Monitoring and Population Ecology
K. Cecala (ARMI) sampling a stream in Shenandoah NP for salamanders. Photo by: E. Grant
Advances in technology (e.g., PIT tags) have allowed scientists to individually mark more types of species than ever before, and concurrent developments in biometrics have allowed scientists to ask more types of questions about animal populations under more circumstances. Some of these developments have been particularly useful when estimating parameters about amphibians, a group that can be difficult to sample (e.g., multiple life stages, small size, difficult to mark, high juvenile mortality).
These developments in marking and estimation have allowed scientists to ask specific questions about the effects of potential stressors or beneficial management actions on amphibian populations, and quantify these responses.
ARMI Products on Monitoring and Population Ecology
* USGS neither sponsors nor endorses non-USGS web sites; per requirement "3.4.1 Prohibition of Commercial Endorsement."
* PDF documents require Adobe Reader or Google Chrome Browser for viewing.
A three-pipe problem: dealing with complexity to halt amphibian declines
Authors: Converse S, Grant EHC | Outlet: Biological Conservation
Natural resource managers are increasingly faced with threats to managed ecosystems that are largely outside of their control. Examples include land development, climate change, invasive species, and emerging infectious diseases. All of these are characterized by large uncertainties in timing, magnitude, and effects on species. In many cases, the conservation of species will only be possible through concerted action on the limited elements of the system that managers can control. However, before an action is taken, a manager must decide how to act, which is ? if done well ? not easy. In addition to dealing with uncertainty, managers must balance multiple potentially competing objectives, often in cases when the management actions available to them are limited. Guidance in making these types of challenging decisions can be found in the practice known as decision analysis. We demonstrate how using a decision-analytic approach to frame decisions can help identify and address impediments to improved conservation decision making. We demonstrate the application of decision analysis to two high-elevation amphibian species. An inadequate focus on the decision-making process, and an assumption that scientific information is adequate to solve conservation problems, must be overcome to advance the conservation of amphibians and other highly threatened taxa.
Multi-year data from satellite- and ground-based sensors show details and scale matter in assessing climate's effects on wetland surface water, amphibians, and landscape conditions
Authors: Sadinski W, Gallant AL, Roth M, Brown J, Senay G, Brininger W, Jones PM, Stoker J | Date: 2018-09-07 | Outlet: PLoS ONE 13(9): e0201951 | Format: URL
Long-term, interdisciplinary studies of relations between climate and ecological conditions on wetland-upland landscapes have been lacking, especially studies integrated across scales meaningful for adaptive resource management. We collected data in situ at individual wetlands, and via satellite for surrounding 4-km2 landscape blocks, to assess relations between annual weather dynamics, snow duration, phenology, wetland surface-water availability, amphibian presence and calling activity, greenness, and evapotranspiration in four U.S. conservation areas from 2008 to 2012. Amid recent decades of relatively warm growing seasons, 2012 and 2010 were the first and second warmest seasons, respectively, dating back to 1895. Accordingly, we observed the earliest starts of springtime biological activity during those two years. In all years, early-season amphibians first called soon after daily mean air temperatures were ? 0°C and snow had mostly melted. Similarly, satellite-based indicators suggested seasonal leaf-out happened soon after snowmelt and temperature thresholds for plant growth had occurred. Daily fluctuations in weather and water levels were related to amphibian calling activity, including decoupling the timing of the onset of calling at the start of season from the onset of calling events later in the season. Within-season variation in temperature and precipitation also was related to vegetation greenness and evapotranspiration, but more at monthly and seasonal scales. Wetland water levels were moderately to strongly associated with precipitation and early or intermittent wetland drying likely reduced amphibian reproduction success in some years, even though Pseudacris crucifer occupied sites at consistently high levels. Notably, satellite-based indicators of landscape water availability did not suggest such consequential, intra-seasonal variability in wetland surface-water availability. Our cross-disciplinary data show how temperature and precipitation interacted to affect key ecological relations and outcomes on our study landscapes. These results demonstrate the value of multi-year studies and the importance of scale for understanding actual climate-related effects in these areas.
Jonathan Rose, USGS
Time-to-detection Occupancy Modeling: An Efficient Method for Analyzing the Occurrence of Amphibians and Reptiles
Authors: Halstead BJ, Kleeman PM, Rose JP | Date: 2018-11-27 | Outlet: Journal of Herpetology 52:416-425 | Format: URL
Occupancy models provide a reliable measure of species distributions while accounting for imperfect detectability. The cost of accounting for false absences is that occupancy surveys typically require repeated visits to a site or multiple-observer techniques. More efficient methods of estimating detection probabilities would allow more sites to be surveyed for the same effort, resulting in more information about the ecological processes leading to occupancy. Time-to-detection surveys allow the estimation of detection probability based on a single site visit by one observer, and therefore might be an efficient technique for herpetological occupancy studies. We evaluated the use of time-to-detection surveys to estimate the occupancy of pond-breeding amphibians at Point Reyes National Seashore, California, USA, including variables that affected detection rates and the probability of occurrence. We found that detection times were short enough and occupancy high enough to reliably estimate the probability of occurrence of three pond-breeding amphibians at Point Reyes National Seashore, and that survey and site conditions had species-specific effects on detection rates. In particular, relative abundance was negatively related to the time to initial detection of all species, and pond area was positively related to time to initial detection for Sierran Treefrogs (Hyliola sierra) and Rough-skinned Newts (Taricha granulosa). Rough-skinned newt time to initial detection also was affected by date, with lowest initial detection time in early summer. California Red-legged Frog (Rana draytonii) time to detection was lowest in ponds with a mean depth of 0.6 m, and higher in shallower and deeper ponds. Probability of occurrence of Sierran Treefrogs and Rough-skinned Newts was negatively related to the presence of fish and pond area. Rarely detected species required constraints on priors to fit time-to-detection models. Time-to-detection surveys can provide an efficient method of estimating detection probabilities and accounting for false absences in occupancy studies of reptiles and amphibians.