Chapter 54 Community Ecology

Essential Knowledge 2.d.1 – All biological systems from cells and

organisms to populations, communities, and ecosystems are affected by complex biotic and abiotic interactions involving exchange of matter and free energy (54.1 - 54.5).

2.e.3 – Timing and coordination of behavior are regulated by various mechanisms and are important in natural selection (54.1).

4.a.5 – Communities are composed of populations of organisms that interact in complex ways (54.1 & 54.2).

Essential Knowledge 4.a.6 – Interactions among living systems and with

their environment result in the movement of matter and energy (54.2).

4.b.3 – Interactions between and within populations influence patterns of species distribution and abundance (54.1).

4.c.4 – The diversity of species within an ecosystem may influence the stability of the ecosystem (54.2).

Community Ecology The study of the interactions between

the species in an area

Interspecific Interactions

Interaction between species May be positive, negative, or neutral Ex:

1. Coevolution2. Predation3. Mimicry4. Competition5. Symbiosis

Coevolution When two species

have reciprocal evolution to each other

Ex: › Flowers and their

pollinators

Predation (+/-) Predator and

prey relationships

Ex – Lynx and Hares

Predation Often results in interesting defenses or

adaptations Ex:

› Plant defenses› Cryptic coloration› Aposematic coloration

Cryptic Coloration A passive defense where the prey is

camouflaged against its environment

Aposematic Coloration

The use of conspicuous colors in toxic or unpalatable organisms to warn off predators

Poison Arrow frogs

Mimicry Defense mechanism where the mimic

has a resemblance to another species, the model

Types:› Batesian› Mullerian

Batesian Mimicry Palatable species mimics an

unpalatable model

Hawk moth larva Snake

Mullerian Mimicry Two unpalatable species resemble each

other

Cuckoo Bee Yellow Jacket

Competition When two species rely on the same

limiting resource Intraspecific competition usually more

severe than Interspecific competition Why?

Competitive Exclusion Principle

Predicts that two species with the same requirement can not co-exist in the same community

One species will survive and the second will go extinct

Ecological Niche The n-hyperspace of requirements for a

species How a species “fits into” an ecosystem Species can not have niche overlap; the

Competitive Exclusion Principle

Niche Types1. Fundamental - what a species is

theoretically capable of using2. Realized - what a species can actually

use

Resource Partitioning A way that species avoid niche overlap

by splitting up the available resources Ex: Anolis lizards

A. distichus A. insolitus

Symbiosis When two different species live

together in direct contact Types:

1. Parasitism2. Commensalism3. Mutualism

Parasitism (+/-) Parasite harms the host Parasites may be external or internal Well adapted parasites don't kill the

host

Parasitic behavior: A female Nasonia vitripennis laying a clutch of eggs into the pupa of a blowfly (Phormia regina)

Commensalism (+/o) One partner

benefits while the other is unchanged

Ex. – Cattle and Egrets

Mutualism (+/+) Both partners

benefit from the interaction

Ex: Pollinators and flowers

Acacia Tree and Ants

Keystone species p. 1204 A keystone species is

a plant or animal that plays a unique and crucial role in the way an ecosystem functions. Without keystone species, the ecosystem would be dramatically different or cease to exist altogether.

Prairie dogs are a keystone species in the Great Plains region of the U.S. and Canada

Prairie dogs are a keystone species in the Great Plains region of the U.S. and Canada.

Keystone species A keystone as an arch's crown secures the

other stones in place. Keystone species play the same role in many ecological communities by maintaining the structure and integrity of the community.

Keystone species often, but not

always, a predator. A keystone species'

disappearance would start a domino effect. Other species in the habitat would also disappear and become extinct.

In terrestrial environments, fire ants function as keystone predators by suppressing the numbers of individuals and species of arthropods that could be harmful to agriculture.

Succession Changes in

species composition over time

Succession Stages Sere: unstable stage usually replaced

by another community rock lichen moss grass shrub

tree forest Climax: stable stage, self-reproducing

Succession Types1. Primary2. Secondary

Primary Succession Building a community from a lifeless

area Ex: volcanic islands

glaciated areas road cuts

Glacier Bay, Alaska Example of primary succession (p.

1209)Glacial retreat

Comment

The first example of primary succession was worked out on the Indiana Dunes

Stages: › Open Beach› Beach Grasses› Conifers (Junipers and Pines)› Oaks› Beech-Maple forest (Climax)

Secondary Succession Where a community has been

disturbed and the soil is mostly intact Ex:

› Cutting down a forest› Blow-outs on the Dunes

Causes of Succession1. Autogenic Factors2. Allogenic Factors

Autogenic Factors Changes introduced by the organisms

themselves Ex: toxins

acids

Allogenic Factors Outside

disturbances Ex: Fire

Floods

Point If you understand the causes and

controlling factors of succession, you can manipulate them

Biogeography Study of the past and present

distributions of individual species and communities

Latitudinal Gradients

Range Limitations1. Lack of dispersion2. Failure to survive in new areas3. Retraction from former range area

Proof Fossil Evidence Pollen Studies Transplant Experiments

Islands Special cases in Biogeography Must be colonized from other areas

Island Species Factors Island size Distance from mainland

Island Size Small islands hold few species Why? Fewer niches available for species to

occupy

Distance from Mainland Closer islands have more species Why? Easier for colonization

Comment Islands tend to have high numbers of

Endemic species Why? Adaptive Radiation and Evolution of

new species

Summary Identify various types of interspecific

interactions. Identify the Competitive Exclusion Principle and

the concept of the Ecological Niche. Recognize species with a large impact. Identify the differences between Primary and

Secondary Succession and the causes of succession.

Recognize some biogeographical aspects of community diversity.