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Data and code from: Unravelling the drivers of island species richness in tropical savannas

Mews, Henrique Augusto1; Nogueira, Denis Silva2; Marimon Junior, Ben Hur3; Constantino, Reginaldo4; Phillips, Oliver Lawrence5; Marimon, Beatriz Schwantes3

Published Apr 02, 2026 on Dryad. https://doi.org/10.5061/dryad.612jm64kr

Data files

Abstract

Despite their ecological and conservation relevance and their potential to advance our understanding of species–habitat relationships, natural island habitats in seasonal tropical terrestrial systems remain inadequately explored. In particular, the processes governing species diversity in these environments are still poorly understood. Here, we examine how island size, geographical isolation, and habitat heterogeneity and availability affect species richness in campos de murundus—literally “fields of earth mounds”—a distinctive ecosystem within South American tropical savannas. Our study targets three major biological groups that dominate and structure murundu communities—trees, herbs, and termites—and is based on an extensive inventory of these taxa across 373 murundu islands sampled within eleven 1-ha plots distributed throughout the vast seasonal floodplains of east-central Brazil. Bayesian mixed-effects models indicated that tree and herb species richness increased with murundu island size, consistent with predictions from island biogeography theory. By contrast, neither isolation nor environmental heterogeneity or habitat availability exerted detectable effects on the species richness of trees, herbs, or termites at the murundu island scale. At the landscape scale, tree alpha diversity was largely driven by metacommunity attributes directly associated with landscape habitat amount, increasing with total abundance and declining with beta diversity. In contrast, termite species richness was weakly explained by the environmental variables considered, showing no clear association with island size, isolation, or environmental heterogeneity. Overall, island size accounted for most of the explained variation in plant species richness, whereas termite assemblages were more strongly associated with spatial eigenvectors at intermediate and fine spatial scales. We conclude that, for woody and non-woody plant communities in hyperseasonal savannas, island species richness is primarily determined by murundu island size and habitat amount, with little evidence of dispersal limitation or strong influences of environmental heterogeneity. At the landscape scale, tree species richness did not respond directly to habitat amount; however, total abundance and gamma diversity increased with habitat amount, which in turn resulted in higher alpha diversity. Beta diversity appears to be more closely linked to the nested composition of species on small islands within larger ones than to spatial turnover. In contrast, termite communities are only weakly structured by the predictors tested, suggesting that stochastic processes, local habitat constraints, and species-specific nesting behaviours play a more prominent role.