Decadal abundance patterns in an isolated urban reptile assemblage: Monitoring under a changing climate

Abstract

Determine seasonal, annual, and decadal patterns of abundance in reptile species and assemblages occupying central Bold Park (~338 ha), an isolated urban bushland remnant in Perth, Southwestern Australia. Fenced pitfall trapping in four sampling sites, representing different habitats and fire history, over the primary reptile activity period for 35 consecutive years with over 17,000 individuals captured during 3300 days of sampling; the trapping regime was modified for the last 28 years. Sampling occurred in one of 35 global biodiversity hotspots that has a Mediterranean climate experiencing a 15% decline from the century average rainfall over the last 50 years.Twenty-nine species were recorded, with 16 captured in 32 or more years and accounting for nearly 97% of all captures; the six most common for 81%. Three taxa became locally extinct. Activity predominates in warmer and dryer months (October to April), peaking in November-December. Species richness remained relatively constant between years with around 73% of known taxa captured annually. Assemblages did not change when analyzing the presence/absence data but moved through five statistically significant assemblages analyzing relative abundance data. Over the last 28 years, relative abundance was significantly and positively correlated with annual rainfall residuals, uniquely for the 4 years preceding annual sampling, resulting in significant changes in total assemblages and significantly similar patterns in four sample sites; the presence/absence data indicated only minor assemblage changes across sites. The number of species recorded annually remained relatively constant, but relative abundance illustrated significant temporal changes in assemblages over decades.The modeled relationship between relative abundance and annual rainfall residuals for 4 years preceding annual sampling is supported by known ecological responses and reptile demographics within this Mediterranean climate. Maintenance of urban biodiversity should consider impacts of a significantly drying climate exacerbating the extinction debt already inherent in isolated bushland populations experiencing limited immigration.

A misleading tail: A long-term study of reptile responses to multiple disturbances undermined by a change in surveying techniques

“…However, Ryan et al [75], discovered that reptiles in the Los Pino Mountains in New Mexico, US, preferred foraging in sunny microhabitats following rainfall events and shaded habitats during dry periods. Further, increased precipitation is also thought to increase reproduction by some reptiles [59]. Whilst our study contrasts in both habitat conditions and species identities to those mentioned above, our results likely point to species-specific responses to rain, as well the difficulties in disentangling the effects of occupancy and activity on reptile detections.…”

“…This enabled us to associate climate data in the season in which surveys were taken. We also calculated mean monthly precipitation for the year preceding the survey, as reptiles are known to increase reproduction following higher than average rainfall [59].…”

Long-term post-fire succession of reptiles in an urban remnant in south-western Australia

“…The impacts of climate change on reptiles and interactions with fire, are poorly understood and require future study. How et al (2022) analysed a 35-year dataset of reptiles in Banksia woodlands near to our study site and found that abundance was significantly correlated with preceding rainfall. They found only limited community compositional change due to annual rainfall variation.…”

“…These altered fire regimes combine with other disturbances, such as edge effects (Urbina- Cardona et al 2006;Garden et al 2007;McAlpine et al 2015), to further alter vegetation structure (Ibanez et al 2017;Gomes et al 2022). In combination, these pressures, along with a changing climate (How et al 2022), have the potential to strongly influence post-fire responses of reptiles in urban remnants. However, whether post-fire responses differ between remnants and contiguous vegetation remains poorly understood and the ecological mechanisms behind any potential differences, even less well understood.…”