Abstract
Disturbances induce changes on habitat proprieties that may filter organism's functional traits thereby shaping the structure and interactions of many trophic levels. We tested if communities of predators with foraging traits dependent on habitat structure respond to environmental change through cascades affecting the functional traits of plants. We monitored the response of spider and plant communities to fire in South Brazilian Grasslands using pairs of burned and unburned plots. Spiders were determined to the family level and described in feeding behavioral and morphological traits measured on each individual. Life form and morphological traits were recorded for plant species. One month after fire the abundance of vegetation hunters and the mean size of the chelicera increased due to the presence of suitable feeding sites in the regrowing vegetation, but irregular web builders decreased due to the absence of microhabitats and dense foliage into which they build their webs. Six months after fire rosette-form plants with broader leaves increased, creating a favourable habitat for orb web builders which became more abundant, while graminoids and tall plants were reduced, resulting in a decrease of proper shelters and microclimate in soil surface to ground hunters which became less abundant. Hence, fire triggered changes in vegetation structure that lead both to trait-convergence and trait-divergence assembly patterns of spiders along gradients of plant biomass and functional diversity. Spider individuals occurring in more functionally diverse plant communities were more diverse in their traits probably because increased possibility of resource exploitation, following the habitat heterogeneity hypothesis. Finally, as an indication of resilience, after twelve months spider communities did not differ from those of unburned plots. Our findings show that functional traits provide a mechanistic understanding of the response of communities to environmental change, especially when more than one trophic level is considered.
Highlights
Fire is an important disturbance that drives the structure and the interactions of ecological communities in flammable ecosystems [1]
Beyond who is present, and who profits and who vanishes from environmental change, a functional approach may inform: how the organisms are morphologically and functionally structured in the community and how they behave, what they do in ecosystems, and which functional traits are selected or filtered out in face of a disturbance
As the adaptation and function of organisms in their environment are expressed by their traits, functional diversity (FD) may be directly related to ecological niche diversity [7,10,11], thereby facilitating the understanding and prediction of community assembly patterns [12,13]
Summary
Fire is an important disturbance that drives the structure and the interactions of ecological communities in flammable ecosystems [1]. Beyond who is present (taxonomic identity), and who profits and who vanishes from environmental change (taxonomic turnover), a functional approach may inform: how the organisms are morphologically and functionally structured in the community and how they behave, what they do in ecosystems, and which functional traits are selected or filtered out in face of a disturbance. Such information represents a more generalist [4], comparative [5,6] and even meaningful [7] view of community diversity which has been gradually incorporated in ecological studies complementing the traditional taxonomic indicators [8,9]. We adopt this approach by analysing beta functional diversity along ecological gradients [7,13]
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