Functional semelparity drives population dynamics and endangers a peripheral population

Abstract

Despite increased risk of extinction through stochastic events, peripheral populations are conservation priorities as the distribution of endangered species tends to contract to the periphery of historic ranges rather than toward the core. Trailing-edge populations and mountain isolates, which may become more common as climate change drives range shifts, are an important realm of inquiry and contain important reserves of genetic variation. We use long-term monitoring data from the southernmost population of a widespread species to test the hypothesis that peripheral populations display distinct demographic profiles from core populations. The red squirrel (Tamiasciurus hudsonicus) is predicted to recede from its southern border in response to climate-induced habitat change. We estimate key demographic parameters for this endangered population using survival and reproduction schedules and compare the dynamics to core populations of this and related species. This peripheral population exhibits higher adult mortality, and suffers associated impacts on reproductive output, which results in a demography distinct from core populations and phylogenetically similar species. Poor adult survival, similar to a population that experiences extremely high hunting pressure, has resulted in this normally iteroparous species becoming functionally semelparous at the periphery. Understanding differences in demographic function between peripheral and core populations is key if management strategies are to be effective in supporting continued persistence of at risk populations in the face of range shifts of species or habitats driven by environmental change. Keywords: Life table, peripheral population, sky island, Tamiasciurus fremonti, Tamiasciurus hudsonicus, trailing edge 1.0 Introduction Informed management of populations facing certain future ecosystem change requires accurate assessments of population size and key demographic parameters, which often can be obtained only through long-term research and monitoring programs (Magurran et al. 2010). Frequently, different stage or age classes of populations experience diverse mortality pressures or exhibit variation in reproductive value (Reid et al. 2004). Early indications of ecological imbalance, future population collapse, or expansion can be recognized by close monitoring of demographics and age distributions. Fine-scale knowledge of variation in species' survival and fecundity between life stages or ages should improve the cost-effectiveness of management programs by allowing conservation effort to be applied where and when the greatest impact can be realized. For example, where mature individuals display the highest reproductive values, efforts could target these individuals for protection (Arrigoni et al. 2011) or removal in the case of invasive species (Harris et al. 2009). As climate change leads to altered species distributions (Parmesan 2006) and less stable environmental conditions, the demographic function of populations can be severely impacted. Populations at the periph...

Endemic diseases affect population dynamics of tree squirrels in contrasting landscapes

“…The Mt. Graham red squirrel population also occurs at the southern edge of the species’ range and has lower adult female survival compared to core populations; reduced productivity observed in this population may be related to an altered age structure of breeding females and have more to do with demographics than genetics (Goldstein et al ). In the Puget Trough, a tendency toward smaller litters, fewer young produced per female known to breed, and overall lower fecundity of western gray squirrels are findings consistent with inbreeding effects possible in a small and isolated population, although we cannot isolate this as the cause.…”

“…Small and meso‐sized mammals may live in spatially structured populations occupying discrete patches of suitable habitat with dispersing animals forming connections that maintain genetic flow and allow for rescue of declining populations (Levins , Hanski , Fronhofer et al ); fragmentation can disrupt these connections and in extreme cases may create population isolates (Bolger et al ). Such insular populations, whether natural or the result of anthropogenic habitat loss, are more likely to have reduced genetic diversity (Frankham ) and can have reduced productivity, adult survival, and persistence (Bolger et al , Rushton et al , Goldstein et al ). Identifying the status of insular populations and the factors impinging on their growth and survival is central to establishing conservation actions to increase their likelihood of persistence.…”

Population Dynamics at the Range Margin: Implications of Climate Change on Sublittoral Blue Mussels (Mytilus trossulus)

“…This is unfortunate since the impact of many ecological processes are detectable only over time with abundance changes as early indications of a shifting range (Lenoir and Svenning, 2015). While population increases and declines may reveal differences in demographic responses across the peripheral and core population transition (Goldstein et al, 2017), potential population synchrony are particularly interesting as they may help unravel the mechanisms that affect population size along range margins (Liebhold et al, 2004). Distant populations may show similar dynamics if they are driven by the same environmental factors that operate at scales larger than the occupancy of distinct populations (Wasson et al, 2016).…”

Antibacterial immune functions of subadults and adults in a semelparous spider

“…The negative correlation between bacterial growth inhibition power and fecundity, and the decreased capacity of producing measurable bacterial growth inhibition and cell wall lysis in more fecund females appear to support this hypothesis, as those females that ‘gave up’ more capacity in the assessed immune measures tended to have a larger number of offspring. Maximising reproductive output through a terminal investment-like scenario would be expected to be favoured by natural selection in environments where adult future mortality rate is high (assuming that this high mortality is not due to pathogens), which is known to be characteristic to populations of semelparous species (Goldstein, Merrick & Koprowski, 2017; Sæther, 1988; Young, 2010).…”