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Munoz F.,Montpellier University | Beeravolu C.R.,IRD Montpellier | Beeravolu C.R.,French National Institute for Agricultural Research | Beeravolu C.R.,Institute Francais Of Pondichery Ifp | And 2 more authors.
PLoS ONE | Year: 2013

Neutral community models have shown that limited migration can have a pervasive influence on the taxonomic composition of local communities even when all individuals are assumed of equivalent ecological fitness. Notably, the spatially implicit neutral theory yields a single parameter / for the immigration-drift equilibrium in a local community. In the case of plants, seed dispersal is considered as a defining moment of the immigration process and has attracted empirical and theoretical work. In this paper, we consider a version of the immigration parameter / depending on dispersal limitation from the neighbourhood of a community. Seed dispersal distance is alternatively modelled using a distribution that decreases quickly in the tails (thin-tailed Gaussian kernel) and another that enhances the chance of dispersal events over very long distances (heavily fat-tailed Cauchy kernel). Our analysis highlights two contrasting situations, where / is either mainly sensitive to community size (related to ecological drift) under the heavily fat-tailed kernel or mainly sensitive to dispersal distance under the thin-tailed kernel. We review dispersal distances of rainforest trees from field studies and assess the consistency between published estimates of/ based on spatially-implicit models and the predictions of the kernel-based model in tropical forest plots. Most estimates of / were derived from large plots (10-50 ha) and were too large to be accounted for by a Cauchy kernel. Conversely, a fraction of the estimates based on multiple smaller plots (1 ha) appeared too small to be consistent with reported ranges of dispersal distances in tropical forests. Very large estimates may reflect within-plot habitat heterogeneity or estimation problems, while the smallest estimates likely imply other factors inhibiting migration beyond dispersal limitation. Our study underscores the need for interpreting / as an integrative index of migration limitation which, besides the limited seed dispersal, possibly includes habitat filtering or fragmentation. © 2013 Munoz et al. Source

Venugopal P.D.,Group for Nature Preservation and Education GNAPE | Venugopal P.D.,Institute Francais Of Pondichery Ifp
Herpetological Journal | Year: 2010

The agamid lizards of the Western Ghats (WG) mountain chain in India are currently threatened by destruction of forests for conversion to plantations. Accurate information on the population status of the agamid lizards in modified habitats is needed for conservation and management considerations, but detailed data on population densities are currently not available. In this study, I estimated the population densities of agamid lizards in human-modified habitats of the Valparai plateau in the southern WG using distance sampling. Nineteen line transects (0.25 km each) in five study sites including abandoned vanilla, abandoned rubber, vanilla and tea plantations and a degraded evergreen forest patch were sampled a minimum of five times each. The population density (individuals/ha) of Calotes ellioti and Draco dussumieri in the vanilla plantation was estimated to be 8.95±2.09 and 1.25±0.40 respectively. The density of Psammophilus blanfordanus, which was detected only in tea plantations, was estimated as 3.13±1.02. Mean rate of encounters (animals/transect) for C. ellioti was highest in the vanilla plantation (1.83, SE=0.41). For D. dussumieri, the mean encounter rates were identical in the vanilla plantation (0.80, SE=0.21) and the abandoned rubber plantations (0.80, SE=0.4). The encounter rates of C. ellioti in the vanilla plantation were higher than those in rainforest fragments in the Valparai plateau. This study helps us understand the role of modified habitats in supporting populations of endemic agamid lizards. Source

Renard Q.,Institute Francais Of Pondichery Ifp | Plissier R.,Institute Francais Of Pondichery Ifp | Plissier R.,IRD Montpellier | Ramesh B.R.,Institute Francais Of Pondichery Ifp | Kodandapani N.,Institute Francais Of Pondichery Ifp
International Journal of Wildland Fire | Year: 2012

Forest fires are a recurrent management problem in the Western Ghats of India. Although most fires occur during the dry season, information on the spatial distribution of fires is needed to improve fire prevention. We used the MODIS Hotspots database and Maxent algorithm to provide a quantitative understanding of the environmental controls regulating the spatial distribution of forest fires over the period 200307 in the entire Western Ghats and in two nested subregions with contrasting characteristics. We used hierarchical partitioning to assess the independent contributions of climate, topography and vegetation to the goodness-of-fit of models and to build the most parsimonious fire susceptibility model in each study area. Results show that although areas predicted as highly prone to forest fires were mainly localised on the eastern slopes of the Ghats, spatial predictions and model accuracies differed significantly between study areas. We suggest accordingly a two-step approach to identify: first, large fire-prone areas by paying special attention to the climatic conditions of the monsoon season before the fire season, which determine the fuels moisture content during the fire season; second, the most vulnerable sites within the fire-prone areas using local models mainly based on the type of vegetation. © IAWF 2012. Source

Ramesh B.R.,Institute Francais Of Pondichery Ifp | Venugopal P.D.,Institute Francais Of Pondichery Ifp | Venugopal P.D.,University of Maryland University College | Pelissier R.,Institute Francais Of Pondichery Ifp | And 4 more authors.
Biotropica | Year: 2010

We describe the mesoscale floristic patterns in the central Western Ghats of Karnataka, India, through combined analysis of woody species abundance and stand structure data from a network of ninety-six 1-ha sampling plots spread across 22,000 km2. A total of 61,906 individuals (≥10 cm gbh) comprising 400 plant species from 254 genera and 75 families were recorded. Euphorbiaceae, Rubiaceae, Lauraceae and Moraceae families constituted 23.5 percent of the total number of species encountered. The relative dominance of species was skewed with Poecilonueron indicum, Xylia xylocarpa, Terminalia tomentosa and Anogeissus latifolia being dominant in some plots. Correspondence analysis (CA) and a nonmetric multidimensional scaling (NMDS) of plots by species abundances data showed similar arching patterns, with significant correlation between the first axis of CA and NMDS (r=0.77). Hierarchical clustering of plot scores along the three first CA axes resulted in splitting the plots into five different categories that broadly reflect the major bioclimatic features of the region. A multiscale bootstrapping test indicated that categorization of the wettest (wet evergreen group 1 and 2) and driest (dry deciduous) groups were robust (P<0.05 with 1000 bootstraps), while the remaining two transitional groups were uncertain (P=0.12 and 0.26 for moist deciduous and semi-evergreen group, respectively). Principal component analysis revealed that plots with similar floristic composition can encompass contrastingly different physiognomic structures (canopy cover, canopy height and mean tree diameter) probably in relation to their levels of disturbance. Observed patterns in the floristic composition have been discussed in the light of the complex interaction between the bioclimatic and disturbance regimes that characterize the region. © 2010 The Author(s). Journal compilation © 2010 by The Association for Tropical Biology and Conservation. Source

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