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The Relationship Between Distribution and Abundance - Chapter 8.

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Presentation on theme: "The Relationship Between Distribution and Abundance - Chapter 8."— Presentation transcript:

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 1)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 Critical temperature limits for shallow water marine fish. Blue = upper lethal limit, red = lower lethal limit. 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

7 Rapoport’s Rules 2)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 3)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. 263 species of British moths Distribution = number of traps scattered around Britain that collected that species. Abundance = average across all sites for all years

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

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