Accounting for dispersal improves the understanding of species abundance patterns

A long-standing question in ecology is how are species population distributed across space. The highest abundance has been hypothesized to be in the spatial or niche center, though mixed patterns from empirical studies has triggered a recent debate. Here we propose a conceptual framework based on environmental suitability and dispersal to interpret the mixed evidence. We demonstrate that the highest abundance could occur in the spatial center, in the niche center, or somewhere in-between the two centers, depending on the environmental setup and dispersal ability. We found that spatial and niche centers rarely overlap, suggesting the counteracting effect between the two factors, rather than reinforcement, is the norm in determining abundance patterns. The varied locations of highest abundance mirror the mixed evidence in literature, suggesting the "abundant-centre" and "abundant-niche centre" hypotheses are not mutually exclusive. This highlights the importance in understanding the biogeographic patterns through the lens of underlying mechanisms.