Theses and Dissertations

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Author: search.filters.author.Dutta, SutirthaStart date: 2020

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    Heat Hardening and the Influence of Thermal Heterogeneity of Habitat on Aboveground Activity in Spiny-tailed Lizard (Saara hardwickii)
    (Wildlife Institute of India, Dehradun, 2025) Vassa, Chirag Nimish; Dutta, Sutirtha; Kher, Varun
    Human induced climate change has challenged the persistence of many organisms at different biotic levels and alter their interaction with the environment. Ectotherms are particularly vulnerable to anthropogenic climate change due to their reliance on external environment for various life history traits. Thermoregulatory behaviour is often used by many ectotherms especially reptiles to regulate their body temperature and will be crucial in imminent future with intensification of climate change. Although behavioural thermoregulation is widely studied, but studies looking at influence of thermal heterogeneity of a habitat on aboveground activity is limited. Moreover, with escalation in global warming ectotherms might have to rely on another mechanism in addition to thermoregulatory behaviour to combat the effect. One such physiological mechanism is heat hardening a quick response to thermal tolerance that temporarily enhances thermal tolerance, allowing lizards to withstand greater temperatures for a short period. Despite its importance very limited data is available for heat hardening capacity in reptiles. This study examined the influence of thermal heterogeneity of a habitat on aboveground activity in spiny-tailed lizard (Saara hardwickii) and assessed their heat hardening capacity. Additionally, trade-off hypothesis was also tested which has been recently proposed to explain the dynamics of thermal tolerance plasticity. I found positive influence of habitat heterogeneity on aboveground activity of the lizard. However, individuals in both the conditions spent similar amount of time in different behaviours. With respect to phenotypic plasticity i.e. heat hardening, I did not find any evidence of thermal tolerance plasticity during my experimental trials but few individuals did show increased thermal tolerance implying intraspecific variation. Additionally, the results from heat hardening experiments found no support for trade-off hypothesis. My study underscores the importance of habitat heterogeneity for species like spiny-tailed lizard which thrives in extreme temperatures. Furthermore, Lack of phenotypic plasticity in thermal tolerance increases it’s risks to overheating and dependency on behavioural thermoregulation.
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    Investigating the roles of fire and cattle grazing on vegetation, invasives, and their implications on Bengal Florican (Houbaropsis bengalensis) breeding habitat use
    (Wildlife Institute of India, Dehradun, 2025) Thammaiah, Aadya; Nath, Anukul; Dutta, Sutirtha
    Grasslands, though ecologically important, are often overlooked in conservation. These ecosystems are shaped by land-use practices such as fire and grazing, which can help maintain open habitats when appropriately applied. Mismanagement, however, can promote invasive species, threatening native biodiversity. The Bengal Florican (Houbaropsis bengalensis), a critically endangered grassland specialist, highlights the need for targeted conservation in such systems. This study assessed the combined effects of fire and grazing on grassland plant communities, including invasive plants, and Bengal Florican breeding habitat selection in Manas National Park. 2. For the vegetation survey, I selected study sites along gradients of fire frequency (based on 23 years of FIRMS data) and grazing intensity (using distance from human settlements as a proxy). At each site, I used circular plots to sample vegetation and assess species composition. To examine drivers of plant and invasive species abundance, I applied linear models (LMs), incorporating key covariates such as distance to forests, roads, and climate moisture index (CMI). I then used Indicator Species Analysis (ISA) to identify species associated with different fire-grazing regimes. I also performed a Linear Discriminant Analysis (LDA) to assess how well vegetation communities and structure could distinguish between different fire conditions. For Bengal Florican habitat assessment, I quantified vegetation structure visually and insect abundance using sweep netting in display and paired control sites. I used Binomial Generalised 8 Linear Models (GLMs) and Conditional Logistic Regression modelling to evaluate habitat selection by the species. 3. Tree and sapling densities peaked under intermediate fire, whereas shrubs and herbs had the highest density in low fire regimes. Saplings, shrub as well as grass cover peaked in low grazing regimes, but herb cover was highest in low grazing conditions. Among invasives, Leea asiatica and Chromolaena odorata were more frequent in intermediate fire, while Mikania micrantha and Ageratum conyzoides thrived under low fire. Grazing showed significant effects only on Mikania micrantha. ISA identified native species such as Dillenia pentagyna as indicators of low grazing and Cymbopogon flexuosus for medium and high fire regimes, among others. Bengal Florican selected sites with higher insect abundance, shorter vegetation (25–50 cm), with low (outside the PA) and high fire frequency (within the PA). 4. My results showed that plant communities showed species-specific responses to fire and grazing conditions. Bengal Florican habitat-use reflected a preference for open, short grasslands with high insect abundance. In conclusion, my study found that effective conservation requires tailored fire and grazing strategies that sustain open structure and control invasives, especially for the conservation of species such as the Bengal Florican.
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    HABITAT SELECTION BY DESERT FOX (Vulpes vulpes pusilla) IN HUMAN MODIFIED LANDSCAPE OF THAR DESERT
    (Wildlife Institute of India, Dehradun, 2024) Krishnapriya, M.; Dutta, Sutirtha; Talukdar, Gautam
    Knowledge about habitat use and selection helps to assess the impact of land use change on wildlife and inform conservation management. This study aims to understand habitat use and den site selection of Desert Fox (Vulpes vulpes pusilla) in the human modified landscape of Desert National Park and it adjoins in Rajasthan. The study was conducted from January 2024 to April 2024 that include the fox breeding season. Species occupancy inside and outside protected areas were examined to understand the effectiveness of protection. Den site selection was examined by comparing habitat, resource, and disturbance variables at the scale of core usage around the den and random control points. Protected area showed a positive effect on occupancy of foxes. Desert fox was found to be using diverse habitat types for denning, however, scrubland tended to be used more than availability and grassland was used less than availability, in the study area. Agriculture did not influence den site. Foxes showed strong avoidance to areas with high human and livestock disturbances and strong preference to areas with abundant Capparis fruiting for denning. Increase in human footprint in the landscape could potentially lower the survivability and reproductive success of foxes by making them prone to direct threats from humans and subsidized predators such as dogs.
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    Thermal Ecology of Spiny-tailed lizard and its vulnerability to climate warming.
    (Wildlife Institute of India, Dehradun, 2021) Tatu, Avichal; Dutta, Sutirtha; Das, Abhijit
    Lizards and other ectotherms survive within their thermal limits and have a well-defined range of body temperatures within which their performance is optimal. Hence, as climate warming accelerates, ectotherms like lizards become increasingly constrained. Saara hardwickii survives in areas where environmental temperatures are already extreme. Therefore, they may be at the risk of extinction due to rising temperatures. In the field, we collected data on field body temperatures and operative temperatures to evaluate and quantify the degree of thermoregulation observed in the lizard and to evaluate changes in activity pattern over months, In the laboratory, we quantified preferred temperature, thermal thresholds and locomotor of the lizard. Using a combination of field and laboratory data, we described how S. hardwickii uses burrows to thermoregulate and evaluated how climate warming will impact locomotor performance and hours of activity in the future. We found that burrows provide an exceptional buffer to the lizards as the temperatures deep inside (~1 m) do not exceed the preferred temperature of the lizard, even in the worst-case climate change scenario (RCP 8.5). Currently, the lizards are restricted to their burrows for six hours during their active period. According to our model, by 2100, the lizards might get restricted to their burrows for 7 hours in the best-case scenario, and for 9 hours in worst-case scenario. Our model suggested decrease in locomotor performance by 2.1%, 9.5% and 28.3% in the best- (RCP 2.6), intermediate- (RCP 4.5), and worst- (RCP 8.5) case scenarios by 2100. Hence, the synergistic effect of loss of activity hours and decline in locomotor performance might result in decreased fitness of S. hardwickii, potentially leading to its extirpation.