Habitat destruction, deforestation, population growth, climate change, and invasive species are the major factors responsible for biodiversity loss at the global level. According to IPBES, invasive species and climate change are the direct and major drivers of biodiversity loss. Invasive alien species are the species that are introduced away from the natural range into non-native regions, causing tremendous harm to native biodiversity and impacting local economies and human and environmental health. Therefore, it is crucial to identify the areas with the highest invasion rates and assess their relationship with environmental and socio-economic factors. The thesis is focused on three main objectives addressing important issues such as the drivers, identifying hotspots or vulnerable regions and niche shift. The specific objectives are: (i) to assess patterns, distribution, and determinants of animal invasion across the globe, (ii) to identify the ‘hotspots’ of invasion and predict the future regions of invasion using a species distribution modelling approach, and (iii) to assess niche dynamics across native and introduced regions of invasive vertebrates.

The primary objective of the study was to ascertain the distribution and spatial patterns of animal-invasive alien species in various geographic regions. Furthermore, it is crucial to identify the socio-economic factors that facilitate the invasion of animals. A total of 2432 invasive animal species were considered for this study. The data were obtained from the Global Invasive Species Database (GISD) and the Centre for Agriculture and Bioscience International (CABI). Species distribution data were collected from the Global Biodiversity Information Network (GBIF) and published literature. Socio-economic data such as GDP, air transport volume, container ship, export, import trade, population density, livestock, etc., were obtained from the World Bank database, Central Intelligence Agency. I have used ecoregions, biomes, realms, countries, and continents as variables for understanding the distribution patterns at a large spatial scale. The study also focused on the distribution of invasive vertebrates in the current and future. The MaxEnt was used to assess the potential distribution of 348 (154 fishes, 30 amphibians, 52 reptiles, 48 birds, and 64 mammals) invasive vertebrates. The invasion hotspots were assessed by overlaying all the 348 layers derived from MaxEnt models. The binary maps were prepared using the 10th percentile Cloglog threshold and were used to estimate the area of suitable habitat. Finally, the study also tried to address the niche dynamics for selected vertebrates to understand if the invasive conserve their niche or show niche shift in the invaded regions.

The results from my study suggest that most of the Oceanic Islands and European countries have higher invasive species per unit area than other parts of the world. Hierarchical cluster analysis shows homogenisation of species diversity belonging to different realms. GLM results show that the Liner Shipping Connectivity Index (LSCI), air freight traffic, GDP, and human capital index significantly correlated with the number of invasive species per country. The number of invasive species significantly influences the presence of a high diversity of threatened species. The Palearctic region has the highest number of invasive species, followed by Nearctic realms. Similarly, the most invasive invertebrates are found in temperate broadleaf and mixed forests. Developed countries have more invasive species than developing countries, and temperate regions are more vulnerable to invasive species than tropical areas.

The hotspots of invasions are the Southeast United States of America, Western Central Africa, Western Europe, Southeast Australia, Southeast Asia, and South America. The suitable habitat area increases for all taxonomic groups except for invasive mammals. Further analysis with functional traits and other factors, such as the number of introduced countries, showed that the number of introduced countries influences the invasive mammal potential range. From the suitable habitat area, it was found that the minimum number of countries with invasive species will increase, which points out the number of invasive species that will spread in the future. Species with the most suitable habitat are Cane toad, Tilapia, Cattle egret, Bell’s dabb lizard, and Siberian chipmunk.

The study also suggests that 60 per cent (150 out of 250) species show very low niche overlap (<0.05). On the contrary, only five species show very high niche overlap (>0.80). These species include Rhinella marina (amphibian), Ramphotyphlops braminus (reptile), Streptopelia decaocto (bird), Callithrix geoffroyi (mammal), and Suncus murinus (mammal). The study also found zero niche expansion for seven fishes, five amphibians, six reptiles, six birds and four mammals, indicating strong niche conservatism. Niche shift (i.e., Expansion >0.5) is observed across 69 (out of 250) invasive vertebrates. Similarly, 13 species show complete expansion (i.e., E =1).

Based on the results of this study, there is an urgent need to prioritise the species which are showing high niche expansion for management action. This study provides detailed information on the distribution of all invasive animal species globally. The study also emphasises the need for better documentation of invasive species from developing countries. An action plan to manage invasive animal species to prevent further invasion and mitigate their impact under future climate change is of utmost importance.