RESUMO
While land use intensification is a major driver of biodiversity change in streams, the nature of such changes, and at which scales they occur, have not been synthesized. To synthesize how land use change has altered multiple components of stream biodiversity across scales, we compiled data from 37 studies where comparative data were available for species' total and relative abundances from multiple locations including reference (less impacted) streams to those surrounded by different land use types (urban, forestry, and agriculture). We found that each type of land use reduced multiple components of within-stream biodiversity across scales, but that urbanization consistently had the strongest effects. However, we found that ß-diversity among streams in modified landscapes did not differ from ß-diversity observed among reference streams, suggesting little evidence for biotic homogenization. Nevertheless, assemblage composition did experience considerable species turnover between reference and modified streams. Our results emphasize that to understand how anthropogenic factors such as land use alter biodiversity, multiple components of biodiversity within and among sites must be simultaneously considered at multiple scales.
Assuntos
Benchmarking , Biodiversidade , Agricultura , Ecossistema , Agricultura Florestal , UrbanizaçãoRESUMO
Site-to-site variation in species composition (ß-diversity) generally increases from low- to high-diversity regions. Although biogeographical differences in community assembly mechanisms may explain this pattern, random sampling effects can create this pattern through differences in regional species pools. Here, we compared assembly mechanisms between spatially extensive networks of temperate and tropical forest plots with highly divergent species pools (46 vs. 607 species). After controlling for sampling effects, ß-diversity of woody plants was similar and higher than expected by chance in both forests, reflecting strong intraspecific aggregation. However, different mechanisms appeared to explain aggregation in the two forests. In the temperate forest, aggregation reflected stronger environmental correlations, suggesting an important role for species-sorting (e.g. environmental filtering) processes, whereas in the tropics, aggregation reflected stronger spatial correlations, more likely reflecting dispersal limitation. We suggest that biogeographical differences in the relative importance of different community assembly mechanisms contribute to these striking gradients in global biodiversity.