Australia: The Land Where Time Began

A biography of the Australian continent 

Riversleigh Bandicoots

Prior to the arrival of Europeans in Australia the diversity of bandicoots in particular habitats appears to have been lower than has been found in the Riversleigh depoists. Usually no more than 4 species occupied the same habitat at the one time. The semi-arid grasslands were the places where bandicoot diversity was highest before Europeans, possibly because of the firestick-farming practiced by the Aboriginal People in which it was customary around Australia to burn off in patches so there was a patchwork of areas of varying stages of recovery. This led to a patchwork of habitats suitable for various species, allowing more species to inhabit an area. These grasslands occurred in places such as the western Nullarbor Plain. In this area bandicoots such as the Pig-Footed Banidcoot (Chaeropus ecaudatis), the Short-nosed Bandicoot (Isoodon obesus) and the Western Barred Bandicoot (Perameles bouganiville) of the family Peramelidae, the Greater Bilby (Macrotis lagitis), of the Thylacomyidae.

The species mix in the grasslands on the Nullarbor Plain, a relatively diverse habitat, where 1 species per genera, and from 2 families existed simultaneously, suggests the component species need to be sufficiently different to exist in the same area. This is the sort of diversity that the firestick-farming encouraged.

The highest bandicoot diversity in New Guinea occurs in the mid montane forests. In these forests there are 3 genera of peroryctids, Microperoryctes, Perorcytes, Echymipera, with a total of 5 species. These bandicoots are much more similar to each other than is the case in sympatric species in Australia, but they are differentiated by size.

At Riversleigh, the bandicoot populations show patterns more like those seen in New Guinea than those seen in modern Australian habitats. One of the deposits at Riversleigh contains about 10 different species, which is more than twice the number known from any modern Australian habitat, or even New Guinea habitat. A possibly reason for the prolific bandicoot populations in the Oligocene-Miocene is that there were no rodents at that time. Bandicoot diets range from carnivorous-omnivorous to herbivorous. In habitats that were once occupied by bandicoots they have now been replaced by rodents. The murids now comprise about 25 % of mammal species known from Australia and New Guinea.

The rodents probably first arrived in Australia sometime in the latter part of the Miocene, and possibly at some point between the Pliocene and the Late Pleistocene at least 3 murid lineages invaded the rainforests of Australia and New Guinea. It seems likely that these invaders replaced some of the bandicoots, especially the smaller species.

It seems likely that the Oligocene-Miocene bandicoots partitioned the food source in some way to allow a number of species to occupy the habitat simultaneously, possibly on the basis of size, some being nocturnal, some being arboreal, etc. The food would have been plentiful, and most likely constant. By the Pleistocene, bandicoot diversity had plummeted to only 1 known species. By this time there were more than 12 rodent species in the Riversleigh rainforest.

Sources & Further reading

Michael Archer, Suzanne J. Hand & Henk Godthelp, Australia's Lost World: Riversleigh, world heritage Site, Reed New Holland