Improved detection of mass effect species assembly for applied metacommunity thinking.
Dispersal mass effects pose major challenges and opportunities for applied metacommunity ecology. A recent paper in Journal of Applied Ecology (https://doi.org/10.1111/1365-2664.13701) presented a mass effect (ME) detection framework and grouped the species prone to ME in an extensive stream diatom survey. We tested the putative ME diatom group and two other reported species groups for signatures of (a) dispersal-based to joint niche-dispersal assembly using the dispersal-niche continuum index and (b) metacommunity homogenization based on total compositional variance and individual species contributions to beta diversity. Signatures of ME were found in all three diatom groups, raising uncertainty about which species were distributed by ME. Due to the ambiguity and data demands we propose an alternate framework that enables more precise and robust ME detection with simpler data requirements. Demonstrating this approach on the same dataset, we assembled a new candidate ME group and systematically removed niche processes, dispersal limitation, stochasticity and generalist tendency as alternative explanations. Synthesis and applications. Mass effects have strong implications for biomonitoring and spatial prioritization within dispersal networks, yet standardized methodology explicitly aligned to ME has been lacking. Ecologists now have options to enable ME research and application in more projects, datasets and study systems. Ultimately these new frameworks will help to integrate metacommunity thinking with more spatially informed resource protection and management.