domingo, 17 de noviembre de 2019

The geographic scaling of biotic interactions 
Miguel B. Araújo Alejandro Rozenfeld


A central tenet of ecology and biogeography is that the broad outlines of species ranges are determined by climate, whereas the effects of biotic interactions are manifested at local scales. While the first proposition is supported by ample evidence, the second is still a matter of controversy. To address this question, we develop a mathematical model that predicts the spatial overlap, i.e. co‐occurrence, between pairs of species subject to all possible types of interactions. We then identify the scale of resolution in which predicted range overlaps are lost. We found that co‐occurrence arising from positive interactions, such as mutualism (+/+) and commensalism (+/0), are manifested across scales. Negative interactions, such as competition (−/−) and amensalism (−/0), generate checkerboard patterns of co‐occurrence that are discernible at finer resolutions but that are lost and increasing scales of resolution. Scale dependence in consumer–resource interactions (+/−) depends on the strength of positive dependencies between species. If the net positive effect is greater than the net negative effect, then interactions scale up similarly to positive interactions. Our results challenge the widely held view that climate alone is sufficient to characterize species distributions at broad scales, but also demonstrate that the spatial signature of competition is unlikely to be discernible beyond local and regional scales.


Expected co‐occurrence across biotic‐interaction space. Colours on the top graph indicate the intensity of the predicted co‐occurrence between species A (y axis) and B (x axis), where increasing gradients of red indicate increased co‐occurrence and increasing gradients of blue indicate decreased co‐occurrence. The light gray line indicates the portion of biotic‐interaction space where co‐occurrence between two species is no different than expected with the null model. The numbers on the y and x axes represent interactions (I) of varying signal (+, −, 0) and strength (≥ 0 ≤ 1). The lower scatter diagrams provide examples of simulated distributions of species A (black) and B (gray), with their respective co‐occurrence (red), for interactions of varying sign and strength. Both species have prevalence ρ= 0.3.

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