Thursday, 8 June 2006

A really cool rainforest

(Actually it's a really cold rainforest right now. But there's no better time to visit.)

I love the rainforests. That's lucky, really, because I spend a lot of time in them, looking at the fauna, falling over the flora and trying to piece together their history from the late Mesozoic to the Pleistocene.

Most of my studies have been in vine forest and vine thicket (dry rainforest) in tropical Queensland. (When I get the scanner—currently on order—I'll put up the pictures.) Now I'm interested in Victoria's cool temperate rainforests, particularly the Myrtle Beech forests of the Otway Ranges.

You probably won't be surprised that the Otway forests are home to a number of endemic species, including a black snail (Victaphanta compacta) (see the article below), stonefly (Eusthenia nothofagi)*, caddisfly (Taskiria otwayensis), burrowing cray (Engaeus fultoni) and grey gum (Eucalyptus aff. cypellocarpa). The Grey Gum is a bit iffy, though. It may or may not be different from the Mountain Grey Gum (Eucalyptus cypellocarpa). The animals are okay, though. They are definitely short-range endemics.

Why do the Otway forests contain so many species that are found nowhere else? The first thing to establish is that isolated blocks of forest often have endemic species. This is nothing unusual.

Rainforests require a high rainfall. (File that under B for the bleedin' obvious.) During the Pleistocene ice ages, the climate was cool and dry and not at all favourable for them. The forest contracted into patches—each patch an island surrounded by a sea of dry-adapted vegetation. Over time, populations of species in the forest islands reacted in exactly the same way as would populations on oceanic islands. Some went extinct because the islands had insufficient resources to support them. Others persisted.

Of the ones that persisted, some were able to move between patches. They maintained a flow of genes between populations so there was no differentiation. The forest patches may have been isolated but the animals (or plants) weren't.

You can see what would happen to those that couldn't move. No exchange of genes with other populations meant that they developed in isolation. Over time each isolated population differentiated from the others. This is probably what happened among the endemic invertebrates in the Otways.

The next step is to use morphological and molecular information about each group of animals (Victaphanta snails, Eusthenia stoneflies etc) to reconstruct their evolutionary history. Then we can see which species are most closely related to those from the Otways.

Which rainforest holds the sister species? I'm putting some money on the Central Highlands of Victoria. But I'm saving a bit for the Tasmanian west coast.

*remind me to tell you the tale about how the presumed extinct Otway Stonefly was found alive and well by a scientist on holiday.

[Thanks to MM yet again for the photograph of the Myrtle Beech forest in the Otways. I think that's somewhere around Mait's Rest. Or Melba Gully.]

No comments: