Detecting Stability and Causes of Change in Population Density - Research Techniques in Animal Ecology - page 198

showed that mortality of gypsy moths caused by a parasitic fly, Compsilura
concinnata, increased dramatically with gypsy moth density on a series of
experimental populations created with different densities at several locations
in the same year (figure 6.2).
The density-dependent response was evidently a behavioral one by the fly.
It was not at all clear the extent to which such responses would occur in stud-
ies in which density varied temporally instead of spatially. Only in the latter
studies would the reproductive response of the fly to changes in gypsy moth
density be measured. Indeed, a 10-year study of parasitism in naturally occur-
ring populations of gypsy moth (Williams et al. 1992) revealed no evidence of
temporal density dependence and far lower levels of parasitism by C. concin-
nata (figure 6.2). The ability of this fly to regulate low densities of gypsy moth
is thus questionable.
Several investigators have surveyed the published literature on life tables in
particular taxa in order to ascertain how often density dependence has been

A B

Figure 6.2 (A) Percentage mortality of gypsy moth caused by the parasitic fly Compsilura concin-
natato a series of experimental populations created with different densities in the same year (Gould
et al. 1990). (B) Time series of percentage mortality caused by C. concinnatain a 10-year study of
gypsy moth in naturally occurring populations (Williams et al. 1992). Solid line in (B) connects con-
secutive generations.