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.