In the face of persistent challenges associated with biodiversity conservation and the imperative to address habitat fragmentation impacts, the critical role of well-informed conservation strategies is paramount. Effective conservation strategies hinge upon a comprehensive understanding of wildlife movement patterns and the intricacies of the landscape. Animal species behaviour and their movement such as dispersal and migration act as one of the measures that ensures their survival in the landscape (Drielsma et al., 2007). United nations 2030 agenda for sustainable development identifies protected areas as a chief unit for wildlife and biodiversity conservation. Across globe, around 2, 02,000 protected areas have been legally designated covering 15% of the earth surface (Rahoof, 2019). In India, there are five kinds of protected areas namely, national parks, wildlife sanctuaries, conservation reserves, community reserves, marine protected areas. (wiienvis.nic.in). Details of protected areas of India are given in Table 1
5.26% of total geographical area of India is under protected area (WII,2021). The protected areas have played an important role in conservation of biodiversity. Since mid-20th century no mammal or bird is claimed to be extinct other than Cheetah (Acinonyx jubatus), pink headed duck (Rhodonessa caryophyllacea) (Divyabhanusinh, 1999; Ghosh-Harihar et al., 2019; MoEF&CC, 2020). Protected areas have played a great role in conservation of some endemic species of Indian subcontinent like one- horned rhinoceros (Rhinoceros unicornis) and Bengal tigers (Panthera tigris tigris) (Talukdar et al., 2008; Jhala et al., 2015; Ghosh-Harihar et al., 2019). However, conservation of species in between protected areas has been a serious cause of concern. The increase in human animal conflict around protected areas have been alarming. Bengal Tiger (Panthera tigris tigris) is one of the largest carnivores and a top predator belonging at the top of the food chain (Sabu et al., 2022). It is native to Indian sub-continent. Top carnivores are crucial for maintaining ecological integrity of a functional ecosystem. Tigers are one of the endangered species. In India tigers are distributed in almost all ten biogeographical zones including mountains, swamps, grasslands, dry and moist deciduous forests, evergreen forests (A. R. Joshi et al., 2016; B. Kumar et al., 2021; Sabu et al., 2022). Approximately, 70% of the world’s tiger population was present in India before 2000 (Nowell, 2000). Along with high population of tigers, India also embraces more than 60% of worldwide genetic variation in them (Mondol et al., 2009). Due to large scale poaching activities and habitat clearance population of tigers are confined to the small patches in the landscape. In 20th century tigers were hunted for commercial gains, chinese medicines and for showcasing bravery leading to decline of tiger population (Gittleman & Gompper, 2001; Sharma et al., 2010). Globally, 76 tiger conservation landscapes (TCL) are recognized which are habitats where tiger presence have been confirmed in last ten years. Six of the TCLs are situated in Indian subcontinent. The significant loss of tiger population resulted in adoption of ‘‘Tx2’’ objective at St. Petersburg, Russia, in 2010 which aims at doubling the population of the carnivore by 2022. Project Tiger by the Government of India is one of the most prominent steps towards this goal. Development of tiger reserves and protected areas were a pioneer step in this direction. However, it is crucial for wildlife sustenance to develop pathways for connecting protected areas together for movement activities like dispersal and migration (Majumder et al., 2012; New et al., 2008). Development of ecological corridors provide functional connectivity among habitat patches. Use of tools like graph theory and circuit theory is seen in wide range of studies for delineating ecological corridors. Movement of animals are crucial for maintaining gene flow and genetic variation. Connectivity among landscapes is vital for maintenance of ecological integrity. Movement of animals in the landscapes are largely for foraging, migration, dispersal or to evade predators. Connected landscapes helps in conservation and management of wildlife population. Natural and anthropogenic disturbances have resulted in the scattered and isolated population of animals. Various definitions are coined for landscape connectivity citing the structural (Brotons et al. 2003; Thies et al. 2003; Taylor et al. 1993; Tischendorf and Fahrig 2000; Schooley and Wiens 2003) as well as functional aspect (Taylor et al. 1993; With et al. 1997) of it. In former case, the connectivity is entirely based on landscape structure while in latter case, the connectivity is defined on the basis of behavioral responses of animals to landscape components (Kindlmann & Burel, 2008).
Circuit theory and graph theory is widely used in modeling ecological corridors. Graph theory based least cost paths are the routes where movement of animals incur lowest cost of transit (Adriaensen et al., 2003). They are single best pathways for movement derived from the resistance surfaces. Globally, many studies have used least cost method for delineating corridor paths. The study by LaRue & Nielsen (2008) identifies least cost pathways for movement of cougar (Puma concolor) in mid-western region of USA. Another study by Wierzchowski et al (2019) utilizes least cost method to derive a transport corridor for moose (Alces alces). A study by Wang et al (2009) identifies costs of various paths for movement of California tiger salamander (Ambystoma californiense) between grasslands and woods. Circuit theory, also uses resistance surface to delineate various probable paths for animal dispersal (Cushman et al., 2013; Dickson et al., 2020; McRae et al., 2008). Circuit theory is particularly useful when it is assumed that the moving individuals have limited knowledge of surrounding landscape (McClure et al., 2016; Maiorano et al., 2017; Keeley et al., 2017)
Validation is a crucial part of such practical studies. It helps in understanding whether the predicted structural corridor is functional corridor. Recent research has introduced statistical methods to substantiate the accuracy of projected wildlife corridors through on-ground datasets (Lalechère & Bergès, 2021). Many of these researches rely on location data, camera trap insights, GPS recordings, or telemetry information for verification purposes (Bond et al., 2017; Koen et al., 2014; Lalechère & Bergès, 2021). However, utilizing telemetry and GPS data is often hindered by their prohibitive costs. In a similar vein, Koen et al. (2014) used locations where animals have experienced road mortality to validate their connectivity model. Furthermore, several researchers have also cross-validated current density maps with radio telemetry data (Bond et al., 2017), which involves comparing the predicted movement pathways of animals with actual recorded movements. (Bond et al., 2017). There are various studies that use proximity analysis to validate the predicted corridors based on the distance between location of animal presence and the predicted path (Bond et al., 2017; Koen et al., 2014; Lalechère & Bergès, 2021). However, animal spotting outside of a protected area is often not recorded and there is very less data available outside of the protected area. In this study, a new corridor-based validation technique is proposed and applied on the corridors predicted using least cost path principle. This corridor assessment method is centered around translating real-world observations into a quantifiable measure of corridor accuracy. Triangulation is a fundamental geometric process used in various fields to create networks of triangles over a set of points. This method is crucial for transforming complex spatial data into a simplified, yet accurate, representation. Triangulation can handle a variety of data types, including those used in Geographic Information Systems (GIS), where it is often employed to model terrain, optimize sensor networks, and more.
The foundational work by Selvi, Oztug Bildirici, and Yerci (2010) discusses the triangulation method for area-line geometry-type changes in map generalization. Pradhan et al. (2007) utilize Delaunay triangulation for GIS terrain data compression, emphasizing its efficiency in handling complex terrain data. Argany et al. (2011) highlight a Voronoi-based approach in GIS for optimizing wireless sensor network coverage, demonstrating the versatility of triangulation in various applications. Further, Wu and Amaratunga (2003) explore wavelet triangulated irregular networks, while Zhang et al. (2018) enhance surface flow routing over drainage-constrained triangulated irregular networks. These studies collectively showcase the adaptability of triangulation in handling spatial data.
In the context of ecological studies, particularly in validating predicted animal corridors, triangulation plays a pivotal role. Animal movement data, typically in the form of geographic coordinates, can be used to create a triangulated network. This network provides a framework for analysing the spatial patterns of animal movement and assessing the accuracy of predicted corridors. Figure 1 explains the triangulation method used on two sets of three points forming points T1 and T2. A line connecting these points is termed as reference line. This process involves connecting the points in a manner that minimizes the total length of the lines while avoiding intersection, creating a Delaunay triangulation. This method ensures that the network is both efficient and accurate. Furthermore, this reference line can be compared with the least cost path predicted by calculating the perpendicular distances between them. The average of perpendicular distance can be taken as corridor score. The lower the value of the corridor score, higher chances are that it is a functional corridor. The novelty of this research lies in its innovative application of triangulation to validate predicted wildlife corridors using empirical animal movement data. This work creates a framework for evaluating the precision of corridor forecasts and analysing spatial trends by using geographic coordinates to create a triangulated network. The implementation of Delaunay triangulation guarantees a precise and effective network, hence augmenting the dependability of the generated reference line. Through perpendicular distance measurements, the analysis compares this reference line with the least cost approach and suggests a measurable corridor score. This approach fills a major gap in the present ecological research methodology by offering a reliable metric for assessing corridor functionality in addition to improving validation approaches (LaPoint et al., 2013).
This research specifically targets the investigation of landscape connectivity for tigers across eight protected areas spanning Haryana, Uttarakhand, and Uttar Pradesh states of India, within the geographically significant Terai Arc Landscape. The primary objective of this research is to introduce and propose a validation technique tailored for predicted corridors. Addressing a critical gap in modern-day corridor modeling techniques, the study recognizes the lack of a standardized validation approach. The method presented in this paper seeks to systematically assess and enhance the reliability of corridor predictions, thereby equipping conservationists with a tool for evidence-based decision-making that positively influences both animal populations and ecosystems