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The numbers of lynx and hare undergo multi-year fluctuations that have interested biologists for over a century. Why do lynx populations increase to record numbers all across Canada only to be followed by record lows 5 years later? The peaks in lynx abundance cycles occur roughly every 10 years – 9.63 years, according to timeseries analysis (Elton & Nicholson 1942)
One hypothesis for the mechanism driving regular and synchronized abundance cycles is the homogenizing effect of predator dispersal (Krebs et al. 2001, Ranta et al. 1997). However, models have indicated that prey densities in the southern portion of the lynx range may be too low to support cyclic predator-prey dynamics (Steury & Murray 2004). The density fluctuations in the southern portions of the range may be a product of an immigration pulse from the core range (McKelvey et al. 2000). Models of lynx hare interactions in the US habitats indicate that low hare densities result in lynx recruitment that does not offset mortality, creating a population sink (Steury & Murray 2004). Essentially, if lynx are interacting as a metapopulation, then cyclical dynamics and overall lynx persistence in the southern range will be directly dependent on dispersal.
An alternative hypothesis is that weakened seasonality associated with climate change (Hurrell 1996) is reducing seasonal forcing that sustains the multi-year oscillator in the predator-prey system (King & Schaffer 2001). Climate has been used mainly to address mechanisms for synchrony and asynchrony (Stenseth et al. 1999, 2004). However, these data were based on a coarse provincial level lynx harvest statistics, which created an east to west gradient, but little north to south variation. In contrast to investigating synchrony, I seek to address the role that climate plays in the deterioration of multi-year cycles in southern portions of the lynx range (Murray & Steury 2007). The theoretical implications of weak seasonality have been mathematically modeled (King & Schaffer 2001), but have not been verified with observed data. I suggest an analysis based on finer-scale data that focuses on the north-south gradient. A compilation of fine-scale harvest data in western Canada, together with associated climate data will uncover if reduced seasonality linked to global warming is the mechanism behind deteriorating population cycles in the southern portion of the lynx range.
