Is there a species swarm paradox? Spatial segregation of related species in the understorey of a tropical plant community

Abstract

Question Individual plants of some highly diverse angiosperm families occur in aggregated spatial patterns in tropical plant communities, which have been defined as species swarms. Although this spatial aggregation seems paradoxical, because related species should segregate in space owing to expected ecological similarities, it has yet to be tested. We assessed whether species of the family Rubiaceae segregate in space in the understorey of a tropical plant community. Location An Atlantic Forest fragment in southeast Brazil. Methods We surveyed all local aggregates of Rubiaceae species within an 18.75‐ha plot across a topographic gradient. Based on the species abundance distribution, we used the 10 most abundant species to model their spatial patterns using univariate and bivariate spline spatial correlations. Bubble graphs were used to show how these species were distributed across the gradient. Results A total of 12,258 individuals of 47 species were found distributed in 543 local aggregates. The 10 studied species corresponded to 86% of the total abundance and were aggregated in space, at distances from 0 to 10–300 m. Pairwise comparisons revealed a segregation pattern at scales ranging from 0 to 10–230 m. Local aggregates were strongly dominated by a single species, whereas many other species occurred at very low abundances. Conclusion The studied species of Rubiaceae shared the understorey environment by occupying different portions of available space. Habitat preferences, negative interactions, dispersal limitation and priority effects may explain the observed spatial patterns. Swarms are not paradoxical because species of Rubiaceae use different microhabitats within the forest understorey.

Post‐drought community turnover and functional redundancy in a tropical forest understorey

“…We used before‐drought abundance data from Ferreira‐Santos et al. (2023). Here, we provide a brief description of the Rubiaceae community survey.…”

“…In Ferreira‐Santos et al. (2023), we traced a parallel between species’ swarms and “The paradox of the plankton” (Hutchinson, 1941), and discussed the paradox such species’ swarms pose to coexistence theory in the understorey of tropical forests. Closely related species tend to respond similarly to environmental conditions, thus increasing competition and limiting the number of coexisting species (Prunier et al., 2012).…”

“…Closely related species tend to respond similarly to environmental conditions, thus increasing competition and limiting the number of coexisting species (Prunier et al., 2012). This paradoxical aggregation of species in swarms is possible because the most‐abundant species partite the understorey by segregating from each other in space (Ferreira‐Santos et al., 2023). Segregation means that the greater abundance of one species is accompanied by the lower abundance of another leading to negative bivariate autocorrelations in spatially explicit models (Ferreira‐Santos et al., 2023).…”

“…This paradoxical aggregation of species in swarms is possible because the most‐abundant species partite the understorey by segregating from each other in space (Ferreira‐Santos et al., 2023). Segregation means that the greater abundance of one species is accompanied by the lower abundance of another leading to negative bivariate autocorrelations in spatially explicit models (Ferreira‐Santos et al., 2023). However, many knowledge gaps remain.…”

“…In the understorey of the Atlantic Forest, functional differences in the photosynthetic performance of Rubiaceae species were important in the shaded forest understorey (Torres-Leite et al, 2019). In Ferreira-Santos et al (2023), we traced a parallel between species' swarms and "The paradox of the plankton" (Hutchinson, 1941), and discussed the paradox such species' swarms pose to coexistence theory in the understorey of tropical forests. Closely related species tend to respond similarly to environmental conditions, thus increasing competition and limiting the number of coexisting species (Prunier et al, 2012).…”