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Trait evolution and the coexistence of a species swarm in the tropical forest understorey
Article first published online: 13 JUN 2012
DOI: 10.1111/j.1365-2745.2012.01993.x
© 2012 The Authors. Journal of Ecology © 2012 British Ecological Society
Additional Information
How to Cite
Sedio, B. E., Wright, S. J. and Dick, C. W. (2012), Trait evolution and the coexistence of a species swarm in the tropical forest understorey. Journal of Ecology, 100: 1183–1193. doi: 10.1111/j.1365-2745.2012.01993.x
Publication History
- Issue published online: 14 AUG 2012
- Article first published online: 13 JUN 2012
- Received 7 February 2011; accepted 15 May 2012 Handling Editor: Will Cornwell
Keywords:
- Barro Colorado Island;
- community assembly;
- determinants of plant community diversity and structure;
- phylogenetic community structure;
- phylogenetic signal;
- Psychotria
Summary
1. A small number of species-rich plant genera make a substantial contribution to the α diversity of tropical forests. These ‘species swarms’ (Gentry 1982) challenge a view of community assembly that maintains that niche overlap, and hence, the likelihood of competitive exclusion should increase with phylogenetic affinity. Related species may, however, occupy different microhabitats within a forest stand or, alternatively, differ ecologically in ways that allow them to coexist syntopically.
2. To explore the relationship between phylogenetic history and niche differentiation among sympatric, congeneric species, we performed phylogenetic analyses of microhabitat preferences, photosynthetic and hydraulic traits, and experimental responses to light and water availability for 20 species of Psychotria (Rubiaceae) from Barro Colorado Island (BCI), Panama.
3. The Psychotria present in small (3-m radius), circular plots were more closely related than expected by chance. Photosynthetic and hydraulic traits were both associated with species habitat distributions, but only hydraulic traits were conserved phylogenetically. Experimental responses to water availability were also conserved phylogenetically. Functional trait analyses revealed little or no evidence of niche partitioning within sites.
4. We conclude that Psychotria species’ responses to both light and moisture availability determine their microhabitat distributions on BCI and that evolutionarily conserved hydraulic traits lead to phylogenetic clustering of co-occurring species.
5. Synthesis. The evolutionary conservation of hydraulic traits related to soil moisture tolerance largely explains phylogenetic clustering in the local assembly of the hyperdiverse genus Psychotria. We suggest that close relatives are unlikely to exclude one another from shared habitats because resource availability is determined largely by asymmetric competition with the overstorey, rather than by competition with neighbouring understorey plants. In light of the recent biogeographic admixture in central Panama, the phylogenetic niche conservatism exhibited by Psychotria on BCI raises the possibility of an association between local microhabitats and the ancestral climatic regimes under which major Psychotria lineages evolved before arriving in sympatry.