Ecology and Evolution Group
Ecology and Evolution Group
Chakravarthy D.,National Center for Biological science |
Chakravarthy D.,Wildlife Conservation Society |
Ratnam J.,Ecology and Evolution Group
Tropical Conservation Science | Year: 2015
Civets are considered potentially important seed dispersers in tropical forests of Asia, but relatively little is known about spatial patterns of dispersal and post-dispersal fates of civet-dispersed seeds. We explored these aspects of civet seed dispersal for two tree species Vitex glabrata (Lamiaceae), also known as smooth chaste tree and Prunus ceylanica (Rosaceae), in Pakke Tiger Reserve, a tropical forest reserve in north-east India. Pakke has five known species of viverrids: small Indian civet (Viverricula indica), large Indian civet (Viverra zibetha), common palm civet (Paradoxurus hermaphroditus), masked palm civet (Paguma larvata) and the binturong (Arctictis binturong). For both tree species, civets as a group dispersed seeds (100% of scats that we found) within 50 meters from fruiting trees and deposited seeds onto multiple substrates including tree branches, forest floor, and fallen logs. However, the distribution of seeds among substrates differed for the two tree species: while most seeds of V. glabrata (> 90%) were deposited onto canopy branches and fallen logs, the majority of P. ceylanica seeds (> 70%) were deposited on the forest floor. For both tree species, seeds deposited on logs experienced higher seed predation than seeds on the forest floor, especially when local seed densities (number of seeds in 1m2 area around the scat and in the scat) were high. Further, seed viability of P. ceylanica was significantly lower on logs (~35%) than on the forest floor (~65%). For both tree species, civets neither dispersed seeds far from fruiting trees nor to sites where seeds experienced either low predation or high survival, suggesting that while civets were legitimate dispersers, they were not especially effective. © Dayani Chakravarthy and Jayashree Ratnam.
Ratnam J.,Ecology and Evolution Group |
Ratnam J.,University of Leeds |
Bond W.J.,University of Cape Town |
Fensham R.J.,Queensland Herbarium |
And 8 more authors.
Global Ecology and Biogeography | Year: 2011
Savannas are defined based on vegetation structure, the central concept being a discontinuous tree cover in a continuous grass understorey. However, at the high-rainfall end of the tropical savanna biome, where heavily wooded mesic savannas begin to structurally resemble forests, or where tropical forests are degraded such that they open out to structurally resemble savannas, vegetation structure alone may be inadequate to distinguish mesic savanna from forest. Additional knowledge of the functional differences between these ecosystems which contrast sharply in their evolutionary and ecological history is required. Specifically, we suggest that tropical mesic savannas are predominantly mixed tree-C4 grass systems defined by fire tolerance and shade intolerance of their species, while forests, from which C4 grasses are largely absent, have species that are mostly fire intolerant and shade tolerant. Using this framework, we identify a suite of morphological, physiological and life-history traits that are likely to differ between tropical mesic savanna and forest species. We suggest that these traits can be used to distinguish between these ecosystems and thereby aid their appropriate management and conservation. We also suggest that many areas in South Asia classified as tropical dry forests, but characterized by fire-resistant tree species in a C4 grass-dominated understorey, would be better classified as mesic savannas requiring fire and light to maintain the unique mix of species that characterize them. © 2011 Blackwell Publishing Ltd.
Krishnaswamy J.,Ashoka Trust for Research in Ecology and the Environment ATREE |
Vaidyanathan S.,Foundation for Ecological Research |
Rajagopalan B.,University of Colorado at Boulder |
Bonell M.,University of Dundee |
And 4 more authors.
Climate Dynamics | Year: 2014
The El Nino Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) are widely recognized as major drivers of inter-annual variability of the Indian monsoon (IM) and extreme rainfall events (EREs). We assess the time-varying strength and non-linearity of these linkages using dynamic linear regression and Generalized Additive Models. Our results suggest that IOD has evolved independently of ENSO, with its influence on IM and EREs strengthening in recent decades when compared to ENSO, whose relationship with IM seems to be weakening and more uncertain. A unit change in IOD currently has a proportionately greater impact on IM. ENSO positively influences EREs only below a threshold of 100 mm day-1. Furthermore, there is a non-linear and positive relationship between IOD and IM totals and the frequency of EREs (>100 mm day-1). Improvements in modeling this complex system can enhance the forecasting accuracy of the IM and EREs. © 2014 Springer-Verlag Berlin Heidelberg.
Kohli M.,Wildlife Conservation Society |
Sankaran M.,Ecology and Evolution Group |
Suryawanshi K.R.,Nature Conservation Foundation |
Mishra C.,Nature Conservation Foundation
Animal Behaviour | Year: 2014
Lean season foraging strategies are critical for the survival of species inhabiting highly seasonal environments such as alpine regions. However, inferring foraging strategies is often difficult because of challenges associated with empirically estimating energetic costs and gains of foraging in the field. We generated qualitative predictions for the relationship between daily winter foraging time, body size and forage availability for three contrasting foraging strategies including time minimization, energy intake maximization and net energy maximization. Our model predicts that for animals employing a time minimization strategy, daily winter foraging time should not change with body size and should increase with a reduction in forage availability. For energy intake maximization, foraging time should not vary with either body size or forage availability. In contrast, for a net energy maximization strategy, foraging time should decrease with increase in body size and with a reduction in forage availability. We contrasted proportion of daily time spent foraging by bharal, Pseudois nayaur, a dimorphic grazer, across different body size classes in two high-altitude sites differing in forage availability. Our results indicate that bharal behave as net energy maximizers during winter. As predicted by the net energy maximization strategy, daily winter foraging time of bharal declined with increasing body size, and was lower in the site with low forage availability. Furthermore, as predicted by our model, foraging time declined as the winter season progressed. We did not find support for the time minimizing or energy intake maximizing strategies. Our qualitative model uses relative rather than absolute costs and gains of foraging which are often difficult to estimate in the field. It thus offers a simple way to make informed inferences regarding animal foraging strategies by contrasting estimates of daily foraging time across gradients of body size and forage availability. © 2014 The Association for the Study of Animal Behaviour.