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.

Habitat loss is one of the greatest threats to biodiversity, exerting negative effects on the ecological viability of natural vegetation remnants. The south Brazilian grasslands belong to one of the largest temperate grassland regions in the world, but have lost 50% of their natural extent in the past 35 years. To date, there is no empirical evidence for the effects of habitat loss on these grasslands' biological diversity, undermining their conservation. Using data from a large‐scale biodiversity survey, we asked if local plant communities respond to levels of habitat loss representative of the entire region (≤50%). Vegetation in grassland remnants was sampled in 24 landscapes at three localities each, using nine plots per locality. To investigate whether species losses were a consequence of stochastic or nonrandom local extinctions and whether plant communities became more homogenized, we evaluated species richness, beta‐diversity components (spatial turnover and nestedness), and phylogenetic diversity, in respect to landscape change. In part of the landscapes, arthropods were sampled to investigate if loss of plant diversity had a cascading effect on other trophic levels. We evaluated generic richness of ants, an omnivore group with high levels of plant associations, in respect to a plant community's phylogenetic diversity. Local plant communities in landscapes with less grassland cover had fewer species, less spatial turnover, increased nestedness and lower phylogenetic diversity. Our results suggest that the observed species loss can be linked to taxonomic homogenization and is nonrandom, decreasing evolutionary diversity within the community. Furthermore, ant richness declined by 50% in plant communities with the lowest phylogenetic diversity, suggesting that effects of habitat loss propagate to higher trophic levels. Policy implications. We conclude that the biological diversity of south Brazilian grasslands, at the producer and consumer level, is at risk under the current rate of land‐use conversion, even at habitat losses below 50%. To avoid substantial biodiversity loss, conservation and more restrictive policies for conversion of native grasslands to different land uses in South Brazil are urgently needed.

Environmental gradients consist of sequential changes in the physical and structural characteristics of a region. These allow us to follow species responses and tolerances under different habitat conditions. Among them, forest fragmentation and succession comprise the most common examples of forest gradients, where organismal responses require distinct morphological, physiological, and behavioral adaptations. However, environmental changes can impose ecological and evolutionary constraints that act on species traits, as well as on local species assemblies through their phylogenetic history. In this study, we evaluated the differences in species distribution and composition on fruit‐feeding butterfly assemblages along forest fragmentation and succession gradients. We combine functional and phylogenetic methods for determining butterfly assemblages, and inferred species resistance and resilience according to habitat changes in tropical forests. We used a database of 471 fruit‐feeding butterflies of 60 species sampled from different environments in the central Amazon rainforest. A total of 13 functional traits were measured, and a phylogenetic tree was obtained for the sampled species. The trait–environment relationship was analyzed along both forest fragmentation and succession gradients, controlling for phylogenetic signal on species distribution and functional composition when necessary. Several traits presented phylogenetic signal, and phylogeny was also driving butterfly species distribution along the successional gradient. After controlling for phylogeny, individual characteristics related to flight speed (thoracic weight) and anti‐predatory strategies (camouflage) increased in early‐successional forests, with large butterflies (body length) prevailing in primary forests. No clear functional and phylogenetic pattern was identified for the fragmentation gradient. Our results are consistent with the idea that butterflies may be employing distinct functional strategies to attenuate habitat change effects. Larger butterflies, with lower dispersal ability, are preferentially susceptible to local extinctions in the early‐successional environments, mainly when forested habitat and its resources become spatially restricted. In addition, several anti‐predatory strategies related to conspicuous colors may be losing their functionality in open areas, where not being distinctive against the background becomes the primary defense against predation.