Can water exclusion limit the ecological impact of invasive cane toads?

Abstract

The proliferation of artificial water points (AWP) to enhance livestock production has fundamentally changed the ecology of dryland ecosystems. By providing a constant source of surface water, AWP can affect the density, distribution and activity of water-dependent native and invasive species. Thus, AWP have the potential to facilitate trophic and competitive interactions, thereby amplifying their impact on the structure and composition of resident animal and plant communities. Recent studies suggest that a strategic manipulation of surface water availability in dryland biomes could be a useful management approach to reduce the negative impacts of native herbivores on vegetation and to mitigate the spread and impact of water-dependent invasive species. However, there is only limited empirical evidence that water exclusion could provide benefits for the ecology and community structure of dryland ecosystems by returning them to their natural water-limited state. Especially for invasive species where the effectiveness of a large scale water exclusion strategy has not been sufficiently evaluated. This is particularly important for high-impact invasive species such as the cane toad Rhinella marina, an anuran that is currently invading northern and arid regions of Australia. Due to their potent chemical defences cane toads put a wide range of native predators at risk of toxic ingestion. During periods of prolonged hot and dry conditions which typically prevail in arid regions, cane toads need regular access to water to survive. In rangeland areas of the Tanami Desert in Australia's Northern Territory, the existence of AWP fitted with two types of reservoirs provided an opportunity to examine whether exclusion from access to surface water at AWP could limit the abundance and ecological impacts of cane toads. Cane toads could readily access surface water at AWP fitted with earthen dams as reservoirs but cane toads could not access surface water at AWP fitted with water tanks. This study has implications for the management of cane toads in Australia'sarid and semi-arid rangelands. The findings demonstrate that excludingwater-dependent species from access to surface water at AWP by changing the waterreservoir system from traditionally used earthen dams to water tanks results in areduction of both their population densities and ecological impacts.

Date of Award	2015
Original language	English