Spider community responds to litter complexity: insights from a small-scale experiment in an exotic pine stand

ABSTRACT Conservation of biodiversity in agroecosystems is an urgent need, and a suitable approach to maximize animal biodiversity and their services is the restoration of habitat heterogeneity. Here we investigated the value of increasing litter complexity in tree plantations of exotic pine for ground spiders. We hypothesized that increasing the litter complexity of these systems, as it would be the case in ecologically designed plantations, would increase spider aggregations. We performed a small-scale litter manipulation experiment within an exotic pine stand in the municipality of Minas do Leão, Rio Grande do Sul, Brazil, and compared spider diversity in simple (only pine needles) and complex substrates (with the addition of diverse native broadleaves). We found 1,110 spiders, 19 families and 32 morphospecies. The most abundant families were Linyphiidae, Theridiidae and Salticidade, and the dominant morphospecies were Thymoites sp. 2 and Lygarina sp. Web-building spiders represented 61% of total spider abundance, and 17 species, while hunting spiders, 49% and 15 species. As expected, densities of spider individuals and species from both web-building and hunting spiders were higher in complex litter substrate. Potential preys (Collembola) also responded positively to the treatment, and had influence of spider community patterns. Our results suggest that ensuring some degree of plant and litter diversity within pine stands (e.g. understory establishment) might foster spider aggregations and possibly help to conserve their diversity at local-scales

Long-term ecological research in southern Brazil grasslands: Effects of grazing exclusion and deferred grazing on plant and arthropod communities

Grazing exclusion may lead to biodiversity loss and homogenization of naturally heterogeneous and species-rich grassland ecosystems, and these effects may cascade to higher trophic levels and ecosystem properties. Although grazing exclusion has been studied elsewhere, the consequences of alleviating the disturbance regime in grassland ecosystems remain unclear. In this paper, we present results of the first five years of an experiment in native grasslands of southern Brazil. Using a randomized block experimental design, we examined the effects of three grazing treatments on plant and arthropod communities: (i) deferred grazing (i.e., intermittent grazing), (ii) grazing exclusion and (iii) a control under traditional continuous grazing, which were applied to 70 x 70 m experimental plots, in six regionally distributed blocks. We evaluated plant community responses regarding taxonomic and functional diversity (life-forms) in separate spatial components: alpha (1 x 1 m subplots), beta, and gamma (70 x 70 m plots), as well as the cascading effects on arthropod high-taxa. By estimating effect sizes (treatments vs. control) by bootstrap resampling, both deferred grazing and grazing exclusion mostly increased vegetation height, plant biomass and standing dead biomass. The effect of grazing exclusion on plant taxonomic diversity was negative. Conversely, deferred grazing increased plant taxonomic diversity, but both treatments reduced plant functional diversity. Reduced grazing pressure in both treatments promoted the break of dominance by prostrate species, followed by fast homogenization of vegetation structure towards dominance of ligneous and erect species. These changes in the plant community led to increases in high-taxa richness and abundance of vegetationdwelling arthropod groups under both treatments, but had no detectable effects on epigeic arthropods. Our results indicate that decision-making regarding the conservation of southern Brazil grasslands should include both intensive and alleviated levels of grazing management, but not complete grazing exclusion, to maximize conservation results when considering plant and arthropod communities

Spider trait assembly patterns and resilience under fire-induced vegetation change in South Brazilian grasslands.

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

Data from: Local biodiversity erosion in South Brazilian grasslands under moderate levels of landscape habitat loss

1.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. 2.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 9 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. 3.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. 4.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 urgent

Data from: Local biodiversity erosion in South Brazilian grasslands under moderate levels of landscape habitat loss

1.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. 2.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 9 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. 3.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. 4.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 urgent

Vegetation variables in burned and unburned experimental plots at different sampling periods.

a<p>showed experimentally based on our measurements.</p>b<p>qualitative observations, and according to Fidelis et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0060207#pone.0060207-Fidelis2" target="_blank">[44]</a>.</p

Description of spider and plant traits used in the study.

<p>Description of spider and plant traits used in the study.</p

Spider assembly patterns in ecological gradients.

<p>Trait convergence assembly pattern (TCAP) under gradients of plant biomass (A) and plant FD (B). Trait divergence assembly pattern (TDAP) in gradient of plant FD (C). The TDAP plot is composed of an ordination diagram generated on Euclidian distances computed on the composition of spiders communities after fuzzy weighting by the traits which maximized the expression of TDAP (body, chel, eye, iw, ow) related to plant FD. Green symbols mean control plots and orange symbols mean burned plots.</p

Summary of the results of spider assembly patterns in ecological gradients.

<p>Spider trait subsets maximizing, at the community level, the expression of trait-convergence assembly patterns (TCAP) and trait-divergence assembly patterns (TDAP) related to plant biomass and plant FD ecological gradients. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0060207#pone-0060207-t001" target="_blank">Table 1</a> for descriptions of trait abbreviations.</p

Relationships between spider traits and vegetation traits in burned and control plots.

<p>Co-inertia analysis results: (A) ordination of control (light-green symbols) and burned plots (dark-orange symbols) based on spider (triangle) and plant traits (square); PCA of (B) spider and (C) plant traits. Short arrows indicate that the plant and animal traits occupy similar positions in the ordination space. Numbers (1 to 7) indicate the blocks. Highlighted traits (B, C) mean significant association with burned or control plots.</p