{'fraction_non_alphanumeric': 0.026555687673404677, 'fraction_numerical': 0.013872374157748711, 'mean_word_length': 5.052757793764988, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
More Thoughts on Vertebrate Predator Regulation of Prey

Kidd and Lewis (1987) made two critical comments on our paper entitled "Can vertebrate predators regulate their prey?" They claimed that the evidence presented for predation-mediated regulation is inconclusive, and they questioned some of the ways we interpreted our data. Their second criticism concerns the dynamics of the examined Microtus population. Kidd and Lewis argued that our data suggest "the possibility of a population fluctuation, albeit of small amplitude" (p. 448). We agree on that. Moreover, recent detailed studies based on the mark-recapture method have confirmed that the vole population fluctuates between years and that the numbers in the autumns of different years vary considerably (fig. 1). The point that we have stressed in our papers (Erlinge et al. 1983, 1984), however, is that the vole population in southern Sweden shows a noncyclic pattern, which is the opposite of the pattern characterizing the microtine populations in northern Sweden (Myllymaki 1977; Hansson 1979; Hornfeldt et al. 1986). This difference means less between-year fluctuation in the south (no marked population crash following a year with peak densities) and a characteristic seasonal pattern with peak numbers in autumn and low densities in spring and early summer every year. Our study aimed to explain this difference. Kidd and Lewis's first comment concerns the regulative significance of predation. They argued that population regulation implies density dependence. The predation rate on voles in our study has not been shown to work in a densitydependent way between years, and the delayed density dependence observed over the year would essentially be destabilizing. Kidd and Lewis are right in many of their comments. We were not able to demonstrate any clear evidence for density-dependent predation in our earlier studies. Instead, we found that predation rate was inversely correlated with changes in vole numbers during most of the year (Erlinge et al. 1983, p. 41, fig. 3). We considered two exceptions important, however. Density-dependent predation occurred in autumn toward the end of the reproductive season and in late spring at the beginning of the breeding season. This timing might have a regulating effect on vole numbers between years. Ricklefs, discussing population regulation, concluded that "for a population to be maintained within narrow limits, stabilizing forces need operate only during a portion of the year that is long enough to