The Puzzles of Population Cycles and Outbreaks of Small Mammals Solved?

Irruption and collapse of a population of pale field-rat (Rattus tunneyi) at Heirisson Prong, Shark Bay, Western Australia

“…The poorer 476 condition of R. tunneyi on Heirisson Prong during the decline phase suggests a food shortage related either to overshooting their food supply or to declining seasonal 478 conditions impacting on food quality and supply as a key cause. This is consistent with Pavey et al (2008)'s conclusion that the decline of rodents after irruption is in 480 part due to starvation resulting from declines in food availability, but at variance with that of Korpimäki et al (2004) who saw food shortage acting primarily to stop 482 population increases as the population approached peak numbers, rather than being responsible for the subsequent decline. 484…”

“…Recent experimental work in tropical savanna has demonstrated the vulnerability of isolated concentrations of R. 488 villosissimus to predation by feral cats (Frank et al 2014). Korpimäki et al (2004) decline. An indication of the impact of feral cats on R. tunneyi on Heirisson Prong can be gauged from the more than three-fold difference in capture success on trapping 496 grids inside the predator refuge to those immediately outside.…”

“…Hence the source (localised mesic refuges) and trigger (exceptional rainfall) for irruption of the R. tunneyi population on Heirisson Prong appears similar in kind 456 to that of R. villosissimus. Korpimäki et al (2004) contended that high rates of population increase in small 458 mammals, leading to either cycles or outbreaks (irruptions), were driven largely by improvements in survival rather than in reproduction. In the case of R. tunneyi on 460…”

Theoretical impacts of habitat loss and generalist predation on predator–prey cycles

“…The multiannual population cycles of certain mammals and their predators in northern latitudes have been studied extensively over the last century (Elton and Nicholson 1942, Keith 1990, Akçakaya 1992, King and Schaffer 2001, Korpimäki et al 2004, Tyson et al 2010, Krebs 2011. The importance of cyclic herbivores, such as snowshoe hares (Lepus americanus) and brown lemmings (Lemmus trimucronatus), to tundra and boreal ecosystems lies at the heart of this interest in oscillatory population dynamics (Krebs 2011).…”

“…Hypotheses for the causes of population cycles have invoked sunspots, weather, forest fires, stress, food shortage, plant defenses, and parasites (Akçakaya 1992). While some of these features likely affect population densities, predation is now widely accepted as a key driver of cyclic fluctuations (Akçakaya 1992, Turchin 2003, Korpimäki et al 2004, Krebs 2011. However, less attention has been given to the cause of the observed reductions in amplitude and densities of cyclic species in their respective southern ranges (Akçakaya 1992), and it is this phenomenon to which this study is devoted.…”