Biology Reference
In-Depth Information
Figure 9.11. Shorter generation times at high temperatures have been suggested to be
one important direct cause of latitudinal gradients in species richness. That generation
times are indeed negatively correlated with temperature was shown by Gillooly and
collaborators for various groups of vertebrates, insects, and zooplankton. The
example illustrated in this figure shows the effect of incubation temperature on
mass-corrected embryonic development time for marine fishes in the field. Other
examples are illustrated in Figure
9.12
. Reprinted from Gillooly, Charnov, West,
Savage, Van, and Brown (
2002
), with the permission of MacMillan Publishing Ltd.,
and the authors.
per year made no contribution to the ability to evolve resistance. However,
a more complete model, also using the effects of pest severity and pest
feeding mode, showed a significant curvilinear effect for generations per
year: species with intermediate numbers of generations per year were best
able to evolve resistance.
Recently, Gillooly et al.(
2002
) described a general model, based on
first principles of allometry and biochemical kinetics, that predicts gen-
eration time (''time of ontogenetic development'') as a function of body
mass and temperature. The model fits data for embryonic development
times from birds, fish, amphibians, aquatic insects, and zooplankton, and
also describes development of other animals at other life-cycle stages.
Invariably, development time of species in all of these groups is negatively
The fossil record shows that some invertebrates with short generation
times, e.g., molluscs, have hardly changed over millions of years, whereas
vertebrates with relatively long generation times have undergone remark-
able changes over much shorter periods (references in Rohde
1992
). But
this observation does not affect our considerations of latitudinal diversity
gradients. We do not compare species richness of molluscs at one latitude
