Bryan F. J. Manly

Assessing habitat selection when availability changes

We present a method of comparing data on habitat use and availability that allows availability to differ among observations. This rnethod is applicable when habitats change over time and when animals are unable to move throughout a predeter- mined study area between observations. We used maximum-likelihood techniques to de- rive an index that estimates the probability that each habitat type would be used if all were equally available. We also demonstrate how these indices can be used to compare relative use of available habitats, assign them ranks, and assess statistical differences between pairs of indices. The set of these indices for all habitats can be compared between groups of animals that represent different seasons, sex or age classes, or experimental treatments. This method allows quantitative comparisons among types and is not affected by arbitrary decisions about which habitats to include in the study. We provide an example by comparing the availability of four categories of sea ice concentration to their use by adult female polar bears (Ursus maritimus), whose movements were monitored by satellite radio tracking in the Bering and Chukchi Seas during 1990. Use of ice categories by bears was nonrandom, and the pattern of use differed between spring and late summer seasons.

Latitudinal patterns in European ant assemblages: variation in species richness and body size

Using published distributions of 65 species from the British Isles and northern Europe, we show that ant assemblages change with latitude in two ways. First, as commonly found for many types of organisms, the number of ant species decreased significantly with increasing latitude. For Ireland and Great Britain, species richness also increased significantly with region area. Second, although rarely demonstrated for ectotherms, the body size of ant species, as measured by worker length, increased significantly with increasing latitude. We found that this body-size pattern existed in the subfamily Formicinae and, to a lesser extent, in the Myrmicinae, which together comprised 95% of the ant species in our study area. There was a trend for formicines to increase in size with latitude faster than myrmicines. We also show that the pattern of increasing body size was due primarily to the ranges of ant species shifting to higher latitudes as their body sizes increased, with larger formicines becoming less represented at southerly latitudes and larger myrmicines becoming more represented at northerly latitudes. We conclude by discussing five potential mechanisms for generating the observed body-size patterns: the heat-conservation hypothesis, two hypotheses concerning phylogenetic history, the migration-ability hypothesis, and the starvation-resistance hypothesis.

Handbook of Capture-Recapture Analysis

In the modern ecology there appears to be an increasing gap between field-based biologists and statisticians as new methods are developed to deal with more complex data. This book aims to bridge that gap with the goal of helping biologists understand state-of-the-art statistical methods for capture–recapture analysis. The editors have gathered the most complete and upto-date information on the subject and only time will tell if this reduces the gap between biologist and statistician. The book comprises of three main sections. Section one is a single chapter which acts as a general introduction to capture–recapture techniques and sets the scene for the rest of the book. It also gives a brief overview and history of capture–recapture methods from their first use in 1802 to the present day, introduces the scientific notation required for the rest of the book and gives a brief summary of the rest of the model chapters. Section two is the largest section and contains seven chapters which deal with the theoretical and statistical aspects of the main capture–recapture models. Section three consists of two chapters which give a series of examples analysed by the methods described in Section two. Chapters 2–8 introduce increasingly complex capture–recapture models from the original simple closed population model to complex multistate models. Although the authors differ between chapters, all follow a similar format and this makes it particularly easy to compare different models. Each chapter starts with a brief history of the model and its original derivation or formulation, including important researchers and crucial papers. Then follows a derivation of the parameter estimates, a list of assumptions of the method and a discussion of the estimate properties. Within each chapter potential model variations are also discussed. Finally there is a worked example using a variety of software programs that apply to the data set (e.g. JOLLY, MARK, CAPTURE), and a summary of the main points of the chapter. The editors suggest reading Chapters one and two thoroughly to understand the theoretical underpinning of the various models before moving on to subsequent chapters. I agree wholeheartedly with their suggestion, as it would be easy to become confused in later chapters without a detailed understanding of the basic models. Once the basics are well understood many will want to move immediately to the model that best fits their data set. As if predicting this possibility, Chapters 4–8 are self-contained, with each one dealing with the appropriate analysis of a specific type of data – closed populations models, open population models, tag recovery models, joint tag recovery and live resighting models and finally multistate models. From a practical viewpoint Chapter 9 is particularly useful. In it the authors use data from three longterm studies (European dippers, polar bears and mallard ducks) to illustrate the models described in earlier chapters using the computer program MARK. It is also a gentle introduction to MARK, which is the most up-to-date and commonly used capture–recapture program (see http://www.warnercnr.colostate.edu/ ~gwhite/mark/mark.htm to download the MARK program, manual and a wealth of other information). It would be helpful while reading this chapter to have the program MARK open on the computer so that you can work through each example using MARK as it’s being analysed in the book. Most examples use the European dipper data set (which is available on the web), but the polar bears are used to demonstrate a model where survival and recapture probabilities are not constant (something most field-based ecologists would have to consider) while the mallards are used to illustrate the tag recovery model. The editors have done an admirable job in trying to make complex capture–recapture models accessible to a greater range of field-based ecologists. Despite the scope and nature of this book, I feel that the best analysis methods will still be when ecologists and statisticians collaborate on a particular data set. I think many ecologists will find the time required to understand anything more than the simplest capture– recapture models prohibitive. This book will not put statisticians out of a job, rather it should allow for a more informed discussion when ecologists and statisticians collaborate on projects involving capture– recapture methods (which should be right from the start).

A Note on the Analysis of Species Co-Occurrences

The analysis of records of species occurrences on islands in an attempt to detect interactions between species has been an area of controversy in recent years in terms of the validity of some of the statistical methods used. In this note I make two contributions to the continuing debate. First, I advocate a generalized Monte Carlo testing procedure because this is easy to implement, is computationally efficient, and has guaranteed properties when the null hypothesis of no species interactions is correct. Second, I propose a test statistic that can be decomposed into a component for each individual species, and I demonstrate how this makes it possible to isolate species with unusual patterns of co—occurrence with other species, even after an allowance for multiple testing is made. See full-text article at JSTOR

Sex differences in Adélie penguin foraging strategies

Abstract Consistent sex differences in foraging trip duration, feeding locality and diet of breeding Adélie penguins (Pygoscelis adeliae) were demonstrated at two widely separated locations over several breeding seasons. Differences in foraging behaviour were most pronounced during the guard stage of chick rearing. Female penguins made on average longer foraging trips than males, ranged greater distances more frequently and consumed larger quantities of krill. In contrast, males made shorter journeys to closer foraging grounds during the guard period and fed more extensively on fish throughout chick rearing. Mean guard stage foraging trip durations over four seasons at Béchervaise Island, Eastern Antarctica and over two seasons at Edmonson Point, Ross Sea ranged between 31 and 73 h for females and 25 and 36 h for males. Ninety percent of males tracked from Béchervaise Island by satellite during the first 3 weeks post-hatch foraged within 20 km of the colony, while the majority (60%) of females travelled to the edge of the continental shelf (80–120 km from the colony) to feed during this period.

Comments on design and analysis of multiple-choice feeding-preference experiments

An approach to the analysis of multiple-choice food selection experiments proposed recently is criticised on three grounds and modified methods are suggested.

Constraints on body size distributions: an experimental approach using a small-scale system

Abstract Holling’s (1992) proposition that discontinuities in biotic and abiotic processes generate structure in ecological systems is examined experimentally by imposing size-specific perturbations on marine sediment assemblages. Two kinds of perturbations were applied: organic enrichment and predation, each at two levels. Perturbations significantly affected the densities and relative abundance of the main invertebrate taxa and these effects were consistent with the known effects of enrichment and predation. However, there was little evidence of significant treatment effects on the overall benthic biomass or abundance size spectrum, supporting the contention that the spectrum is conservative and is probably constrained by habitat architecture.

Maximum Likelihood Estimation for the Double-Count Method With Independent Observers

influenced the detection probabilities included perpendicular distance of bear groups from the flight line and the number of individuals in the groups. A series of models were considered which vary from (1) the simplest, where the probability of detection was the same for both observers and was not affected by either distance from the flight line or group size, to (2) models where probability of detection is different for the two observers and depends on both distance from the transect and group size. Estimation procedures are developed for the case when additional variables may affect detection probabilities. The methods are illustrated using data from the pilot polar bear survey and some recommendations are given for design of a survey over the larger Chukchi Sea between Russia and the United States.

The Use of Discrete-Choice Models for Evaluating Resource Selection

Using a multinomial logit model, the discrete-choice model for human behavior is developed for the analysis of resource selection by animals. This model has the advantage that resource availability can vary between animals and over time. Furthermore, the characteristics of the animals under study can be incorporated into the model. Methodology for estimating the multinomial logit model from a sample of alternative units is presented.

Estimation of stage-specific survival rates and other parameters for insect populations developing through several stages

SummaryA method of analysis is suggested for data obtained by sampling an insect population while the individuals in the population are developing through several stages. The method allows the estimation of (i) the numbers entering each stage, (ii) the mean duration of each stage, and (iii) daily survival rates. A basic assumption made is that the time of entry to a stage follows a normal distribution.The method is illustrated on data from a field population of grasshoppers and a laboratory population of locusts.