Global Warming, Elevational Range Shifts, and Lowland Biotic Attrition in the Wet Tropics

Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT 06269, USA.
Science (Impact Factor: 33.61). 11/2008; 322(5899):258-61. DOI: 10.1126/science.1162547
Source: PubMed


Many studies suggest that global warming is driving species ranges poleward and toward higher elevations at temperate latitudes,
but evidence for range shifts is scarce for the tropics, where the shallow latitudinal temperature gradient makes upslope
shifts more likely than poleward shifts. Based on new data for plants and insects on an elevational transect in Costa Rica,
we assess the potential for lowland biotic attrition, range-shift gaps, and mountaintop extinctions under projected warming.
We conclude that tropical lowland biotas may face a level of net lowland biotic attrition without parallel at higher latitudes
(where range shifts may be compensated for by species from lower latitudes) and that a high proportion of tropical species
soon faces gaps between current and projected elevational ranges.

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    • "This is mainly due to the limited time to adapt to new climate conditions, the presence of soil barriers (Feeley et al., 2011), and the dependence on biotic factors, such as the availability of pollinators and mycorrhizal fungi. Unlike large basins such as the Amazon in South America or the Congo River in Africa, where species lack thermal gradients (Colwell, Brehm, Cardelus, Gilman, & Longino, 2008;Wright, Muller-Landau, & Schipper, 2009), there is an expanding altitudinal spectrum in the Dagua Canyon and the Cauca River Valley. Both have altitudinal gradients within less than 15 km of the lowlands of the alluvial plain. "
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    ABSTRACT: Full text at Epiphytic orchids are fundamental elements of the dynamics and composition of tropical ecosystems; there are an estimated 19,000 species worldwide, of which 85 occur in the dry forests of the basins of the Cauca and Dagua rivers in the Valle del Cauca Department in southwestern Colombia. These plants form the interface between the forest and the atmosphere and depend on aerial nutrient sources, rain, and water vapour for survival. This physiological dependence on the climate makes them especially sensitive to changes in the atmosphere and temperature, so they are ideal models for the study of climate change (CC). The objective of this study was to detect changes in the spatial distribution of seven orchid species in the tropical dry forest in the department of Valle del Cauca and their significance in terms of conservation planning for CC. A maximum entropy algorithm was used for modelling, and nine variables were analysed. Presence data for 30 municipalities came from 31 field trips, herbarium data, and the literature, and the current potential distribution was compared against the SRES-A2 scenario developed by the Intergovernmental Panel on Climate Change (IPCC) and modelled for the 2080-2100 time horizon. For the set of seven species, the results show an altitudinal increase under the future CC scenario compared to the present, but the responses vary among taxa, elevation, and location, depending on the degree of thermal specialization. Under the future CC scenario, the suitability of mid-mountain areas will increase at the expense of the basal areas where dry forest orchids are currently found, and the Cordillera Occidental will have a greater concentration of suitable areas than the Cordillera Central. Variables such as accessibility, land coverage, temperature, and water availability explain 88.6% of the model. A strategy to combat the impending loss of biodiversity due to CC is the establishment of Altitudinal Migration Corridors (AMCs) that connect the forest relics of the alluvial plain with the mid-mountain areas. Areas with a probability of species occurrence greater than P = 0.75 have been identified with MaxEnt software, and these areas constitute “thermal refugia”, which, together with existing protected areas, form the backbone of this conservation strategy. Protection of xeric shrublands and the appropriate management of phorophytes would not only facilitate the dispersion processes of these orchids but also the survival of other flora and fauna in the dry forest of the Valle del Cauca River against CC.
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    • "In this sense, species with continuing westward distributional shifts may run out of climate space (Ohlem€ uller , 2011) as distributional edges abut mountains. The suitable climate of species with centers of distributions in the Great Plains will become increasingly compressed , potentially causing a biological attrition effect similar to that predicted for tropical lowlands (Colwell et al., 2008). We stress, however, that we modeled changes in potential richness derived from species distribution models, which may or may not reflect actual changes in species richness. "
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    • "Over the last century, a decreasing trend in summer monsoon, along with an increase in surface temperature of about 0.9˚C was observed during the winter months in western Himalayas (Dash et al. 2007). Although, the velocity of change in temperature is lowest in the mountainous ecosystems (Loarie et al. 2009); even with the slightest change, these ecosystems are more exposed to the cascading impacts of climate change (Nogués-Bravo et al. 2007; Colwell et al. 2008). What is so far not clearly understood is how these impacts of climate will be distributed within the different forest types in the Himalayan mountain system. "

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