James D. Nichols

Estimation of Recruitment from Immigration Versus In Situ Reproduction Using Pollock's Robust Design

Recruitment to animal populations can occur through both immigration and in situ reproduction. These two components of recruitment are conceptually distinct and lead to different mechanistic models of population dynamics. We describe a capture- recapture design that can be used to obtain separate estimates of these two recruitment components. We then illustrate the use of our method and estimators with capture-recap- ture data from a population of Microtus pennsylvanicus at the Patuxent Wildlife Research Center in Maryland.

Demography of the everglade kite: Implications for population management

Abstract Simple deterministic and stochastic population models are used to examine the demographic patterns of the Everglade Kite population. These efforts are directed at making inferences about the evolution of the kite life-history pattern, and at providing guidelines for the management of the kite population. The Everglade Kite has apparently evolved high adult survival rates, in partial response to a variable reproductive output. Proper management of this population should include the protection of adults from catastrophic mortality sources, and the provision of adequate water-levels to ensure reproductive success.

Spatio-temporal dynamics of species richness in coastal fish communities

Determining patterns of change in species richness and the processes underlying the dynamics of biodiversity are of key interest within the field of ecology, but few studies have investigated the dynamics of vertebrate communities at a decadal temporal scale. Here, we report findings on the spatio–temporal variability in the richness and composition of fish communities along the Norwegian Skagerrak coast having been surveyed for more than half a century. Using statistical models incorporating non–detection and associated sampling variance, we estimate local species richness and changes in species composition allowing us to compute temporal variability in species richness. We tested whether temporal variation could be related to distance to the open sea and to local levels of pollution. Clear differences in mean species richness and temporal variability are observed between fjords that were and were not exposed to the effects of pollution. Altogether this indicates that the fjord is an appropriate scale for studying changes in coastal fish communities in space and time. The year–to–year rates of local extinction and turnover were found to be smaller than spatial differences in community composition. At the regional level, exposure to the open sea plays a homogenizing role, possibly due to coastal currents and advection.

Small mammal populations at hazardous waste disposal sites near Houston, Texas, USA

Small mammals were trapped, tagged and recaptured in 0.45 ha plots at six hazardous industrial waste disposal sites to determine if populations, body mass and age structures were different from paired control site plots. Low numbers of six species of small mammals were captured on industrial waste sites or control sites. Only populations of hispid cotton rats at industrial waste sites and control sites were large enough for comparisons. Overall population numbers, age structure, and body mass of adult male and female cotton rats were similar at industrial waste sites and control sites. Populations of small mammals (particularly hispid cotton rats) may not suffice as indicators of environments with hazardous industrial waste contamination.

On valuing patches: estimating contributions to metapopulation growth with reverse-time capture–recapture modelling

Metapopulation ecology has historically been rich in theory, yet analytical approaches for inferring demographic relationships among local populations have been few. We show how reverse-time multi-state capture–recapture models can be used to estimate the importance of local recruitment and interpopulation dispersal to metapopulation growth. We use ‘contribution metrics’ to infer demographic connectedness among eight local populations of banner-tailed kangaroo rats, to assess their demographic closure, and to investigate sources of variation in these contributions. Using a 7 year dataset, we show that: (i) local populations are relatively independent demographically, and contributions to local population growth via dispersal within the system decline with distance; (ii) growth contributions via local survival and recruitment are greater for adults than juveniles, while contributions involving dispersal are greater for juveniles; (iii) central populations rely more on local recruitment and survival than peripheral populations; (iv) contributions involving dispersal are not clearly related to overall metapopulation density; and (v) estimated contributions from outside the system are unexpectedly large. Our analytical framework can classify metapopulations on a continuum between demographic independence and panmixia, detect hidden population growth contributions, and make inference about other population linkage forms, including rescue effects and source–sink structures. Finally, we discuss differences between demographic and genetic population linkage patterns for our system.

The need for accuracy in modelling: An example

Abstract The need for accurate information in modelling depends on the objectives of the effort, but trustworthy data are essential for a model intended for use in the management of natural resources. This point is illustrated by referring to a recently published model of canvasback ducks. We demonstrate that several key assumptions are not supported by biological evidence, and that inferences drawn from the mmodel could be dangerously misleading if they were used to guide the management of canvasback ducks.

Mathematical models and population cycles: A critical evaluation of a recent modeling effort

Hutchinson (1975, p. 497) recently observed that i t is very easy to make a mathematical model of an oscillating population . This ease of construction has no doubt been partially responsible for the abundance of modeling efforts dealing with population cycles . Numerous models have been used to investigate cyclic behavior of small mammal populations, and these constructs form a diverse group with respect to both structure and intended function (see review in Conley and Nichols, 1978). Many early modeling efforts directed at the phenomenon of population cycles represented very general hypotheses and were thus quite general in structure (e.g. Hutchinson, 1948; Wangersky and Cunningham, 1958). These models were useful in demonstrating the potential importance of such factors as time lags to the production of cyclic population behavior. However, the past two decades have included a number of detailed empirical studies on oscillating small mammal populations (see review in Krebs and Myers, 1974). This empirical work has been appropriately accompanied by the refinement of old hypotheses and the development of new ones.

Estimating Abundance for Closed Populations with Mark—Recapture Methods

• Estimating N is much more difficult than you might initially expect • A variety of methods can be used: o Census – assume count all animals in the population o Sample plots – assume count all animals on plots o Transect methods – estimate detection probability as a function of distance from a line transect or point to animals o Capture-recapture – estimate capture probability – our focus • Or, can abandon estimation and use an index – often done, seldom tested • Essentially comes down to dealing with counting animals and relating the count to the number in the population somehow.

A STOCHASTIC POPULATION MODEL OF MID-CONTINENTAL MALLARDS

We developed a simulation model that integrates information on factors affecting the population dynamics of mallards in the mid-continental region of the United States. In the model we vary age, body mass, and reproductive and molt status of simulated females. Females use several types of nesting and foraging habitat in 15 geographic areas. Deterministic and stochastic events cause mortality or attribute changes on a daily basis, depending on current attributes, habitat, area, calendar date, wetland conditions, temperature, and various mortality agents. Because the model encompasses the entire year, it can be used to examine cross-seasonal effects. A simulated increase in nest success from 0.14 to 0.17 changed the annual rate of population growth from -6% to -1 %. A simulated 75% reduction in lead poisoning changed the rate from -6% to -3%.

Modeling Heterogeneous Detection Probabilities

Unmodeled variation, or heterogeneity, in detection probabilities will result in biased estimates of occupancy probabilities. In this chapter we consider occupancy models that allow for heterogeneous detection probability among units, including models with discrete support (finite mixtures) or continuous mixtures such as the beta or logit-normal models, and we also consider the Royle and Nichols (2003) model that arises by considering that heterogeneity in detection probability is derived from variation in abundance. We also note how covariates that are thought to influence detection probability can also be incorporated. Examples are given of fitting and interpreting these models to avian detection/nondetection data, and anuran calling survey data.