Ecology - Community Species Diversity Final Flashcards
How does “membership” in a community depend on the regional species pool and dispersal?
Regional species pools and dispersal ability (species supply)
(2) Environmental (abiotic) conditions
(3) Species interactions
How does “membership” in a community depend on abiotic conditions?
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.
How does “membership” in a community depend on species interactions
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
What is the relationship between overlap of resource use and competition?
greater the overlap of resource use, the more competition between species
How might specialization in resource use affect community species diversity?
species have a high degree of specialization, it can result in less competition and high species richness
In terms of species diversity, what would you expect in a community with a broad resource spectrum?
a diversity of resources would be available for use by a wide variety of species
How does MacArthur’s (1958) study of resource partitioning in a community of warblers in New England forests relate to community species diversity?
resource ratio hypothesis: species coexist by using resources in different proportions
What is Tilman’s resource ratio hypothesis and how does it relate to species coexistence?
resource ratio hypothesis: species coexist by using resources in different proportions
How might disturbance or stress relate to community species diversity?
disturbance (or stress) keeps a dominant competitor from reaching carrying capacity, competitive exclusion might not occur, and coexistence may be possible
What is Hutchinson’s “Paradox of the Plankton” and how does it relate to disturbance?
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
What is Connell’s Intermediate Disturbance Hypothesis and what does it predict in terms of community species richness?
the highest levels of community richness will be maintained at intermediate levels of disturbance
How did Sousa test the Intermediate Disturbance Hypothesis?
boulders of intermediate size, and therefore disturbance maintained the highest level of community species diversity
How did Hacker and Gaines (1997) incorporate positive interactions (i.e. mutualisms and commensalisms) into the intermediate disturbance hypothesis
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)
Under what conditions might positive interactions be more common?
Evidence suggests that positive interactions are more common under relatively high levels of disturbance (and stress or predation
What did Hacker and Gaines (1997) study in a New England salt marsh reveal?
They concluded that positive interactions were critically important in maintaining species diversity, especially at intermediate stress levels
According to Huston’s dynamic equilibrium model under what conditions will maximum species diversity in a community be achieved?
maximum species diversity will occur when disturbance level and rate of competitive displacement are equal and are at intermediate levels
Why do Menge and Sutherland (1987) argue that predation should NOT be considered the same as disturbance?
Menge and Sutherland (1987) argue that because predation is a biological interaction, it should be considered separately!
What do Menge and Sutherland (1987) propose is the role of stress in ordering natural communities?
With community complexity inversely related to environmental stress
What does their model predict is the relationship between predation and stress?
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!
How do Menge and Sutherland (1987) incorporate recruitment into their model and how do they view the relationship between competition and recruitment?
If recruitment is low, competition might not be important because resources would not be limiting
* As recruitment increases, competition becomes more important
What are Lottery & Neutral Models and how do they relate to community structure?
Lottery models and neutral models emphasize the role of chance in maintaining community species diversity
Under what conditions do lottery and neutral models most likely explain community structure?
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
Why did Paine consider the starfish Pisaster to be a keystone species in a rocky intertidal community?
removal of a keystone predator (a starfish) led to a reduction in species richness from 15 species to 8 species!
How might the intensity of predation affect species diversity ion a community?
Intense predation pressure may reduce richness by driving prey species (whether or not they are strong competitors) to extinction
What is the relationship between productivity and depth in aquatic environments and why?
aquatic environments, productivity declines with depth as temperature and light levels fall
Do patterns of productivity in animal communities track those plant communities?
the productivity of animal communities follows the same trends
Under what conditions might an increase in productivity lead to an increase in species richness?
Increased productivity might lead to increased species richness if it leads to an increased range of available resources
What relationship did Pianka (1967) find between lizard diversity in the deserts of the southwest and length of growing season?
positive relationship between species richness of lizard communities in the deserts of the southwest and length of the growing season
What relationship did Brown and Gibson (1983) find between the diversity of cladoceran zooplankton and total productivity in eleven unpolluted lakes in Indiana?
positively correlated with total productivity of those lakes
What did the same authors observe in the three polluted lakes they studied?
several studies that suggest the greatest species diversity occurs at intermediate levels of productivity
What is the “Paradox of Enrichment” and how might you account for it?
even a decrease in species diversity,
What did relationship did Abramsky and Roseznweig (1983) observe between species diversity of desert rodents in Israel and precipitation?
it seems that when increased productivity is accompanied by an increased range of resources, an increase in species richness should follow
Why might structurally more complex environments accommodate extra species?
most studies of spatial heterogeneity have related the species richness of the animal community to the structural diversity of the plants in their environment
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?
positive relationship between bird species diversity and foliage height (a measure of habitat complexity) for 13 different communities from Maine to Panama
How might predictable, seasonally changing environments support higher species diversities?
seasonal environments may provide more opportunities for temporal niche differentiation, which can ultimately lead to higher species diversity
How might a stable environment support more species? How might it not support more species?
expected to support more species because there may be more opportunities for specialization
How might you characterize an environmentally harsh habitat?
the more “harsh” an environment is, the fewer species should be able to occupy it
What are some of the problems associated with attributing low species diversity of some habitats with environmental harshness?
many of the so-called harsh environments are characterized by other features associated with low species richness
What is the “evolutionary time” hypothesis for explaining differences in patterns of species diversity?
some communities may show low species richness because of insufficient time for re-colonization or for subsequent evolution after a major disturbance
How might this hypothesis be used to explain the difference in temperate tree species diversity between Europe and North America?
the major mountain ranges in Europe run east to west, whereas in North America they run north to south!
What is the general pattern for latitudinal species gradients?
decrease in diversity that occurs from the tropics to the poles
What is the general pattern for altitudinal species gradients?
altitude communities usually occupy smaller, more isolated areas than lowlands at equivalent latitudes
