Transcript Chp8

The Relationship Between Distribution and Abundance
- Chapter 8
Scale of
Variations in Geographic Range size
• Within a taxonomic
group, most species
have a small
geographic range:
Geographic Ranges Vary With Latitude
The geographic range
size of mammals
increases with latitude
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
This works generally works out for terrestrial
animals, but is a bit different for marine
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.
Critical temperature limits for shallow
water marine fish. Blue = upper lethal
limit, red = lower lethal limit.
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
Rapoport’s Rules
3) Lack of competition in polar areas.
Because fewer species, level of competition may
be smaller
Not yet tested
Boundaries of Geographical Ranges
• Can be abrupt or gradual
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
263 species of British moths
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