Long-Term Monitoring of Frog Populations in Response to Environmental Watering in the Gwydir River Catchment, New South Wales, Australia

Abstract

<p>Water is the basic ecological requirement for frogs associated with floodplain wetlands. River regulation severely reduces inundation of wetland habitats in riverine and floodplain environments, contributing to the decline of frog populations. Delivering environmental water to mimic flooding regimes is an effective strategy for improving habitat for the persistence of frog communities. Though inundation has the potential to influence frog diversity and community composition, long-term trends are poorly understood.</p> <p>My thesis focused on understanding frog responses to wetland inundation in the Gwydir wetlands in the northern Murray-Darling Basin, an internationally recognised and significant site, that is severely affected by river regulation. In my thesis, I aimed to (1) investigate the variation in frog abundance, richness, dominance (the inverse of species evenness), and beta diversity (comparisons of community composition between communities) over a five-year period and explore how this variation related to change in inundation extent, temperature, rainfall, and vegetation cover; and (2) assess the variation in chorusing activity of frog communities due to wetland inundation by using passive acoustic monitoring to document and examine chorus patterns before and after the arrival of water from environmental flows.</p> <p>I analysed frog survey data that were collected using visual encounter and timed-calling methods from 2015 to 2019, in September and November each year, with follow up surveys in February 2017 and March 2019. The analysis revealed a significant positive impact of wetland inundation on the abundance, species richness and beta diversity (comparisons of community composition between communities) patterns of the frog community, and the abundance of <i>Limnodynastes tasmaniensis, Limnodynastes fletcheri, Crinia parinsignifera, Litoria peronii</i>, and <i>Litoria latopalmata</i>. Richness of frogs was higher in warmer temperatures, and frog community dominance (the inverse of species evenness) decreased with decreasing vegetation cover. The method of sampling (visual encounter survey vs. times-auditory surveys) had little effect on the positive associations with wetland inundation.</p> <p>Chorusing activity data in response to wetland inundation were collected from automated call recorders, for four nights immediately before and after two flow events (1) in OctoberNovember 2019 for five sites and (2) in February-March 2020 for one site. Total species richness of calling male frogs significantly increased after the arrival of water, but chorusing patterns varied somewhat among species and sites. For example, wetland inundation positively affected choruses of <i>Limnodynastes tasmaniensis</i>, and negatively affected choruses of <i>Limnodynastes fletcheri</i>. Further, some species were detected both before and after flow, whereas <i>Cyclorana alboguttata</i> was only detected before flow and <i>Cyclorana verrucosa, Cyclorana cultripes</i>, and <i>Limnodynastes salmini</i> were only detected after flow. Collectively, my results demonstrate the overall positive impact of environmental flow on floodplain frogs and highlight interspecific variation that occurs within the community</p>