A new paper using the comprehensive data-set on the functional traits of European cave spiders that I was involved in a few years ago, have now been published in Global Ecology and Biogeography. In the paper, we took advantage of the very comprehensive data-sets of functional traits and communities of spiders from different caves (which are impoverished communities in terms of species compared to above-ground habitats) to investigate broader theoretical ecology questionson whether communities tend o be assembled based on environmental filtering (the conditions in the habitat acts as a filter to only some species and traits to become established, which leads to lower differences in functional traits than expected by chance) or limiting similarity (where a reduction of niche overlap means that functional traits are more different than expected by chance). In the paper, we find that even in subterranean environments with very strong environmental selection pressures, neither of the two processed tended to dominate in most caves (trait differences did not differ from chance), although with some suggesting environmental filtering might play a dominant role and others (especially the species rich caves) suggest that limiting similarity and hence interspecific competition could play an important role.
Abstract
Aim
Quantifying the relative contribution of environmental filtering versus limiting similarity in shaping communities is challenging because these processes often act simultaneously and their effect is scale-dependent. Focusing on caves, island-like natural laboratories with limited environmental variability and species diversity, we tested: (i) the relative contribution of environmental filtering and limiting similarity in determining community assembly in caves; (ii) how the relative contribution of these driving forces changes along environmental gradients.
Location
Europe.
Time period
Present.
Major taxa studied
Subterranean spiders.
Methods
We used data on distribution and traits for European cave spiders (n = 475 communities). We estimated the trait space of each community using probabilistic hypervolumes, and obtained estimations of functional richness independent of the species richness of each community via null modelling. We model functional diversity change along environmental gradients using generalized dissimilarity modelling.
Results
Sixty-three percent of subterranean spider communities exhibited a prevalence of trait underdispersion. However, most communities displayed trait dispersion that did not depart significantly from random, suggesting that environmental filtering and limiting similarity were both exerting equally weak or strong, yet opposing influences. Overdispersed communities were primarily concentrated in southern latitudes, particularly in the Dinaric karst, where there is greater subterranean habitat availability. Pairwise comparisons of functional richness across caves revealed these effects to be strongly scale-dependent, largely varying across gradients of cave development, elevation, precipitation, entrance size and annual temperature range. Conversely, geographical distance weakly affected trait composition, suggesting convergence in traits among communities that are far apart.
Main conclusions
Even systems with stringent environmental conditions maintain the potential for trait differentiation, especially in areas of greater habitat availability. Yet, the relative influence of environmental filtering and limiting similarity change with scale, along clear environmental gradients. The interplay of these processes may explain the assembly of species-poor subterranean communities displaying high functional specialization.
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