Our research focuses on the population dynamics of plants and how they are influenced by impacts of natural disturbances and global environmental change. We are particularly interested in the interactive effects of fire, grazing and drought in grasslands and woodlands in southern Australia, and how climate change, fragmentation and shrub encroachment affect ecosystems.

Monday, 4 September 2017

The "wow" moments in ecology

Every now and then you read a paper or, better still, make an observation that makes you step back and go "wow! Isn't that awesome?"

I had one of those moments recently. It involved the a) reading of a paper that b) made me recall an observation I made a few years ago which intrigued me at the time. I'd filed away the observation hoping to re-visit it one day. Maybe that day has arrived! Such moments reminds you of why you do what you do (in my case, studying the dynamics of ecosystems) and the excitement that can be generated by new discovery.

All good questions in ecology stem from observations of nature that generate testable hypotheses. For me, natural history informs what I do on so many levels. Observing the form of plants invariably gets you thinking about the function of plants. Looking at a stand of trees gets you thinking about why there are no seedlings. Compiling a species list for a 1m2 quadrat and getting to 42 plant species invariably gets you to thinking about the mechanisms that allow so many species to coexist in such a small area. It's how careers are built - curiosity demands explanation.

Recently I stumbled across a paper in Ecology - in a new (and welcome) section of the journal titled The Scientific Naturalist - that excited me no-end. A bunch of ecologists (Dell et al. 2017) had been burning pine savanna in the USA when they stumbled across one answer to a question that has rarely been asked: where do invertebrates hide to survive fire? Typical answers include: they shelter under rocks, down burrows, under bark. But, it seems that survival might actually include climbing / walking / jumping up tree trunks to escape the direct flame zone.

Sticky tape acts as an effective trap for grasshoppers and other invertebrates moving up trunks to escape fire

Using sticky tape sourced from the local hardware store, wrapped around tree trunks to trap insects as they move up trees (you can figure out direction of travel, abundance and species composition using this simple method), the researchers describe a hitherto poorly documented phenomenon. Insects moving up trees makes sense if fire is frequent and flames are low. But it can't be a chance thing; something must trigger this response. Wow! How cool is this??

What's really great is Dell et al's explanation for the behaviour they observed. I'd have imagined that insects would be responding to chemical cues from smoke. Given there are over 60 different compounds in smoke, it makes sense - to me - that one of these chemicals might trigger such a uniform and rapid response. Smoke drifts ahead of the flame zone and therefore provides some time for insects to respond.

But no, the authors suggest that insects respond to the sounds of an approaching fire. We have a testable hypothesis right there! Apparently the frequency ranges associated with fire lie well within the arthropod hearing range. Who would have guessed!

So how does this relate to my own observations? Well, I read the paper and realised that I too had seen this behaviour. But I'd seen so much more!!! When burning tropical savanna at the Territory Wildlife Park in Darwin a few years ago, I was stunned when we saw ants, beetles, FROGS and GECKOS all using the trunk of a smooth-barked eucalypt tree as a veritable highway as a fire moved closer. They were all going one way - up the trunk. Not far, but definitely up. In these fires, being 2-3 m up a tree will be usually outside the flame zone and, as long as they can withstand the convective heat for a short period, then their chance of survival seemed pretty good.

The curious observation of animal movements up trees in the face of oncoming fire needs to be better documented. How common is it? What species typically respond in this way? Do they survive fire? How does the invasion of Gamba Grass into tropical savanna affect this survival strategy? What's the cue or cues that act as triggers for movement? If frogs are responding to the noise of a fire, then this suggests their hearing is more than just about finding a partner (i.e. sexual selection), it's about survival in a fire-prone landscape. Now that's cool! And probably rarely, if ever, been thought possible. I guess that was a bit of a "wow" moment for me.

Dell et al. (2017) An arthropod survival strategy in a frequently burned forest. Ecology doi:10.1002/ecy.1939