Geology topics

David A. Miller

Publications and source records attributed to David A. Miller.

8 recordsLinked to original sources

USGS2025

Independent and interactive effects of disease and methylmercury on demographic rates across multiple amphibian populations

Disease, alone or combined with other stressors such as habitat loss and contaminants, affects wildlife populations worldwide. However, interactions among stressors and how they affect demography and populations remain poorly understood. The amphibian chytrid fungus ( Batrachochytrium dendrobatidis ; Bd) is a sometimes-lethal pathogen linked with population declines and extirpations of amphibians globally. Laboratory evidence shows ubiquitous contaminants like methylmercury (MeHg) can reduce vigor and survival of amphibians, but population-level effects remain unclear. We used non-lethal sampling to assess how Bd and MeHg affected survival of juvenile and adult amphibians in 20 populations across the USA. Survival of several species declined with increasing Bd loads, including some species previously considered resistant to Bd (e.g., eastern newt [ Notophthalmus viridescens ]). Although our sampling for MeHg was less intensive than for Bd, we found MeHg can both directly reduce survival and synergistically magnify the effects of Bd infection. For a population of foothill yellow-legged frogs ( Rana boylii ), the estimated reduction in survival from MeHg exceeded that from Bd. Although effects varied widely among populations and species, our results help clarify the potential for synergistic effects of disease and contaminants and emphasize the complexity of identifying and quantifying the population-level effects of interactions among stressors.

Scientific Reports↗

USGS2012

The U.S. Geological Survey Amphibian Research and Monitoring Initiative-2011 Annual Update

Welcome to the inaugural issue of ARMI's Annual Update. This update provides highlights and significant milestones of this innovative program. ARMI is uniquely qualified to provide research and monitoring results that are scalable from local to national levels, and are useful to resource managers. ARMI has produced nearly 400 peer-reviewed publications, including 18 in 2011. Some of those publications are highlighted in this fact sheet. ARMI also has a new Website (armi.usgs.gov). You can now use it to explore an up-to-date list of ARMI products, to find summaries of research topics, to search for ARMI activities in your area, and to obtain amphibian photographs. ARMI's annual meeting was organized by Walt Sadinski, Upper Midwest Environmental Science Center, and held in St Louis, Missouri. We met with local scientists and managers in herpetology and were given a tour of the herpetology collection at the St. Louis Zoo.

Fact Sheet↗

USGS2011

Stochastic population dynamics in populations of western terrestrial garter snakes with divergent life histories

Comparative evaluations of population dynamics in species with temporal and spatial variation in life‐history traits are rare because they require long‐term demographic time series from multiple populations. We present such an analysis using demographic data collected during the interval 1978–1996 for six populations of western terrestrial garter snakes ( Thamnophis elegans ) from two evolutionarily divergent ecotypes. Three replicate populations from a slow‐living ecotype, found in mountain meadows of northeastern California, were characterized by individuals that develop slowly, mature late, reproduce infrequently with small reproductive effort, and live longer than individuals of three populations of a fast‐living ecotype found at lakeshore locales. We constructed matrix population models for each of the populations based on 8–13 years of data per population and analyzed both deterministic dynamics based on mean annual vital rates and stochastic dynamics incorporating annual variation in vital rates. (1) Contributions of highly variable vital rates to fitness (λ s ) were buffered against the negative effects of stochastic variation, and this relationship was consistent with differences between the meadow (M‐slow) and lakeshore (L‐fast) ecotypes. (2) Annual variation in the proportion of gravid females had the greatest negative effect among all vital rates on λ s . The magnitude of variation in the proportion of gravid females and its effect on λ s was greater in M‐slow than L‐fast populations. (3) Variation in the proportion of gravid females, in turn, depended on annual variation in prey availability, and its effect on λ s was 4–23 times greater in M‐slow than L‐fast populations. In addition to differences in stochastic dynamics between ecotypes, we also found higher mean mortality rates across all age classes in the L‐fast populations. Our results suggest that both deterministic and stochastic selective forces have affected the evolution of divergent life‐history traits in the two ecotypes, which, in turn, affect population dynamics. M‐slow populations have evolved life‐history traits that buffer fitness against direct effects of variation in reproduction and that spread lifetime reproduction across a greater number of reproductive bouts. These results highlight the importance of long‐term demographic and environmental monitoring and of incorporating temporal dynamics into empirical studies of life‐history evolution.

California↗

USGS2010

Calibrating recruitment estimates for mourning doves from harvest age ratios

We examined results from the first national-scale effort to estimate mourning dove ( Zenaida macroura ) age ratios and developed a simple, efficient, and generalizable methodology for calibrating estimates. Our method predicted age classes of unknown-age wings based on backward projection of molt distributions from fall harvest collections to preseason banding. We estimated 1) the proportion of late-molt individuals in each age class, and 2) the molt rates of juvenile and adult birds. Monte Carlo simulations demonstrated our estimator was minimally biased. We estimated model parameters using 96,811 wings collected from hunters and 42,189 birds banded during preseason from 68 collection blocks in 22 states during the 2005–2007 hunting seasons. We also used estimates to derive a correction factor, based on latitude and longitude of samples, which can be applied to future surveys. We estimated differential vulnerability of age classes to harvest using data from banded birds and applied that to harvest age ratios to estimate population age ratios. Average, uncorrected age ratio of known-age wings for states that allow hunting was 2.25 (SD 0.85) juveniles:adult, and average, corrected ratio was 1.91 (SD 0.68), as determined from harvest age ratios from an independent sample of 41,084 wings collected from random hunters in 2007 and 2008. We used an independent estimate of differential vulnerability to adjust corrected harvest age ratios and estimated the average population age ratio as 1.45 (SD 0.52), a direct measure of recruitment rates. Average annual recruitment rates were highest east of the Mississippi River and in the northwestern United States, with lower rates between. Our results demonstrate a robust methodology for calibrating recruitment estimates for mourning doves and represent the first large-scale estimates of recruitment for the species. Our methods can be used by managers to correct future harvest survey data to generate recruitment estimates for use in formulating harvest management strategies.

Journal of Wildlife Management↗

USGS2009

Individual variation in baseline and stress-induced corticosterone and prolactin levels predicts parental effort by nesting mourning doves

Endocrine systems have an important mechanistic role in structuring life-history trade-offs. During breeding, individual variation in prolactin (PRL) and corticosterone (CORT) levels affects behavioral and physiological processes that drive trade-offs between reproduction and self-maintenance. We examined patterns in baseline (BL) and stress induced (SI; level following a standard capture-restraint protocol) levels of PRL and CORT for breeding mourning doves ( Zenaida macroura ). We determined whether the relationship of adult condition and parental effort to hormone levels in wild birds was consistent with life-history predictions. Both BL PRL and BL CORT level in adults were positively related to nestling weight at early nestling ages, consistent with the prediction of a positive relationship of hormone levels to current parental effort of adults and associated increased energy demand. Results are consistent with the two hormones acting together at baseline levels to limit negative effects of CORT on reproduction while maintaining beneficial effects such as increased foraging for nestling feeding. Our data did not support predictions that SI responses would vary in response to nestling or adult condition. The magnitude of CORT response in the parents to our capture-restraint protocol was negatively correlated with subsequent parental effort. Average nestling weights for adults with the highest SI CORT response were on average 10–15% lighter than expected for their age in follow-up visits after the stress event. Our results demonstrated a relationship between individual hormone levels and within population variation in parental effort and suggested that hormonal control plays an important role in structuring reproductive decisions for mourning doves.

Hormones and Behavior↗

USGS2008

Predators of Dusky Canada Goose goslings and the effect of transmitters on gosling survival

The population of Dusky Canada Geese (Branta canadensis occidentalis) has been in long-term decline, likely due to reduced breeding productivity. To identify causes of mortality, we monitored goslings marked with radio transmitters on the western Copper River Delta, Alaska, from 1997 to 1999. Almost all gosling mortality (96%; 81 of 84) was due to predation, with mink (Mustela vison) and Bald Eagles (Haliaeetus leucocephalus) the most important predators. Bald Eagles are also major nest predators and, thus, appear to play a key role in limiting the breeding productivity of Dusky Canada Geese. Daily survival rate for goslings to 28 d of age was lower (0.011; 95% CI 0.002-0.024) for those with transmitters than for those without, but did not differ for older goslings (29-45 d). Although finer resolution in the timing of the transmitter effect within the first 28 d was not possible, we found that, by limiting our sample to goslings that survived until after 2-3 d posthatching, support for a transmitter effect was much reduced. Younger, smaller birds are inherently more vulnerable than older birds to transmitter effects. In addition, the process of radio-marking may have delayed the departure of goslings from nests and increased their risk of mortality shortly after hatching. Although radio transmitters may often be the only practical means for determining causes of mortality for young waterfowl, we suggest caution in using transmitters because of their potential negative effects, particularly during the first few days after hatching. ?? 2008 Association of Field Ornithologists.

Journal of Field Ornithology↗

USGS2006

Effects of abdominally implanted radiotransmitters with percutaneous antennas on migration, reproduction, and survival of Canada geese

Abdominally implanted radiotransmitters with percutaneous antennas are increasingly used to monitor movements, survival, and reproduction of waterbirds. However, there has been relatively little assessment of the effects of such radios on avian demographic parameters or migration. We implanted either a 26- or 35-g abdominal transmitter with percutaneous antenna in 198 adult female lesser Canada geese ( Branta canadensis parvipes ) in Anchorage, Alaska during 2000 and 2001. We compared migration chronology, reproductive effort, and survival of radiomarked females to 118 control females marked with leg bands. Arrival dates following spring migration were similar among females in different treatments in 2001. However, in 2002, wind direction during late migration was less favorable, and arrival of females with 35-g radiotransmitters lagged 1–2 days behind that of control females. Nest initiation dates, clutch size, and mean egg volume were similar for 152 nests of females that lacked radios and 62 nests of radiomarked females. Estimated nesting propensity for females with operable radiotransmitters was 61% and 72% in 2001 and 2002, respectively. Apparent annual survival (ϕ = 0.82, 95% confidence interval: 0.76 to 0.87) was similar among treatments in the first year after geese were marked. In the second and third years after marking, model-averaged estimates for survival of females with large radiotransmitters were 10% lower than estimates for control females. However, the effect of large radios on long-term survival was equivocal because of uncertainty surrounding treatment estimates. We conclude that abdominally implanted radiotransmitters with percutaneous antennas had small effects on migration chronology but no apparent effects on fecundity. Abdominal transmitters can provide unbiased estimates of anserine survival in the first year after deployment. Because of the potentially greater effects of larger transmitters on migration and long-term survival, we recommend that biologists minimize the size of implanted transmitters and deploy radios with caution if long-term survival of marked birds is a concern.

Alaska↗

USGS2005

Predator functional response and prey survival: Direct and indirect interactions affecting a marked prey population

1. Predation plays an integral role in many community interactions, with the number of predators and the rate at which they consume prey (i.e. their functional response) determining interaction strengths. Owing to the difficulty of directly observing predation events, attempts to determine the functional response of predators in natural systems are limited. Determining the forms that predator functional responses take in complex systems is important in advancing understanding of community interactions. 2. Prey survival has a direct relationship to the functional response of their predators. We employed this relationship to estimate the functional response for bald eagle Haliaeetus leucocepalus predation of Canada goose Branta canadensis nests. We compared models that incorporated eagle abundance, nest abundance and alternative prey presence to determine the form of the functional response that best predicted intra-annual variation in survival of goose nests. 3. Eagle abundance, nest abundance and the availability of alternative prey were all related to predation rates of goose nests by eagles. There was a sigmoidal relationship between predation rate and prey abundance and prey switching occurred when alternative prey was present. In addition, predation by individual eagles increased as eagle abundance increased. 4. A complex set of interactions among the three species examined in this study determined survival rates of goose nests. Results show that eagle predation had both prey- and predator-dependent components with no support for ratio dependence. In addition, indirect interactions resulting from the availability of alternative prey had an important role in mediating the rate at which eagles depredated nests. As a result, much of the within-season variation in nest survival was due to changing availability of alternative prey consumed by eagles. 5. Empirical relationships drawn from ecological theory can be directly integrated into the estimation process to determine the mechanisms responsible for variation in observed survival rates. The relationship between predator functional response and prey survival offers a flexible and robust method to advance our understanding of predator-prey interactions in many complex natural systems where prey populations are marked and regularly visited. ?? 2006 British Ecological Society.

Journal of Animal Ecology↗