|Al Gentry Award-Best Poster 2010|
Best Student Poster Presentation
Abstract. Spatial point patterns are the footprints of underlying biological processes. For plants, seed arrival patterns vary depending upon their dispersal mode and form the primary matrix upon which further forces shape spatial patterns. To address the relevance of seed dispersal to plant community structure, we examined linkages between dispersal mode and spatial aggregation of trees for a tropical dry forest community on the Mudumalai Forest Dynamics Plot (50 ha). Spatial patterns were examined via the pair correlation function (Ω statistic) and statistics derived from cluster models (Matern process). Considering only trees that had ≥ 10 individuals (48 species), we found that tropical dry forest trees exhibited extensive spatial aggregation. The degree of spatial aggregation at Mudumalai was remarkably similar to wet forests in tropical Asia. Species with limited-dispersal (mechanically-dispersed species) were more aggregated than those with more frequent long-distance dispersal (animal-dispersed species) at smaller spatial scales (< 50 m). Animal-dispersed species had larger cluster radius, with bird-dispersed species having the largest radii. These results are in concordance with Siedler & Plotkin (2006) and Li et al. (2009) who find that mechanically-dispersed species are more aggregated than animal-dispersed species. These results demonstrate that seed dispersal has a strong influence on the spatial patterning of plant communities.
More about Soumya Prasad's study:
Large herbivorous mammals are known to be important seed dispersers and predators, and also important drivers of sapling and adult tree mortality. In tropical Asia, large fauna have witnessed tremendous declines in their abundances and ranges in historical times. Thus, plants which depend upon large fauna for long distance dispersal might have limited ability to move across fragmented landscapes under changing climates. However, very little is understood about seed dispersal by large mammals or about seed dispersal characteristics of tropical dry forests which support among the highest biomass of large mammals.
Soumya Prasad is in the process of defending her thesis on seed dispersal in tropical dry forests of southern India. Her work has focused on understanding the role of ruminants in seed dispersal, and also on characterizing seed dispersal for a tropical dry forest plant community located on the Mudumalai Forest Dynamics Plot (50 ha; annual rainfall = 1200 ± 103 mm). Mudumalai is located within an extensive tropical dry forest landscape in southern India (> 5000 sq.km) and harbors an intact, abundant and diverse large mammalian assemblage.
Soumya has characterized dispersal modes and fruit morphology for nearly 90% of woody plant community on the Mudumalai plot. For this, she used techniques such as camera traps and tree watches. She also measured fruit and seed traits for this plant community. Soumya linked the information on dispersal modes and fruit traits with the spatial patterns of the plant species, using the long-term dataset for the Mudumalai plot maintained by her colleagues H.S. Dattaraja, H.S. Suresh and R. Sukumar. Since 1988, all stems over 1 cm DBH have been mapped and monitored annually at Mudumalai by the IISc team. Using spatial point process statistics, Soumya found that the degree of spatial aggregation exhibited by trees on the Mudumalai plot varied with seed dispersal mode. These results imply that seed dispersal has a strong influence on the spatial structure of plant communities. Demonstrating these linkages between seed dispersal and plant community structure, at a site with an intact frugivore assemblage, helps address long-standing debates on the relevance of dispersal to long-lived plant communities.
Illustrations (from top to bottom): Soumya Prasad ; the dry tropical forest landscape at Mudumalai ; Soumya Prasad setting up camera traps to identify frugivores at Mudumalai ; Camera trap records of frugivory at Mudumalai: (a) Asian elephant feeding on Careya arborea; (b) Chital deer feeding on Phyllanthus emblica; (c) Sloth bear feeding on Ziziphus mauritiana.
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