Abstract The mechanisms linking productivity to patterns of species richness, species prevalence, and beta diversity remain contested and may be scale‐dependent. We address productivity–diversity relationships in arthropod communities across two subarctic landscapes. Using the normalized difference vegetation index (NDVI) as a proxy for plant productivity, we targeted three different spatial scales: the local scale (0–10 km), the landscape scale (10–50 km), and the regional scale (>300 km). At each scale, we examined variation in species richness (alpha diversity), in species prevalence patterns, and in spatial turnover (beta diversity) along gradients of productivity. We hypothesized that alpha diversity will increase towards highly productive areas regardless of the scale assessed, and that this increase will be associated with either (a) higher, (b) equal, or (c) lower mean species prevalence towards increasing productivity. We expected to encounter the biggest difference in species turnover between low‐ and high‐productivity sites at the landscape scale, owing to maximized effects of both environmental filtering and dispersal constraints at these two ends of the gradient. We found a positive relationship between alpha diversity and productivity across all scales and arthropod community types. Species‐specific prevalence did not differ between the low and high ends of the productivity gradient, and similar proportions of the species pools were shared among sites under both conditions. As a net outcome, the increase in alpha diversity did not translate into higher community dissimilarity at the highly productive sites. Our findings also suggest that while higher productivity can sustain a larger species pool, this is not reflected in higher turnover among sites. Rather, the majority of species are widely represented along the productivity gradient, with a specific subset of species present in high‐ and low‐productive sites. The same patterns prevail across scales and across flying and ground‐dwelling arthropods. We conclude that patterns of alpha and beta diversity observed here are consistent with scenario (b) advanced a priori, that is, with equal mean species prevalence across the productivity gradient. A fraction of the local species pool is restricted to conditions of either low or high productivity, causing variation in species richness but not in species turnover.
Peña‐Aguilera et al. (Sun,) studied this question.