• Chapter 53 – Community Ecology

What is a community?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

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

NicheNiche

• Two 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 Coloration Aposematic Coloration

Batesian Mimicry

Mullerian Mimicry

HerbivoryHerbivory

• Herbivory: 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, example = acacia trees and ants

• Commensalism: an interaction between species where one benefits while the other is neither harmed nor helped; a +/0 interaction, example = egrets and water buffalo

• Parasitism: a +/- interaction in which one organism (parasite) derives nourishment from another (host); pathogen = lethal

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

Mutualism

Commensalism

MutualismMutualism

Which forest is more diverse?Which forest is more diverse?

• Species diversity has 2 components:

• Species richness: total number of different species

• Relative abundance: proportion each species represents

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

Species Diversity

Trophic StructureTrophic Structure

• Feeding relationships• Transfer of energy up

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

• Food Chains, food webs

Trophic Levels

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

Examples of Keystone SpeciesExamples of Keystone Species

Sea Star

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