The Predators of Nagarahole

Nagarahole is home to a large number of predators,
the three key predators among them being the tiger,
wild dog and leopard. Scientific studies carried out in
the park by Dr.K.Ullas Karanth reveal that the three
co-exist in high densities. Field observations and citation also seem to validate the principle of coexistence; some such instances are listed below.

  • Wild dogs were observed scavenging tiger and leopard kills when they were away.
  • On one occasion a tiger and leopard fed on kills less than 300 meters apart unaware of their presence.
  • A pack of wild dogs were 50 meters away from a resting tiger without either being aware of each other's presence
  • Several citations showed that leopards flee tigers and wild dogs by climbing trees, tigers however appropriated wild dog and leopard kills.
While it is evident that forests are an epitome to nature’s principle on coexistence, it will be interesting to unravel this mystery of coexistence among predators. Going by nature’s philosophy on the survival of the fittest, we first need to look at the herbivore density and the availability of prey species in any environment. The density and variety of prey can influence predator distribution in the forest. For example a forest inhabited only by hares cannot expect to hold tigers as hares make too small a meal for tigers regardless of the number of hares in that forest. Furthermore the variety of prey determines the variety of predators in the ecosystem.
Prey species are classified by their mass, measured in Kilograms. Nagarahole is home to a sizeable number of large sized herbivores (defined as weighing more than five kilos). There are seven key species of ungulates and two species of primates, together they occur at a mean estimated density of 108 animals per square kilometer. The average body weight of the animals amounts to a biomass density of 14746 Kgs/ sq. km in Nagarahole, while the Mara in Africa has a biomass density of 19200 Kgs/ sq. km. The seven key species (chital, sambar, gaur, wild pig, muntjak and the langur) constitute over 90% of the predator's diet and can thus be classified as the principal prey species. Studies show that their density is measured at 91 animals per sq. km, compounding this to the total biomass favored by each predator in % reveals the following
Tiger           : 97.6% (% of 7 species preyed on)
Leopard      : 89.2%
Wild dog     : 96.8 %
It seems evident that there is a dietary overlap among the predators i.e. they more or less hunt the same species. While the results seem inconclusive, further sub-division of the principle prey by body weight and a measure of species selectivity by each predator has unraveled this mystery.
Segmentation by body weight:
Small:
Animals weighing between 5-30 Kgs: Langur, young chital and young pig.
Medium:
 Animals weighing between 31-175 Kgs: Adult chital and yearling, adult pig, young sambar and yearling, and young gaur.
Large:
 Prey over175 Kgs: Adult sambar and adult gaur.
Predatory prey choice by prey size:
Tiger:               39% small, 44% medium, 17% large.
Leopard:          48% small, 51% medium, 1% large.
Wild dog:         43% small, 56% medium, 1% large.
The average weight of prey killed by the three predators respectively: Tiger - 92 Kgs, Leopard - 38 Kgs and Wild dog - 43 Kgs. The niche occupied by each predator showed that there was species selectivity among the predators. While the tiger favored the large and medium species, Leopards chose small and medium species much similar to the wild dogs. Further more tiger perdition showed a bias towards adult male chital, sambar and wild pig, Wild dogs were found to prey selectively on adult male chital while leopards avoided them. The study shows that in Nagarahole coexistence is based on choice and the availability of prey in the appropriate size class.
Behavioral and hunting techniques and patterns also seem to play an important role in the relationship between species. The study showed that wild dogs hunted almost always during the day. The dog course or run down their prey and therefore find it easier to hunt when visibility is good. Additionally they prey mainly on chital which are more active during the day. Tigers and leopards were found to be more nocturnal hunters thus there is temporal (time) separation from the dogs, however the leopards were found to be more active during the day in comparison to tigers. The leopard’s activeness during day could be due to a choice of its prey like the langur and chital that are active during the day.
Observations reveal that tigers and wild dogs are socially dominant over leopards but however not resulting in spatial separation. However tiger and leopards kill and eat wild dogs occasionally. The impression is that the need to defend kills does not play a significant role because of the dense cover and high tree density in Nagarahole.
Thus it can be summarized that ecological factors such as availability of appropriate size prey, dense cover and high tree density are of primary importance in Nagarahole when it comes to predator densities.
Interestingly enough even folklore never crowned the tiger as king of the jungle.
 
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