Refugia revisited: individualistic responses of species in space and time

Abstract

Climate change in the past has led to significant changes in species' distributions. However, how individual species respond to climate change depends largely on their adaptations and environmental tolerances. In the Quaternary, temperate-adapted taxa are in general confined to refugia during glacials while cold-adapted taxa are in refugia during interglacials. In the Northern Hemisphere, evidence appears to be mounting that in addition to traditional southern refugia for temperate species, cryptic refugia existed in the North during glacials. Equivalent cryptic southern refugia, to the south of the more conventional high-latitude polar refugia, exist in montane areas during periods of warm climate, such as the current interglacial. There is also a continental/oceanic longitudinal gradient, which should be included in a more complete consideration of the interaction between species ranges and climates. Overall, it seems clear that there is large variation in both the size of refugia and the duration during which species are confined to them. This has implications for the role of refugia in the evolution of species and their genetic diversity.

Figure 1.

Schematic map showing some types of refugia for Europe and western Asia. Interglacial refugia for cold-adapted species are shown in blue, glacial refugia for temperate species in red. Long-term refugia, indicated by dark blue/red, are a subset of all refugia that are inhabited throughout at least one full glacial/interglacial cycle. The areas shown in paler colour are refugia in the sense that they are inhabited during the contraction phase, but are not inhabited during the expansion phase owing to the spread of ice sheets during glacials (cold-adapted species), or excessive temperatures and/or too high aridity during interglacials (temperate species). Also shown, in yellow, are interglacial refugia along the oceanic/continental gradient, with a continental refugium in the east and cryptic refugia further west. The ice sheet for the Last Glacial Maximum is taken from Ehlers & Gibbard (2004). The diagram is schematic; not all of the refugia would have been occupied simultaneously, but the ranges are based on real examples taken from table 1.

Figure 2.

Conceptual figure showing the relationship between size of a potential refugium and time to extinction of the population (caused by demographic or genetic stochasticity). Each line represents a range of areas occupied by populations of a given species. The time required for population extirpation is dependent on the size of the habitat patch, and the horizontal dashed lines indicate the minimum viable refugium size, i.e. the relative sizes required to survive millennial-scale events, 10 kyr interglacials and 100 kyr glaciations. The slope of the curve depends on several factors such as body size, generation length and, as illustrated here, trophic level. Dash-dotted curve, trophic level 0; solid curve, trophic level 1.