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Abstract
Background: Biodiversity is perceived to decline from lowlands towards mountain peaks and away from the Equator towards the Poles, but supporting data for most groups of organisms are lacking, especially at the local scale.
Aims: Elevational gradients of fern species richness in tropical forest habitats were analysed to test the hypotheses that fern species composition patterns were similar between elevational gradients, that total species richness of complete elevational gradients gradually declined due to changing climatic conditions with increasing distance from the Equator, and that the elevation of highest species richness gradually declined with increasing latitude.
Methods: We used plot-based elevational fern species richness surveys compiled from recent field work and own published studies, between 18° N and 18° S along the Andean mountain range, and compared the transects of patterns of species richness and composition, and distribution of taxa.
Results: Taxonomic composition was highly similar among tropical regions. Elevational richness patterns were symmetrically hump-shaped and overall richness was virtually equal along most of the tropical latitudinal gradient. In contrast, the subtropical localities at the edges of our study area, ca. 18° N and 18° S, showed strikingly different patterns from those in the tropical zone.
Conclusions: Within the tropics, there appears to be no latitudinal diversity gradient of ferns at the local scale. We suggest that, in tropical habitats, species richness of ferns at the local scale is limited by the number of species that can co-occur and that the available niche space is saturated.
Acknowledgements
We thank D. Torres, L. Cotugno, R. Güdel, E. Gortaire, W. Santillán, W. Pérez and people from the local communities for their invaluable help, support and enthusiasm during the fieldtrips, Guango lodge for allowing us to work in their private forest, and B. León, M. Sundue and A. Smith for their assistance in species identification. We are grateful for the institutional support of Ministerio del Ambiente of Ecuador (MAE) and for the permit to carry out this study, and to the staff at the herbarium QCA (Pontificia Universidad Católica del Ecuador). This study was funded by the Schweizer Nationalfonds (SNF) and the German Academic Exchange Service (DAAD). We gratefully acknowledge the correction of our wording and grammar by Guy Atchison.
Additional information
Notes on contributors
Laura Salazar
Laura Salazar is interested in the ecology and conservation of ferns in Ecuador and their diversity along elevational gradients.
Jürgen Homeier
Jürgen Homeier is a plant ecologist interested in the performance of tropical plants along environmental gradients.
Michael Kessler
Michael Kessler is interested in the diversity and biogeography of tropical montane plant and animal communities, with a special focus on ferns.
Stefan Abrahamczyk
Stefan Abrahamczyk is interested in diversity patterns and plant–animal interactions, especially of hummingbirds.
Marcus Lehnert
Marcus Lehnert is interested in plants systematics, biogeography and DNA barcoding, with a focus on cryptogams.
Thorsten Krömer
Thorsten Krömer is interested in diversity, ecology, systematics and conservation of vascular epiphytes, with a special focus on Bolivia and Mexico.
Jürgen Kluge
Jürgen Kluge is a biogeographer interested in the spatial patterns of plant distributions, especially along tropical elevational gradients.