Trends in Kangaroo Numbers in Western New South Wales and their relation to Rainfall

Abstract

Annual aerial counts of kangaroos within randomly selected blocks of the western plains of New South Wales showed that the numbers of kangaroos doubled between 1975-76 and 1982, and that the widespread drought of 1982 reduced the populations on average by 43%. Localized reductions of similar magnitude occurred after regional droughts in 1977 and 1980 within parts of the monitored area. The observed trends in kangaroo numbers, with eastern and western blocks treated separately, were correlated with annual rainfall with a time lag of 6 months in the response. The relationships show that kangaroos reach their maximum rate of increase following rainfall 100 mm above the annual average in the east and approximately 50 mm above the annual average in the west. At average annual rainfall kangaroos increase at 25% (greys) and 35% (reds) per annum in the east and at 25% (greys) and 30% (reds) per annum in the west. Rate of increase is zero when rainfall is 100 mm below average in the east and approximately 60 mm below average in the west. When rainfall is below these values, kangaroo numbers decline.

Do Harvest Refuges Buffer Kangaroos Against Evolutionary Responses to Selective Harvesting?

“…1). This pattern is consistent with that observed in natural populations (Caughley et al 1984, Bayliss 1985, Cairns and Grigg 1993. Harvesting reduces simulated kangaroo abundance, and kangaroo numbers fluctuate around a lower mean value.…”

Population growth rate and its determinants: an overview

“…Examples have been reported for red kangaroo (Caughley et al 1984;Bayliss 1985;Cairns & Grigg 1993;McCarthy 1996), Pacific black duck (Anas superciliosa) and maned duck (Chenonetta jubata; Briggs & Holmes 1988), magpie goose (Bayliss 1989), feral buffalo (Bubalus bubalis) (Freeland & Boulton 1990;Skeat 1990) and feral cattle (Bos taurus) (Skeat 1990), feral pig (Caley 1993) and house mouse . Lebreton & Clobert (1991) urge caution in simple regression analysis of the effects of environmental variables, because although estimates of slope are not biased, their variances are, and this leads to problems in significance testing.…”

Characterizing demographic parameters across environmental gradients: a case study with Ontario moose (Alces alces)

“…Open circles represent K as estimated using uncorrected instantaneous growth rate (r t ), and solid lines the trend in the associated partial residuals, whereas plus symbols and dashed lines the values and trends for K as estimated using instantaneous growth rates corrected for moose harvest (r t,c ). K increases with increases in foraging habitat and productivity, but declines with annual timber harvest (R v www.esajournals.org ically to changes in rainfall as it strongly influences forage abundance (Caughley et al 1984), timber wolf population density tracks habitat characteristics associated with prey foraging requirements (Mladenoff and Sickley 1998), and the density of California gnatcatchers (Polioptila californica) declines with loss of sage scrub and increasing distance between habitat patches (Akçakaya and Atwood 1997). However, changes in density alone may be insufficient to assess the quality of a landscape for animal populations and can lead to inaccurate population projections without estimating associated demographic parameters (Van Horne 1983).…”

“…Given that disturbance increases deciduous forage abundance (Peek et al 1976, Stephenson et al 2006, and increased forage availability improves moose survivorship and browsing efficiency (Peek 1974, MacCracken et al 1997, Brown 2011, we predicted that moose demographic parameters should be positively influenced by increases in both of these landscape characteristics. This work builds upon previous findings that populations of numerous taxa respond to changes in environmental conditions across space (e.g., Caughley et al 1984, Stenseth et al 2002, Saether et al 2008) and evaluates the commonly held but rarely tested assumption that demographic parameters of any population are largely dependent on associated bioclimatic gradients (Rempel 2011).…”

“…This is at least partly attributable to the relative difficulty of obtaining sufficient time series data on abundance across large areas, which limits most studies of demography to a single population or a small number of discrete subpopulations in a relatively small area (e.g., Clutton-Brock et al 1996, MacCracken et al 1997, Coulson et al 2001, Stephenson et al 2006. Those few studies with sufficient data have often focused on characterizing spatial variation in temporal population dynamics (i.e., cyclic vs. non-cyclic populations) rather than sources of spatial variation in key demographic parameters (e.g., Caughley et al 1984, Forchhammer et al 1998, Stenseth et al 2002, Lima et al 2003. Identifying how and why basic demographic parameters change over space could be useful for a wide variety of practical applications in conservation biology and wildlife management (Saether et al 2008).…”