Calling phenology of a diverse amphibian assemblage in response to meteorological conditions

Phenological mismatches mitigate the ecological impact of a biological invader on amphibian communities

Horizon scans have emerged as a valuable tool to anticipate the incoming invasive alien species (IAS) by judging species on their potential impacts. However, little research has been conducted on quantifying actual impacts and assessing causes of species-specific vulnerabilities to particular IAS due to persistent methodological challenges. The underlying interspecific mechanisms driving species-specific vulnerabilities therefore remain poorly understood, even though they can substantially improve the accuracy of risk assessments. Given that interspecific interactions underlying ecological impacts of IAS are often shaped by phenological synchrony, we tested the hypothesis that temporal mismatches in breeding phenology between native species and IAS can mitigate their ecological impacts. Focusing on the invasive American bullfrog (Lithobates catesbeianus), we combined an environmental DNA (eDNA) quantitative barcoding and metabarcoding survey in Belgium with a global meta-analysis, and integrated citizen-science data on breeding phenology. We examined whether the presence of native amphibian species was negatively related to the presence or abundance of invasive bullfrogs and whether this relationship was affected by their phenological mismatches. The field study revealed a significant negative effect of increasing bullfrog eDNA concentrations on native amphibian species richness and community structure. These observations were shaped by species-specific vulnerabilities to invasive bullfrogs, with late spring- and summer-breeding species being strongly affected, while winter-breeding species remained unaffected. This trend was confirmed by the global meta-analysis. A significant negative relationship was observed between phenological mismatch and the impact of bullfrogs. Specifically, native amphibian species with breeding phenology differing by 6 weeks or less from invasive bullfrogs were more likely to be absent in the presence of bullfrogs than species whose phenology differed by more than 6 weeks with that of bullfrogs. Taken together, we present a novel method based on the combination of aqueous eDNA quantitative barcoding and metabarcoding to quantify the ecological impacts of biological invaders at the community level. We show that phenological mismatches between native and invasive species can be a strong predictor of invasion impact regardless of ecological or methodological context. Therefore, we advocate for the integration of temporal alignment between native and IAS's phenologies into invasion impact frameworks.

Potential effects of traffic noise on anuran call characteristics in Louisiana, USA during winter

Urban environments expose wildlife to levels of anthropogenic noise they would not experience in rural areas (e.g., traffic noise), and research suggests that many species adjust their acoustic signals for optimal transmission in urban soundscapes. However, our understanding of anuran (order Anura) responses to noise pollution in urban environments of the southeastern United States is limited, particularly for species that can breed during winter. Our goal was to examine how vocal anuran advertisement call characteristics during winter varied with increasing distance from roadways in bottomland hardwoods of Louisiana, USA. We deployed acoustic recording units at two sites (i.e., rural and urban) perpendicular to Interstate 10 at 200-, 400-, and 600-m intervals (i.e., close, middle, and far) from November 2019 to January 2020. We detected Cajun Chorus Frogs (Pseudacris fouquettei) and Cricket Frogs (Acris spp.) at our rural site, and only detected Cricket Frogs at our urban site. At the rural site, Cajun Chorus Frogs produced longer duration notes at the far location compared to the middle location. At the urban site, Cricket Frogs produced higher dominant frequency calls at the close location compared to the far and middle locations and longer duration notes at the far location compared to the close location. We were unable to account for additional factors in our models (e.g., temperature, noise levels), but our results generally align with previous research. Our study provides baseline data for future research to examine the potential effects of traffic noise on winter advertisement calls in locations with similar environmental conditions and species.

Occupancy modelling reveals a highly restricted and fragmented distribution in a threatened montane frog (Philoria kundagungan) in subtropical Australian rainforests

In the last several decades, habitat loss, overexploitation, invasive organisms, disease, pollution and, more recently, climate change have led to catastrophic declines in amphibian biodiversity. Montane amphibian species, particularly those with narrow distributions and specific habitat requirements are likely to be at particular risk under future climate change scenarios. Despite this, fundamental ecological data are lacking for most of these species. Philoria kundagungan is a poorly known representative of a range-restricted genus of montane amphibians from eastern Australia. Using an occupancy framework, we conducted repeated call playback surveys at 32 sites across the mountainous regions of south-east Queensland and north-eastern New South Wales, Australia, to investigate: (1) the current extent of this species’ geographic range, and (2) environmental predictors of this species’ presence. We found that P. kundagungan has a highly restricted and fragmented distribution, being limited to ~11 km2 of potentially suitable habitat, and that its presence is strongly associated with high elevation (>800 m). Our survey protocol resulted in a high probability of detection (>70%) at occupied sites from relatively few visits. From these baseline data, future studies will have the ability to determine changes in this species’ geographic range and occupancy rate in response to the ever-increasing threats faced by P. kundagungan, thereby supporting more effective conservation strategies and policy decisions.