Influence of check dams on the activity pattern and morphometric traits of overwintering tadpoles in the Western Himalaya

Delaying metamorphosis in low-temperature conditions by anuran larvae known as ‘overwintering’ have been poorly studied, especially in terms of habitat ecology and behavioural aspects. The present study investigates some of the ecological aspects of overwintering tadpoles of the genus Nanorana in the Western Himalaya in an anthropogenically modified stream where check dams have altered the natural habitat, which can potentially influence the amphibian ecology. We present insights on the influence of check dams on the tadpole activity pattern and morphometric traits useful in the conservation planning of the narrowly distributed and understudied species, which are most sensitive to habitat modification. We monitored natural and modified pool habitats in the stream during winter and post-winter seasons based on the visual density of tadpoles to assess the diurnal and seasonal emergence pattern with associated habitat variables. Generalized Linear Mixed Modeling (GLMM) was used to understand the influence of various habitat variables on the visible density of tadpoles. Fine-scale temporal scan sampling of tadpoles was carried out to complement the understanding of the visible density variation and analyzed using circular plots and activity overlap estimation. Variation in morphometric traits was assessed using field morphometry and photogrammetry. Mean tadpole visible density at nighttime was higher in modified pools than natural pools during winter, but there was no statistically significant difference during daytime; the nocturnal pattern changed in the post-winter, where visible density was higher in natural pools. Tadpole visible density was influenced by the interaction of mean canopy cover with water temperature, instream cover items richness, mean canopy cover percentage, water temperature, leaf litter depth, water velocity and interaction of time of the day with pool modification. Tadpole activity patterns varied significantly between pool types during post-winter, where modified pool population increased daytime activity and thus the activity overlap reduced from winter (90.8%) to post-winter (64.5%). During both seasons, the mean body size of the natural pool population was significantly lower than the modified pool population; mean relative tail length was significantly lower in natural pools during post-winter; mean tail depth was significantly lower in natural pools during winter. The study presents evidence of the influence of anthropogenic habitat alterations on behaviour and morphometric traits of overwintering tadpoles, which needs to be further investigated. We also discuss the variation in nocturnal emergence, habitat selection and morphometric trait patterns in the modified habitat, potential reasons and similar behaviour in other aquatic organisms, which need to be considered while developing conservation strategies for the overwintering tadpoles in the region.