Climate change affects the outcome of competitive interactions?an application of principal response curves

Abstract

It has been hypothesised that climate change may affect vegetation by changing the outcome of competitive interactions. We use a space-for-time approach to evaluate this hypothesis in the context of alpine time-of-snowmelt gradients. Principal response curves, a multivariate repeated-measurement analysis technique, are used to analyse for compositional differences in local ridge-to-snowbed gradients among 100 m altitudinal bands from 1,140 to 1,550 m a.s.l., corresponding to a temperature gradient of 2.5 degrees C (local lapse rate is 0.6 degrees C). The interaction between time-of-snowmelt and altitude is strongly significant statistically, indicating that the altitudinal gradient cannot be explained simply by the physiological responses of the species, but that there are also changes in the outcome of competitive interactions. At higher altitudes, there is a decrease in the time-of-snowmelt ranges of species which have intermediate times-of-snowmelt optima, whereas snowbed (chinophilous) species have wider time-of-snowmelt ranges. As snowbed species can survive, grow and reproduce at very early snow-free sites at high altitudes, the most likely explanation for their absence from all but the latest time-of-snowmelt habitats at lower altitudes is competitive exclusion by more vigorous lee-side species. This suggests that with future climate change snowbed species will experience, in addition to habitat fragmentation and reduced size of habitats due to increased temperature and snowmelt, an indirect effect due to competitive exclusion from late-snowmelt sites by species that have their optima outside snowbeds.

Changes in Tree Growth, Biomass and Vegetation Over a 13-Year Period in the Swedish Sub-Arctic

“…The decrease of snowbed vegetation reflects a shift from a sparse vegetation cover to denser vegetation characterized by species found in the surrounding vegetation (Heegard 2002;Heegaard and Vandvik 2004;Björk and Molau 2007). It is suggested that snowbed plants are restricted by growing season length and the availability of phosphorus (Björk and Molau 2007).…”

Disparities between observed and predicted impacts of climate change on winter bird assemblages

“…Biotic interactions under a variety of observational, experimental and theoretical settings have been found to play a significant role determining how species' distributions are structured and how they will be likely to respond to climate change (Davis et al 1998;Anderson et al 2002;Heegaard & Vandvik 2004;Araújo & Luoto 2007;Brooker et al 2007;Heikkinen et al 2007). A third factor would include spatial variation in the response of species and communities to changing climates (Visser et al 2003;Genner et al 2004), which could result in outcomes that, when summarized geographically, could differ from historic associations.…”

Community ecology in the age of multivariate multiscale spatial analysis

“…There are however few alternatives for dealing with multiple species responses in multivariate autoregressive models (but see Jin et al [2005]; M13 in Table 1). Alternatively, restricted permutations may also help by considering the appropriate number of ''exchangeable units'' (and consequently degrees of freedom) in multi-way sampling designs, particularly when sites are embedded within ecological classes (Anderson andter Braak 2003, Couteron andPe´lissier 2004, Heegaard and August 2012 261 SPATIAL MULTIVARIATE ANALYSIS Vandvik 2004). Another approach is to filter out (remove) the effects of spatial dependence by detrending (''spatial filtering'' sensu Griffith [2000]; M7 in Table 1).…”