Aim It is widely accepted that biodiversity is influenced by both niche‐related and spatial processes from local to global scales. Their relative importance, however, is still disputed, and empirical tests are surprisingly scarce at the global scale. Here, we compare the importance of area (as a proxy for pure spatial processes) and environmental heterogeneity (as a proxy for niche‐related processes) for predicting native mammal species richness world‐wide and within biogeographical regions. Location Global. Time period We analyse a spatial snapshot of richness data collated by the International Union for Conservation of Nature. Major taxa studied All terrestrial mammal species, including possibly extinct species and species with uncertain presence. Methods We applied a spreading dye algorithm to analyse how native mammal species richness changes with area and environmental heterogeneity. As measures for environmental heterogeneity, we used elevation ranges and precipitation ranges, which are well‐known correlates of species richness. Results We found that environmental heterogeneity explained species richness relationships better than did area, suggesting that niche‐related processes are more prevalent than pure area effects at broad scales. Main conclusions Our results imply that niche‐related processes are essential to understand broad‐scale species–area relationships and that habitat diversity is more important than area alone for the protection of global biodiversity.

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Agricultural intensification has led to dramatic diversity losses and impoverishment of the arable vegetation in much of Europe. We analyzed the status of farmland phytodiversity and its determinants in 2016 in northwest Germany by surveying 200 conventionally managed fields cultivated with seven crops. The study was combined with an analysis of edaphic (soil yield potential), agronomic (crop cover, fertilizer and herbicide use) and landscape factors (adjacent habitats). In total, we recorded 150 non-crop plant species, many of them nitrophilous generalist species, while species of conservation value were almost completely absent. According to a post-hoc pairwise comparison of the mixed model results, the cultivation of rapeseed positively influenced non-crop plant species richness as compared to winter cereals (wheat, barley, rye and triticale; data pooled), maize or potato. The presence of grassy strips and ditch margins adjacent to fields increased plant richness at field edges presumably through spillover effects. In the field interiors, median values of non-crop plant richness and cover were only 2 species and 0.5% cover across all crops, and at the field edges 11 species and 4% cover. Agricultural intensification has wiped out non-crop plant life nearly completely from conventionally managed farmland, except for a narrow, floristically impoverished field edge strip.

9Biodiversity theories are not very often explicitly consulted in conservation practice, but 10 implicitly many conservation decisions rely on theory. Biodiversity theories can inform 11 important conservation actions such as assessments of species richness and extinction or 12 habitat loss and fragmentation. Popular examples of biodiversity theories are niche theory and 13 island biogeography theory, whereas neutral theory is less known. Here, we review the 14 implications of biodiversity theories for conservation practice, focusing on neutral theory. 15 Neutral theory assumes that the establishment and success of an individual in a community 16 does not depend on its species identity, but is instead predominantly driven by a stochastic 17 process. We found that drift and stochasticity appear much less frequently in conservation 18 studies than selection processes typical of niche theory. This might be because habitat-19 specificity is not supported by neutral theory, but is common among rare and vulnerable 20 species. Furthermore, neutral theory makes less intuitive assumptions than niche theory and 21 does not consider trophic interactions. However, models based on neutral theory proved to be 22 useful in some biodiversity hotspots. Moreover, some models based on neutral theory and support protected area design. We propose that neutral theory can serve as a valuable first-28 order approximation to reduce complexity and by design account for drift and stochasticity.