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

Abstract

On Java during the Pleistocene, tigers of more than 300 kg occurred, but these are restricted to a single Late Pleistocene faunal unit, while Early and Middle Pleistocene tigers possessed body masses comparable to those of historic Javanese and extant Sumatran tigers. The aim of this study is to test if competition for prey with other hypercarnivorous taxa such as sabertoothed cats and the large Merriam's Dog was the driver for the increase in body mass of tigers. We calculated body masses and prey mass spectrum for tigers and potential competitors using linear regressions. Niche overlap was then estimated based on the prey mass spectrum after which niche overlaps were used as indicators for competition potentials. Reconstructed body mass for Homotherium ultimum, Hemimachairodus zwierzyckii, Megacyon merriami are 154 kg (comparable to Homotherium from Untermassfeld), 130 kg and 52 kg, respectively. The niche overlap between tigers and Merriam's Dog is highest (100%) while it is comparatively low (60 %) between tigers and Homotherium ultimum. In order to reduce competition, tigers seem to have increased body mass to avoid competition especially with Merriam's Dog whereas Merriam's Dog on its turn seems to have decreased body mass to avoid competition with tigers. The sabertoothed cats on the other hand seem to have been unable to adapt and went extinct.

A new specimen-dependent method of estimating felid body mass

“…Some have used simple isometry to estimate fossil specimens (Sorkin, 2008;Christiansen & Harris, 2009). Others have developed regression equations that predict the body mass of extinct species based on allometric relationships between bone measurements and body masses of living felids (Anyonge, 1993;Christiansen & Harris, 2005;Volmer, Hertler & van der Geer, 2016). Today, usually the latter method of estimating body masses has been used to estimate not only the body mass of extinct felids, but also other large prehistoric mammals (Christiansen, 1999;Wheeler & Jefferson, 2009;Figueirido et al, 2010;Soibelzon & Schubert, 2011).…”

Testing the Competition Hypothesis: How Niche Overlap Between Carnivoramorphans and Creodonts Changed From the Start to the End of the Eocene

“…Similarly, the large body size of P. concolor means that it cannot fulfill its daily caloric needs by exclusively hunting the same small prey as L. canadensis, though P.concolor is not precluded from occasionally feeding on small prey (Hemmer 2004). Calculating Prey-Focus Mass (PFM), which is based on the predator's body mass and the body masses of the prey species within the same geographic area, can be used infer the potential sizes of prey species a carnivore is able to access (Hemmer 2004;Volmer et al 2016;Christison et al 2020).…”

“…Behavioural shifts are a form of character displacement that can allow multiple species of morphologically similar carnivoran to coexist in the same community (Brown and Wilson 1956;Strong et al 1979;Dayan and Simberloff 1998;Volmer et al 2016). One example are the neotropical felids: jaguar (Panthera onca), cougar (Puma concolor), ocelot (Leopardus pardalis), jaguarundi (Herpailurus yagouaroundi), margay (Leopardus wiedii), and oncilla (Leopardus tigrinus) exhibit geographic overlap and morphological similarity (Di Bitetti et al 2010;Silva-Pereira et al 2011;Sánchez-Barradas and Villalobos 2020).…”

“…To PFMs for each species were then grouped into size categories following the methods of Hemmer (2004), Volmer (2008), andVolmer et al (2016), with the assumption being that the PFM of a carnivorous species, combined with their foraging strategy (e.g. group hunting, scavenging) will determine which prey-mass category the species will focus on.…”

“…To test the competition hypothesis, I explore the niches of creodont and carnivoramorphan species using a combination of dietary and locomotor indicators (Van Valkenburgh and Koepfli 1993;Hemmer 2004;Friscia et al 2007;Hertler and Volmer 2008;Friscia and Van Valkenburgh 2010;Polly 2010;Volmer et al 2016;Slater and Friscia 2019). The dietary niches of extinct species can be inferred by examining their tooth and cranial morphology, then making comparisons to extant species whose diets are well-understood (Van Valkenburgh and Koepfli 1993;Meachen and Van Valkenburgh 2009).…”