Hydrologic Variability Governs Population Dynamics of a Vulnerable Amphibian in an Arid Environment

Abstract

Dynamics of many amphibian populations are governed by the distribution and availability of water. Therefore, understanding the hydrological mechanisms that explain spatial and temporal variation in occupancy and abundance will improve our ability to conserve and recover populations of vulnerable amphibians. We used 16 years of survey data from intermittent mountain streams in the Sonoran Desert to evaluate how availability of surface water affected survival and adult recruitment of a threatened amphibian, the lowland leopard frog (Lithobates yavapaiensis). Across the entire study period, monthly survival of adults ranged from 0.72 to 0.99 during summer and 0.59 to 0.94 during winter and increased with availability of surface water (Z = 7.66; P < 0.01). Recruitment of frogs into the adult age class occurred primarily during winter and ranged from 1.9 to 3.8 individuals/season/pool; like survival, recruitment increased with availability of surface water (Z = 3.67; P < 0.01). Although abundance of frogs varied across seasons and years, we found no evidence of a systematic trend during the 16-year study period. Given the strong influence of surface water on population dynamics of leopard frogs, conservation of many riparian obligates in this and similar arid regions likely depends critically on minimizing threats to structures and ecosystem processes that maintain surface waters. Understanding the influence of surface-water availability on riparian organisms is particularly important because climate change is likely to decrease precipitation and increase ambient temperatures in desert riparian systems, both of which have the potential to alter fundamentally the hydrology of these systems.

Informing recovery in a human-transformed landscape: Drought-mediated coexistence alters population trends of an imperiled salamander and invasive predators

“…For example, in northwestern Florida, pond-level extinction of the mole salamander (A. talpoideum) was associated with drying of ponds during a severe drought (Walls et al, 2013). Variation in availability of surface water strongly influences recruitment, survival, and growth of amphibian populations across a wide range of habitats (Church et al, 2007;Hamer et al, 2016;Hossack et al, 2013;Zylstra et al, 2015).…”

Surface‐water availability governs survival of an amphibian in arid mountain streams

“…Survival was higher during warmer parts of the year and lower during winter when ambient temperatures often fall below 5°C. This pattern corroborated previous findings based on an independent source of data (long‐term counts; Zylstra et al., ) as well as our incidental observations of lethargic frogs at pool edges on very cold winter mornings. Contrary to our expectations, however, apparent survival decreased as dew point increased.…”

Drought‐mediated extinction of an arid‐land amphibian: insights from a spatially explicit dynamic occupancy model

“…Finally, we modeled the observation process separately from ecological processes because observers may fail to detect frogs when a site is truly occupied (Royle and Kéry , Zylstra et al. ). Because we assumed changes in occupancy would occur only between sampling periods, multiple surveys of a site within a sampling period allowed us to estimate detection probability ( p ) or the probability of detecting ≥1 post‐metamorphic frogs if the site is occupied.…”

“…Although abundance of lowland leopard frogs fluctuates in response to hydrologic conditions (Zylstra et al. ), there is growing evidence of systematic declines and extirpations in populations across this region (Sredl et al. , Witte et al.…”

“…In southeastern Arizona, lowland leopard frogs primarily inhabit stream reaches in arid mountain canyons, environments that are rare on the landscape, highly dynamic, and likely to change in response to anticipated shifts in climate and other anthropogenic threats (Grimm and Fisher 1992, Sredl 2005, Wallace et al 2010, Jaeger et al 2014. Although abundance of lowland leopard frogs fluctuates in response to hydrologic conditions (Zylstra et al 2015), there is growing evidence of systematic declines and extirpations in populations across this region (Sredl et al 1997, Witte et al 2008, Savage et al 2011. Identifying factors associated with these declines is a conservation priority and can provide insight into the dynamics of this and other sensitive species that depend on surface water in arid mountain systems.…”