Absolute Population Estimates Using Capture–Recapture Experiments

The main methods used to estimate population size using capture–recapture for both closed and open populations are described, including the Peterson–Lincoln estimator, the Schabel census, Bailey’s triple catch, the Jolly–Seber stochastic method, and Cormack’s log-linear method. The robust design approach is described. R code listings for commonly used packages are presented. The assumptions common to capture–recapture methods are reviewed, and tests for assumptions such as equal catchability described. The use of programs to select model assumptions are described. The main methods for marking different animal groups are described, together with the use of natural marks and parasites and DNA. Marking methods include paint marks, dyes, tagging, protein marking, DNA, natural marks, tattooing, and mutilation. Methods for handling and release are described.

The Construction, Description, and Analysis of Age-Specific Life-Tables

Methods for constructing a life-table and budget for a species are described, and the various methods for the analysis of stage-frequency data reviewed. Stage-frequency data comprise counts of the individuals in different development stages in samples taken from a population over a period of time. The analysis of stage-frequency data to estimate the durations of the stages, the numbers entering stages, and survival rates is described. Examples of survivorship curves are presented, and the calculation of population growth rate described. Analysis of life-table data and demographic methods, including key-factor analysis, are described.

Age-Grouping, Time-Specific Life-Tables, and Predictive Population Models

This chapter describes techniques to create life-tables for animals whose generations overlap widely. Age-grouping is a prerequisite for these methods, which have been most widely applied to vertebrate populations. Age cannot be inferred from the developmental stage without reference to the environment. The speed of development may be temperature-dependent or influenced by factors such as oxygen and food availability. The methods for ageing animal groups, including invertebrates, fish, reptiles, amphibians, birds, and mammals, are reviewed. Time-specific life-tables, population modelling, and Leslie matrices are described. R code to analyze Leslie matrix dynamics is presented.

Estimation of Productivity and the Construction of Energy Budgets

Methods to assess the size of a population and the interactions between populations in terms of biomass (weight of living material) or energy content are described. Biomass can be expressed as wet weight, dry weight (DW), shell-free dry weight (SFDW), ash-free dry weight, or as the amount of organic carbon present. The energy content of a material may be determined directly by oxidation, either by potassium dichromate in sulphuric acid, or by burning in oxygen and determining the amount of heat liberated. The latter method—bomb calorimetry—is most convenient and is widely used in ecology, but it involves drying the material, and volatile substances can be lost. Methods to estimate standing-crop, energy density, feeding and assimilation, and production are reviewed. Energy budgets can usefully be summarized and compared if the efficiencies of various processes are calculated. Dynamic energy budget models are introduced.

Estimates of Species Richness and Population Size Based on Signs, Products, and Effects

Comparative surveys of species richness for some animal groups can be undertaken by surveying signs or products such as footprints, faeces, nests, burrows, or cast skins. Measures of the size of populations based on the magnitude of their products or effects are often referred to as population indices. Methods based on the collection of insect exuviae and frass are described and their efficiency discussed. Vertebrate monitoring based on a variety of signs is described. Methods that use plant damage criteria to assess insect herbivore abundance are presented. Methods to determine the relationship between plant damage and insect abundance are described.

Relative Methods of Population Measurement and the Derivation of Absolute Estimates

Relative sampling methods usually requiring comparatively simple equipment are described. These often concentrate the animals and provide impressive collections. Factors affecting the size of relative samples are reviewed to show that biological interpretation can be difficult. A wide variety of methods for aquatic and terrestrial sampling are reviewed, including pitfall, interception, light, sticky, and flight traps, electric fishing, drift samplers, and gill nets. The use of baited traps, including vertebrate hosts, is discussed. Removal trapping to estimate population density is described, and R software code listed.

Wildlife Population Estimates by Census and Distance Measuring Techniques

Methodologies based on counting the number of sightings to estimate are described. These techniques are particularly useful for large or easily seen animals such as birds, large grassland mammals, whales, crocodilians, and large, active insects such as butterflies. Point and line survey methods are described. Distance sampling methods, including Fourier series estimators, are presented, and R code listings to undertake the computations presented. Plotless density estimators are described based on nearest-neighbour, and closest-individual measurements are described.

Observational and Experimental Methods to Estimate Natality, Mortality, Movement, and Dispersal

This chapter describes the methods of directly quantifying the various processes that produce population change, natality, fertility, mortality, and dispersal. Natality is the number of births, fertility is the number of viable eggs laid by a female, and fecundity is a measure of the total egg production. The measurement of fecundity in various animal groups is reviewed. Stock-recruitment relationships used in fisheries research and the Moron–Ricker curve are described. The analysis of mortality within a generation is discussed, and apparent, real, and indispensable mortality defined. The term ‘dispersal’ covers any movement away from the initial locality, to define neighbourhood dispersal for the process by which individuals migrate into and via adjacent areas, and jump dispersal for longer-distance dispersal where individuals are transported or purposively move quickly to a new area. The determination of the home range or territory of an individual or, for social animals, a colony, is described.

Introduction to the Study of Animals

Because the objective of a study will largely determine the methods used, it is essential to define the objectives at the outset. Very broadly, studies may be defined as either extensive and intensive. Extensive studies are carried out over larger areas or longer time periods than intensive studies, and are frequently used to provide information on distribution and abundance for conservation or management programmes. Intensive studies involve the repeated observation of the population of an animal. The different types of population estimates—absolute, relative, and intensity—are described. The estimation of error and confidence intervals, including jackknife and bootstrap techniques, is described.

Species Richness, Diversity, and Packing

Methods to measure species richness and α‎-, β‎-, and γ‎-diversity are reviewed. A useful classification is α‎-diversity, the diversity of species within a community or habitat, β‎-diversity, a measure of the rate and extent of change in species along a gradient from one habitat to others, and γ‎-diversity, the richness in species of a range of habitats in a geographical area. Species inventories are frequently required for conservation management. Because a complete census is rarely feasible, the community must be sampled, and methods are needed to estimate via sampling the total taxa number present. A wide range of species richness estimators are described and their applicability reviewed. Models for species abundance, including geometric, log-normal, and broken stick are presented. Rarefaction techniques to compare species richness in communities sampled with differing effort are described. Methods to compare α‎-diversity between samples are described. Techniques to study community structure are introduced, and measures of niche size and overlap are presented. Similarity, indices are reviewed, and R code to measure niche overlap is presented.