608 Latitudinal and Elevational Range Shifts under Contemporary Climate Change For instance, topographic heterogeneity is associated with low climate change velocity (Loarie et al., 2009) and should enhance the long-term conservation capacity of nature reserves (Ackerly et al., 2010) by providing short-distance escapes for species facing climate change (Scherrer and Koărner, 2011) However, depending on the magnitude of climate change and the degree of topographic heterogeneity within species ranges, topographic heterogeneity may just temporarily buffer biodiversity before starting to act as a climatic trap by increasing spatial isolation and extinction risks (Forero-Medina et al., 2011) Nevertheless, it is also increasingly clear that the traditional habitat-management recommendations may be insufficient for safeguarding biodiversity from climate-driven extinctions, and therefore species-management recommendations are being proposed, notably assisted migration (also called assisted colonization or managed translocation) (Thomas, 2011) Among others, dispersal-limited or small-range species might not be able to be saved by more traditional habitat-management recommendations, such as increasing landscape connectivity to enhance species migration (Heller and Zavaleta, 2009; Thomas, 2011) Assisted migration is controversial, especially given the fear that translocated species could increase the risk of native species extinctions in their new recipient habitats (Ricciardi and Simberloff, 2009) However, for climate-threatened, dispersallimited, or small-range species, it has been suggested that translocation might be the only successful management strategy, and therefore should be implemented provided that risks of extinction to native species in recipient habitats are small (Morueta-Holme et al., 2011; Thomas, 2011) To help managers in making decisions between habitat- and species-management recommendations, a decision framework has already been proposed for assessing when species translocations are possible (Hoegh-Guldberg et al., 2008) Future Challenges Despite the increasing number of studies documenting latitudinal and elevational range shifts under contemporary climate change, a better understanding of current range shifts is still needed for developing well-founded predictive models of future range shifts More research efforts are needed to better understand climate change effects on species ranges at low latitudes and especially within the Tropics, the most speciesrich part of the world and the area hosting most threatened taxa (IUCN, 2004) So far, evidence of recent species range shifts in the Tropics have been mostly documented along elevational gradients (Pounds et al., 1997; Raxworthy et al., 2008; Chen et al., 2009; Feeley et al., 2011; Juvik et al., 2011) with at most a handful of reports for plants (Feeley et al., 2011; Juvik et al., 2011) Although the magnitude of climate warming varies geographically, most tropical areas have warmed just as much as temperate areas (IPCC, 2007a) Furthermore, small changes in temperature conditions in the Tropics may have much stronger biotic impact than similar changes in temperate areas Notably, recent research into the thermal tolerance of terrestrial insects shows that tropical insects are closer to their maximum thermal tolerance than temperate insects (Deutsch et al., 2008), suggesting that tropical species and their ranges may be particularly sensitive to climate warming Importantly, crash-range shifts are therefore more likely in the Tropics (Pounds et al., 1997) than elsewhere Even more alarming, there not exist biodiversity source pools now living in hotter places (as such areas not exist) that are available to replace climatically displaced or declining species in tropical lowland ecosystems, potentially leading to lowland biotic attrition in the lowland tropical areas (Colwell et al., 2008), with unknown consequences for ecosystem functioning Another future challenge is to achieve a better understanding of the mechanisms involved in species range shifts Notably, it is still unresolved how the different population dynamics involved at both the range edges is driving species range shifts Are colonization and establishment processes occurring more rapidly at the front edge of a species’ range than mortality and extinction processes at the rear edge? For instance, the rear edge of a species’ range is likely to host a relatively high genetic diversity due to selection pressure over time (Hampe and Petit, 2005), thus having a high potential for delaying range contractions under contemporary climate change Therefore, rear edges may be disproportionately important for the survival and evolution of species (Hampe and Petit, 2005) Surprisingly, fewer studies have focused on contemporary range shifts at the trailing edge of species’ ranges in comparison to the leading edge This lack of focus on range shifts at the trailing edge of species’ ranges is even more important along the latitudinal gradient for long-lived plants such as woody species (Jump et al., 2009) In short, there is also an urgent need to improve our understanding of species range shifts at the trailing edge of species’ ranges Additionally, the strong variation in the magnitude of contemporary range shifts among species raises questions about the underlying reasons and whether the magnitude of shifts is linked to species traits A recent study focusing on the relationship between species traits and the magnitude of recent shifts at the leading edge found low explanatory power, suggesting that trait-based range shift forecasts face several challenges (Angert et al., 2011) Finally, the occurrence of unexpected range shifts (such as stasis or even downslope shifts) is an understudied phenomenon of high importance for predicting range responses to future climate change (Lenoir et al., 2010a) This is linked to our current lack of knowledge regarding the effect of biotic interactions and dispersal constraints on species distributions Addressing these challenges will allow the development of improved predictive models of future range shifts Indeed, with exactly this aim, recent discussions have raised the need for improving the field of species distribution modeling (SDM) by developing more mechanistic, hybrid approaches such as coupling stochastic population models with dynamic bioclimatic habitat models (Keith et al., 2008) or by better accounting for nonclimatic factors and ecological complexity, notably biotic interactions and dispersal constraints (Morin and Lechowicz, 2008) See also: Climate Change and Extinctions Climate, Effects of Evolution in Response to Climate Change Introduced Species,