A. Patterns of Species Diversity

1. More species in the tropics than in the temperate zone

2. More species with larger areas (spatial heterogeneity?) (Still more in tropics than temperate zones)

3. More species in areas with more spatial heterogeneity -- Need to measure aspects of heterogeneity that species utilize

4. More species in unpolluted areas than polluted

5. More species in deep water marine habitats than shallow

6. More species on islands near emigration source (mainland) than on more distant islands

B. Processes that have been hypothesized to cause patterns of species diversity

1. Stability of the habitat

a. competition based with competition leading to increased resource specialization (need evolutionary time)

b. assumes that resources can be more finely divided in a more stable habitat so that resource specialists can exist (need evolutionary time)

c. are habitats in the tropics more stable--what do we mean by 'stable'

d. are there additional resources that can be exploited in a more stable habitat (linked to differentials in productivity among habitats and temporal stability of those additional resources)

e. are patterns of species diversity correlated with measures of environmental stress (e.g. temperature variation, precipitation variation...)

2. Structural heterogeneity of the habitat (usually discussed as competition based but could be predation/physical factor refugia, etc.)

3. Competition --- reduction in physical stress leads to increased resource stability and increased competition and then reduction in niche breadth and reduction in resource overlap leading to increased specialization and thus more species

4. Predation

a. reduction in physical stress leads to increased predation which leads to reduction in competitive exclusion

b. do not expect increased resource specialization of prey

c. do expect increased rates of predation in the tropics

5. Area

a. increases in area may increase the probability of genetic isolation and thus speciation

b. increases in area increases the probable number of habitat types (i.e. structural heterogeneity)

6. All of the above are intertwined, most have a competition base or at least a competition component, the links to competition are

a. finer division of resources, so specialization not competitive exclusion OR

b. utilization of resources that cannot be exploited elsewhere OR

c. prevention of competitive exclusion by increased rates of another process such as predation