Manipulating wetland hydroperiod to improve occupancy rates by an endangered amphibian: modelling management scenarios

Abstract

1.Environmental managers have the difficult task of ensuring species persistence despite considerable uncertainty about their response to management. Spatially explicit population models provide one solution for simulating the dynamics of species and evaluating alternative management regimes. 2. We used a Bayesian model to investigate wetland occupancy dynamics of the endangered growling grass frog Litoria raniformis at a wastewater treatment plant in southern Victoria, Australia. We coupled prior information from earlier research on this species with our survey data to quantify the effects of patch-scale variables and connectivity on the probabilities of occupancy, population extinction and colonization. Hydroperiods of 13 sites were experimentally enhanced to bolster occupancy rates by L. raniformis. We used simulations to assess the extent to which the enhanced hydroperiod regime improved the viability of the focal metapopulation. 3. Occupancy rate increased by 15% among the enhanced sites in 2013-2014, whereas the rate of occupancy among unenhanced sites fell by 11% in that year. Forward simulation using the dynamic occupancy model suggested that the minimum occupancy rate across the metapopulation would be 18% higher if the enhanced hydroperiod regime was retained over the next 20 years. 4. Mean posterior effects of patch-scale variables and connectivity on the occupancy dynamics of L. raniformis were consistent with the prior effect in all cases, with only small changes to the size of these effects. There was no clear effect of water chemistry on occupancy dynamics. 5. Synthesis and applications. This work suggests that managing the hydroperiod of constructed wetlands can be an effective tool for the conservation of amphibians and demonstrates the utility of spatially explicit models for assessing metapopulation viability. We encourage managers to experimentally test the efficacy of manipulating patch-scale variables to improve occupancy rates within amphibian metapopulations.

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).…”

“…One strategy to reduce negative effects of climate change is to manage for climate resilience, such as through maintenance of habitat heterogeneity and population connectivity or by protecting particularly important habitats that are resistant to change (Pittock et al, 2008;Wilby et al, 2010). For example, land managers can construct or modify basins or manage flows so water bodies hold water long enough to benefit target species (Chandler et al, 2015;DeMarais and Minckley, 1993;Hamer et al, 2016).…”

Frog survival and population viability in an agricultural landscape with a drying climate

“…Population viability analysis (PVA) is an effective, transparent and widely used process (Brook, Cannon, Lacy, Mirande, & Frankham, ; Brook, Lim, Harden, & Frankham, ; Lindenmayer & Lacy, ; Towns, Parrish, & Westbrooke, ) for synthesizing demographic data and exploring the long‐term impacts of stochastic and deterministic factors on the persistence of populations (Reed, O'Grady, Brook, Ballou, & Frankham, ). There has been contention about the accuracy and role of PVA in predicting extinction probabilities, particularly with scant data (e.g., Coulson, Mace, Hudson, & Possingham, ); however, comprehensive studies have unequivocally advocated the importance and robust nature of PVA in producing unbiased predictions (Akçakaya & Sjögren‐Gulve, ; Brook et al, ; Hamer et al, ). One PVA simulation model, VORTEX, is frequently used as a predictive tool by the Species Survival Commission of the International Union for Conservation of Nature (IUCN) (e.g., Estrada et al, ).…”

Az Egyek-pusztakócsi mocsarak (Hortobágyi Nemzeti Park) kétéltűfaunája

“…A mocsarak természetes állapotának fenntartásában alapvető fontossággal bír a megfelelő élőhely-kezelési mód (kis intenzitású legeltetés és égetés pár évente), amely elősegítheti a kétéltűek sikeres reprodukcióját (Mester et al 2015b). A csapadékhiányos, száraz évek során a mocsarak megfelelő vízutánpótlása szintén fontos a vízhez szorosabban kötődő fajok (pettyes és dunai tarajosgőte, vöröshasú unka, zöldbékák) védelme szempontjából (Semlitsch 2000, Tóth & Puky 2009, Hamer et al 2016. A rekonstruált és természetes gyepek mint zöld folyosók továbbá fontos szerepet játszanak a kétéltűek mocsarak közötti diszperziójában és a szaporódóhelyekre történő vonulásában (Semlitsch 2008), ezért a gyepek védelme és megfelelő kezelése ugyancsak fontos feladat (Smith & Sutherland 2014).…”