A field experiment to discover how drought and environmental-water interacts with disease to influence frog survival. (APSF 20024)

APSF 20024 | Amount: $42,000 | Project Leader: D Driscoll | Project Period:

A project undertaken at Deakin University, and supervised by Don Driscoll.

Prolonged drought associated with climate change is driving widespread loss of frogs from Australian landscapes, altering food webs, and reducing ecosystem services. Environmental watering offers a way to prevent declines, but these watering solutions are complicated by interactions with the amphibian disease chytridiomycosis. Chytrid has driven declines in 43 Australian species including seven extinctions. Chytrid could interact with drought in multiple ways  because it dies if it dries out, and its success depends on transmission to new vulnerable hosts.

Disease transmission can increase when frogs shelter together in shared refuges during dry periods. Further, young frogs can be more vulnerable to infection due to compromised immune systems resulting from accelerated development in drying ponds. If land managers respond to drought by providing moist refuges to reduce mortality from early pond drying, they might also increase disease transmission. Similarly, using environmental watering to prevent early pond drying might produce frogs with strong immune systems, but wet conditions may also increase the risk of chytrid infection. We urgently need to understand these interactions because frogs are already declining from both drought and chytrid, with no effective management response available.

This study aims to discover how environmental-water and chytrid interact to influence frog survival using a field experiment. We will focus on the endangered Bibron’s toadlet (Pseudophryne bibronii) because drought and chytrid is suspected to have caused widespread declines. Bibron’s toadlets breed in small, ephemeral pools in autumn, a system with enormous potential for assistance through environmental water because very small amounts of water are needed.

Brown Toadlet male found on the east side of Sugar Loaf Road, Denver. (Picture credit. David De Angelis)

Our objectives for this project are:

1.  To experimentally evaluate the potential for environmental watering to increase toadlet recruitment to metamorphosis while discovering any effects of watering on chytrid prevalence and other frog species.

2.  To experimentally evaluate the potential for artificial damp refuges to increase toadlet survival between years, while discovering effects of watering refuges on chytrid prevalence.

Ongoing e-water programs are associated with mega-litre scale watering projects and appear to have benefitted spring breeding frogs in some circumstances (Hoffmann 2018; Wassens et al. 2019). In contrast, this study will be the first attempt to use small-scale ewater to sustain an autumn-breeding frog. The project will set the groundwork for future research into scaling up e-watering approaches, such as integrating ecological, spatial, social and economic models to discover where our approaches will have the most benefit and can be cost effectively deployed. Such future research would enable strategic planning using methods we develop in this study.