Community diversity

Question 1

How did Charles Elton describe a community in 1927?

Answer 1

not mere assemblages of species living together, but closely-knit communities or societies comparable to our own.

Question 2

How did Robert Whittaker describe a community in 1975?

Answer 2

an assemblage of populations of plants, animals, bacteria and fungi that live in an environment and interact with one another, forming a distinctive living system with its own composition, structure, environmental relations, development and function.

Question 3

How did Robert Rickleaf describe a community in 1990?

Answer 3

the associations of plants and animals that are spatially delimited and that are dominated by one or more prominent species or by a physical characteristic (no mention of interactions)

Question 4

Give the common definition of a community

Answer 4

A group of organisms belonging to a number of different species that co-occur in the same habitat or area and interact through tropic and spatial relationships

Question 5

Give the common definition of community ecology

Answer 5

the study of patterns and processes involving at leave 2 species at a particular location

Question 6

What is species relative abundance?

Answer 6

the percentage of each species contributing to the total number of individuals of all species

Question 7

What do the results of Simpson’s index indicate?

Answer 7

1 = low diversity
0 = high diversity

Question 8

Define a disturbance

Answer 8

an event that changes a community, removes organisms from it, and alters resource availability

Question 9

What are the 2 types of community disturbances

Answer 9

physical disturbances and biotic disturbances

Question 10

Define a keystone species

Answer 10

a species that has a disproportionately strong influence within a particular ecosystem, such that its removal results in severe destabilisation of the ecosystem and can lead to further species losses.

Question 11

Give an example of a mutualistic keystone species

Answer 11

cleaner wrasse

Question 12

Define a guild

Answer 12

a group of species that depend on the same resource for survival and reproduction

Question 13

Define a functional group

Answer 13

a group of species that performs the same function within the ecological community (e.g. grazers, predators)

Question 14

Describe community interactions of a dung beetle

Answer 14

over 7,000 species in the same guild, but with 3-7 distinct functional groups: dwellers, tunnellers and rollers

Question 15

What is a foundation species?

Answer 15

the dominating species, with a great abundance or biomass, affecting community structure.

Question 16

Give an example of a dominant/foundation species

Answer 16

a spruce tree in tiaga/borreal forrests

Question 17

How do you measure community importance of a species?

Answer 17

by the change in the community trait (e.g. the species richness, productivity of producers, abundance of functional groups etc) per unit change in the abundance of the proposed keystone species.

Question 18

What is the equation for calculating the total impact of a species?

Answer 18

community importance x proportional abundance or biomass the the community

Question 19

How do you calculate the direct connectedness of a food web?

Answer 19

number of links / number of species (S)^2

Question 20

How do you calculate the connectivity of a food web?

Answer 20

(2(number of links) / (S(S-1)) )x100

Question 21

Describe the basic structure of a food web in term of functional levels

Answer 21

basal species eaten by numerous intermediate species, which are then eaten by a top predator

Question 22

Give 3 example of indirect community interactions

Answer 22

trophic cascades, indirect commensualism, apparent competition

Question 23

Give an example of indirect commensualism

Answer 23

beavers gnaw on tree stumps, which changes the chemical composition of their sprouting leaves, providing better nutrition to the leaf beetles feeding on them.

Question 24

Give an example of apparent competition

Answer 24

Brassica nigra grass provide cover for small herbivorous mammals (e.g. mice), which in turn reduces the density of Nassella pulchra

Question 25

What does it mean by ‘species interaction strength’?

Answer 25

the strength of a link between two species in a food web

Question 26

Give 2 ways you can measure a species interaction strength?

Answer 26

finding out the % prey of the stomach content, or exclude the predator from the community and observe the effects in prey abundance

Question 27

Give the 3 basic trophic levels of a simple community

Answer 27

producers, grazers and predators

Question 28

Give an example of top-down control

Answer 28

Distribution of wolves influence elk movements in Yellowstone National Park

Question 29

What effects the distribution of wolves in YNP?

Answer 29

elks (prey), cougars (competition), coyotes (interference competition)

Question 30

Give an example of bottom-up control

Answer 30

grasslands in new mexico consist of 2 trophic levels: plants and rodents. After 10 years without rodent, there’s no effect on plant population, but a change in rainfall has a strong effect, suggesting bottom-down control.