Diversity and ecology of spider assemblages in secondary forests of the southern Mata Atlântica, Brazil - Implications for environmental conservation
The objective of my thesis was to assess the diversity and the ecology of spider assemblages in secondary forests of the southern Mata Atlântica, with impact for environmental conservation and the protection of the regional biodiversity. My approach to address these questions was carried out in the...
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|Summary:||The objective of my thesis was to assess the diversity and the ecology of spider assemblages in secondary forests of the southern Mata Atlântica, with impact for environmental conservation and the protection of the regional biodiversity. My approach to address these questions was carried out in the frame of a multi-taxon approach of the bilateral cooperation project SOLOBIOMA. The aim of this project was the evaluation of the value of different secondary forest stages for the conservation of the local and regional biodiversity and implications for soil function. Therefore my work addresses the diversity of spiders by describing and analyzing a large sampling carried out in different succesional stages of forest, as well as investigating the ecology of the predatory spider assemblage in an experimental approach of the interactions of spiders with habitat structures and nutritional resources in the soil food web.
To assess the conservation value of secondary forests and their contribution to maintain the regional diversity I compared the spider assemblages of secondary forests of different age (stage) and old-growth forests (chapter 2 & 3). We sampled spiders using a standard protocol in 24 sites of three successional stages and old-growth forests in two nature reserves in the state of Paraná in Brazil. The sampled region represents a relatively good preserved region of the Mata Atlântica, where the matrix of a patchy landscape is still forest.
Generic richness and diversity showed no differences between successional stages but guild diversity did. A high alpha diversity and a high turnover among sites as well as the lack of differences in richness between the stages support the value of secondary forests for species conservation in the studied region. Beta diversity turned out to be strongly based on turnover, not on gain/loss during succession. The spatial levels contributed more to beta diversity than expected, without the expected strong influence of the forest stage. Patterns were consistent for both identification levels and every method, leading to the conclusion that one of two parts of the sampling protocol and identification to genera are sufficient to assess the diversity of spiders under conservation interest.
During the experimental approach (chapter 4) I discovered that adding artificial litter had no effect on the studied taxa, adding food had a positive effect on decomposers independent from the forest stage, but not on predators. These results suggest that the soil fauna in tropical forests in general is food limited and the lack of a bottom-up effect on predators suggest that these organisms are not predominantly regulated by the abundance of prey but rather by competition or predation. However, it would be premature to conclude from one single experiment that the processes influencing the soil and epigeic fauna are generally similar across different successional stages, we can see evidence for distinct functional similarity. These results highlight the value of secondary forests for the conservation of forest species and associated ecological processes.
I conclude from the results of the biodiversity study and the experiment that maintaining the heterogeneity of a mosaic landscape seems to be a good recommendation for conservation of the regional invertebrate biodiversity and its ecosystem function in the southern Mata Atlântica. Our analyses from a spider perspective point out to the importance of a pattern of different land use and regeneration types as well as old-growth forest in protected areas to maximize conservation success. To guarantee a protection of the widest range of spider diversity on the long term the protection of large, contiguous areas of forest should be reached and, if a decision is obligate, preferred to the protection of small (mostly isolated) old-growth forest remnants.|