Research Article: Karanth KU, Srivathsa A, Vasudev D, Puri M, Parameshwaran R, Kumar NS. Spatio-temporal interactions facilitate large carnivore sympatry across a resource gradient. Proc Biol Sci. 2017 Feb 8;284(1848):20161860. doi: 10.1098/rspb.2016.1860. 

Blog Author: Chandan Kumar Pandey

Key takeaways: 

  • Tigers, leopards, and dholes are the three larger carnivores of the Indian subcontinent and share similar habitats in the Malenad landscape of the Western Ghats, albeit confined only to protected areas.
  • Competition among these species not only impacts their populations but has cascading effects on other wildlife in the forest, too. 
  •  It is crucial to understand how these three species of carnivores modulate their temporal (based on time) and spatial (based on space) activity  to avoid conflict. 
  • Researchers conducted observational studies using camera traps in four protected areas (Bandipur, Bhadra, Nagarahole and Biligiri Rangaswamy) to understand the activity patterns of these three carnivores. 
  • Camera traps from these areas yielded a total of 2,451 images of tigers (503), leopards (1,018) and dholes (930).
  • Overall results suggested that in areas where the number of prey is low, the three carnivore species compete with each other by utilizing the same space or being active at the same time. However, the carnivore species avoid competing with each other by utilizing the same space at different times. The results suggest that the three carnivores rarely (less than 1% of the time) appeared together at the same place and time. 
  • The results have a significant implication on conservation of large carnivores that are present in the same area. In order to allow peaceful coexistence amongst these carnivores, it is recommended that prey populations must be increased, and protected areas should ensure connectivity to allow the movement of large carnivorous species.

 

For years, ecologists have been studying how different species of carnivores can coexist. In a large landscape, they coexist by inhabiting or using separate areas (spatial separation). However, due to the shrinking of forest patches, such spatial separation is not possible.  This can lead to intense competition, such as fighting over food and sometimes, excluding other species from the area. To understand how these species coexist, scientists look at factors like dietary habits, movement within the landscape, time periods of activity, and  adaptations to avoid competition. Understanding these mechanisms provides more information regarding the organization of animal communities. 

Previously, researchers have used radio collaring methods to study individual behaviors and how animals respond to competition. However, one also needs to understand the dynamic interactions within, and between, populations. The research team, led by Dr K. Ullas Karnath, conducted a study in the Western Ghats, India, focusing on three large carnivores: dhole, leopard, and tiger. These species have overlapping diets and compete for prey and are hence, sympatric. The researchers analyzed camera trap photographs to see how these species share resources over space and time. They included different study sites with varying population densities of the carnivores and their prey.

The study was conducted in four wildlife reserves: Nagarahole, Bandipur, Biligiri Rangaswamy Temple (BRT), and Bhadra. These reserves have different numbers of carnivore and prey animals, (gradient of population). To understand space and time use by the three carnivore species, the researchers deployed 562 camera traps in these four wildlife reserves from January to June 2013. The camera traps captured a total of 2,451 photographs, of which 503, 1,018, and 930 belonged to dholes, leopards, and tigers, respectively.

To check if species avoid each other through changes in activity timelines, scientists noted the time at which each target animal was photographed. Further they collapsed all data into 24 hrs, with 1 hour time interval, ignoring the calendar dates. They then compared the activity pattern for each pair of species to understand if they were active at different times. They found that dholes were mostly active during the day, and tigers and leopards at night. Moreover, even though tigers and leopards are more active during the night, leopards were more active at twilight. However, in the Bhadra tiger reserve, where prey  density is low, all three carnivores were more active throughout the day. 

Researchers employed a method called “space usage analysis” to examine how animals utilize their habitats. This approach involves dividing the larger area into smaller sections and determining if the species is present or absent in each section. To gauge how often animals shared or avoided the same areas, they used a measurement called the “interaction factor.” The “interaction factor” is defined as a ratio of the number of sections where both species were present to  the product of the number of cells where only one of two species was present. A value of one indicated that they used the areas independently. Animals were considered to occur together more frequently than expected if the interaction factor was greater than one, and less frequently if it was less than one. The interaction factor values in the study ranged from 0.97 to 1.14, suggesting that the species used the areas independently. However, for most species pairs at all sites, the value of “interaction factor’’ was more than 1, suggesting some degree of similarity in space use. 

In reserves with fewer prey densities (Bhadra), tigers and leopards showed the highest level of space-sharing. In BRT where prey density is higher than in Bhadra, tigers and dholes share the same spaces. Leopards, however, were found at low densities and did not overlap with other predators in that reserve. In Nagarahole, where prey density is highest, there was no strong evidence of species sharing space together. But in Bandipur, where the prey is also high, there was indication that leopards shared space with dholes and tigers more often than expected as the “interaction factor” was 1.13 and 1.1 respectively. 

Researchers used two methods for assessing the occurrence of tiger, leopards and dholes over space and time. For the first method, they create a matrix where each row, column and each cell represents the camera trapping site, hours of day and number of species that were photographed at the site in that hour, respectively. They counted how many times each species was spotted in a specific place during an hour. They used this matrix to estimate the proportion of times when each species was alone, when two species were seen together, and when all three were seen together. In the second method, the ‘time-to-encounter’ was estimated to understand the minimum time elapsed between photo trapping of one animal and another carnivore species on the same camera trap. If the observed time-to-encounter was shorter, it suggested species aggregation, meaning they tended to be in the same space at similar times. 

The results suggest that the three species rarely appeared together at the same place and time, less than 1% of the time. Moreover, Bhadra showed the least sharing across space and time. This suggests that even though carnivores are active during the same time, they are avoiding the usage of the same space.  However, the authors suggest this could be due to the low carnivore density in Bhadra leading to artifact of lower rate of photo-capture . In high prey density parks such as Nagarahole and Bandipur, there was some overlap among species. For example, leopards and tigers shared more time and space in comparison with dholes in Nagarahole and Bandipur. However, in Biligiri, where leopard density is low, tigers and dholes share more space and time. Even when there was overlap of space and time among the carnivore species, the time-to-encounter was high, which suggests avoidance behavior.  

The results from the study suggest that when resources and space are adequate, these species tend to avoid competition by utilizing separate spaces or by changing their activity time. On the other hand, under scarcity of resources and space, sympatric carnivore species occurred together in space and time. Sympatric carnivores avoid competition by utilizing the space at different times at a finer scale. Competition among these predators can lead to changes in lower trophic levels, affecting other species like mesopredators and prey animals. The study focused on four reserves with different predator and prey densities, providing valuable insights into how these sympatric carnivores adapt to their environment. With protected areas becoming more and more isolated and prey populations shrinking due to human-related pressures, this study was crucial in understanding the ecology of these endangered predator species. 

 

Link to original article, here.

Keywords: sympatric carnivores, Tiger, Leopard, Dhole, Western Ghats, Inter-species competition, camera traps, coexistence.