These were calculated from Caughley 1977 with age jc smoothed survivor Brought

These were calculated from caughley 1977 with age jc

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These were calculated from Caughley (1977) with age (jc), smoothed survivor- Brought to you by | University of Washington Libraries Authenticated Download Date | 10/13/19 7:05 PM
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DEMOGRAPHY OF FOXES IN AUSTRALIA 253 TABLE 3. - Life table for female foxes constructed from 1995 sample. Age Class X 0 1 2 3 4 5 6 7 8 9 10 Total F x 159 47 15 11 6 11 2 4 2 1 1 259 Smoothed Fx 159 45.24 19.04 10.89 7.14 5.07 3.79 2.95 2.35 1.92 1.60 259 Life Table lx d x q x 1.000 0.285 0.120 0.069 0.045 0.032 0.024 0.019 0.015 0.012 0.010 0.715 0.165 0.051 0.024 0.013 0.008 0.005 0.004 0.003 0.002 0.001 0.715 0.579 0.425 0.348 0.289 0.250 0.208 0.211 0.200 0.167 0.100 TABLE 4. - Life table for female foxes constructed from 1996 sample. Age Class JC 0 1 2 3 4 5 6 7 8 9 10 Total Fx 178 53 *20 9 6 4 2 1 2 1 3 279 Smoothed Fx 178 53.84 17.99 9.35 5.85 4.05 2.99 2.31 1.85 1.51 1.26 279 Life Table U d x q x 1.000 0.303 0.101 0.053 0.033 0.023 0.017 0.013 0.010 0.008 0.007 0.697 0.202 0.048 0.020 0.010 0.006 0.004 0.003 0.002 0.001 0.001 0.697 0.667 0.475 0.377 0.303 0.261 0.235 0.231 0.200 0.125 0.143 s;hip (F x ), probability at birth of surviving to age χ (1 Χ ), probability of dying at each age interval (d x ), and mortality rate (q x ). Females lived up to 10 years of age (< 1 % of total sample) with 3 % of all age classes (8 % of adults) surviving past the age of 6. The greatest mortality occurred in the first year of life. The age structures were compa- red between years using the likelihood ratio statistic (G 2 ) (Bishop et al. 1975) and were not significantly different (P = 0.57). Brought to you by | University of Washington Libraries Authenticated Download Date | 10/13/19 7:05 PM
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254 MAMMALIA DISCUSSION The validity of time specific life tables using indirect methods, as reported here, can be questioned where stationary age structure is assumed (Caughley 1977 ; Udevitz and Ballachey 1998). Minor deviations in adult survival can result in substantially bia- sed assumptions about population stability (Eberhardt 1985). The similarity of the female age structures between years suggests that we are dealing with a stationary age distribution. In this study we have also assumed a zero rate of increase after analysis of seasonal spotlight counts over three fox generations. This assumption is supported by other factors. The most common causes of death within fox populations are human induced (Storm et al. 1976; Pils and Martin 1978 ; Harris and Smith 1987). Since the collapse of the fur market in Australia in 1988 (Ramsay 1994), commercial harvesting of fox populations has become minimal. As harvesting ceased, landholders looked to the distribution of 1080 (sodium monofluoroacetate) baits to control fox populations (Saunders et al. 1995). The preferred method involves the use of commercially manu- factured baits containing 3 mg of 1080. In New South Wales the legislatively required procedure for laying these baits is to bury them in shallow depressions (5-10 cm.) which reduces non-target risk (Saunders et al. 2000). Baiting is now widespread and constant and would not cause a more pronounced perturbation in any one year (Saun- ders et al. 1999). The proportion of juveniles to adults within fox populations is a reliable indicator of the intensity of control measures (Phillips 1970; Harris 1977) being close to unity where population control is light and as high as 5 : 1 where sub- stantial control operations are undertaken. The ratio of juveniles to adults in this study (1.27 : l, N = 520) suggests an ongoing * average' level
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