. Biology of New World Microtus. Rodents; Rodents; Microtus; Voles. 580 Taitt and Krebs 100. 1968 69 70 71 72 73 74 75 76 77 78 Fig. 3. Population densities of Microtus pennsylvanicus on a control oldfield at Pinawa, Manitoba (reproduced, with permission, from Mihok, in press). Berkeley led by Pearson, Lidicker, and Pitelka. Unfortunately, like most vole population studies, techniques have not been standardized and we can only hope that results are comparable, as Pearson (1971) demonstrated for two studies. Lidicker (1973) reported the longest time series for this species (13 years), but we co
. Biology of New World Microtus. Rodents; Rodents; Microtus; Voles. 580 Taitt and Krebs 100. 1968 69 70 71 72 73 74 75 76 77 78 Fig. 3. Population densities of Microtus pennsylvanicus on a control oldfield at Pinawa, Manitoba (reproduced, with permission, from Mihok, in press). Berkeley led by Pearson, Lidicker, and Pitelka. Unfortunately, like most vole population studies, techniques have not been standardized and we can only hope that results are comparable, as Pearson (1971) demonstrated for two studies. Lidicker (1973) reported the longest time series for this species (13 years), but we consider only the first 5 years to be sufficiently accurate for this analysis. Lidicker (1973) found annual fluctuations to be common on Brooks Island and Krebs (1966) reported cases of annual fluctuations on the mainland. Krohne (1982) recently reported annual fluctuations in perennial grasslands in northern California. Densities varied greatly in dif- ferent areas. Lidicker's (1973) Brooks Island densities were 3-10 times those reported in areas on the mainland. This difference may be due to an island effect or a difference in techniques. For main- land sites, cyclic peak densities averaged 570 voles/ha, and cyclic lows average 15/ha. Annual fluctuations on the mainland reached average maxima of 85/ha and average minima of 20/ha. We do not know if M. californicus cycles in southern California. Blaustein (1980) reported declines that could be either cyclic or the result of an irregular annual fluctuation with frequent extinctions. For the studies summarized in Table 4, we suggest that there were 7 years. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Tamarin, Robert H; American Society of Mammalogists. [Stillwater, Okla. ] : American Society of Mammalogists ; Shippensburg, Pa. : distributed by Vertebrate Mus
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