Large monsters from mainland
Tigers once were giants in Java. Their body masses reached up to 300 kg (Volmer et al., 2016), a size recorded only for Siberian tigers today. In contrast, prehistoric tigers in Java, were only up to sizes of 75 – 141 kg (Mazák, 1981). It is not to mention that Homo erectus must have been an easy catch for them.
But what actually forced tigers to develop into such giant man-eaters?
Tigers were present in Java since 1.2 million years (van den Bergh et al., 2001a). Colder climate during the Pleistocene concluded into lower sea levels, and lower sea levels let so called Sundaland getting exposed. First tigers must have reached Java by swimming and had a size comparable to Java tigers today. However, later sea-levels became even lower and Java was connected to the mainland via landbriges(De Vos and Long, 2001; van den Bergh et al., 2001b). New species from continental Asia expanded into the Southeast Asian Archipelago, and it might be, that larger tigers were also invading Java during the late Pleistocene (starting by around 126,000 years ago) and meeting their smaller cousins. The Bergman as well as the Island rule, though, would support the existence of smaller tigers rather than larger tigers, which are more adapted to cold climates (Bergmann rule) and Bali tigers adapted extreme small sizes of down to 60 kg as adaption to Islands (Island rule).
However, when smaller tigers are better to subsist on the Islands why did the large Ngandong tiger dominate? Size change of terrestrial carnivores on Islands was influenced, especially by the availability of prey of appropriate body size(Lyras et al., 2010). When prey appropriate for the carnivores body size was not available, carnivores changed their size in response to the available prey offer(Lyras et al., 2010).
Prey was actually present in a huge variation of sizes, ranging from Muntjaks, Lydekker deer, Duboisia antelopes, buffalos, rhinoceros and elephants(van den Bergh et al., 2001b; Volmer, 2013). In total sizes of at least 10 kg up to several tons were represented in the prey spectrum. At a first glance no need to change the body sizes in tigers, no matter if small or large. However, tigers were for sure not the only predators around this time in Java.
In case of the large predators in Java, there were also Homotherium ultimum, Megantereon sp. and a Merriam’s dog present. These animals were hunting prey of the sizes of 20 – 100 kg, and although there were small differences, there must have been high competition expected for animals in these prey classes (Volmer et al., 2016).
However, there was no strong niche overlap between tigers and Homotherium ultimum, and thus, it was considered as unlikely that competition pressure by Homoterium forced tigers to increase their body mass.
however, Merriam’s dog and the short-faced hyaena had the highest competition potential. How did tigers react on the high competition pressure?
When prey kills the predator
“Very large prey such as elephants (only calves are killed by tigers), or low-density ungulates such as muntjac and four-horned antelope, do not appear to be important in predator diets” (Andheria et al., 2007). Usually larger prey is harder to overcome than smaller prey, because it requests a larger amount of power from the predator to tackle and overcome the prey animal, which is of cause defending itself. Thus, only tigers and lions occasionally hunt on large animals, mainly the calves, weak or old individuals(Joubert, 2006; Power and Shem Compion, 2009; Sunquist, 1981)
Around 10% of tigers die because of hunting injuries (Grey, 2009). The hoofs of giraffes or the horns of buffalo can kill a lion, and elephants, rhionoceroses and hippos can kill a lion or tiger by their sheer power. Lions in the Serengeti are known as risk-sensitive foragers maximizing food intake such that their modal prey size is 150 kg (Packer, 1986; Packer et al., 1990)).
Large size, less competition
So wasn’t it even more risky to increase size and focus on large prey? Yes and no. The increase of body size in Java tigers made it less risky to hunt large prey, but also necessary. The prey size needs to be optimal for the predators energy intake, and by increasing the size it was less dangerous as well as more energy efficient to hunt large prey. In this way, Ngandong tigers were minimizing the overlap of prey profiles with Homotherium, Megantereon and Merriam’s dog(Hertler and Volmer, 2008). Thus, the large size of Ngandong tigers could have also been developed as a consequence of competition rather than the invasion of large tigers from the mainland. However, during the following Punung faunal level, tigers decreased in size competition and developed into tigers typically of the size for Java tigers.
Andheria, A.P., Karanth, K.U., Kumar, N.S., 2007. Diet and prey profiles of three sympatric large carnivores in Bandipur Tiger Reserve, India. Journal of Zoology 273, 169-175.
De Vos, J., Long, V.T., 2001. First settlements: Relations between Continental and Insular Southeast Asia, in: Sémah, F., Falguères, C., Grimaud-Hervè, D., Sémah, A.-M. (Eds.), Origine Des Peuplements et Chronologie des Cultures Paléolithiques dans le Sud-Est Asiatique, Semanjung, Paris, pp. 225-249.
Grey, J., 2009. Prey selection by tigers (Panthera tigris tigris) in the Karnali Foodplain of Bardia National Park, Nepal. Imperial College, London, p. 60.
Hertler, C., Volmer, R., 2008. Assessing prey competition in fossil carnivore communities — a scenario for prey competition and its evolutionary consequences for tigers in Pleistocene Java. Palaeogeography, Palaeoclimatology, Palaeoecology 257, 67-80.
Joubert, D., 2006. Hunting behaviour of lions (Panthera leo) on elephants (Loxodonta africana) in the Chobe National Park, Botswana. African Journal of Ecology 44, 279-281.
Lyras, G.A., van den Geer, A.A.E., Rook, L., 2010. Body size of insular carnivores: evidence from the fossil record. Journal of Biogeography 37, 1007-1021.
Mazák, V., 1981. Panthera tigris. Mammalian Species, 1-8.
Packer, C., 1986. The ecology of sociality in felids. , in: Rubenstein, D., Wrangham, R.W. (Eds.), Ecological aspects of social evolution: birds and mammals. Princeton University Press, Princeton, pp. 429–451. .
Packer, C., Scheel, D., Pusey, A.E., 1990. Why Lions Form Groups: Food is Not Enough. The American Naturalist 136, 1-19.
Power, R.J., Shem Compion, R.X., 2009. Lion Predation on Elephants in the Savuti, Chobe National Park, Botswana. African Zoology 44, 36-44.
Sunquist, M.E., 1981. The Social Organization of Tigers (Panthera tigris) in Royal Chitawan National Park, Nepal, Smithsonian Contributions to Zoology No 336. Smithsonian Institution.
van den Bergh, G.D., de Vos, J., Sondaar, P.Y., 2001a. The Late Quaternary palaeogeography of mammal evolution in the Indonesian Archipelago. Palaeogeography, Palaeoclimatology, Palaeoecology 171, 385-408.
van den Bergh, G.D., de Vos, J., Sondaar, P.Y., 2001b. The Late Quaternary palaeogeography of mammal evolution in the Indonesian Archipelago. Palaeogeography, Palaeoclimatology, Palaeoecology 171, 385-408.
Volmer, R., 2013. Struktur und gemeinsame Nutzung von Nahrungsressourcen in fossilen Carnivoren-Gilden. Goethe University, Frankfurt.
Volmer, R., Hertler, C., van der Geer, A., 2016. Niche overlap and competition potential among tigers (Panthera tigris), sabertoothed cats (Homotherium ultimum, Hemimachairodus zwierzyckii) and Merriam’s Dog (Megacyon merriami) in the Pleistocene of Java. Palaeogeography, Palaeoclimatology, Palaeoecology 441, 901-911.