Population Dynamical Responses to Climate Change

It is well established that climatic as well as biological factors, in concert, form the mechanistic basis for our understanding of how populations develop over time and across space. Although this seemingly suggests simplicity, the climate-biology dichotomy of population dynamics embraces a bewildering number of interactions. For example, individuals within a population may compete for space and other resources and, being embedded in an ecosystem, individuals in any population may also interact with individuals of competing species as well as those from adjacent trophic levels. In principal, the effects of climate change may potentially extend through any of these interactions. In this chapter, we focus on the extent to which evolutionarily distinct species at different trophic levels respond to similar changes in climate. By using a broad spectrum of statistically and ecologically founded approaches, we analyse concurrently the influence of climatic variability and trophic interactions on the temporal population dynamics of species in the terrestrial vertebrate community at Zackenberg. We describe and contrast the population dynamics of three predator species (arctic fox Alopex lagopus, stoat Mustela erminea and long-tailed skua Stercorarius longicaudus), two herbivore species (collared lemming Dicrostonyx groenlandicus and musk ox Ovibos moschatus) and five wader species (common ringed plover Charadrius hiaticula, red knot Calidris canutus, sanderling Calidris alba, dunlin Calidris alpina and ruddy turnstone Arenaria interpres) with respect to intra-specific density dependence, consumer-resource interactions and direct as well as indirect inter-trophic level mediated effects of varying snow-cover. We found that the temporal population dynamics of all three predators, both herbivores and three out of five wader species, displayed significant direct density dependence. Only two species (sanderling and long-tailed skua) displayed dynamics characterised by delayed density dependence. The direct effects of previous winter's snow were related to over-wintering strategies of resident and migrating species, respectively. The dynamics of all four resident species were significantly affected by variations in snow-cover and explained up to 65% of their inter-annual dynamics. The three predators differed in their numerical response to changes in prey densities. Whereas the population dynamics of arctic fox were not significantly related to changes in lemming abundance, both the stoat and the breeding of long-tailed skua were mainly related to lemming dynamics. The predator-prey system at Zackenberg differentiates from previously described systems in high-arctic Greenland, which, we suggest, is related to differences in the compositions of predator and prey species. The significant inter-trophic interactions are centred on the collared lemming as a result of which there is a significant potential for indirect climate effects mediated across the established consumer-resource interactions.