The mystery of Australia's small mammal declines

Across the top end of Australia, from Cape York to the Kimberly Mountains, populations of smaller marsupials and native rodents are collapsing.  What's going on?

Tapping into traditional knowledge to help solve a mystery (photo by Ian Morris)

Tapping into traditional knowledge to help solve a mystery (photo by Ian Morris)

Several studies in recent years have documented the declines.  A few have shown major changes in a single location, such as Kakadu National Park.  Others have compiled scattered information over a much broader area; one innovative study used interviews with Aboriginal communities to piece together evidence (find study here).

The bottom line: many species that used to be common have become vanishingly rare, or have geographic ranges that are collapsing. 

What is causing all this?  No one is sure.  Some suspect it could be severe overgrazing by livestock, especially during droughts.  During such times the vegetation can become badly damaged--as we're seeing at present in many areas

Others think altered fire regimes are the cause.  And yet others suspect predation by feral cats, with a possible role for lethal cane toads for certain predatory mammals.

Whatever the cause, this might be a new biodiversity crisis for the Land Down Under, which has already lost more native mammal species than any other continent.  

Earth's big predators 'being decimated'

Being the 'king of the jungle' is not as fun as it sounds.  An international research team has just published a paper in Science showing that most of the 31 largest mammal predators on Earth are in dire straits.

Tigers in trouble (photo by Priya Davidar).

Tigers in trouble (photo by Priya Davidar).

These mega-predators, which include tigers, polar bears, wolves and sea otters, among others, are being decimated by habitat loss and human persecution.  Only a quarter of the species, such as the American black bear and puma (mountain lion), are showing some signs of population stability. 

Most predators are in precarious shape.  The tiger, for instance, is clinging to survival in just 7% of its original geographic range and just 5% of its original numbers.

The authors go beyond describing the ongoing decline of big predators; they also highlight the varied ecological consequences.  Large predators can play a dominating role in ecosystems, having profound impacts on many other species and ecosystem processes.

One of the coauthors of the study, Euan Richie of Deakin University in Australia, has written a lively summary of its key conclusions and implications. 

Clearly, one of the greatest challenges humankind faces is maintaining living space for species that need large expanses of habitat to survive.