Demography of snowshoe hare population cycles

Abstract

Cyclic fluctuations in abundance exhibited by some mammalian populations in northern habitats (“population cycles”) are key processes in the functioning of many boreal and tundra ecosystems. Understanding population cycles, essentially demographic processes, necessitates discerning the demographic mechanisms that underlie numerical changes. Using mark–recapture data spanning five population cycles (1977–2017), we examined demographic mechanisms underlying the 9–10‐yr cycles exhibited by snowshoe hares (Lepus americanus Erxleben) in southwestern Yukon, Canada. Snowshoe hare populations always decreased during winter and increased during summer; the balance between winter declines and summer increases characterized the four, multiyear cyclic phases: increase, peak, decline, and low. Little or no recruitment occurred during winter, but summer recruitment varied markedly across the four phases with the highest and lowest recruitment observed during the increase and decline phase, respectively. Population crashes during the decline were triggered by a substantial decline in winter survival and by a lack of subsequent summer recruitment. In contrast, initiation of the increase phase was triggered by a twofold increase in summer recruitment abetted secondarily by improvements in subsequent winter survival. We show that differences in peak density across cycles are explained by differences in overall population growth rate, amount of time available for population growth to occur, and starting population density. Demographic mechanisms underlying snowshoe hare population cycles were consistent across cycles in our study site but we do not yet know if similar demographic processes underlie population cycles in other northern snowshoe hare populations.

Large-scale population disappearances and cycling in the white-lipped peccary, a tropical forest mammal

“…Although the conditions necessary for cycling to occur are understood and can be demonstrated mathematically, the specific drivers of cyclicity are diverse and vary within and among species. Endogenous factors include variations in reproductive output and other inherited qualities [ 12 ] or genetic drift [ 13 ], while exogenous factors include interactions with predators [ 14 ], diseases [ 15 ], food availability [ 16 , 17 ], and physical impacts, such as fires and floods [ 18 ]. Dispersal dynamics and social behaviors also influence the shape of cycles [ 2 ].…”

“…Potentially cyclic population dynamics have been documented in small populations of temperate ungulates in fragmented ranges [ 19 ], but given the altered nature of these populations, it is difficult to assess whether these represent cases of cycling in the same way documented for snowshoe hares ( Lepus americanus ) [ 14 , 17 ] and small rodents such as lemmings and voles [ 20 ], given the reduced size of the populations and the fragmented nature of their range.…”

Yearly Variations in GCM Concentrations in Female Mountain Hares (Lepus timidus) and the Effect of Pregnancy

“…We validated a noninvasive method for measuring gestagen metabolites as indicators of different states of pregnancy in female mountain hares and showed variations in a population of free-ranging mountain hares over a period of six years. These results are important for understanding how the timing of the mountain hare reproduction period varies from year to year [ 32 ]. They also improve the interpretation of faecal glucocorticoid results when collecting “anonymous” faeces in free-ranging populations during reproductive periods.…”

An experimental analysis of density dependence in meadow voles: Within‐season and delayed effects

“…Snowshoe hares (Lepus americanus) similarly undergo cyclic fluctuations in abundance, and manipulation experiments have demonstrated that these cycles are primarily driven by fluctuating predation risk (Krebs et al, 2018). The same type of CMR analysis in wild populations of snowshoe hares indicated that both survival and recruitment were related to cycle phase (Oli et al, 2020). Ultimately, survival and recruitment rates in hares are likely both a consequence of the same extrinsic factor: predation.…”