Richard A. How

Reptile populations in southwestern Australia are experiencing a changing Mediterranean climate, characterised by recent sustained declines in rainfall alongside rising temperatures. Body condition is a sensitive, individual‑level metric that can reveal ecological stress before population declines become evident. Long‑term and seasonal trends in body condition across an urban reptile assemblage of 29 species were assessed to determine population resilience and identify potential early‑warning signals of decline. We analysed 40 years of monitoring data for multiple reptile species, quantifying decadal and seasonal variation in body condition across sex, adults, juveniles, and hatchlings. Seasonal trajectories were evaluated in relation to reproductive timing and demographic structure. Long‑term patterns were compared with regional climatic trends and contextualised using published studies on rainfall effects on these ectothermic taxa. Decadal analyses revealed persistent declines in adult body condition across many common species, with weaker or more variable responses in juveniles and hatchlings, indicating chronic environmental pressures acting disproportionately on older cohorts, particularly adult females. Seasonal analyses showed strong demographic structuring, with reproductive females exhibiting pronounced late‑spring to early-summer declines linked to oviposition or births. Seasonal patterns also differed among species, some exhibiting minimal seasonal variation. These patterns were not explained by short‑term rainfall or detectability but aligned with regional declines in rainfall that supported global evidence that low precipitation negatively affects reptile physiology. Temporal trajectories in body condition provide a sensitive early‑warning indicator of population vulnerability under a drying climate occurring in a global biodiversity hotspot subjected to increasing demands on natural ecosystems. When combined with documented declining activity, these trends suggest elevated local extinction risk for several taxa, specifically those with restricted distributions or requiring specialised habitats, highlighting the need for species‑specific, climate‑sensitive conservation strategies. Integrating body condition into long‑term monitoring programs will improve the capacity to detect ecological stress and guide proactive management.

We integrate demography, morphology and genetics to assess the biology and population structure of the endemic Kimberley rock-rat (Zyzomys woodwardi), a habitat specialist of the monsoonal tropics. The species is confined to the extreme north-west of the continent and 16 adjacent islands that were part of the mainland during the last Pleistocene glaciation. Islands became isolated from ~6500 years before present (BP), with their current populations being considered relictual. This, together with habitat patchiness and sedentary behaviour, promotes marked genetic and morphological variation. Capture rates were high on islands. All populations show a strong preference for moist rocky gullies containing boulder substrates and vine forest floristics. Demographics show large seasonal variation in activity and movement, with breeding occurring throughout the year. There is no sexual dimorphism. Analyses of skull metrics showed clear evidence of dwarfism in island populations, contrary to gigantism commonly observed in murids. Genetic data showed that islands have smaller effective population sizes than does the mainland. There are strong genetic affinities among localities within geographically proximate groups, with evidence groups having remained isolated from one another since before the last glacial maximum. A reduction in the reliability of wet-season conditions, and more frequent prolonged dry periods, may directly affect the environmental niche occupied by the species. Introduced species, including feral cats (Felis catus), and increased fire, potentially compound these pressures and reduce population viability. Although the species is currently listed as Least Concern because of the extent of its distribution and local abundance, fragmentation leaves local populations vulnerable to extinction with the prospect of recolonisation problematic.

Endemic rodents constitute 19% of Australian terrestrial mammal species and this proportion is higher in arid zones and the north. We report substantial genetic diversity and population structure in the common rock‐rat Zyzomys argurus, a saxicoline murid whose range extends across northern Australia and into the continent's interior. Samples of 686 individuals from 68 locations, encompassing the western half of the species' range, provide one of the most geographically and numerically extensive genetic studies of an Australian rodent. The Great Sandy Desert, a prominent feature over the last 0.5 my bp acts as a significant barrier to gene flow. Continental islands, formed during the past 10 000 years following the end of the most recent Pleistocene glacial maximum, have populations with lower heterozygosity and marked differentiation from each other and the adjacent mainland. On the mainland, despite considerable differentiation between locations, there is only weak evidence for isolation by distance and where it occurs it is associated with drainage basins. In the Pilbara, analyses of genetic structure within localized sub‐locations, just a few kilometres apart, indicate considerable variation between them (F_ST) and inbreeding within (F_IS). We interpret this in the context of cyclonic and other extreme rainfall events that occur episodically, leading to boom‐bust population cycles. Populations decline into refugia of isolated rock patches during extended periods of poor resources with consequent low genetic diversity (H_e) and large differentiation from others. Populations that irrupt after major episodic rainfall increases resource states, have a more extensive distribution with greater heterozygosity because of gene flow between previously isolated refugia and less differentiation between the locations. These observations have conservation significance for threatened congeneric species and other Australian arid rodents by demonstrating, in this common exemplar, the reduced evolutionary potential imposed by both transient isolation due to climatic variation and longer term disruptions by geographic barriers.

Context: Annual patterns in behaviour and demography define longer-term changes in reptile populations, probability of species detection and risks of local extinction. Aims: To determine seasonal activity and demographic parameters of species in an isolated assemblage adapted to a seasonally predictable climate. Methods: A 37-year pitfall trapping, capture–release study in a 338-ha inner-city bushland experiencing a Mediterranean climate. Pit trap methodology changed after 7 years. Results: Reproductive activity of 29 species peaked during austral spring to early summer with hatching or births occurring from late summer to early autumn. Growth, as determined from size changes over demi-monthly periods, indicated sexual maturity varied from <1 year to 5 years. Five of eight uniquely marked species had longevity exceeding a decade while individuals within six species moved over a kilometre. Dimorphism in adult length and mass was significantly greater in females for 15 of the 18 species with adequate data. Adult male activity peaked earlier in spring than adult females’ over the latter 30 years; hatchlings had different species-specific activity and annual cohort survival patterns. Activity declined in adults through summer and autumn before brumation in late autumn and winter in all species and age-size categories. Capture frequency in most species changed between methodologies. Conclusions: Species had broadly similar seasonal activity but different demographic parameters within an isolated reptile assemblage currently experiencing increasing temperature and declining rainfall. Implications: Comprehending seasonal variation is essential for interpreting decadal-long changes in reptile numbers experiencing a drying climate that alters activity, reproduction and survival to inform species detectability and likely extinction risk.

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.

Aim Determine seasonal, annual and decadal patterns of abundance in reptile populations and assemblages occupying an isolated urban bushland remnant Location Bold Park (~338 ha), Perth, Southwestern Australia Time period 1986-2021 Major taxa studied: Squamate reptiles Methods Fenced pitfall trapping in four sampling sites representing different habitats and fire history over the primary reptile activity period and 35 consecutive years; trapping regime was modified for the last 28 years. Results The location occurs in one of 35 global biodiversity hotspots and 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. Assemblage structure didn’t change when analysing presence/absence data but shifted through five statistically significantly assemblages analysing relative abundance data. Over the last 28 years relative abundance was significantly and positively correlated with annual rainfall residuals for the three years preceding annual sampling, resulting in significant changes in total assemblage structure and significantly similar patterns in four sample sites; presence/absence data indicated minor assemblage structure changes. Main conclusions Annual species number remained relatively constant but relative abundance illustrated significant temporal changes in assemblage structure over decades; presence/absence did not. The modeled relationship between relative abundance and annual rainfall residuals for the three 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.

Historical population contraction and expansion events associated with Pleistocene climate change are important drivers of intraspecific population structure in Australian arid-zone species. We compared phylogeographic patterns among arid-adapted Dasyuridae (Sminthopsis and Planigale) with close phylogenetic relationships and similar ecological roles to investigate the drivers of phylogeographic structuring and the importance of historical refugia. We generated haplotype networks for two mitochondrial (control region and cytochrome b) and one nuclear (omega-globin) gene from samples distributed across each species range. We used Φ_ST to test for a genetic population structure associated with the four Pilbara subregions, and we used expansion statistics and Bayesian coalescent skyline analysis to test for signals of historical population expansion and the timing of such events. Significant population structure associated with the Pilbara and subregions was detected in the mitochondrial data for most species, but not with the nuclear data. Evidence of population expansion was detected for all species, and it likely began during the mid-late Pleistocene. The timing of population expansion suggests that these species responded favorably to the increased availability of arid habitats during the mid-late Pleistocene, which is when previously patchy habitats became more widespread. We interpret our results to indicate that the Pilbara region could have acted as a refugium for small dasyurids.