7842

• UCREFRP Catalog Number: 7842
• Author: Knopf, F. L.
• Title: Biological Diversity in Wildlife Management.
• USFW Year: 1992.
• USFW - Doc Type: 1992.
• Copyright Material: NO

greatest percentage of adults because those older and more experienced individuals
aggressively exclude younger, inexperienced ones. For instance, most of the cotton
rats occurring on the large patches are predicted to be adults, whereas individuals
on medium patches will be younger animals. Voles persist longest on large patches,
so we predict that large patches will have the highest percentage of adults. Deer
mice will have the highest percentage of adults on small patches because they persist
longest there.
Due to high variability in the data, we used the Friedman's method for randomized
blocks to test for patch effects. Data are separated by patch size and blocked by year
for each season. Percentages of adult cotton rats did not differ significantly between
medium and large patches. The lack of statistical significance may be due to the
small numbers of cotton rats on medium patches. More than 90 percent of all males,
and more than 88 percent of all females occur on the large patches which represent
only 3.7 out of 29.6 acres ('/s of the original field). Thus, if cotton rats were unable
to sustain themselves on large patches then they would probably become extinct from
the entire study site.
Percentages of adult male and female prairie voles differed significantly among
patches during winter seasons (males: X1 = 7.14, p<0.05; females: X' I = 12.3,
p<0.05); and spring seasons (males: X2] = 10.29, p<0.01; females: X? ] = 6. 0,
12 p-0.05). The pooled data for winter and spring are presented in Figure 2. There
tended to be higher percentages of adults on large patches for all seasons. As expected,
the deer mouse response was opposite to that of the prairie vole. Percentages of adult
male deer mice were higher on small patches, but not significantly. Except in the
summer, percentages of adult female deer mice were also higher on small patches,
but not significantly.
Finally, cotton rats, prairie voles and deer mice should have greater percentages
of reproductive adults in source habitats where individuals persist the longest. We
classified adults as reproductively active based on testes position (scrotal), and nipple
size (medium or large). Reproductive activity did not differ significantly among
patches for any species. However, percentages of reproductively active male and
female cotton rats were always higher on large patches. There were no apparent
trends for voles and deer mice.
Habitat fragmentation had different effects on the age structure and reproductive
activity of small mammals within habitat patches of different sizes. Fragmentation
affected biological diversity: there are fewer rodent species on small patches because
of the absence of cotton rats. However, the higher densities of small-bodied species
on smaller patches may be due to competitive release from the cotton rat. There
were no obvious effects of fragmentation on the age structure and reproductive activity
of prairie voles and deer mice. However, cotton rats, prairie voles and deer mice
were utilizing the landscape differently. We suggest that the demographic conse-
quences of body size are necessary population statistics when considering what area
of habitat fragment is needed to sustain populations (Belovsky 1987).
There are several lessons from this study that are germane to understanding the
relationship of population processes and biological diversity:
(1) It is difficult to generalize about the effects of habitat fragmentation on population
processes of different species;
(2) Competition may be a factor superimposed on source/sink dynamics. The effect
258 ? Trans. 57`h N. A. Wildl. & Nat. Res. Conf. (1992)