FSD 2010 - Muller-Landau

5th International Symposium-Workshop on Frugivores and Seed Dispersal (1985-2010)

Helene C. Muller-Landau

Smithsonian Tropical Research Institute, Apartado Postal 084303092, Balboa, Ancon, Panamá, República de Panamá.

mullerh(a)si.edu

Activities

My research is broadly concerned with the patterns, causes and consequences of plant diversity. The patterns of interest include the diversity of ways in which plant species make a living, the diversity of plant species that can coexist within the same area, and the diversity of plant communities around the globe. In terms of causes I examine proximate correlates such as climatic factors and functional traits as well as the ultimate causes deriving from selective forces, physiological constraints and underlying tradeoffs. One major focus of my research has been seed dispersal. I’ve analyzed interspecific and interannual differences in seed production and seed dispersal of tropical tree species, examined the relative importance of seed dispersal to seedling recruitment in tropical forests, used models to investigate the consequences of different seed dispersal strategies for community-level patterns in general, and conducted theoretical studies of seed dispersal evolution. I believe that a better, more mechanistic understanding of plant communities is urgently needed in order for us to accurately predict long-term impacts of growing anthropogenic influences - especially in communities such as tropical forests that are dominated by long-lived organisms. I hope that my research will not only contribute to such a basic ecological understanding of plant communities, but also enhance our ability to assess and manage human influences on them.

Abstract

The tolerance-fecundity tradeoff and the maintenance of seed size diversity: theory and tests in a tropical forest.

Helene Muller-Landau, S. Joseph Wright, Osvaldo Calderon, Andres Hernandez

Smithsonian Tropical Research Institute, Smithsonian Institution

Seed size commonly varies by five to six orders of magnitude among coexisting plant species, a pattern ecologists have long sought to explain. Higher competitive ability combined with strong competitive asymmetry can in theory allow coexistence through a competition-colonization tradeoff, but empirical evidence is inconsistent with this mechanism. I hypothesize that seed size diversity is maintained by a tradeoff between stress-tolerance (ability to recruit in hazardous sites) and fecundity. I present a simple, new model of this tolerance-fecundity tradeoff. Analyses of this model show that the tolerance-fecundity tradeoff enables stable coexistence of large numbers of species in heterogeneous habitats. Under this mechanism, the more tolerant species win all regeneration sites that are highly stressful and some of those that are less stressful, while the more fecund species win most but not all of the less stressful sites. I test the assumptions and predictions of the tolerance-fecundity and competition-colonization models using empirical data from a moist tropical forest on Barro Colorado Island Panama. The results show that the tolerance-fecundity model provides a far better fit than the competition-colonization model. Altogether, theory and empirical evidence suggest that the tolerance-fecundity tradeoff is the best explanation for the maintenance of diversity of seed size within plant communities.

Recent References

Muller-Landau, H. C., S. J. Wright, O. Calderon, R. Condit, and S. P. Hubbell. 2008. Interspecific variation in primary seed dispersal in a tropical forest. Journal of Ecology 96:653-667.

Jones, F. A. and H. C. Muller-Landau. 2008. Combining inverse modeling, seed trap data, and genetic identification of parent trees to better estimate seed dispersal. Journal of Ecology 96:642-652.

Muller-Landau, H. C. 2008. Colonization-related tradeoffs in tropical forests and their role in the maintenance of plant species diversity. Pages 182-195 in Tropical Forest Community Ecology. W. P. Carson and S. A. Schnitzer, editors. Blackwell Scientific.

Muller-Landau, H. C. 2007. Predicting the long-term effects of hunting on plant species composition and diversity in tropical forests. Biotropica 39 (3):372-384.

Beckman, N. and H. C. Muller-Landau. 2007. Differential effects of hunting on pre-dispersal seed predation, primary dispersal and secondary seed removal of two tropical tree species. Biotropica 39 (3):328-339.

Former FSD presentations

Muller-Landau, H. C. and F. R. Adler. 2007. How seed dispersal affects interactions with specialized natural enemies and their contribution to diversity maintenance. Pages 407-426 in Seed Dispersal: Theory and its Application in a Changing World. A. J. Dennis, E. W. Schupp, R. J. Green, and D. W. Westcott, editors. Wallingford, UK: CAB International.

Muller-Landau, H. C., S. J. Wright, O. Calderón, S. P. Hubbell, and R. B. Foster. 2002. Assessing recruitment limitation: concepts, methods and examples for tropical forest trees. Pages 35-53 in Seed Dispersal and Frugivory: Ecology, Evolution and Conservation. J. Levey, W. R. Silva and M. Galetti, editors. Oxfordshire, UK: CAB International.