Temporal changes in spatial variation: Partitioning the extinction and colonisation components of beta diversity

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Shinichi Tatsumi, Hokkaido Research Center, Forestry and Forest Products Research Institute, Hokkaido, Japan, Ryosuke Iritani, Interdisciplinary Theoretical and Mathematical Science Program (iTHEMS), RIKEN, Wako, Japan and Marc W. Cadotte, Department of Biological Sciences, University of Toronto - Scarborough, Toronto, ON, Canada

Background/Question/Methods
The last two decades have witnessed unprecedented changes in beta diversity, the spatial variation in species composition, from local to global scales. However, analytical challenges have hampered empirical ecologists from quantifying the extinction and colonization processes behind these changing beta diversity patterns. Here, we developed a novel numerical method to additively partition the temporal changes in beta diversity into components that reflect local extinctions and colonizations. We derived mathematical equations that partition the extirpation and colonization components and conducted sensitivity analyses. We then applied the partitioning method to long-term forest and coral reef datasets.
Results/Conclusions
Sensitivity analyses showed that the extinction and colonization components of beta diversity can be additively partitioned using our method. By applying the method to empirical datasets, we revealed spatiotemporal community dynamics that were otherwise undetectable. In mature forests, we found that local extinctions resulted in tree communities becoming more spatially heterogeneous, while colonizations simultaneously caused them to homogenize. In coral communities, we detected nonrandom community disassembly and reassembly following an environmental perturbation, with a temporally varying balance between extinctions and colonizations. Partitioning the dynamic processes that underlie beta diversity can provide more mechanistic insights into the spatiotemporal organization of biodiversity.