• Chapter 54 – Community Ecology

• WHAT IS A COMMUNITY???– A community is a

group of populations of various species living close enough for potential interaction

Community InteractionsCommunity Interactions• Interspecific – interactions between

different species within a community

– Competition– Predation– Herbivory– Symbiosis– Disease

CompetitionCompetition

• Interspecific competition occurs when species compete for a resource that is in limited supply

• Competitive exclusion principle: one species will use the limiting resources more efficiently thereby eliminating the local competitor.– Example: barnacle species in Scotland

• BARNACLE BACKGROUND:– What do you notice about the distribution of

the two barnacles?– What abiotic factor(s) may contribute to their

distribution patterns?

• What happened when Chthamalus was removed from the habitat?– What is the difference between

a realized niche and a fundamental niche?

BEFORE

AFTER

Competitive Exclusion Principle Competitive Exclusion Principle and the Concept of Nicheand the Concept of Niche

• Relates to concept of Niche: the sum total of the biotic and abiotic resources used by a species’– Fundamental niche = potential– Realized niche = actual

NicheNicheTwo species cannot occupy

the same niche = leads to competition

• Resource partitioning: altering ones niche to avoid competition; lizard example

• Character displacement: characteristics become more divergent; finch beak example

Resource Partitioning

Character Displacement

PredationPredation• Predator kills and eats prey; a +/- interaction

• Predator mechanisms: acute senses, claws, teeth, fangs, stingers, poison, speed, agility, coloration, and camouflage

• Defense mechanisms: alarm calls, maternal/paternal protection, mechanical defenses (spikes, spines, and hard shells), chemical defenses (toxins, poisons, and bad taste), coloration (aposematic coloration) and mimicry (Batesian and Mullerian).

Coloration and MimicryColoration and Mimicry

Cryptic ColorationAposematic Coloration

Batesian Mimicry

Mullerian MimicryBatesian Mimicry

HerbivoryHerbivory• A +/- interaction in which an herbivore eats

parts of a plant or alga

• Predator mechanisms: include specialized teeth or digestive systems, enhanced senses, and selective eating (leaving part of plant behind)

• Similar defense mechanisms as with predation, but chemical defenses and coloration are most common

SymbiosisSymbiosis• Mutualism: an interaction that

benefits both species; a +/+ interaction– acacia trees and ants

• Commensalism: an interaction between species where one benefits while the other is neither harmed nor helped; a +/0 interaction

– egrets and water buffalo• Parasitism: a +/- interaction in which

one organism (parasite) derives nourishment from another (host); pathogen = lethal

– Tape worm and human

• Can you think of any additional examples (at least 1 of each)?

Mutualism

Commensalism

MutualismMutualism

Which forest is more diverse? Explain your rationale.

Which forest is more diverse?Which forest is more diverse?Species diversity has 2

components:① Species richness: total

number of different species② Relative abundance:

proportion each species represents

• Answer = Ecologists would say community 1 has greater species diversity

Species Diversity

• Compare and contrast food webs and food chains.– What is the value of using

each as a tool?

Trophic StructureTrophic Structure

• Feeding relationships• Transfer of energy up

trophic levels– Primary producers– Primary consumers– Secondary consumers– Tertiary consumers– Quaternary consumers

Trophic Levels

• Identify a 6 level food chain in this Antarctic marine food web.

• Do you think this type of food chain is common? Why or why not.

Analyze the following graphs Analyze the following graphs to define what a to define what a keystone keystone species species is.is.

Dominant and Keystone Dominant and Keystone SpeciesSpecies

• Dominant species: most abundant and have the most biomass, impact on a community can vary

• Keystone species: not abundant, but play critical role because of the niche they occupy within the community– examples include sea stars and sea otters

DisturbanceDisturbance• An event that changes a community by

removing organisms and altering resources– Examples include a storm, fire, flood, drought,

overgrazing, or human activity• Can have long-term, positive effects

Prairie Disturbance Recovery

SuccessionSuccession• Transition in the species

composition of a community overtime

• Primary succession: begins in a lifeless area with no soil, example – a new volcanic island

• Secondary succession: when an existing community has been cleared by some disturbance, leaves soil intact

Ecological Succession

Applying the Applying the Concepts…Concepts…

• Two identical plots were staked out. Each included a few sagebrush plants and numerous wildflowers (5 different species of equal proportions).

• One plot was enclosed to keep out kangaroo rats, the most common grain-eaters of the area.

• After 2 years - in the fenced plot 4 of the wildflower species were no longer present, but 1 species had dramatically increased. There was no change in the control plot.

• USING THE PRINCIPLES OF ECOLOGY…– Propose a hypothesis to explain her results.– What additional evidence would support your hypothesis?

Applying the Applying the Concepts…Concepts…

• Sometime in 1986, near Detroit, a freighter pumped out water ballast containing larvae of European zebra mussels. The molluscs multipled wildly, spreading through Lake Erie and entering Lake Ontario. In some places, they have become so numerous that they have blocked the intake pipes of power plants and water treatment plants, fouled boat hulls, and sunk buoys.

• USING THE PRINCIPLES OF ECOLOGY…– What makes this kind of population explosion occur?– What might happen to native organisms that suddenly must share

the Great Lakes ecosystem with zebra mussels? – How would you suggest trying to solve the mussel population

problem?