William Link, Ph.D. (Former Employee)
Science and Products
Filter Total Items: 44
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Occam's shadow: levels of analysis in evolutionary ecology - where to next?
Evolutionary ecology is the study of evolutionary processes, and the ecological conditions that influence them. A fundamental paradigm underlying the study of evolution is natural selection. Although there are a variety of operational definitions for natural selection in the literature, perhaps the most general one is that which characterizes selection as the process whereby heritable variation
Authors
E.G. Cooch, E. Cam, W. A. Link
Of bugs and birds: Markov Chain Monte Carlo for hierarchical modeling in wildlife research
Markov chain Monte Carlo (MCMC) is a statistical innovation that allows researchers to fit far more complex models to data than is feasible using conventional methods. Despite its widespread use in a variety of scientific fields, MCMC appears to be underutilized in wildlife applications. This may be due to a misconception that MCMC requires the adoption of a subjective Bayesian analysis, or perhap
Authors
William A. Link, Emmanuelle Cam, James D. Nichols, Evan G. Cooch
Model-based estimation of individual fitness
Fitness is the currency of natural selection, a measure of the propagation rate of genotypes into future generations. Its various definitions have the common feature that they are functions of survival and fertility rates. At the individual level, the operative level for natural selection, these rates must be understood as latent features, genetically determined propensities existing at birth.
Authors
W. A. Link, E.G. Cooch, E. Cam
Scaling in sensitivity analysis
Population matrix models allow sets of demographic parameters to be summarized by a single value λ, the finite rate of population increase. The consequences of change in individual demographic parameters are naturally measured by the corresponding changes in λ; sensitivity analyses compare demographic parameters on the basis of these changes. These comparisons are complicated by issues of scale. E
Authors
W. A. Link, P.F. Doherty
A hierarchical analysis of population change with application to Cerulean Warblers
Estimation of population change from count surveys is complicated by variation in quality of information among sample units, by the need for covariates to accommodate factors that influence detectability of animals, and by multiple geographic scales of interest. We present a hierarchical model for estimation of population change from the North American Breeding Bird Survey. Hierarchical models, in
Authors
W. A. Link, J.R. Sauer
Statistical mapping of count survey data
We apply a Poisson mixed model to the problem of mapping (or predicting) bird relative abundance from counts collected from the North American Breeding Bird Survey (BBS). The model expresses the logarithm of the Poisson mean as a sum of a fixed term (which may depend on habitat variables) and a random effect which accounts for remaining unexplained variation. The random effect is assumed to be s
Authors
J. Andrew Royle, W. A. Link, J.R. Sauer
Estimating transition probabilities in unmarked populations: Entropy revisited
The probability of surviving and moving between 'states' is of great interest to biologists. Robust estimation of these transitions using multiple observations of individually identifiable marked individuals has received considerable attention in recent years. However, in some situations, individuals are not identifiable (or have a very low recapture rate), although all individuals in a sample c
Authors
E.G. Cooch, W. A. Link
Modeling pattern in collections of parameters
Wildlife management is increasingly guided by analyses of large and complex datasets. The description of such datasets often requires a large number of parameters, among which certain patterns might be discernible. For example, one may consider a long-term study producing estimates of annual survival rates; of interest is the question whether these rates have declined through time. Several stat
Authors
W. A. Link
Factors influencing counts in an annual survey of Snail Kites in Florida
Snail Kites (Rostrhamus sociabilis) in Florida were monitored between 1969 and 1994 using a quasi-systematic annual survey. We analyzed data from the annual Snail Kite survey using a generalized linear model where counts were regarded as overdispersed Poisson random variables. This approach allowed us to investigate covariates that might have obscured temporal patterns of population change or indu
Authors
R.E. Bennetts, W. A. Link, J.R. Sauer, P.W. Sykes
Predicting chick survival and productivity of Roseate Terns from data on early growth
Early growth of Roseate Tern (Sterna dougallii) chicks is a strong predictor of chick survival and hence of productivity. We developed discriminant functions to predict chick survival from body-masses measured during the first 3 days of life. Productivity is estimated by assuming that almost all A-chicks (first-hatched in each brood) survive to fledging, and using the discriminant functions to p
Authors
I.C.T. Nisbet, J. S. Hatfield, W. A. Link, J. A. Spendelow
Controlling for varying effort in count surveys: An analysis of Christmas Bird Count data
The Christmas Bird Count (CBC) is a valuable source of information about midwinter populations of birds in the continental U.S. and Canada. Analysis of CBC data is complicated by substantial variation among sites and years in effort expended in counting; this feature of the CBC is common to many other wildlife surveys. Specification of a method for adjusting counts for effort is a matter of some c
Authors
W. A. Link, J.R. Sauer
Regional analysis of population trajectories from the North American Breeding Bird Survey
The North American Breeding Bird Survey (BBS) was started in 1966, and provides information on population change and distribution for most of the birds in North America. The geographic extent of the survey, and the logistical compromises needed to survey such a large area, present many challenges for estimation from BBS data. In this paper, we describe the survey and discuss some of the limitatio
Authors
J.R. Sauer, W. A. Link
Science and Products
Filter Total Items: 44
No results found.
Filter Total Items: 124
Occam's shadow: levels of analysis in evolutionary ecology - where to next?
Evolutionary ecology is the study of evolutionary processes, and the ecological conditions that influence them. A fundamental paradigm underlying the study of evolution is natural selection. Although there are a variety of operational definitions for natural selection in the literature, perhaps the most general one is that which characterizes selection as the process whereby heritable variation
Authors
E.G. Cooch, E. Cam, W. A. Link
Of bugs and birds: Markov Chain Monte Carlo for hierarchical modeling in wildlife research
Markov chain Monte Carlo (MCMC) is a statistical innovation that allows researchers to fit far more complex models to data than is feasible using conventional methods. Despite its widespread use in a variety of scientific fields, MCMC appears to be underutilized in wildlife applications. This may be due to a misconception that MCMC requires the adoption of a subjective Bayesian analysis, or perhap
Authors
William A. Link, Emmanuelle Cam, James D. Nichols, Evan G. Cooch
Model-based estimation of individual fitness
Fitness is the currency of natural selection, a measure of the propagation rate of genotypes into future generations. Its various definitions have the common feature that they are functions of survival and fertility rates. At the individual level, the operative level for natural selection, these rates must be understood as latent features, genetically determined propensities existing at birth.
Authors
W. A. Link, E.G. Cooch, E. Cam
Scaling in sensitivity analysis
Population matrix models allow sets of demographic parameters to be summarized by a single value λ, the finite rate of population increase. The consequences of change in individual demographic parameters are naturally measured by the corresponding changes in λ; sensitivity analyses compare demographic parameters on the basis of these changes. These comparisons are complicated by issues of scale. E
Authors
W. A. Link, P.F. Doherty
A hierarchical analysis of population change with application to Cerulean Warblers
Estimation of population change from count surveys is complicated by variation in quality of information among sample units, by the need for covariates to accommodate factors that influence detectability of animals, and by multiple geographic scales of interest. We present a hierarchical model for estimation of population change from the North American Breeding Bird Survey. Hierarchical models, in
Authors
W. A. Link, J.R. Sauer
Statistical mapping of count survey data
We apply a Poisson mixed model to the problem of mapping (or predicting) bird relative abundance from counts collected from the North American Breeding Bird Survey (BBS). The model expresses the logarithm of the Poisson mean as a sum of a fixed term (which may depend on habitat variables) and a random effect which accounts for remaining unexplained variation. The random effect is assumed to be s
Authors
J. Andrew Royle, W. A. Link, J.R. Sauer
Estimating transition probabilities in unmarked populations: Entropy revisited
The probability of surviving and moving between 'states' is of great interest to biologists. Robust estimation of these transitions using multiple observations of individually identifiable marked individuals has received considerable attention in recent years. However, in some situations, individuals are not identifiable (or have a very low recapture rate), although all individuals in a sample c
Authors
E.G. Cooch, W. A. Link
Modeling pattern in collections of parameters
Wildlife management is increasingly guided by analyses of large and complex datasets. The description of such datasets often requires a large number of parameters, among which certain patterns might be discernible. For example, one may consider a long-term study producing estimates of annual survival rates; of interest is the question whether these rates have declined through time. Several stat
Authors
W. A. Link
Factors influencing counts in an annual survey of Snail Kites in Florida
Snail Kites (Rostrhamus sociabilis) in Florida were monitored between 1969 and 1994 using a quasi-systematic annual survey. We analyzed data from the annual Snail Kite survey using a generalized linear model where counts were regarded as overdispersed Poisson random variables. This approach allowed us to investigate covariates that might have obscured temporal patterns of population change or indu
Authors
R.E. Bennetts, W. A. Link, J.R. Sauer, P.W. Sykes
Predicting chick survival and productivity of Roseate Terns from data on early growth
Early growth of Roseate Tern (Sterna dougallii) chicks is a strong predictor of chick survival and hence of productivity. We developed discriminant functions to predict chick survival from body-masses measured during the first 3 days of life. Productivity is estimated by assuming that almost all A-chicks (first-hatched in each brood) survive to fledging, and using the discriminant functions to p
Authors
I.C.T. Nisbet, J. S. Hatfield, W. A. Link, J. A. Spendelow
Controlling for varying effort in count surveys: An analysis of Christmas Bird Count data
The Christmas Bird Count (CBC) is a valuable source of information about midwinter populations of birds in the continental U.S. and Canada. Analysis of CBC data is complicated by substantial variation among sites and years in effort expended in counting; this feature of the CBC is common to many other wildlife surveys. Specification of a method for adjusting counts for effort is a matter of some c
Authors
W. A. Link, J.R. Sauer
Regional analysis of population trajectories from the North American Breeding Bird Survey
The North American Breeding Bird Survey (BBS) was started in 1966, and provides information on population change and distribution for most of the birds in North America. The geographic extent of the survey, and the logistical compromises needed to survey such a large area, present many challenges for estimation from BBS data. In this paper, we describe the survey and discuss some of the limitatio
Authors
J.R. Sauer, W. A. Link