Introduction
In the past few decades, there has been a shift in wildlife biology studies from single species targeted approach to ecosystem conservation approach (Linnell & Strand, 2000). This holistic approach reveals how interspecific interactions can alter community structures and ecosystem functioning (Ford & Goheen, 2015). One such interaction is intraguild competition among large carnivores that shape the predatory guild (Palomares & Caro, 1999). Often considered as keystone species in the terrestrial ecosystems (Caro & O’Doherty,1999), ecological effects of large carnivores extend down to herbivores and plants (Ritchie & Johnson, 2009) thereby structuring ecosystems along multiple food web pathways. Therefore, safeguarding of viable large carnivore populations is essential for ecosystem equilibrium, that cannot be ensured without understanding their demographic responses to each other.
Over the years, it has been established that competition among predators can be direct or indirect (Case & Gilpin, 1974; Macdonald, 1983; Crooks & Soule, 1999; Ritchie & Johnson, 2009; Letnic, Ritchie, & Dickman, 2012). The indirect form is termed as exploitative competition (Case & Gilpin, 1974). Wherein resources are harvested disproportionately by one predator and are not available for other competing predators (Vance, 1984). This type of interaction is mostly unidirectional with larger body sized carnivores i.e. apex predators (Ordiz, Bischof, & Swenson, 2013), dominating the guild. Evolutionarily, competitively subordinate carnivores have adapted to exploitative competition by opting for differential life-history strategies like group living, reduced overlap in diet, Spatio-temporal activity and habitat use (Creel & Creel,1996; Durant, 2000; Creel, 2001; Durant, 2002).
On the other hand, interference interaction is a rather direct form of competition in the predatory guild (Vance,1984). Some manifestations of interference competition are interspecific territoriality, kleptoparasitism and direct killing (Linnell & Strand, 2000). However, interference competition is not easy to demonstrate, because it is multifaceted and involves an array of factors acting along, such as anthropogenic disturbance, alterations in community structure of prey and other predators and the overall productivity of ecosystems (Greenville, Wardle, Tamayo, & Dickman, 2014; Newsome & Ripple, 2015; Swanson et al., 2014). Therefore, there is a dearth of theoretic and practical understanding of interference competition because of the lack of replicability of such ’natural experiments’ (Linnell & Strand, 2000).
Most of our understanding on intraguild competition comes from studies on exploitative competition, although interference competition is critical in multi-predator systems and is always functioning in the background (Periquet, Fritz, & Revilla, 2015). Shreds of evidence from classic ecology studies indicate that subordinate predator experience low recruitment rates and even face extirpations in a high apex predator density scenario (Carbyn, Armbruster, & Mamo, 1994; Clark, 1994; Lindström, Brainerd, Helldin, & Overskaug, 1995; Henke & Bryant, 1999). However, an inverse pattern is observed when interference competition is removed. A recent continent-wide review shows expansion of golden jackals (Canis aureus ) as a response to grey wolf (Canis lupus ) exterminations in Europe due to persecution by humans. (Krofel, Giannatos, Cirovic, Stoyanov, & Newsome, 2017). Ecosystems wherein social and solitary predators share space, intraguild competition often shape trends of group sizes in social carnivores. The group size of subordinate predators such as African wild dogs (Lycaon pictus) (Creel & Creel,1996; Creel & Creel, 1998), Spotted hyenas (Crocuta crocuta) (M’soka, Creel, Becker, & Droge, 2016) and cooperative breeding mongooses (Suricata suricata ) (Clutton‐Brock et al., 1999) have been studied to be inversely related to lion densities, over temporal and spatial scales.
One such sympatric guild of solitary and social carnivores, found in South-east Asian forests is of tiger (Panthera tigris ), dhole (Cuon alpinus ) and leopard (Panthera pardus ). Tigers are considered to be top predators whereas dhole and leopard are intermediate predators, forming an asymmetric guild (Steinmetz, Seuaturien, & Chutipong, 2013). In the Indian subcontinent dholes have been widely studied along with tigers and leopards, to understand sympatric interactions among the three carnivores (Acharya, 2007; Johnsingh,1992; Karanth & Sunquist, 2000; Wang & Macdonald, 2009; Wegge, Odden, Pokharel, & Storaas, 2009; Steinmetz, Seuaturien, &, Chutipong, 2013; Rayan & Linkie, 2016). Competition between these carnivores is likely because of the high overlap in diet spectrum (Karanth & Sunquist, 1995). Prey rich forests facilitate sympatry between the carnivores (Karanth & Sunquist, 2000; Wang & Macdonald, 2009; Karanth, 2017). Studies in sub-optimal habitat conditions with scarce resources have shown evidence of intraguild predation among the sympatric carnivores (Steinmetz, Seuaturien, &, Chutipong, 2013; Rayan & Linkie, 2016). Conversely, tiger depleted systems have shown a significant increase in dhole site occupancy (Steinmetz, Seuaturien, & Chutipong, 2013; Rasphone, Kery, Kamler, & Macdonald, 2019).
Pack size, however, is a vital aspect and considered to be a function of population size in social predators (Fernández et al., 2020) but it remains unaddressed for the dhole. So far, we have no long-term studies to assess and understand various ecological factors that determine group size dynamics of dhole, as seen in case of other subordinate social predators (Périquet, Fritz, & Revilla, 2014; Green, Farr, Holekamp, Strauss & Zipkin, 2019).
We observed a significant variation in pack size of dholes at the two neighbouring protected areas having similar ecological settings, Tadoba Andhari Tiger Reserve and Navegaon Nagzira Tiger Reserve in the Central Indian Landscape, Maharashtra, India and attempted to investigate factors underlying this variation in pack size of dholes. Group size variation is a crucial characteristic of carnivore sociality (Macdonald,1983) and is an attribute of differential ecological settings over temporal and spatial scale (Markham, Gesquiere, Alberts, & Altmann, 2015). Largely governed by co-predator density and prey abundance (Gusset & Macdonald, 2010). Furthermore, availability of habitat, topography and habitat features elicit prey distribution and encounter rate at a given place and time (White & Garrott, 2005; Fedriani, Fuller, Sauvajot, & York, 2000).
After investigating factors linked with pack size variation of dholes at the two reserves, we further elucidate our local scale patterns at a wider scale by doing a distribution-wide assessment of pack size across dhole ranging countries. 1. Hypothesis: High apex predator density negatively affects pack size of subordinate carnivores (Groom, Lannas, & Jackson, 2017). Prediction: Areas with higher tiger density will show smaller pack sizes and vice-versa. 2. Hypothesis: When tiger density are low pack sizes are determined by prey abundance. Prediction: Dhole pack size will positively correlate to higher prey abundance. 3. Hypothesis: Terrain ruggedness influences pack size as dholes are cursorial predators (White & Garrott, 2005). Prediction: Areas with high ruggedness will correspond to low pack sizes and vice-versa.