Ecology - Community Species Diversity Final

Question 1

How does “membership” in a community depend on the regional species pool and dispersal?

Answer 1

Regional species pools and dispersal ability (species supply)
(2) Environmental (abiotic) conditions
(3) Species interactions

Question 2

How does “membership” in a community depend on abiotic conditions?

Answer 2

species may be able to get to a community but be unable to tolerate the abiotic conditions
* For example, a lake might not support organisms that require fast-flowing water
* Many species that are dispersed in ballast water cannot survive in a new habitat because of temperature, salinity, etc.

Question 3

How does “membership” in a community depend on species interactions

Answer 3

Coexistence with other species is also required for community membership
* Other species may be required for growth, reproduction, or survival
* Species may be excluded by competition, predation, parasitism or disease

Question 4

What is the relationship between overlap of resource use and competition?

Answer 4

greater the overlap of resource use, the more competition between species

Question 5

How might specialization in resource use affect community species diversity?

Answer 5

species have a high degree of specialization, it can result in less competition and high species richness

Question 6

In terms of species diversity, what would you expect in a community with a broad resource spectrum?

Answer 6

a diversity of resources would be available for use by a wide variety of species

Question 7

How does MacArthur’s (1958) study of resource partitioning in a community of warblers in New England forests relate to community species diversity?

Answer 7

resource ratio hypothesis: species coexist by using resources in different proportions

Question 8

What is Tilman’s resource ratio hypothesis and how does it relate to species coexistence?

Answer 8

resource ratio hypothesis: species coexist by using resources in different proportions

Question 9

How might disturbance or stress relate to community species diversity?

Answer 9

disturbance (or stress) keeps a dominant competitor from reaching carrying capacity, competitive exclusion might not occur, and coexistence may be possible

Question 10

What is Hutchinson’s “Paradox of the Plankton” and how does it relate to disturbance?

Answer 10

conditions in the lake changed seasonally, which kept any one species from outcompeting the others
* As long as conditions changed before competitively superior species reached carrying capacity, coexistence would be possible

Question 11

What is Connell’s Intermediate Disturbance Hypothesis and what does it predict in terms of community species richness?

Answer 11

the highest levels of community richness will be maintained at intermediate levels of disturbance

Question 12

How did Sousa test the Intermediate Disturbance Hypothesis?

Answer 12

boulders of intermediate size, and therefore disturbance maintained the highest level of community species diversity

Question 13

How did Hacker and Gaines (1997) incorporate positive interactions (i.e. mutualisms and commensalisms) into the intermediate disturbance hypothesis

Answer 13

incorporated positive interactions (i.e., mutualisms and commensalisms) into the intermediate disturbance hypothesis
* Evidence suggests that positive interactions are more common under relatively high levels of disturbance (and stress or predation)

Question 14

Under what conditions might positive interactions be more common?

Answer 14

Evidence suggests that positive interactions are more common under relatively high levels of disturbance (and stress or predation

Question 15

What did Hacker and Gaines (1997) study in a New England salt marsh reveal?

Answer 15

They concluded that positive interactions were critically important in maintaining species diversity, especially at intermediate stress levels

Question 16

According to Huston’s dynamic equilibrium model under what conditions will maximum species diversity in a community be achieved?

Answer 16

maximum species diversity will occur when disturbance level and rate of competitive displacement are equal and are at intermediate levels

Question 17

Why do Menge and Sutherland (1987) argue that predation should NOT be considered the same as disturbance?

Answer 17

Menge and Sutherland (1987) argue that because predation is a biological interaction, it should be considered separately!

Question 18

What do Menge and Sutherland (1987) propose is the role of stress in ordering natural communities?

Answer 18

With community complexity inversely related to environmental stress

Question 19

What does their model predict is the relationship between predation and stress?

Answer 19

predation is most important when environmental stress is low
* As stress increases, importance of predation decreases, and competition increases in importance
* At high stress levels, neither is important!

Question 20

How do Menge and Sutherland (1987) incorporate recruitment into their model and how do they view the relationship between competition and recruitment?

Answer 20

If recruitment is low, competition might not be important because resources would not be limiting
* As recruitment increases, competition becomes more important

Question 21

What are Lottery & Neutral Models and how do they relate to community structure?

Answer 21

Lottery models and neutral models emphasize the role of chance in maintaining community species diversity

Question 22

Under what conditions do lottery and neutral models most likely explain community structure?

Answer 22

all species have equal chances of obtaining resources that were made available by disturbances, and this allows coexistence
* Species must have similar interaction strengths and growth rates and be able to respond quickly to disturbances that free up resources

Question 23

Why did Paine consider the starfish Pisaster to be a keystone species in a rocky intertidal community?

Answer 23

removal of a keystone predator (a starfish) led to a reduction in species richness from 15 species to 8 species!

Question 24

How might the intensity of predation affect species diversity ion a community?

Answer 24

Intense predation pressure may reduce richness by driving prey species (whether or not they are strong competitors) to extinction

Question 25

What is the relationship between productivity and depth in aquatic environments and why?

Answer 25

aquatic environments, productivity declines with depth as temperature and light levels fall

Question 26

Do patterns of productivity in animal communities track those plant communities?

Answer 26

the productivity of animal communities follows the same trends

Question 27

Under what conditions might an increase in productivity lead to an increase in species richness?

Answer 27

Increased productivity might lead to increased species richness if it leads to an increased range of available resources

Question 28

What relationship did Pianka (1967) find between lizard diversity in the deserts of the southwest and length of growing season?

Answer 28

positive relationship between species richness of lizard communities in the deserts of the southwest and length of the growing season

Question 29

What relationship did Brown and Gibson (1983) find between the diversity of cladoceran zooplankton and total productivity in eleven unpolluted lakes in Indiana?

Answer 29

positively correlated with total productivity of those lakes

Question 30

What did the same authors observe in the three polluted lakes they studied?

Answer 30

several studies that suggest the greatest species diversity occurs at intermediate levels of productivity

Question 31

What is the “Paradox of Enrichment” and how might you account for it?

Answer 31

even a decrease in species diversity,

Question 32

What did relationship did Abramsky and Roseznweig (1983) observe between species diversity of desert rodents in Israel and precipitation?

Answer 32

it seems that when increased productivity is accompanied by an increased range of resources, an increase in species richness should follow

Question 33

Why might structurally more complex environments accommodate extra species?

Answer 33

most studies of spatial heterogeneity have related the species richness of the animal community to the structural diversity of the plants in their environment

Question 34

What did MacArthur and MacArthur (1961) find concerning the relationship between bird species diversity and foliage height for 13 different communities from Maine to Panama?

Answer 34

positive relationship between bird species diversity and foliage height (a measure of habitat complexity) for 13 different communities from Maine to Panama

Question 35

How might predictable, seasonally changing environments support higher species diversities?

Answer 35

seasonal environments may provide more opportunities for temporal niche differentiation, which can ultimately lead to higher species diversity

Question 36

How might a stable environment support more species? How might it not support more species?

Answer 36

expected to support more species because there may be more opportunities for specialization

Question 37

How might you characterize an environmentally harsh habitat?

Answer 37

the more “harsh” an environment is, the fewer species should be able to occupy it

Question 38

What are some of the problems associated with attributing low species diversity of some habitats with environmental harshness?

Answer 38

many of the so-called harsh environments are characterized by other features associated with low species richness

Question 39

What is the “evolutionary time” hypothesis for explaining differences in patterns of species diversity?

Answer 39

some communities may show low species richness because of insufficient time for re-colonization or for subsequent evolution after a major disturbance

Question 40

How might this hypothesis be used to explain the difference in temperate tree species diversity between Europe and North America?

Answer 40

the major mountain ranges in Europe run east to west, whereas in North America they run north to south!

Question 41

What is the general pattern for latitudinal species gradients?

Answer 41

decrease in diversity that occurs from the tropics to the poles

Question 42

What is the general pattern for altitudinal species gradients?

Answer 42

altitude communities usually occupy smaller, more isolated areas than lowlands at equivalent latitudes