Wetland Hydrology, Not Altered Phenology, Challenges Reticulated Flatwoods Salamander (Ambystoma bishopi) Management Under Future Climate Change
Shifts in phenology have been one of the most frequently documented effects of climate change across a wide variety of taxonomic groups. These shifts can alter both species and ecosystem level processes and, for species of conservation concern, may impact the effectiveness of ongoing management programs. Here, we used ten breeding seasons (2010–2020) of drift fence data to quantify the breeding phenology of the imperiled Reticulated Flatwoods Salamander (Ambystoma bishopi) at two breeding wetlands in Florida. We then used downscaled climate projections from three Global Circulation Models (GCMs; Hadley Centre Global Environment Model 2 Earth Systems, Hadley Centre Global Environment Model 2 Carbon Cycle, and the Community Climate System model version 4) each with two emission scenarios to forecast how flatwoods salamander breeding phenology may change from 2030–2099. We combined these forecasts with an existing hydrologic model that was built using the same climate data to examine how wetland hydrology and phenology may interact to impact salamander recruitment in future years. We found that large movements (≥ 5 individuals) of adult salamanders moving into breeding wetlands were tightly linked to precipitation events with minimum temperatures above freezing, while juvenile emigration was less strongly tied to precipitation and occurred on more days than adult immigration. Under all six GCM-emission scenario combinations, only one scenario suggested that there would be fewer immigration opportunities by the year 2099, and two scenarios (both high emission) indicated that the timing of immigration may shift to later in the fall breeding period. All projections predicted that only a few years will have an ideal intersection of phenology and hydrology for flatwoods salamander reproduction but that many years would have marginal conditions where recruitment may still be possible. Because the frequency of successful breeding years affects population viability in flatwoods salamanders, ongoing management programs must ensure that populations are reproducing frequently enough to remain viable. Overall, our results indicate that altered wetland hydrology (e.g., shorter hydroperiods during the breeding season) and other effects of climate change (e.g., sea level rise) are more likely to contribute to flatwoods salamander declines over the next several decades than phenological shifts.
(A) Adult Reticulated Flatwoods Salamanders (Ambystoma bishopi) immigrating into wetlands and (B) metamorphs emigrating out of wetlands were captured at two wetlands on Eglin Air Force Base, Florida from 2010–2020. Salamander movements are plotted with precipitation events, which account for multiple days of rain ending with at least three consecutive dry days. Day 0 represents the day before precipitation began, and negative values are dry periods between precipitation events. Captures were only included if at least five individuals were captured on a single dry day or across a single precipitation event.
Characteristics of successful Reticulated Flatwoods Salamander (Ambystoma bishopi) breeding seasons from a breeding site on Eglin Air Force Base, Florida. Salamanders were monitored using a drift fence over ten breeding seasons (2010–2020), and only three of those seasons saw mass emigration of metamorphs during the spring. Shaded areas and bars on the left represent adult immigration, while shaded areas and bars on the right represent metamorph emigration. Black dots represent the beginning of precipitation events with temperatures conducive to salamander movements that occurred from 13 October through 31 December. Water levels were measured with pressure transducers placed in monitoring wells.
Potential movement opportunities for Reticulated Flatwoods Salamanders (Ambystoma bishopi) at Eglin Air Force Base, Florida were assessed under three climate models and two emission scenarios (RCP 4.5 and 8.5). Movement opportunities were defined as precipitation events with mean daily minimum temperatures between 5.3 and 20.9°C. The potential movement period was constrained to 13 October through 31 December of each breeding season. Lines represent ten-year moving averages.
Predicted movement opportunities for Reticulated Flatwoods Salamanders (Ambystoma bishopi) at breeding wetlands on Eglin Air Force Base, Florida from 2030–2099. A movement opportunity is defined as a precipitation event with mean minimum temperatures between 5.3 and 20.9°C that occurs from 13 October through 31 December. These values are based on observed phenological variation. Black dots represent the 1st and last movement opportunity, while blue dots represent the 4th movement opportunity.
Examples of predicted conditions during future Reticulated Flatwoods Salamander (Ambystoma bishopi) breeding seasons for a single breeding site. Categories of breeding outcomes are defined in the Methods. These predictions were based on the CCSM4 global circulation model and two representative concentration pathways (RCPs): (A) peak carbon emissions by 2040 (RCP 4.5) and (B) carbon emissions continue to increase through 2100 (RCP 8.5).
Contributor Notes
Associate Editor: J. M. Davenport.