Community ecology

Question 1

What is a community?

Answer 1

An association of interacting populations, usually defined by nature of their interaction &/or the place they live

Question 2

What did Clements propose?

What is this also referred to as?

Answer 2

Communities are like ‘super-organisms’
- where species are bound to each other by their interactions

a ‘closed community’
= clear & sharp community boundaries

Question 3

What did Gleason argue?

What is this also referred to as?

Answer 3

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

Question 4

What are ecotones?

Answer 4

Boundaries between communities/habitats

Question 5

Give an example of a closed community

Answer 5

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

Question 6

What might the appearance of interconnected closed communities be due to?

Answer 6

Common environmental needs

- rather than interdependence among species

Question 7

What is primary succession?

Answer 7

Where communities develop from new, never-before occupied space

Question 8

What is secondary succession?

Answer 8

The recolonisation process where communities are affected by the occurrence of disturbances e.g. fire

Question 9

What are founder controlled communities?

Answer 9

Communities where any species has an equal chance to colonise the gap

• future composition determined by chance
• maintains diversity

Question 10

Which type of species do founder controlled communities select for?

Answer 10

R species

- large clutch & fast development

Question 11

What are dominance controlled communities?

Answer 11

Outcome can be predicted by competitiveness of species

• undergoes succession often
• maintains less diversity

Question 12

Which type of species do dominance controlled communities select for?

Answer 12

Initially R species

But K species eventually dominate

Question 13

How can we quantify/describe the differences between communities?

Answer 13

> species composition/diversity

> trophic structure

Question 14

How can we describe species composition/diversity?

Answer 14

Species richness

Shannon Index

Question 15

What is species richness?

What is the problem with the method?

Answer 15

Count no. of species within fixed area

Ignores species evenness (population/frequency of each species)

Question 16

What does the Shannon Index incorporate?

Answer 16

Richness & evenness

Question 17

What is the trophic structure of a community determined by?

Answer 17

Feeding relationships between orgs

Question 18

What is a food chain/web?

Answer 18

Transfer of food energy from source in autotrophs through herbivores & carnivores

Question 19

Elton pointed out that there are normally how many trophic levels?

Answer 19

4-5

Question 20

What factors affect the no. of trophic levels in communities?

Answer 20

> Bottom-up regulation

> Top-down regulation

Question 21

What is bottom-up regulation?

Answer 21

Imperfect transmission of energy controlled by primary production

Question 22

What is top-down regulation?

Answer 22

Top predator controls the structure of the ecosystem

Question 23

What is a keystone species?

Answer 23

A species that have a disproportionate effect on the community

Question 24

Give examples of keystone species

Answer 24

Coral in eastern US coast
- shelter to 300+ invertebrate species

African elephants
- destruct feeders but increase grass growth

Question 25

Describe the results of the experiment with insecticide runoff

What does this show?

Answer 25

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