Geology topics

William R. Gould

Publications and source records attributed to William R. Gould.

24 records · Page 2Linked to original sources

USGS2006

Abundance: Population size and density estimation

Estimates of population size (total number of individuals) or density (number of individuals per unit area) are some of the most basic requirements for wildlife research and management. This article provides a brief overview of approaches for wildlife population estimation. These include habitat-based approaches such as quadrat, line intercept, distance, and repeated count methods, as well as animal-based approaches such as capture–recapture and harvest methods. In contrast to methods that only index changes in these parameters, estimates of size or density must account for the probability that an individual will be included in the sample used for estimation. The essential differences in the approaches are in how the samples are obtained and how the sampling probabilities are estimated.

Book chapter↗

USGS2005

Mark-resight superpopulation estimation of a wintering elk Cervus elaphus canadensis herd

We executed four mark-resight helicopter surveys during the winter months January–February for each of the three years 1999–2001 at 7–10 day intervals to estimate population size of a wintering elk Cervus elaphus canadensis herd in northern New Mexico. We counted numbers of radio-collared and uncollared elk on a simple random sample of quadrats from the study area. Because we were unable to survey the entire study area, we adopted a superpopulation approach to estimating population size, in which the total number of collared animals within and proximate to the entire study area was determined from an independent fixed-wing aircraft. The total number of collared animals available on the quadrats surveyed was also determined and facilitated detectability estimation. We executed superpopulation estimation via the joint hypergeometric estimator using the ratio of marked elk counted to the known number extant as an estimate of effective detectability. Superpopulation size estimates were approximately four times larger than previously suspected in the vicinity of the study area. Despite consistent survey methodology, actual detection rates varied within winter periods, indicating that multiple resight flights are important for improved estimator performance. Variable detectability also suggests that reliance on mere counts of observed individuals in our area may not accurately reflect abundance.

Colorado, New Mexico↗

USGS2004

Seasonal changes in 17-ß estradiol of the Rio Grande Chub ( Gila pandora ) in south-central New Mexico

Timing of gametogensis and thus spawning can be inferred through changes in plasma concentrations of gonadal hormones. In preparation for ovulation and spawning, mean concentrations of 17ß-estradiol in a population of Rio Grande chub ( Gila pandora ) occupying the Rio Bonito, New Mexico, peaked at 37.6 ng/mL on 16 June and declined to 1.50 ng/mL by 11 August. Similarly, the gonadal somatic index (GSI) increased from 9.02 on 21 May ( n = 9) to 11.85 on 16 June ( n = 2) and declined to 6.10 on 11 August ( n = 2). Peak concentrations of 17ß-estradiol and elevated GSI in June coincided with peak daylength for the year (14 h and 12 min) and average water temperature of 15.1°C. Concentrations of 17ß-estradiol remained low through 3 October indicating no additional spawning events in the Rio Grande chub population. We demonstrated 17ß-estradiol is a nondestructive and thus useful tool in estimating timing of spawning in a wild fish population.

Southwestern Naturalist↗

USGS2003

Comparison of helicopter and ground surveys for North American elk Cervus elaphus and mule deer Odocoileus hemionus population composition

Both ground and helicopter surveys are commonly used to collect sex and age composition data for ungulates. Little attention has been paid, however, to whether data collected by each technique are similar. We compared helicopter and ground composition data for both elk Cervus elaphus and mule deer Odocoileus hemionus across a variety of habitats in the state of Washington, USA. We found that ground and helicopter counts differed (P's < 0.002) consistently in male age structure estimates for elk, and that the two survey methods differed in estimates of adult sex ratios for mule deer (P = 0.023). Counts from helicopters provided larger sample sizes, tended to be more consistent annually in their results, and were corroborated by other demographic studies of the test populations. We conclude that helicopter and ground surveys differ for male age structure and perhaps male:female ratios, but are similar for young:female ratios. Managers should maintain a standardized technique using the same survey vehicle for trend analysis of composition data.

Washington↗

USGS1998

Estimation of temporal variability of survival in animal populations

Temporal variation of demographic characteristics for animal populations is of interest to both ecologists and biological modelers. The standard deviation of a series of estimated parameter values (e.g., estimated population size) or some function thereof (e.g., log of the estimated parameters) is commonly used as a measure of temporal variability. These measures of temporal variation overestimate the true temporal variation by not accounting for sampling variability inherent to the estimation of unknown population parameters. Using a variance-components approach to partitioning the total variability of an estimated parameter, we demonstrate the ease with which sampling variation can be removed from the observed total variation of parameter estimates. Estimates of temporal variability of survival are given after removal of sampling variation for three bird species: the federally listed Roseate Tern ( Sterna dougallii ), Black-capped Chickadees ( Parus atricapillus ), and Mallard ducks ( Anas platyrhynchos ). Sampling variation accounted for the majority of the total variation in the survival estimates for nearly all of the populations studied. Substantial differences in observed significance levels were observed when testing for demographic differences in temporal variation using temporal variance estimates adjusted and unadjusted for sampling variance.

Ecology↗

USGS1995

Survival and population size estimation in raptor studies: A comparison of two methods

ABSTRACT.--The Jolly-Seber model is a capture-recapture model that can provide less-biased survival and population size estimates than those produced from simple counting procedures. Parameter estimation by simple counts and Jolly-Seber methods are based on certain assumptions that directly determine the validity of estimates. Evuluation of assumptions for parameter estimation is a focus of this paper and used as a basis for determining which methods are more likely to produce better estimates. An example of population size and survival estimation for a peregrine falcon(Falco peregrinus) population in western Greenland is used to compare the two methods.Based on results from the Greenland peregrine population, and an assessment of the underlying assumptions of simple counts and the Jolly-Seber model,we suggest that Jolly-Seber estimation of survival and population size is less biased than simple counts in studies with marked birds. We recommend the use of a Jolly-Seber analysis of data when capture-recapture techniques are employed in raptor population studies.

Journal of Raptor Research↗