Invasive species are one of the major drivers of change in the structure of native ecological communities. Human activities, whether direct or indirect, are the leading cause of the introduction of new species in ecosystems, with some eventually becoming invasive. When native ecological communities are less complex and offer low resistance to new species, the invasion by a new species becomes more pervasive. Dryland ecosystems such as the Thar Desert provide such low resistance for new species. Over time, several human-introduced species in the Thar Desert have transitioned into invasive species, exerting widespread impacts on native ecological communities.

Both plant and animal invasive species cause changes in the composition of native communities through various pathways. They may modify resource availability, thus favouring certain species over others, or directly and indirectly pose competitive threats to native communities, thereby altering their composition and behaviour. Studies aiming to understand the impacts of such invasions often focus solely on either plant or animal invasive species. Their examination typically centers on the effects on a single group of species. This approach results in a significant knowledge gap regarding the understanding of both plant and animal invasive species on multiple guilds within an ecosystem, including prey, predators, and scavengers. Moreover, even studies considering multiple guilds often overlook the contribution of scavenging guilds in ecosystem functioning.

I studied the impact of two prominent invasive species—the mesquite tree Prosopis juliflora and free-ranging dogs Canis lupus familiaris on the native faunal species assemblage of the Thar Desert. I selected three major groups of native faunal communities. The first group consisted of the mesopredator guild composed of foxes, jackals, and small cats. The second group comprised a prey guild composed of various rodent species, and the third group was a scavenger guild made up of different avian scavenger species. This study took place in two different sites in the Thar Desert—the Banni grasslands of Kutch and the grasslands of Bikaner in Western Rajasthan. I used different methodological approaches to quantify the effect of these invasive species on the spatiotemporal use of resources by different native guilds.

To assess the impact of Prosopis encroachment and dogs on the mesopredator guild in the Thar Desert, I utilized a landscape-level network of camera trap grids to collect detection data on native predators, which encompassed meso-predator species along with dogs. I employed high-resolution multispectral images from Sentinel-2 and synthetic aperture radar images to extract data on various land cover types, including the expansion of invasive Prosopis as a habitat variable. I analysed both the detection data and habitat variables using an occupancy model approach to determine the influence of Prosopis encroachment on the spatial utilization patterns of the meso-predator guild.

My results showed a varying effect of Prosopis encroachment on the mesocarnivore guild, benefiting generalist species such as golden jackal Canis aureus and jungle cat Felis chaus, while negatively affecting open habitat specialist species such as Indian desert fox Vulpes v. pusilla, Indian fox Vulpes bengalensis, and desert cat Felis lybica ornata. All mesocarnivores showed strong avoidance of dogs along either the spatial or temporal niche axis, likely to evade interference competition. The high prevalence of dogs in these landscapes could lead to the competitive exclusion of smaller native species, such as the Indian fox, resulting in a local decline in their population. My study shows significant impacts of both plant and animal invasive species on native mesocarnivores, altering their distribution and activity patterns with potential consequences for long-term population persistence. We suggest control of the rapid expansion of Prosopis in the areas prioritised for conservation of open habitat specialists such as desert fox, Indian fox, and desert cat, and removal or restriction on the movement of dogs in sensitive wildlife habitats.

I used a grid-based Sherman live-trapping approach to compare rodent abundance under different habitat types representing different scales of Prosopis invasion. Rodents, being primary consumers, are likely to be the first to respond to changes in the structure and composition of native vegetation. The sampling plots were divided into five categories representing different stages of Prosopis invasion and other land cover types. These consisted of restored native grassland, agriculture fallow, open brushland, sparse-Prosopis plots, and Prosopis-dominated plots. We also examined the impact of woody invasion on the response of native rodents towards moonlight and temperature. As hypothesized, we found a significantly higher abundance of rodent species in the native grassland habitat compared to sparse-Prosopis and agricultural fallow habitats. However, there was no significant difference in rodent abundance and diversity between the grassland and Prosopis-dominated habitats. Thus, species richness and abundance of rodents were the highest in the restored grasslands and dense Prosopis thickets, and the lowest in the sparse Prosopis, potentially showing a “U” shaped response to Prosopis invasion. We observed the species-specific effect of Prosopis on the activity of Indian gerbil Tatera indica, lesser bandicoot Bandicota bengalensis, and soft-furred field rat Millardia meltada. Habitat type mediated the effect of different environmental factors (moonlight and temperature) on the activity of the most commonly occurring species T. indica, while the activity of M. meltada showed a weak association with environmental factors. B. bengalensis was the most generalist species, showing similar activity across all habitat types.

With regard to the scavenging guild, predominantly composed of vulture species, I studied the competitive interaction between dogs and vultures. First, I estimated the dog population using photographic capture-recapture at various dump sites to see if the dog population scales with carcass availability. Later, I used an experimental approach to understand the competitive interaction between dogs and vultures at carcass dump sites. I implemented four treatments to observe vulture feeding at provisioned carcasses using camera traps. The first treatment involved a long-term Supplementary Feeding Site (SFS), where carcasses are regularly dumped and left open for consumption by both dogs and vultures. Second, to control for the effect of human presence, carcasses were placed 200 to 500 meters away from the center of the SFS. Third, carcasses were positioned more than 2 kilometres away from the SFS to assess the site's effect. Fourth, carcasses were enclosed within a 250x250 meter chain-linked fenced area within 100m of the SFS to exclude dogs. We compared species composition, arrival latency, time spent, and frequency of agonistic interactions across these treatments.

Estimation of the dog population at 24 out of 30 dump sites identified showed that for each unit increase in carcass number, the dog population at the site increased by 10 individuals. This linear relationship indicates a strong positive association of dog population with carcass availability. Furthermore, the total available carcasses per day at each of these dump sites exceed the consumption capacity of the dog population found at those sites by a mean surplus of 83%. In our study, we observed a total of 49 carcasses across four different treatments to examine competitive interactions between dogs and vultures. Our analysis revealed that griffon vultures spent twice as much time on a carcass when it was excluded from dogs compared to those at open dumpsites where dogs were present. Additionally, the presence of a high number of dogs at dump sites limited the feeding of griffon vultures during the afternoon hours between 11 AM and vi 2 PM, whereas in the absence of dogs, their feeding lasted for longer hours, starting from 8 AM and lasting until 4 PM. Total consumption time by vultures increased with the amount of time spent by dogs around a carcass. The proportion of individuals feeding out of the total individuals that arrived before the carcass was monopolized in the enclosure was twice as high compared to the open treatment near dump sites. Even when griffon vultures monopolized the carcass, interference by dogs reduced their feeding time by 28%.

The total time spent by dogs showed a significant negative impact on the proportion of individuals feeding. Overall, our experiment demonstrated that the presence of dogs has a significant negative effect on the feeding of griffon vultures, leading to reduced food intake at supplementary feeding sites. These findings have important implications for the management of these feeding sites for the conservation of resident vultures, which are declining in numbers.

A supplementary feeding site serves as an important tool for vulture conservation, providing a safe and consistent supply of food. I examined the current carcass management system in the Thar region to identify opportunities for optimizing these supplementary feeding sites for vulture conservation and the livelihoods of the people involved. I conducted in-person surveys and semi-structured open-ended interviews with individuals involved in various stages of carcass processing and management to understand carcass management practices, the roles of different stakeholders, and the challenges they face.

My study showed that traditional carcass disposal practices at village outskirts have disappeared since the decline of the vulture population in the 1990s. The policies for carcass management following the vulture decline lack an understanding of the livelihood impacts resulting from the loss of ecosystem services provided by vultures. This has led to a more centralized system in which private contractors collect carcasses from large areas to process them at remote dump-sites, resulting in the loss of livelihood for small-scale skinner families. Furthermore, the lack of engagement among various stakeholders involved in carcass management limits the application of supplementary feeding sites for vultures to small areas only. My study provides stakeholder mapping and recommendations for optimizing carcass management to benefit both vulture conservation and the livelihoods of the people involved.