Biology Reference
In-Depth Information
regions of introduction.
For sugar cane, one might expect that the length of time since intro-
duction would be one of the most significant determinants of the num-
ber of pest arthropods encountered.The dates of introduction, for exam-
ple, varied from 500
B
.
C
. to 1840
A
.
D
. No relationship with time could be
shown, however, but a strong correlation existed between pest arthropod
diversity and the area of sugar cane under cultivation at present (fig. 15.1).
In this case, accumulation of species seems to have been influenced by the
ecological setting of the region.This setting, which influenced the extent
of cultivation that was practical, also supplied arthropods in more or less
proportional numbers. These arthropods seem to have colonized sugar
cane in a relatively short time, reaching a numerical plateau set by the
ecological features of the region.
A second study, of the herbivorous insects associated with cacao (
Theo-
broma cacao
) in different world regions, showed a similar pattern (Strong
1974a). Of 1,905 insects, more than 80% occurred in only one cacao-
growing region. Again, the diversity of insects was closely correlated with
the area of cacao under cultivation.This relationship apparently developed
Fig. 15.1.
The number of herbivorous arthropods associated with sugar cane in
different world regions in relation to the area of sugar cane under cultivation.
Symbols:
- continental Americas,
- Asia,
- West Indies,
- Europe and Africa,
+
- Oceania. (Reprinted with permission from D. R. Strong, E. D. McCoy, and
J. R. Ray. 1977. Time and the number of herbivore species: The pests of sugar
cane.
Ecology
58:167-175. © 1977 Ecological Society of America.)
