by Cameron Lukos
In order for species to survive environmental change and avoid extinction, they have to be able to either track suitable environmental conditions or adapt to the changed environment. Whether and how species adapt to environmental change is largely unknown. Wasof et al. (2013) examined specifically the realized niche width (ecological amplitude), and the realized niche position (ecological optimum). A realized niche is the actual space that a species inhabits and the resources it can access as a result of limiting biotic factors present in the habitat. They created the niche width from a beta diversity metric, which increases if the focus species co occurs with other species. Wasof et al. used a detrended correspondence analysis (DCA) to represent the locations of the niche positions and then developed their own approach to run species specific DCAs to allow the focal species to shift its realized niche while others stayed put. Wasof et al. concluded that none of the 26 species maintained their realized niche width and position along the latitudinal gradient. A few species shifted their realized niche width but all of the species shifted their position. Most of the species that shifted their position shifted their realized niche for areas where soil nutrients and pH were poorer and more acidic. The results suggest that these plants are locally adapting or have plasticity. The pattern casts doubt on the idea that realized niches are stable in space and time. Wasof et al. created identical sampling designs across seven regions along an 1800 km latitudinal gradient from northern France to central Sweden and Estonia via Belgium, western and eastern Germany, and south Sweden. The gradient encompassed most of the temperate deciduous forest in northwest Europe. In each region they sampled 5×5 km landscapes containing a set of deciduous forest patches. The landscapes all shared similar features in terms of patch morphology and relative proportions of meadows to agricultural land and forests. To assess the shifts in realized niches of species along the gradient Wasof et al. focused on a subset of understory plants species that were part of the species pool of all the regions. Twenty six species were sufficiently frequent to be used for analysis. The assessment used Ellenberg indicator values (EIV) to rank the plant species along their optimum for light, soil nutrients, soil pH, soil moisture, temperature, and continentality. They first calculated the mean EIV to estimate the environmental conditions. Then they computed the median and range EIVs and then used GLMs.
Wasof et al. found that soil nutrient and pH values decreased with increasing latitude but latitudinal changes were significant for soil moisture. They did not find any significant variation in environmental heterogeneity across landscapes for light soil nutrients and soil moisture but as latitude increased environmental heterogeneity in soil pH increased, but only marginally. The latitudinal changes in the niche width and position differed between species. The majority conserved a similar niche width along the latitudinal gradient; some showed a positive linear, concave or convex relationship with latitude. The DCA scores showed that 22 of the 26 species moved northward and their position shifted to a nutrient-poorer and more acidic soils. Those that had a convex relationship showed the same relationship with nutrients and pH. The concave relationship was a split result with some showing a positive correlation with nutrients and acidity or a negative relationship.
Wasof, S. ,Jonathan Lenoir, Emilie Gallet-Moron, Aurélien Jamoneau,J örg Brunet,Sara A. O. Cousins, Pieter De Frenne, Martin Diekmann, Martin Hermy, Annette Kolb, Jaan Liira, Kris Verheyen, Monika Wulf, Guillaume Decocq 2013. Ecological niche shifts of understorey plants along a latitudinal gradient of temperate forests in north-western Europe Species’ realized-niche shifts across latitude. Global ecology and biogeography, 22, 1130-1140. http://bit.ly/1oWnq83