Declining home range area predicts reduced late‐life survival in two wild ungulate populations

Abstract

Demographic senescence is increasingly recognised as an important force shaping the dynamics of wild vertebrate populations. However, our understanding of the processes that underpin these declines in survival and fertility in old age remains limited. Evidence for age-related changes in foraging behaviour and habitat use is emerging from wild vertebrate studies, but the extent to which these are driven by within-individual changes, and the consequences for fitness, remain unclear. Using longitudinal census observations collected over four decades from two long-term individual-based studies of unmanaged ungulates, we demonstrate consistent within-individual declines in home range area with age in adult females. In both systems, we found that within-individual decreases in home range area were associated with increased risk of mortality the following year. Our results provide the first evidence from the wild that age-related changes in space use are predictive of adult mortality.

Does Physical Activity Age Wild Animals?

“…A first step for example, could be to quantify exercise and physiological markers during the mating season of polygynous species such as red deer Cervus elephaus or black grouse Lyrurus tetrix, across multiple breeding seasons. This could prove insightful in describing differing rates of senescence between individuals, as indicated by, for instance, declining home range sizes (Froy et al, 2018). With the right techniques, there is huge potential in existing study systems to investigate the impacts of activity on animal senescence.…”

“…More recently, however, focussed-studies on multiple taxa have shown otherwise (Nussey et al, 2013;Jones et al, 2014). In many species, individuals continue living well beyond their functional peaks (Froy et al, 2018), and often carry on reproducing albeit at a declining rate (Nussey et al, 2013;Jones et al, 2014). Aging in animals can be considered in terms of the decline in the body's performance (functional senescence) or the decline in fertility rate coupled with an increased risk of mortality (demographic senescence).…”

Energetic constraints on mammalian home‐range size

“…The metabolic theory of ecology, and related concepts, predicts that the rate of resource uptake, transformation and allocation to processes important for fitness are determined by metabolic rate (Brown, Gillooly, Allen, Savage, & West, ; Brown, Hall, & Sibly, ; Hennemann, ; Humphries & Mccann, ; McNab, ). Home range, the area where animals spend most of their time foraging, resting and reproducing, varies among and within species and can determine individual reproductive success and survival (Burt, ; Froy et al, ). The benefits of large home ranges include better access to resources, food and mates, but large ranges can also generate energetic and predation costs (McNab, ; Tamburello, Côté, & Dulvy, ).…”

Comparing individual and population measures of senescence across 10 years in a wild insect population

“…This has been addressed using individual measures of mortality in the following year (Froy et al. ), but comparisons of actuarial and phenotypic senescence estimates from entire adult lifespans have not been attempted before (to our knowledge). We are aware of only two studies that compared the relationship between ageing trajectories of different traits and their relationship to lifespan in the field (Hayward et al.…”

“…The statistical power of such an analysis is reduced when demographic senescence estimates are based on cohorts within overlapping generations because partially shared environmental histories mean that actuarial senescence estimates are nonindependent. This has been addressed using individual measures of mortality in the following year (Froy et al 2018), but comparisons of actuarial and phenotypic senescence estimates from entire adult lifespans have not been attempted before (to our knowledge). We are aware of only two studies that compared the relationship between ageing trajectories of different traits and their relationship to lifespan in the field (Hayward et al 2015) and in the lab (Briga 2016), reporting heterogeneous associations among ageing trajectories and lifespan, suggesting asynchrony of senescence across different traits.…”