We Made Your Bed, Why Won’t You Lie in It? Food Availability and Disease May Affect Reproductive Output of Reintroduced Frogs

Abstract

Mitigation to offset the impacts of land development is becoming increasingly common, with reintroductions and created habitat programs used as key actions. However, numerous reviews cite high rates of poor success from these programs, and a need for improved monitoring and scientific testing to evaluate outcomes and improve management actions. We conducted extensive monitoring of a released population of endangered green and golden bell frogs, Litoria aurea, within a created habitat, as well as complementary surveys of a surrounding wild population. We then compared differences between the created habitat and natural ponds where extant frogs either bred or didn’t breed in order to determine factors that contributed to the breeding failure within the created habitat. We evaluated differences of L. aurea abundance, abundance of other fauna, vegetation, water quality, habitat structure, invasive fish, and disease between the three pond types (created habitat, breeding ponds, non-breeding ponds). We discovered that vegetation and invertebrate diversity were low within the created habitat, potentially reducing energy and nutritional resources required for breeding. Also, a greater proportion of frogs in the created habitat were carrying the chytrid fungal pathogen, Batrachochytrium dendrobatidis, compared to the wild populations. In addition to causing the potentially fatal disease, chytridiomycosis, this pathogen has been shown to reduce reproductive functioning in male L. aurea, and subsequently may have reduced reproductive activities in the created habitat. Conspecific attraction, pond hydrology, and aquatic vegetation may also have had some influence on breeding behaviours, whilst the presence of the invasive mosquitofish, Gambusia holbrooki, and heterospecific tadpoles were unlikely to have deterred L. aurea from breeding within the created habitat. Through the use of scientific testing and monitoring, this study is able to make recommendations for future amphibian breed and release programs, and suggests planting a diversity of plant species to attract invertebrates, creating some permanent ponds, connecting habitat with existing populations, trialling artificial mating calls, and following recommendations to reduce the prevalence of disease within the population.

Informing compensatory habitat creation with experimental trials: a 3-year study of a threatened amphibian

“…The presence of other tadpoles may also have prevented breeding, and should be investigated further. The greater abundance of L. aurea in ponds with higher aquatic insect diversity is probably related to a greater variety of prey items, and resource availability (Hamer et al, 2002; Bower et al, 2014; Klop-Toker et al, 2016), and concurs with previous research finding a positive relationship between invertebrate diversity and L. aurea abundance, as well as reducing the likelihood of extinction at an occupied site (Valdez et al, 2015). Although air temperature was not significant in our models, water temperature was positively correlated with abundance, possibly because water temperature is more indicative of the weather on a given day.…”

Disease and climate effects on individuals drive post‐reintroduction population dynamics of an endangered amphibian

“…, Klop‐Toker et al. , Murphy and Gratwicke ), it is imperative to quantify the effects of Bd on host populations using imperfect observational data. It is our hope that the framework developed here can be leveraged to better understand factors determining introduction success, and to develop more effective conservation interventions.…”

“…Some introductions in other systems have failed due to chytridiomycosis (Stockwell et al 2008, Soorae 2010, but the successful introduction of R. sierrae in Yosemite provides evidence that introductions can succeed even when Bd persists. Given the ongoing efforts to captively breed and then reintroduce threatened amphibians (Brannelly et al 2016, Klop-Toker et al 2016, Murphy and Gratwicke 2017, it is imperative to quantify the effects of Bd on host populations using imperfect observational data. It is our hope that the framework developed here can be leveraged to better understand factors determining introduction success, and to develop more effective conservation interventions.…”

Elevated salinity blocks pathogen transmission and improves host survival from the global amphibian chytrid pandemic: Implications for translocations

“…It is worth noting that there are probably scenarios where manipulating salinity on a scale that would be detectable in systems where salinity is naturally low could be difficult. Nevertheless, some systems such as coastal estuarine systems that are a mosaic of oligohaline and fresh water, as is the case in the environment of many persisting L. aurea populations (Klop‐Toker et al., ; Valdez et al., ), may offer opportunities to pursue this as a passive strategy, for example, by manipulation of tidal flows and inundation at a landscape level, or actively by the addition of sea salt to water bodies.…”