological SuccessionEcological Succession – Transition in species competition over time. (Yellowstone Fires – did not take long for vegetation to return)

(A) Primary – no soil to forest ecosystem.

(B) Secondary – Existing community cleared by some disturbance (fire etc.) Happens if soil is still intact.Happens if soil is still intact.(C ) Climax Community – last stage of succession (usually does not happen due to disturbance in a ecosystem). There may not be such a thing since most stable communities do not reach a stable climax diversity. Disturbances are ongoing in ecosystems.

(D). This is due to continued disturbances in ecosystems.

E. Organisms sometimes induce succession 1 of 2 ways:

1. Inhibition – Early species prevent rather than assist colonization by other species.

2. Facilitation – One species actually “paves the way” for another species making the ecosystyem more favorable for the 2nd species.

BiogeographyStudy of past and present distribution of species. (All Flora & Fauna).

1. Island Biogeography – 5 ?’s (2 factors that determine the rate at which new species eventually inhabit an island.)

(a). Rate of immigration.

(b). Rate of extinction of species on the island.

(c). Major Features of Island Biogeography

1). If several islands are close together to the mainland, the largest island will have the greatest # of species & the lowest extinction rate.

2). Usually the smallest most distant island from the mainland will have the least # of species & lowest immigration rate.

Humans have caused the greatest disturbance and thus the greatest impact on ecosystems.

Sympatric – Reproductively isolated subpopulation in the midst of its parent population.

1. Resource partitioning would most likely occur in sympatric populations of species with a similar ecological niche.