Community Ecology

What is a Community

A community is any assemblage of populations in an area or habitat.

Communities differ dramatically in their species richness and relative abundance.- species richness: number of species contained- relative abundance: number of members of each different species

Interspecific Interactions and Community Structure

Interspecific interactions: interactions belonging between populations of different species under one community

Intraspecific: between members of the Same species

Niche

• Each organism has it’s own niche (it’s own position and function within a community)

• Connections between animals in a given community is shown if the food chain (the way in which each organism depends on each other for food)

Food Chain• The food chain consists of producers, primary consumers, secondary

consumers, and tertiary consumers.• Autotrophs produce all available food (have the largest biomass +

energy)• Primary Consumers eat producers• Secondary Consumers eat primary consumers and producers• Tertiary Consumers eat all of the above.• Decomposers are responsible for decomposing organic matter so

nutrients can be recycled.• Toxins increase in an ecosystem are more concentrated and more

dangerous further up the trophic pyramid. • Less energy and biomass is represented towards the top of the food

chain.

Interspecific Interactions and Community Structure

Interspecific Interactions and Community Structure

Interspecific Interactions and Community Structure

Ecological niche- sum total of a species’ use of biotic and abiotic resources in its environment- how a species “fits into” an ecosystem- where it is and what it does

Interspecific Interactions and Community Structure

Predation- includes the killing of one animal by another, herbivory, and parasitism- predator adaptations - plant defenses against herbivores- animal defenses against predators

Interspecific Interactions and Community Structure

- aposematic coloration: animals with effective chemical defenses are brightly colored to act as a warning: mimicry

Interspecific Interactions and Community Structure

- mimicry: a species of prey will gain protection through mimicry

Interspecific Interactions and Community Structure

Interspecific Interactions and Community Structure

Dominant species and keystone species exert strong controls on community structure

Dominant species: species that have the highest abundance or biomass

Keystone species: species that exert strong control on community structure by the ecological niches

Population Ecology

• When studying population size, density, distribution patterns, and age structure all play a role.

• Age structure histograms= one way to predict the population growth

• Survivorship curves is a second way to predict population growth: the number of individuals surviving to a certain age.

• Growth of population can be represented by the number of crude births minus the number or crude deaths divided by the size of the population.

• Carrying Capacity= the maximum number of individuals of a species that a habitat can support. Many populations do not reach their carrying capacity.

Exponential & Logistic Growth

• Two types of growth include: exponential growth and logistic growth.

• Exponential growth occurs when a population has a well equipped environment, and growth is unrestricted (no disease/ predation, good resources, no limits to reproduction)

• Exponential Growth occurs quickly.• Logistic growth occurs when a population becomes restricted.• Two types of life history strategies: R- selected and K-Selected.• R- strategists produce a lot of offspring to ensure survival.• K- Strategists survive in stable environments and are usually

larger animals ( no real competition with other competitors)

Exponential Growth Curve

Logistic Growth Curve

Ecological Succession• Ecological Succession= the predicted procession of plant communities over a

short time period.• Primary Succession= succession where no previous organisms have ever existed• “Pioneers” = Lichens; invade an area and erode rock surface, which over time

becomes soil:::: composed of fungus and photosynth algae.• Once erosion has occurred, this sets the area up for organisms. Lichens are

eventually replaced by moss/ferns, which are then replaced with grasses and shrubs, deciduous trees then take over, and eventually evergreens replace all

• Lichens die out because they cannot compete with new plants for minerals, sunlight, ect.

• This sequence is otherwise known as a sere• The final community that is produced is known as a climax community• Where new community develops where a previous community was destroyed is

known as secondary succession.

Secondary succession

• After an event (forest fire)• In a place that had a prior ecosystem• Soil is already present for don’t need pioneer

community.• Roots and seeds may be present in the soil

Human Impact• Greenhouse effect: (increased atmospheric of C02 (burning of fossil

fuels) have added to the warming of the earth. Polar ice caps have began to melt, flooding occurs, changes in precipitation patterns, and changes in plant life world wide.)

• Ozone depletion: (CFCs, and other pollution)• Increased Acid Rain: (sulfur dioxide due to burning of fossil fuels

pollutes, clouds then form sulfuric and nitric acid)• Deforestation: (cleared forests, erosion, floods, changes in weather

can occur)• Pollution: (biomagnification occurs; increased toxic levels as we

reach the top of the food pyramid)• Reduction in biodiversity: (habitats have been destroyed, things that

could have been beneficial to humans have now become extinct.