Abstract
Beta diversity – the variation in species composition among spatially discrete communities – and sampling grain – the size of samples being compared – may alter our perspectives of diversity within and between landscapes before and after agricultural conversion. Such assumptions are usually based on point comparisons, which do not accurately capture actual differences in total diversity. Beta diversity is often not rigorously examined. We investigated the beta diversity of ground-foraging ant communities in fragmented oil palm and forest landscapes in Sabah, Malaysia, using diversity metrics transformed from Hill number equivalents to remove dependences on alpha diversity. We compared the beta diversities of oil palm and forest, across three hierarchically nested sampling grains. We found that oil palm and forest communities had a greater percentage of total shared species when larger samples were compared. Across all grains and disregarding relative abundances, there was higher beta diversity of all species among forest communities. However, there were higher beta diversities of common and very abundant (dominant) species in oil palm as compared to forests. Differences in beta diversities between oil palm and forest were greatest at the largest sampling grain. Larger sampling grains in oil palm may generate bigger species pools, increasing the probability of shared species with forest samples. Greater beta diversity of all species in forest may be attributed to rare species. Oil palm communities may be more heterogeneous in common and dominant species because of variable community assembly events. Rare and also common species are better captured at larger grains, boosting differences in beta diversity between larger samples of forest and oil palm communities. Although agricultural landscapes support a lower total diversity than natural forests, diversity especially of abundant species is still important for maintaining ecosystem stability. Diversity in agricultural landscapes may be greater than expected when beta diversity is accounted for at large spatial scales.
Highlights
The conversion of tropical forest landscapes to agriculture is a major factor driving the global biodiversity crisis (Sodhi et al 2010)
Our results show that the ground-foraging ant communities in tropical oil palm are not as homogeneous, in comparison with forest communities, as is often expected for fauna in large-scale monocultures
As shown in previous studies, homogenization or differentiation of communities in fragmented and heavily modified landscapes is contingent on spatial configuration of the landscape, and the varying successional pathways undergone by each discrete community (ArroyoRodrıguez et al 2013)
Summary
The conversion of tropical forest landscapes to agriculture is a major factor driving the global biodiversity crisis (Sodhi et al 2010). Biodiversity worldwide is increasingly being fractionated into landscape matrices characterized by mosaics of pristine forest and agricultural lands In such fragmented ecosystems, multiple factors may alter assemblages occupying different tracts of the mosaic. Beta diversity – the variation in species composition among spatially discrete communities (Whittaker 1972; Flohre et al 2011) – and the spatial scale of sampling are not usually rigorously examined. Such studies may have distorted and oversimplified the more nuanced effects of agricultural conversion on native diversity. Beta diversity and its underlying processes in landscapes fragmented by agriculture are not well understood, especially in the tropics (Karp et al 2012; Barton et al 2013)
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