Biology subjects

Athreya, R.

Publications and source records attributed to Athreya, R..

8 recordsLinked to original sources

bioRxiv2026

Differences in functional guild responses to elevation and topography in Himalayan ant communities

We investigated the influence of small-scale topographic and associated microclimatic drivers on the elevational patterns of functional alpha and beta diversity in ant communities of eastern Himalayas. Ants were sampled along three elevational transects spanning [~]1000-2000 m on two nearby mountain slopes, but differing in aspect, inclination and summit height. Ant genera were quantified at the quadrat level, yielding an abundance of 3090 genus-quadrats (from 22577 individuals in 1215 quadrats), almost evenly split between the two mountain slopes. Each ant was assigned to guilds along functional axes of thermal niche, trophic position and competitive abilities. Comparative analyses of functional diversity profiles along the two mountain slopes revealed no differences in the composite multi-guild alpha and beta diversity but significant differences amongst individual guild profiles. Seven of the eleven functional guilds showed strong elevational trends along the steeper north-facing slope, compared to only two of eleven on the shallower south-facing slope. These results indicate that similar functional space can be maintained despite taxonomic turnover within guilds or shifts in their relative abundances highlighting the influence of fine-scale topographic variation on community assembly. Alternatively, these findings demonstrate that the pattern of multivariate functional diversity across elevation does not necessarily provide an understanding of changing composition of the communities therein.

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bioRxiv2025

Width of Range Overlap in Congeneric Bird Species Pairs Along An Elevational Gradient In The Eastern Himalayas

We investigated the distribution of range overlap between contiguous pairs of congeneric bird species along a 200-2800 m elevational gradient in the eastern Himalayas. Over a 3-year field survey between from 2012 to 2014 we recorded 15867 birds comprising 245 species in elevational intervals of 50 m. From this data set, we selected 107 congeneric pairs and fit a logistic curve to the abundance ratio versus elevation data to estimate the width of transition zone over which the species ratio changes from 90% to 10%. We found that the distribution of the transition widths range from < 50 m (about a quarter of the pairs) to more than 500 m. This lack of physical exclusion suggests that there is considerable niche separation between closely related species. For a smaller subset of species pairs with better quality data and model fit we investigated the correlation between the degree of range overlap (transition width) on the one hand, and phylogenetic distance and morphological trait difference on the other. We found a significant correlation with mass, beak width and wing size, but not with tarsus length, beak length and phylogenetic distance. This suggests that mass beak width and wing size may play an important role in niche differentiation in the area.

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bioRxiv2023

Tropical montane gradients elucidate the contributions of functional traits to competitive and environmental fitness

Functional traits can be classified as alpha or beta, based on their relative importance in determining a species competitive and environmental fitness, respectively. However, the link between a trait and its contribution to a particular aspect of fitness is not always straight-forward. We investigated phylogenetic and functional diversity for bird communities along a 200-2800 m elevational transect in the eastern Himalayas. We hypothesized that beta traits, associated with environmental tolerances, would exhibit a directional change in mean values, while alpha traits, linked to competitive strategies, would show a decrease in dispersion with elevation. Our findings showed that most functional traits exhibited a decrease in dispersion with elevation. However, surprisingly, the mean values of these traits also exhibited a significant relationship with elevation, suggesting their involvement in both competitive and environmental fitness. Furthermore, we observed that morphological traits, traditionally considered beta traits associated with environmental tolerance, were influenced more strongly by resource availability and habitat structure rather than aspects of temperature or air density. These results challenge the simplistic classification of traits as either alpha or beta. We suggest that future studies should carefully analyze the variation in mean values and dispersion of individual traits before assigning them solely to a particular category of fitness. The results contribute to a broader understanding of the complex interactions between functional traits, fitness, and environmental conditions in Himalayan bird communities.

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bioRxiv2022

Testing a theoretical framework for the environment-species abundance paradigm: a new approach to the Abundant Centre Hypothesis

The linkage between environment, a species fitness and its abundance is central to the theory of evolution. So far, all studies of this linkage have been heuristic and empirical due to an inability to determine fitness either experimentally (independent of abundance) or theoretically (from species-environment interaction). One category of such studies involves the Abundant Centre Hypothesis which posits that a species abundance rises to a maximum at the centre of its range. We argue that the confusing mix of results from ACH studies arises from ignoring the central premise that the abundance distribution cannot be independent of the environment. First, we employed a theoretical framework to identify an environmental context (an elevational transect; 200-2800 m in the eastern Himalayas) likely to favour ACH. We then improved upon some previously identified conceptual and methodological shortcomings of ACH studies. Using systematically collected bird data (245 species; 15867 records) from that transect we found that the community average abundance profile is symmetric, as expected by ACH. Notwithstanding which, the abundance profiles of individual species showed a small degree of asymmetry which was correlated with elevation. This elevational dependence may be due to the hard elevational limits at the lower and upper ends of the mountain, as expected from theoretical considerations. We also showed that the average abundance profile shape is close to gaussian, while ruling out uniform and inverted-quadratic shapes. This work demonstrates that selecting a particular category of environmental contexts can help in integrating theoretical tools into a field dominated by empirical studies. Such a union should spur the development of more detailed and testable theoretical models for better insights in an important field.

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bioRxiv2021

Taxonomic scale dependency of Bergmann's patterns: A cross-scale comparison of hawkmoths and birds along a tropical elevational gradient

Bergmanns rule predicts a larger body size for endothermic organisms in colder environments. The multiplicity of patterns and processes is expected because body size and temperature are two most fundamental factors on which many physiological, ecological and evolutionary processes depend, affecting all levels of biological organization, from individuals to communities. The confounding results from previous studies may be due to the differences in taxonomic (intraspecific, interspecific and community) and spatial (latitudinal vs elevational) scales. We compared Bergmanns patterns for endotherms (Aves) and ectotherms (Lepidoptera: Sphingidae) along a same 2.6 km elevational transect in the eastern Himalayas. Using a large data spanning 3,302 hawkmoths (76 morpho-species) and 15,746 birds (245 species), we compared the patterns at the intraspecific (hawkmoths only), interspecific and community scales. At the interspecific scale, we account for phylogenetic non-independence in body mass by using a heirarchical linear mixed effects model for hawkmoths, and a phylogenetic generalised least squares model for birds. We assess the importance of using abundance-weighted metrics at the community scales, after accounting for spatial auto-correlation in communities. Hawkmoths exhibited positive Bergmanns pattern at the intraspecific and abundance-weighted community scale. Intraspecific variation accounted for a substantial 33% variation at the community level. Contrary to this, birds exhibited a strong converse-Bergmanns pattern at interspecific and community scales, both with- and without-abundance. Overall, all metrics which incorporate local traits and/or species abundances show stronger correlations than when this information is lacking. The multiplicity of patterns at a single location provides the opportunity to disentangle the relative contribution of individual- and species-level processes by integrating data across multiple nested taxonomic scales for the same taxa. We suggest that future studies of Bergmanns patterns should explicitly address taxonomic- and spatial-scale dependency, with species relative abundance and intraspecific trait variation as essential ingredients especially at short elevational scales.

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bioRxiv2019

Functional randomness despite high taxonomic turnover across an elevational gradient in a global biodiversity hotspot: A case study of hawkmoths and birds

AimWe examined the patterns and processes of taxonomic and functional dissimilarities for two disparate organismal groups (ectothermic hawkmoths and endothermic birds) across a broad tropical elevational gradient. LocationEaglenest Wildlife Sanctuary (northeast India), eastern Himalayan global biodiversity hotspot. Taxon4,731 hawkmoths; 15,387 birds MethodsTurnover and nestedness components for taxonomic and functional dissimilarities were obtained using the methods developed by Baselga (2013) and Leprieur et al., 2012. We used Generalized Dissimilarity Modeling (GDM) with geographic distance, contemporary and historic climatic variables to assess the relative importance of dispersal and environmental processes in determining the beta diversity. Functional redundancy (FRed) was calculated for both organismal groups using the Simpsons diversity indices. Null modeling was used to determine randomness in species and trait distributions. ResultsTurnover dominated taxonomic and functional dissimilarities, however the contribution of nestedness was considerably higher to the latter. Overall, the rate of dissimilarity with distance, for both facets of diversity, was significantly higher for birds, with stronger contributions of geographic distance and historic climate; whereas the hawkmoth dissimilarities were strongly correlated with only contemporary climate. Taxonomic dissimilarities deviated significantly from null, whereas functional dissimilarities exhibited high redundancy and randomness. Main ConclusionsOverall, our results suggest that while the drivers of beta-diversity exhibit idiosyncrasy and taxon-specificity; for a given taxa, they are consistent across the two facets of dissimilarity. More importantly, regardless of the principal predictor, the net result was that of high taxonomic turnover, which is de-coupled to a high degree from functional turnover in these tropical ecosystems. The large redundancy in trait values, despite high species turnover, indicates functional resilience of these tropical communities. The consistency of this pattern, across two disparate organismal groups, is suggestive of a key mechanism in which tropical communities may retain functionality of ecosystems in a changing environment.

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bioRxiv2019

Intraspecific trait variability and community assembly in hawkmoths (Lepidoptera: Sphingidae) across an elevational gradient in the eastern Himalayas, India

O_LIRecent progress in functional ecology has advanced our understanding of the role of intraspecific (ITV) and interspecific (STV) trait variation in community assembly across environmental gradients. Studies on plant communities have generally found STV as the main driver of community trait variation, whereas ITV plays an important role in determining species co-existence and community assembly. However, similar studies of faunal taxa, especially invertebrates, are very few in number.\nC_LIO_LIWe investigated variation of hawkmoth (Lepidoptera: Sphingidae) traits along an environmental gradient spanning 2600 m in the eastern Himalayas and its role in community assembly, using the morpho-functional traits of body mass (BM), wing loading (WL) and wing aspect ratio (AR).\nC_LIO_LIWe employ the recently proposed T-statistics to test for non-random assembly of hawkmoth communities and the relative importance of the two opposing forces for trait divergence (internal filters) and convergence (external filters).\nC_LIO_LICommunity-wide trait-overlap decreased for all three traits with increasing environmental distance, suggesting the presence of elevation specific optimum morphology (i.e. functional response traits). Community weighted mean of BM and AR increased with elevation. Overall, the variation was dominated by species turnover but ITV accounted for 25%, 23% and <1% variability of BM, WL and AR, respectively. T-statistics, which incorporates ITV, revealed that elevational communities had a non-random trait distribution, and that community assembly was dominated by internal filtering throughout the gradient.\nC_LIO_LIThis study was carried out using easily measurable morpho-traits obtained from calibrated field images of a large number (3301) of individuals. That these also happened to be important environmental response traits resulted in a significant signal in the metrics that we investigated. Such studies of abundant and hyperdiverse invertebrate groups across large environmental gradients should considerably improve our understanding of community assembly processes.\nC_LI

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bioRxiv2019

High throughput photogrammetric measurement of morphological traits in free-ranging phototropic insects

O_LIRemote measurement of morphological traits in free-ranging animals is very useful for many studies, but such non-invasive photogrammetric methods are limited to large mammals and have yet to be successfully applied to insects which dominate terrestrial ecosystem diversity and dynamics. Currently, insect traits are measured using collected specimens; the process of collection and maintenance of specimens can impose a heavy and unnecessary cost when such specimens themselves are not needed for the study.\nC_LIO_LIWe propose a rapid, simple, accurate, and semi-automated method for high-throughput morphometric measurements of phototropic insects from shape and size calibrated digital images without having to collect a specimen. The method only requires inexpensive, off-the-shelf, consumer equipment and freely available programming (R) and image processing (ImageMagick) tools.\nC_LIO_LIWe demonstrate the efficacy of the method using a data set of 3675 images of free-ranging hawkmoths (Lepidoptera: Sphingidae) attracted to a light screen. Comparison of trait values from a subset of these images with direct measurements of specimens using a scale showed a high degree of correspondence. We have also identified several error metrics which help in assessing the method in an objective manner.\nC_LIO_LIAlthough this method was developed for nocturnal phototropic insects, it can be used for any other (small) animal that can be imaged on a simple graph paper. While this technique will be generally useful for a variety of studies of insect traits, we suggest that it is particularly suited as a commensal on multi-epoch and multi-location population monitoring of insects in the context of climate and land-use change, where repeated sampling obviates the necessity of collecting specimen every time. It will help in accumulating a large amount of reliable trait data on hundreds of thousands of individual insects without an overwhelming expenditure on collection, handling, and maintenance of specimens.\nC_LI

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