On the rarity of big fierce carnivores and primacy of isolation and area: tracking large mammalian carnivore diversity on two isolated continents

Abstract

The hypothesis that low productivity has uniquely constrained Australia's large mammalian carnivore diversity, and by inference the biota in general, has become an influential backdrop to interpretations of ecology on the island continent. Whether low productivity has been primary impacts broadly on our understanding of mammalian biogeography, but investigation is complicated by two uniquely Australian features: isolation and the dominance of marsupials. However, until the great American biotic interchange (GABI), South America was also isolated and dominated by pouched carnivores. Here, we examine the low-productivity hypothesis empirically, by comparing large mammalian carnivore diversities in Australia and South America over the past 25 Myr. We find that pre-GABI diversity in Australia was generally comparable to or higher than diversity in South America. Post-GABI, South American diversity rose dramatically, pointing to isolation and phylogenetic constraint as primary influences. Landmass area is another important factor. Comparisons of diversity among the world's seven largest inhabited landmasses show that large mammalian hypercarnivore diversity in Australia approached levels predicted on the basis of landmass area in Late Pleistocene-Recent times, but large omnivore diversity was low. Large marsupial omnivores also appear to have been rare in South America. Isolation and competition with large terrestrial birds and cryptic omnivore taxa may have been more significant constraints in this respect. Relatively high diversity has been achieved in Late Quaternary America, possibly as a result of 'artificially' high immigration or origination rates, whereas that in contemporaneous Africa has been surprisingly poor. We conclude that isolation and landmass area, rather than productivity, are the primary constraints on large mammalian carnivore diversity. Our results quantify the rarity of large hypercarnivorous mammals worldwide.

Climate change frames debate over the extinction of megafauna in Sahul (Pleistocene Australia-New Guinea)

“…As commonly used in the context of extinctions in Sahul, the term megafauna refers to an arbitrary compilation of relatively large mammalian, reptilian, and avian taxa, ranging in size from ∼10 kg or less up to >2,000 kg (20)(21)(22)(23). In addition to Diprotodon optatum and Thylacoleo carnifex (Fig.…”

Contribution to the knowledge of the Sparassocynidae (Mammalia, Metatheria, Didelphoidea), with comments on the age of the Aisol Formation (Neogene), Mendoza Province, Argentina

“…However, dasyurids and most thylacinids appear less derived than A. henkgodthelpi in, for example, their more V-shaped centrocristae and better-developed protocones and conules. A straight centrocrista occurs only in the modern thylacinid Thylacinus cynocephalus and the Oligo-Miocene fossil forms T. macknessi, T. potens, and Wabulacinus ridei (Wroe and Musser 2001: character 10), all of which are much larger than A. henkgodthelpi (estimated body mass >5kg; Wroe et al 2004, Travouillon et al 2009). Dasyurids are also characterised by a relatively anteriorly-placed StD (further anterior than the metacone, close to the ectoflexus) that is distinctly larger than StB, particularly in smaller (<100g) forms, such as species of Sminthopsis, Antechinus and Planigale (Archer 1976;Wroe 1997); this is unlike the very small, labiolingually compressed StD directly labial to the metacone seen in A. henkgodthelpi.…”

Megafaunal extinction in the late Quaternary and the global overkill hypothesis

“…To a lesser degree, and through a filter barrier that clearly excluded taxa not adapted to high latitudes, this also applies to the Americas through intermittent connection to Eurasia-Africa and each other. Area correlates positively with species richness and maximal body mass (Wroe et aL 2004a) and communities with higher species richness are less susceptible to invading species (Case 1990). On the basis of size and isolation, the faunas of the Americas and Australia were inherently more vulnerable to stress than those of Afro-Eurasia.…”

“…Alroy (1999,2001) contends that rather than go extinct, megafaunal species should have benefited from climatic change during the terminal Pleistocene in North America, because rising temperatures and rainfall increased productivity. Superficially, this makes sense, but the relationship between climate, productivity and species richness is not simple (Kondoh 2001, Wroe 2004a) and global-warming, as well as cooling, have precipitated widespread extinctions in past and present biomes (Bown et al 1994, McLaughlin et al 2002. Global warming may locally increase or decrease productivity (Knapp et al 2002), but the imposition of a more productive environment can spell doom for species that are not adapted to newly emerging habitats.…”