Arid zone plants and animals are amazingly adept at toughing it out through the extremes of desert environments. After years of waiting underground, frogs burst forth in their thousands following a good rain. Many plants go dormant during long dry times, conserving just enough energy to spring into new growth and flower when conditions improve. Animals like bilbies can survive without drinking free water, managing to find the moisture they need in the grubs and tubers they eat.
A burrowing frog (Neobatrachus centralis) emerges from the sand after rain
But with the increasingly hot conditions predicted (and already observed) under climate change, how much “extreme” can these ecosystems take? For better or worse, we’re starting to find out.
The 123 km2 Arid Recovery Reserve is a restoration experiment and living laboratory for conserving and understanding arid ecosystems. So far, 2019 is the driest year since the reserve was established in 1997. It’s followed two years of well below average rainfall. What’s more, the 2018-19 summer was a real scorcher. The average maximum temperature was 38 °C. Half the days were 40 °C or above (46 days out of 93), and some heatwaves went for 11 days straight.
The last time a summer was so extreme (in 2001), stick-nest rats suffered 80% mortality due to the hot conditions. We saw the same trends play out again this summer with a significant decline in rat activity . Of 25 active stick-nest rat nests monitored in one part of the reserve in April 2018, only seven were still active at the same time this year. Unlike most of the other small to medium sized mammals in the reserve, stick-nest rats do not dig burrows. They live mostly above ground in shallow scrapes beneath the stick castles that they build. However, we do know that they will seek shelter down bettong and bilby burrows in summer to try and avoid the hot temperatures. They’re also more particular in the food plants they need. Stick-nest rats are herbivores with a preference for succulent plants with high water content – the more succulent and juicy the better. The stick-nest rats have likely had the added strain of reduced food resources with the drought limiting plant growth and a reduction in those more palatable food plants from overgrazing by other reintroduced herbivores.
What can be done in such a situation? We don’t want to lose stick-nest rats from the reserve. They are an important part of the ecosystem and a species in need of feral predator-free safe havens like Arid Recovery. The population here is also the only one persisting in the arid part of its former range. What’s more, there are tantalising hints that our stick-nest rats may have started to adapt to arid conditions in their 20 years back in the desert so their genetic changes could be important. We also want to understand what is going on, and what might work to improve the population’s survival here and elsewhere. Finally, what are the implications for stick-nest rats and other species in the arid zone as the climate continues to warm?
So we direct our concerns for our much loved stick-nest rats into sciencing-up this problem, trying a range of interventions and testing each to see what works.
We’re monitoring the remaining active nests closely with camera traps to record how active rats are and to pick up whether they breed this year. We are implementing a “rain” experiment by carting water and spraying it onto 100 m2 plots to simulate a solid dump of rain (the equivalent of 24 mm) with the aim of stimulating growth of stick-nest rats’ preferred food plants. The vegetation’s response will be compared with control areas which receive only natural rainfall (if any). Rainfall is naturally extremely patchy in the arid zone and normally animals can move towards areas that have received rain or animals hang on in patches that have received rain and then recolonise other areas over time. Unfortunately, fenced reserves are often not large enough to catch random rainfall events and they do not allow animals to move or recolonise between widely spaced patches of habitat. Mimicking patchy rainfall events may be the best way to ensure arid zone fenced reserves retain species during long droughts.
We are also studying how rats cope with temperature extremes and how they use different shelters during hot periods. Understanding their thermal requirements may enable us to augment their shelters to improve their thermal insulation.
The weather bureau is predicting another nasty summer. We hope our interventions help the stickies get through it. But if they don’t, we’ll have learnt a lot more about the thresholds the species can tolerate and bring up a whole set of new questions about what their long-term future in the arid zone might be.
How can you help?
If you’re local we’d love some extra helpers to cart water. Get in touch with us at firstname.lastname@example.org. You can also adopt a stick-nest rat or make a donation at www.aridrecovery.org.au – this will help us support stickies through the drought and help us do the research to understand what works.