1. The Relationship Between Distribution and Abundance - Chapter 8

2. Spatial Scale of Geographic Ranges

3. Variations in Geographic Range size
Within a taxonomic group, most species have a small geographic range:

4. Geographic Ranges Vary With Latitude
The geographic range size of mammals increases with latitude

5. Rapoport’s Rules Climatic variability is higher at high latitudes
Only organisms that can survive a broad range of climates will survive
Thus, they can occupy a broader geographical range
This works generally works out for terrestrial animals, but is a bit different for marine organisms.

6. Temperature Tolerance Range
Water temperature is more stable at the equator and at the poles. Because there is a large temperature difference in the temperate latitudes, we would expect to see an adaptive difference to temperature variation in the middle latitudes.
Thibodaux
Critical temperature limits for shallow water marine fish. Blue = upper lethal limit, red = lower lethal limit.

7. Rapoport’s Rules
Product of Glaciation, particularly in the Northern Hemisphere.
Only those animals with a high dispersal capacity were able to colonize northern areas, thus having a large geographical range.
Does not explain for Southern Hemisphere
However, glaciation is probably a contributing factor

8. Rapoport’s Rules Lack of competition in polar areas.
Because fewer species, level of competition may be smaller
Not yet tested

9. Boundaries of Geographical Ranges
Can be abrupt or gradual

10. Relationship Between Distribution and Abundance
There is a positive correlation between distribution and abundance – Hanski’s Rule.
Distribution = number of traps scattered around Britain that collected that species.
Abundance = average across all sites for all years
263 species of British moths

11. Hanski’s Rule Explained
Sampling Model – more rare (or hard to catch) species may not show up in all traps.
Ecological Specialization Model (Brown’s Model) – Species able to exploit a wide range of resources become both widespread and common.
Generalists versus a specialists
Local Population Model (metapopulation) – populations are found in discrete patches.
Species differ in their capacity to disperse
Species that disperse more are likely to be more common and more widespread