Biology subjects

Vidya, T. N. C.

Publications and source records attributed to Vidya, T. N. C..

4 recordsLinked to original sources

bioRxiv2018

Overwhelming presence of non-food vegetation undermines the reliability of NDVI as a surrogate of forage abundance for a large herbivore in a tropical forest habitat

The use of remotely-sensed vegetation indices has increased in wildlife studies but field-based support for their utility as a measure of forage availability largely comes from open-canopy habitats. In this paper, we assessed whether the popular vegetation index, NDVI, actually represents forage availability for Asian elephants in a southern Indian tropical forest. We found that the number of food species was a small percentage of all plant species, and the abundance of food species compared to total species abundance varied across different vegetation categories. NDVI was not a good measure of food abundance in any vegetation category partly because of a) small to moderate proportional abundances of food species relative to the total abundance of all species in that category (herb and shrub categories), b) abundant overstorey vegetation resulting in low correlations between NDVI and food abundance despite a high proportional abundance of food species and a concordance between total abundance and food species abundance (graminoid category), and c) the relevant variables measured and important as food at the ground level (count and GBH) not being related to primary productivity (trees and recruits). NDVI had a negative relationship with the total abundance of graminoids, which represent a bulk of elephant and other herbivore diet, because of the presence of other vegetation types and canopy cover that positively explained NDVI. We also found that spatially interpolated total graminoid abundance modelled from field data outperformed NDVI in predicting total graminoid abundance, although interpolation models of food graminoid species abundance were not satisfactory. Our results reject the utility of NDVI as a surrogate of elephant forage abundance in tropical forests with multistorey vegetation, a finding that has implications for studies of other herbivores in such habitats.

ecology↗

bioRxiv2017

Effects of Social Organization, Trap Arrangement and Density, Sampling Scale, and Population Density on Bias in Population Size Estimation Using Some Common Mark-Recapture Estimators

Mark-recapture estimators are commonly used for population size estimation, and typically yield unbiased estimates for most solitary species with low to moderate home range sizes. However, these methods assume independence of captures among individuals, an assumption that is clearly violated in social species that show fission-fusion dynamics, such as the Asian elephant. In the specific case of Asian elephants, doubts have been raised about the accuracy of population size estimates. More importantly, the potential problem for the use of mark-recapture methods posed by social organization in general has not been systematically addressed. We developed an individual-based simulation framework to systematically examine the potential effects of type of social organization, as well as other factors such as trap density and arrangement, spatial scale of sampling, and population density, on bias in population sizes estimated by POPAN, Robust Design, and Robust Design with detection heterogeneity. In the present study, we ran simulations with biological, demographic and ecological parameters relevant to Asian elephant populations, but the simulation framework is easily extended to address questions relevant to other social species. We collected capture history data from the simulations, and used those data to test for bias in population size estimation. Social organization significantly affected bias in most analyses, but the effect sizes were variable, depending on other factors. Social organization tended to introduce large bias when trap arrangement was uniform and sampling effort was low. POPAN clearly outperformed the two Robust Design models we tested, yielding close to zero bias if traps were arranged at random in the study area, and when population density and trap density were not too low. Social organization did not have a major effect on bias for these parameter combinations at which POPAN gave more or less unbiased population size estimates. Therefore, the effect of social organization on bias in population estimation could be removed by using POPAN with specific parameter combinations, to obtain population size estimates in a social species.

ecology↗

bioRxiv2017

Niche construction in evolutionary theory: the construction of an academic niche?

In recent years, fairly far-reaching claims have been repeatedly made about how niche construction, the modification by organisms of their environment, and that of other organisms, represents a vastly neglected phenomenon in ecological and evolutionary thought. The proponents of this view claim that the niche construction perspective greatly expands the scope of standard evolutionary theory and that niche construction deserves to be treated as a significant evolutionary process in its own right, almost at par with natural selection. Claims have also been advanced about how niche construction theory represents a substantial extension to, and re-orientation of, standard evolutionary theory, which is criticized as being narrowly gene-centric and ignoring the rich complexity and reciprocity of organism-environment interactions. We examine these claims in some detail and show that they do not stand up to scrutiny. We suggest that the manner in which niche construction theory is sought to be pushed in the literature is better viewed as an exercise in academic niche construction whereby, through incessant repetition of largely untenable claims, and the deployment of rhetorically appealing but logically dubious analogies, a receptive climate for a certain sub-discipline is sought to be manufactured within the scientific community. We see this as an unfortunate, but perhaps inevitable, nascent post-truth tendency within science.

evolutionary biology↗

bioRxiv2017

Group size constraints may mask underlying similarities in social structure: a comparison of female elephant societies

We report on female Asian elephant social structure in Nagarahole and Bandipur National Parks (Kabini population), southern India, and examine the role of group size in affecting the outcome of social structure analysis in female elephants, which show high fission-fusion dynamics. Based on five years of data, we found the Kabini association network structured into highly modular communities that we call clans. We then modified the dataset (to obtain the Kabini 500-m dataset) to match sampling methods previously used in a study each of Asian (Uda Walawe) and African savannah (Samburu) elephants, so that network and association statistics could be compared across populations. Measures of association and network structure previously used were more similar amongst the Asian elephant populations compared to Samburu. The Samburu population formed a hierarchically-nested multilevel society whereas the Asian populations did not. However, we found hierarchical clustering levels in all three populations using Louvain community detection. Moreover, the average community sizes obtained through the Louvain method were not significantly different across populations, indicating basic similarities in social structure. Since fission-fusion dynamics allow for community members to form groups of different sizes, we examined the effect of average group size on association and network statistics. Higher average association index and degree, and lower average path length in Samburu compared to the Kabini 500-m dataset were explained by the larger average group size in Samburu. Thus, underlying similarities in the social networks of species showing fission-fusion dynamics may be obscured by differences in average group size.\n\nSignificance StatementVarious measures of associations and social network analyses have been used to compare social structures of different populations. We studied the social structure of female Asian elephants in a southern Indian population and compared it with those of a Sri Lankan Asian elephant population and an African savannah elephant population. We showed that, while there were social differences between the Asian and African savannah elephant populations using previous methods, there were basic similarities across all three populations using a method of network community detection. This discrepancy across analyses partly stemmed from differences in average group size between populations. Average group size in fission-fusion societies variously affected different association and network statistics, which has implications for inferences about social structure.

animal behavior and cognition↗