Q1: Diversity maintenance despite competitive exclusion

Question 1

What is meant by equilibrial and non-equilibrial mechanisms for the maintenance of species diversity?

Answer 1

Equilibrial mechanisms for the maintenance of species diversity are those explanations that suppose a stable coexistence of species, which returns to its former stability if perturbed. Equilibrial mechanisms are generally controlled by species interactions and have a deterministic effect on diversity stability. Non-equilibrial mechanisms assume species diversity is subjected to repeated disturbance and reorganization such that equilibrium is never reached.

Question 2

Describe the the niche diversification hypothesis, is it equilibrial or non-equilibrial?

Answer 2

The more species are specialized, the less competitive exclusion will occur, resulting in a greater number of species that can co-exist. Equilibrial.

Question 3

What are the assumptions of the niche diversification hypothesis?

Answer 3

• resources are variable (so no specific niche to occupy)
• resources do not substantively change over time
• resources are partitioned such that each species is the best competitor in its particular niche, and that resources remain available following a disturbance

Question 4

What are the predictions of the niche diversification hypothesis?

Answer 4

It predicts that the system will be returned to its pre-disturbance state because the relative niches are still available for the specialists to recover into, without the competitive exclusion risk.

Question 5

What’s an example of the niche diversification hypothesis not being explanatory?

Answer 5

It fails to account for known dynamics like disturbance-driven diversity and high generalist diversity.

Question 6

Describe the compensatory mortality hypothesis, is it equilibrial or non-equilibrial?

Answer 6

Equilibrial. Proposes that higher mortality on the most abundant prey species, usually via generalist predation, results in the inferior competitor among the prey species then becoming the most common, and thus repeating the cycle.

Question 7

What are two examples of equilibrial hypotheses for species maintenance?

Answer 7

Niche diversification and compensatory mortality hypotheses.

Question 8

What are the assumptions of the compensatory mortality hypothesis?

Answer 8

• all species are equally susceptible to predation

- resource availability remains constant during a disturbance

Question 9

What does the compensatory mortality hypothesis predict?

Answer 9

This hypothesis is an example of negative frequency-dependent regulation of the common species, and predicts reduced competitive exclusion between the prey species, which promotes their diversity.

Question 10

What is a fatal flaw with the compensatory mortality hypothesis?

Answer 10

The assumption of equal susceptibility to predation rarely occurs in nature over time periods where evolutionary selection can occur.

Question 11

What are two non-equilibrium hypotheses for species diversity maintenance?

Answer 11

The intermediate disturbance hypothesis and the gradual change hypothesis.

Question 12

What is the intermediate disturbance hypothesis?

Answer 12

Diversity is maximized with disturbance regimes of intermediate duration, intensity and frequency. When disturbance is severe, diversity drops due to competitive dominance by only highly tolerant species and early colonizers that might be less competitive against others. When disturbance is small, strong competitors are favored and the community is subject to competitive exclusion

Question 13

What are the assumptions of the intermediate disturbance hypothesis?

Answer 13

• space is the primary limiting factor for diversity

- abiotic disturbances maintain and maximize it

Question 14

What does the intermediate disturbance hypothesis predict?

Answer 14

That communities subjected to severe disturbances are driven by density-independent physical processes.

When the disturbance is intermediate the community is structured by density-dependent species interactions, and when the disturbance is mild the communities are mostly structured by intraspecific competition

Question 15

What is the gradual change hypothesis?

Answer 15

Competitive exclusion is avoided by a gradually changing environment. Species occupy a temporal niche and when the environment changes, the most successful species changes to those suited to the new conditions

Question 16

What are the assumptions of the gradual change hypothesis? What supporting evidence is there for it?

Answer 16

• Niche partitioning in time, where different species are assumed to be competitively superior over others for different conditions.
• Assumes that species have a differential response to environmental change

Was observed by Hutchinson in phytoplankton communities.

Question 17

What is the larval recruitment hypothesis? Is it equilibrial or nonequilibrial?

Answer 17

Non-equilibrial.

Suggests that the supply of larvae largely determines population abundance and species diversity in a given area.

Question 18

What are the assumptions of the larval recruitment hypothesis?

Answer 18

• mortality is high and is primarily the result of density-independent mortality from a vulnerable life stage in difficult environmental conditions, which leads to limited recruitment supply to a habitat
• the supply of recruits is below the carrying capacity of the habitat

Question 19

When would the larval recruitment hypothesis not be explanatory?

Answer 19

If the community in question does not have organisms with a larval stage or analogous dispersal stage.

Question 20

What is a good example of the larval recruitment hypothesis being explanatory and why?

Answer 20

Coral reef communities, because most organisms on reefs have a larval stage.