Chapter 54Community Ecology

Community Ecology

• The study of the interactions between the species in an area.

Interspecific Interactions• Interaction between species.• May be positive, negative, or

neutral (in regards to fitness)• Ex:

Predation Mimicry Competition Symbiosis

Predation (+/-)

• Predator and prey relationships.

• Ex – Lynx and Hares

Herbivory (+/-)

• When an organism eats parts of a plant or algae.

• Herbivore – may have special adaptations to find their prey.

• Plants – may have adaptations to avoid being eaten.

Predation/Herbivory

• Often results in interesting defenses or adaptations.

• Ex:• 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• Müllerian

Batesian Mimicry

• Palatable species mimics an unpalatable model.

Hawk moth larva Snake

Müllerian 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 exact requirement cannot co-exist in the same community.

• The better adapted species will survive and the less adapted will go extinct.

Think, Pair, Share

• Discuss if the Competitive Exclusion Principle explain the spacing of fast food restaurants on the “strip” in most towns.

Ecological Niche• The sum of a species’ use of

the biotic and abiotic resources in its environment is called the species’ ecological niche.

• How a species “makes its living” in its ecosystem.

• Species can not have niche overlap, the Competitive Exclusion Principle

Niche Types

1. Fundamental - what a species is theoretically capable of using.

2. Realized - what a species can actually use.

Think, Pair, Share

• Again in terms of fast food restaurants, explain the concept of a fundamental vs. realized niche.

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. Parasitism

2. Commensalism

3. Mutualism

Parasitism (+/-)

• Parasite harms the host.• Parasites may be external or

internal.• Well adapted parasites don't kill

the host.

• https://www.youtube.com/watch?v=uvdiYg6ZN-U Sci-Show Parasites

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

Species with large impacts

• Some species have larger impacts on a community structure than others.

• Ex:• Dominant Species• Keystone Species• Foundation Species

Dominant Species

• A species that is the most abundant or has the highest biomass in a community.

• Has a major effect on a community both biotically and abiotically.

Reason for Dominance?

• Best Competitor?

• Best in avoiding predators and disease?

• Invasive species may fit the last explanation.

Example

• Chestnuts – used to make up to 40% of the forest.

• Lost between 1910-1950 because of fungus disease.

• Major impact on wood and nut industries.

Response

• Some tree species increased in abundance to fill the gap.

• Mammals and birds did OK.

• 7 species of insects went extinct.

Keystone Species

• Not a dominant species, but has a major impact in the community structure.

• Often a top predator that controls the numbers of other species.

• Ex. Sea Otters

Foundation Species

• Species that cause physical changes in the environment that affect others.

• Ex. Beavers, Bison, Black Rush

• https://www.youtube.com/watch?v=ysa5OBhXz-Q

• How wolves change rivers

Succession

• Changes in species composition over time.

Succession Stages

• Climax Community - An ecological community in which populations of plants or animals remain stable and exist in balance  with each other and their environment.

Succession Types

1. Primary

2. Secondary

Primary Succession

• Succession with only abiotic materials as the starting substrate

• Ex: volcanic islands glaciated areas road cuts

Secondary Succession

• Succession with biotic materials (living or dead) as the starting substrate

• Ex: • Cutting down a forest• Forest fire• Tornado/storm damage

Steps of Succession

• Pioneer Species – the first organisms to appear in the area in primary succession

• Usually moss or lichens

What do Pioneer Species Change?

• Enrich the soil – as generations die, their remains decompose and add nutrients to the soil (often N).

• The soil is now able to support a greater variety of species such as grasses and small shrubs.

• Which occurs faster, primary or secondary succession?

• What can you do to speed up succession?

Point

• If you understand the causes and controlling factors of succession, you can manipulate them.

Some points about Succession

• The Organisms are changing in the area over time. General pattern is an increase in biodiversity.

• The Climate of the area is NOT changing over time.

Other Changes

• Soil – becomes richer in N, more depth, better water retention etc.

• Light – can decrease at ground level because of shading by taller plants.

Summary

• Know the various types of interspecific interactions.

• Know the Competitive Exclusion Principle and Niche Concept.

• Know Species with large impacts.

Summary

• Know some examples and causes of succession.