Community ecology Flashcards
What is a community?
An association of interacting populations, usually defined by nature of their interaction &/or the place they live
What did Clements propose?
What is this also referred to as?
Communities are like ‘super-organisms’
- where species are bound to each other by their interactions
a ‘closed community’
= clear & sharp community boundaries
What did Gleason argue?
What is this also referred to as?
Communities are associations of species assembled by chance, independent of other species presence/absence
an ‘open community’
= community boundaries are indistinct & species should have independent boundaries
What are ecotones?
Boundaries between communities/habitats
Give an example of a closed community
Some plant species only grow in non-serpentine soils, some only grow in ecotone, some only grow in serpentine soils & some are unresponsive to different soil types
What might the appearance of interconnected closed communities be due to?
Common environmental needs
- rather than interdependence among species
What is primary succession?
Where communities develop from new, never-before occupied space
What is secondary succession?
The recolonisation process where communities are affected by the occurrence of disturbances e.g. fire
What are founder controlled communities?
Communities where any species has an equal chance to colonise the gap
- future composition determined by chance
- maintains diversity
Which type of species do founder controlled communities select for?
R species
- large clutch & fast development
What are dominance controlled communities?
Outcome can be predicted by competitiveness of species
- undergoes succession often
- maintains less diversity
Which type of species do dominance controlled communities select for?
Initially R species
But K species eventually dominate
How can we quantify/describe the differences between communities?
> species composition/diversity
> trophic structure
How can we describe species composition/diversity?
Species richness
Shannon Index
What is species richness?
What is the problem with the method?
Count no. of species within fixed area
Ignores species evenness (population/frequency of each species)
What does the Shannon Index incorporate?
Richness & evenness
What is the trophic structure of a community determined by?
Feeding relationships between orgs
What is a food chain/web?
Transfer of food energy from source in autotrophs through herbivores & carnivores
Elton pointed out that there are normally how many trophic levels?
4-5
What factors affect the no. of trophic levels in communities?
> Bottom-up regulation
> Top-down regulation
What is bottom-up regulation?
Imperfect transmission of energy controlled by primary production
What is top-down regulation?
Top predator controls the structure of the ecosystem
What is a keystone species?
A species that have a disproportionate effect on the community
Give examples of keystone species
Coral in eastern US coast
- shelter to 300+ invertebrate species
African elephants
- destruct feeders but increase grass growth
Describe the results of the experiment with insecticide runoff
What does this show?
Kills zooplankton
- -> phytoplankton explode
- -> reduces no. of periphyton (not enough light)
- -> reduction in no. of tadpole species
Indirect effects due to community connectivity can have unexpected & catastrophic affects
