Demographics, reproduction, growth, and abundance of Jollyville Plateau salamanders (Eurycea tonkawae)

Abstract

Insights into the ecology and natural history of the neotenic salamander, Eurycea tonkawae, are provided from eight years of capture‐recapture data from 10,041 captures of 7,315 individuals at 16 sites. Eurycea tonkawae exhibits seasonal reproduction, with peak gravidity occurring in the fall and winter. Size frequency data indicated recruitment occurred in the spring and summer. Open‐population capture‐recapture models revealed a similar seasonal pattern at two of three sites, while recruitment was dependent on flow at the third site. Females can reach sexual maturity within one year, and oviposition likely takes place below ground. The asymptotic body length of 1,290 individuals was estimated as 31.73 mm (at ca. two years of age), although there was substantial heterogeneity among growth trajectories. Longevity was approximately eight years, and the median age for a recaptured adult was 2.3 years. Abundance estimated from closed‐population and robust‐design capture‐recapture models varied widely within and among sites (range 41–834), although, surprisingly, dramatic changes in abundance were not observed following prolonged dry periods. Seasonal migration patterns of second‐year and older adults may help explain lower ratios of large individuals and higher temporary emigration during the latter half of the year, but further study is required. Low numbers of captures and recaptures precluded the use of open‐population models to estimate demographic parameters at several sites; therefore, closed‐population (or robust‐design) methods are generally recommended. Based on observations of their life history and population demographics, E. tonkawae seems well adapted to conditions where spring flow is variable and surface habitat periodically goes dry.

Density‐dependent and density‐independent drivers of population change in Barton Springs salamanders

“…We did not find evidence for an immediate effect of spring discharge, suggesting that other correlated factors (e.g., flow velocity, dissolved oxygen concentration) do not directly affect salamander abundance at these sites (although flow velocity may be an important factor at other sites; Dries & Colucci, ). Similarly, there was no effect of seasonality, in contrast to other closely related central Texas Eurycea with seasonally dependent dynamics (Bendik, ; Pierce et al., ). Seasonal changes in light availability and air temperature are probably less likely to influence large systems with potentially vast subterranean habitat such as the Barton Springs segment of the Edwards Aquifer, in contrast to shallower groundwater systems.…”

“…Because other closely related Eurycea inhabiting central Texas springs and streams exhibit seasonal patterns of reproduction and population demographics (Bendik, ; Pierce, McEntire, & Wall, ), we tested for a seasonal effect on E. sosorum abundance to represent un‐sampled covariates. We used a discrete Fourier series to represent seasonality as the following sum: α × cos(2π d /12) + β × sin(2π d /12), where d is an integer representing the month of the year and α and β are model coefficients representing the strength of the seasonality effect.…”

How Metamorphosis Is Different in Plethodontids: Larval Life History Perspectives on Life-Cycle Evolution

“…For example, both desmognathan larvae (e.g., Beachy 1995a; Bruce 2016a,b) and spelerpine larvae (Bruce 1980; Voss 1993) grow less than 1 mm/mo. These low rates of larval growth also appear to hold for paedomorphic spelerpines (Niemiller et al 2016; Bendik 2017). …”

Species delimitation in endangered groundwater salamanders: Implications for aquifer management and biodiversity conservation

“…Groundwater development since the 1950s (46), combined with more recent, rapid residential development (47), has resulted in intensive pumping, decreased well yields, local water table declines, and diminished baseflow to springs and streams (48)(49)(50)(51). Aquifer drawdown and the resulting reduction or cessation of springflow has resulted in habitat loss and fragmentation for groundwater species, compounded by reduced water quality from urban development (52)(53)(54)(55). As a result, 13 groundwater-dependent species endemic to the Edwards Aquifer are listed as threatened or endangered under the US Endangered Species Act (ESA) (56-58),…”