Search Results

There is good physiological documentation of the survival of parasites (generally the ‘off-host’ stages) in environments that would be considered hostile to life and characterized by freezing, extreme desiccation, and so on. Equivalent adaptations may occur in free-living organisms, and are not therefore a feature of parasitism. However, these mechanisms are relevant to the ability of some parasites to persist in ecosystems at the margins of survival of life (as in hot and cold deserts). It is a feature of many such severe environments that constraints are relaxed periodically, even if very briefly, creating a ‘window of opportunity’ when transfer from host to host may occur. It is of even greater interest that, in some cases, transmission may continue even when external conditions appear to be most extreme and when it might be predicted that transmission should be arrested. In these situations, the host is typically regarded as the ‘safe’ environment while the external environment is viewed as hostile. In contrast, there is now abundant evidence that the host actually represents the most hostile environment in the parasite’s life cycle, constituting a finely tuned ‘killing machine’. The mechanisms of the various lethal factors are well documented, together with the reciprocal parasite adaptations for evasion and suppression of attack. This review takes an ecological perspective. Variations in parasite infectivity for particular host types and in host susceptibility to infection determine that some ‘environments’ (hosts) are more hostile than others. The shifting balance between prevailing host and parasite types determines the ability of parasites to persist in the spectrum of environments within the ecosystem. Even the ‘favourable’ environments (in which surviving infections reproduce) may be responsible for major mortality within parasite populations and this contributes to the regulation of the interactions.

This chapter examines the effect of climate change on Arctic ecosystems using social-ecological systems (SES) analysis. It also considers the effect of global climate change on the social dynamics of people living in the Arctic and how it might continue to do so. The chapter examines the effects of rapid climate change on Arctic SESs by focusing on two examples of ecological processes: wildfire disturbance and sea-ice coverage.

Among the large cetaceans, gray whales (Eschrichtius robustus) are unique in three important ways: They are benthic feeders; they undertake one of the longest migrations of any mammal; and they may be fully recovered from overharvesting by commercial whaling. The eastern gray whales migrate annually between the mating regions and calving lagoons on the west coast of Baja California, Mexico, to summer feeding grounds in the northern Bering Sea and the Chukchi Sea. This chapter explores the arctic ecosystem dynamics that justify such a migration and the impacts of the whales upon the system. It concludes with an oceanographic production model that both explains the current location of major gray whale feeding sites and can be used for predictive purposes.