Community Ecology & Species Interactions - Bio 1108

community ecology

the study of how populations of species interact and form functional communities

communities

complex entities that can be characterized by their structures (the types and numbers of species present) and dynamics (how communities change over time such as succession)

Importance of Community Studies

Helps understand competitive interactions and resource sharing among species and essential for insights into bio diversity and ecosystem health

symbiosis

relationship in which two species live in close or long-term association with each other and at least one species benefits

mutualism

both species benefit

commensalism

one species benefits while the other is not benefited or harmed

parasitism

one species (parasite) benefits and the other (host) is harmed

competition

interaction in which organisms compete to use the same limited resource (food, space, mates, etc)

intraspecific competition

between individuals of the same species

interspecific competition

between individuals of different species

exploitation competition

organsims compete indirectly through the consumption of a limited resource

interference competition

individuals interact directly with one another by physical force or intimidation

competitive exclusion principle

complete competitors cannot coexist

• species with the same requirements cannot live together in the same place with the same resources

• Established by Georgy Gause

fundamental niche

full range of conditions where a species could live

realized niche

actual niche a species occupies

resource partitioning

differentiation of niches, both in space and time, that enable similar species to coexist in a community

• seen by Robert MacArthur examined coexistence between 5 species of warblers feeding within spruce trees in New England

Character displacement

tendency for two species to diverge in morphology and resources use due to competition

• ex. Galapagos finches

sympatric

species that occupy the same geographic area

allopatric

species that occupy different geographic area

how lethal they are for prey, length of association between consumer and prey

how predation is classified (two factors)

Antipredation strategies

chemical defense, aposematic coloration, cryptic coloration, mimicry, displays of intimidation

chemical defense

organisms emit a toxic, repellent, stinging, etc. substance to deter being eaten by predation

• bombardier beetle ejects hot spray

aposematic coloration

organism has warning coloration which advertises an its unpalatable taste

• many lethal tropical frogs have bright coloration

cryptic coloration

organisms camouflage with their environments

• stick insects, sea horses

Müllerian mimicry and Batesian mimicry

types of mimicry

mimicry

resemblance of mimic to another organism (model)

Müllerian mimicry

noxious species converge to reinforce warning (both have actual defenses)

• black and yellow stripes of bees and wasps

1.3 or 30%

The amount/percentage that G. Evelyn Hutchinson says species have to differ to be sympatric species

Batesian mimicry

harmless species mimics a harmful or unpalatable on e

• Scarlet king snake and coral snake

displays of intimidation

• deceive predator about ease of eating prey

• porcupine fish inflates itself

  • frilled lizards

Defense strategies

fighting, agility, armor, and masting

fighting

the defense strategy that may use horns and antlers

agility

the defense strategy grasshoppers’ show through powerful jumping ability

armor

the defense strategy turtle shells and beetle exoskeleton display for defense

masting

synchronous production of progeny satiate predators and allow some young to survive

• High seed production in trees

• periodical cicadas

generalist herbivore

herbivore that can feed on many plant species

specialist herbivores

restricted to one or two host plants

small species

Is herbivory more lethal to small species or larger species?

donor-controlled system

prey supply determined by factors other than predation (e.g. food supply)

• removal of predators has no effect on prey density

predator-controlled system

predation reduces supply of prey

• removal of predator results in supply of prey

Parasitism

one organism feeds off another but does not usually kill it outright

parasite

predatory organism in parasitism

host

prey in parasitism

4:1

Parasites may outnumber free-living species by this ratio

Bottom-up model

food limitation controls population density

• plants regulate the population size of all other species that rely on them as the source of energy

nitrogen-limitation hypothesis

increasing supply of nitrogen to plants will increase herbivore population size, survivorship, growth and fecundity

top-down model

natural enemies control population densities

• predators control prey population

• herbivores control plant population

• evidence from studies where natural enemies are introduced to control exotic pest species

species diversity

number of different species in a habitat and the relative abundance of each species

species richness

number of different species in a habitat

species eveness

relative abundance of each speicies

Shannon diversity index

this measures the species diversity of a community

Elton’s diversity-stability hypothesis

Disturbances in a species-rich community are cushioned by large numbers of interacting species and do not produce as drastic an effect as it would on a less diverse community, better diversity=better stability

succesion

sequential appearance and disappearance of species in a community over time

primary ecological succession

the process of ecological development that occurs in an area where no previous ecosystem existed

secondary ecological succession

the process of ecological recovery and development that occurs in an area
where a previous ecosystem was disturbed or destroyed

climax community

the final, stable stage of ecological succession in a specific environment

Community succession theory

Frederic Clements emphasized that succession has a distinct end point – the climax community

facilitation

colonizing species may change the environment so that it becomes more suitable for the next species