Download ICA 1 SPECIES ABUNDANCE + LOCAL SPECIES DIVERSITY 1

ICA 1 SPECIES ABUNDANCE + LOCAL SPECIES DIVERSITY
1. Figure 1. Are most species in a community common or rare? Rare
What is meant by ‘relative abundance’…use it in a sentence. Relative abundance, the
proportion of individuals in a community represented by a given species, differs
greatly among species.
2. What problems arise in determining the number of rare species in a community?
Rare species are likely to be under-sampled; or not found at all in a census.
3. Figure 2. What can be ‘read’ from a dominance-diversity (species abundance) curve?
A. Number of species
B. Pattern of relative importance of each species
4. What two variables describe ‘species diversity’ in a local community? Species
richness and evenness among species in relative abundance
What is the difference between species diversity and species richness?
Richness = # of species; Diversity = # of species + evenness among species
5. Figure 3. Which community is more diverse? Community at top Why? Both have
same number of species, but one at top has much greater evenness in relative
abundance among species.
6. Figure 4. Which community is the most diverse? Community A
What two conditions result in its being the most diverse? It has both the greatest
number of species and the greatest evenness in relative abundance among species.
7. What factors affect SD at a LOCAL scale?
1. Abiotic factors 2. Biological interactions 3. Dispersal limitation 4. Human
introduction 5. Chance
8. Figure 5 (Abiotic factors). 1. Summarize the major result of the study.
SD of unfertilized plot was steady while that of fertilized plot decreased through time
2. What 2 components does H’ incorporate? Sp. richness and relative abundance
3. What combo of these components yields greatest value of H’? High number of
species and evenness among species in relative abundance.
4. Explain the results in terms of competition and niche theory. In fertilized plots, one
species may exploit nutrients and out-compete many species, thus expanding its niche
breadth. Many species are eliminated by superior competitor. In unfertilized plots, not
enough nutrients are present for that superior species to express its competitive ability
and so all species remain in the community.
9. Biotic hypotheses to explain variation in species diversity (SD):
1. Explain how >heterogeneity in space (and time) relates to niche theory
and accounts for > SD. More variation in space and time add to the resource axis
and expand the potential number of niches available, lower niche overlap, and
allow more species to co-exist.
2. Figure 6. Explain how host-specific natural enemies maintain species diversity.
Enemies kill all seeds/seedlings near the parent tree, opening up space for other
species and maintain SD.
Figure 7. How does density- (and/or distant-) dependent mortality contribute?
Seeds/seedlings occur in highest density close to parent tree. Enemies are
attracted to high density (or don’t move far from parent tree) causing highest
mortality near to parent tree.
Is the hypothesis more important to have a mechanism to reduce dominance by a
common or rare species? Common Explain. Without a mechanism to reduce
dominance by a common species, it becomes yet more common and eliminates other
more rare species from the community.
3. Explain how competition results in greater SD. In evolutionary time, it causes
adjustment in niches to minimize overlap and eliminates competitive exclusion.
Figure 8. Using niche theory, explain how more species can be added to a
community. 1. Expand resource axis and increases total niche space 2. increase
niche overlap 3. decrease niche breadth
4. Why does intermediate disturbance lead to greater SD?
A. Too low – competitive exclusion can occur
B. Too high – limited number of species can adapt to this high of stress
5. Using the equilibrium hypothesis, how can greater SD be achieved?
1. more additions (e.g. speciation) 2. fewer deletions (e.g. extinctions)
10. Figure 9. What is the relationship between local and regional diversity?
As regional diversity increases, so does local diversity, but at a lower level.
All regional species are not part of local community.
11. Figure 10. What factors/processes affect regional diversity? Increase by immigration
and speciation; decrease by extinction
By what process does regional SD get narrowed down to a lower local SD?
habitat selection
What additional local processes narrow it down further? competitive exclusion;
predatory exclusion; chance extinction
12. What is ‘species sorting’? processes that determine local community composition.
How does it relate to environmental filters? They are environmental conditions that
eliminate species that cannot tolerate those conditions.
13. Where should species sorting be greatest? When regional species pool is largest
Under what conditions does ecological release happen? When species pool is small
and competition is relaxed.
How does it provide evidence that local interactions control SD? A local process is
identified that can change local SD.
14. Measures of species richness…
alpha – local # species in small area of homogeneous habitat
beta - # species turnover between habitats
gamma - total # species in all habitats within a barrier-free geographic area
delta – available species pool within dispersal distance (up to continental scale)
15. Figure 11. What is the relationship between species richness and area? Species
richness increases with increasing area.
On what scale are the two variables plotted? Both are on log scale.
How is the relationship stated quantitatively? log S = log c + z log A = linear
16. Why do larger areas have more species?
A. Larger areas give larger samples. B. greater habitat heterogeneity C. if island,
bigger target for immigrants D. larger populations have greater genetic diversity,
broader distributions over habitats and large enough size to prevent stochastic extinction
17. Figure 12. Summarize patterns of what controls these species-area relationships.
Island area and/or habitat diversity control, but differ among taxa in importance.