Estimating Animal Abundance: Review III

Schwarz, Carl; Seber, G. A. F.

doi:10.1214/ss/1009212521

Cited by 412 publications

(119 citation statements)

References 337 publications

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“…Conventional capture-mark-recapture (CMR) studies have been commonly used to estimate the sizes of wild populations (reviewed in Schwarz and Seber 1999). However, their invasive approach renders them inappropriate for the study of rare or elusive species.…”

Section: Introductionmentioning

confidence: 99%

Field surveys of capercaillie (Tetrao urogallus) in the Swiss Alps underestimated local abundance of the species as revealed by genetic analyses of non-invasive samples

et al. 2009

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An increasing number of species are becoming threatened by habitat loss and fragmentation. Therefore, solid estimates of the species' abundance in the remaining populations are required to develop suitable conservation measures and to monitor their effectiveness. The capercaillie (Tetrao urogallus L.) has experienced a dramatic decline in central Europe and has disappeared from large areas of its former natural range. In Switzerland, the species' distribution, habitat requirements and demographic status were studied and evaluated in an attempt to support appropriate management decisions to conserve the species. National surveys of the capercaillie in Switzerland have traditionally been obtained from male counts at leks. However, individual attendance to the lek is sex-and agespecific. Thus, male counts at leks may provide a biased estimate of local population sizes. In the present study, we compared two alternative indirect methods to estimate the sizes of local populations at eight study sites situated in the Alps and Prealps of Switzerland. We first assessed the sizes of local populations from the observed density and distribution of direct and indirect evidence of the species' presence during field surveys. Feather and faeces samples collected during field surveys were genotyped at twelve nuclear microsatellite loci and a sex-specific nuclear gene fragment. Individual genotypes were used as genetic tags to estimate the sizes of the eight local populations using an urn model developed for small populations. The index of local population sizes assessed from field surveys was lower than the number of unique genotypes at each study site, which itself underestimated the abundances of populations in most cases. Based on our results, the genetic tagging method appeared to be less biased than the field survey method. However, an alternative faeces sampling scheme, resulting in 2-3 genotypings per individual, could further improve the accuracy of the size estimates of local populations. Our study confirms that genetic tagging methods are a valuable tool to estimate the sizes of local populations and to monitor the response of rare and elusive species to management actions.

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Section: Introductionmentioning

confidence: 99%

Field surveys of capercaillie (Tetrao urogallus) in the Swiss Alps underestimated local abundance of the species as revealed by genetic analyses of non-invasive samples

et al. 2009

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“…Bellows 1981;Turchin 2003;Sibly et al 2005). There is also a developed methodology how to measure the size of a population (Sutherland 1996;Thomas 1996;Schwarz and Seber 1999;McCallum 2000;Williams et al 2002). However, real populations-or rather estimates of population size-rarely follow the course predicted by theoretical models.…”

Section: Introductionmentioning

confidence: 99%

Process and measurement errors of population size: their mutual effects on precision and bias of estimates for demographic parameters

Hovestadt

Nowicki

2008

Biodivers Conserv

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Knowing the parameters of population growth and regulation is fundamental for answering many ecological questions and the successful implementation of conservation strategies. Moreover, detecting a population trend is often a legal obligation. Yet, inherent process and measurement errors aggravate the ability to estimate these parameters from population time-series. We use numerical simulations to explore how the lengths of the time-series, process and measurement error influence estimates of demographic parameters. We first generate time-series of population sizes with given demographic parameters for density-dependent stochastic population growth, but assume that these population sizes are estimated with measurement errors. We then fit parameters for population growth, habitat capacity, total error and long-term trends to the 'measured' time-series data using non-linear regression. The length of the time-series and measurement error introduce a substantial bias in the estimates for population growth rate and to a lesser degree on estimates for habitat capacity, while process error has little effect on parameter bias. The total error term of the statistical model is dominated by process error as long as the latter is larger than the measurement error. A decline in population size is difficult to document as soon as either error becomes moderate, trends are not very pronounced, and time-series are short (\10-15 seasons). Detecting an annual decline of 1% within 6-year reporting periods, as required for the European Union for the species of Community Interest, appears unachievable.

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“…Nevertheless, in the first step of our analysis we evaluated the validity of this assumption. This was done through assessing the survival (/) and recruitment (B) of individuals between capture sessions with the open population Jolly-Seber type models (Schwarz and Arnason 1996;Schwarz and Seber 1999). Strictly-speaking / should be called residence as it is affected not only by mortality but also by emigration, yet we retain the term survival for the sake of consistency with the standard mark-recapture nomenclature.…”

Section: Discussionmentioning

confidence: 99%

Monitoring crayfish using a mark-recapture method: potentials, recommendations, and limitations

et al. 2008

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Crayfish are regarded as useful indicators of environmental quality and freshwater biodiversity. However, reliable methods for monitoring their populations are needed so that this potential can be fully utilised. We report and discuss methodological aspects of the white-clawed crayfish (Austropotamobius pallipes complex) survey conducted in Piedmont, Italy, with the use of mark-recapture. The results suggest that the method can serve as a convenient tool for estimating the size of crayfish populations and inferring their temporal trends. The two populations investigated appeared closed except for wintertime and July. Consequently, the Robust Design, which is regarded as the most reliable mark-recapture approach, can be easily applied. The minimum effective sampling plan for monitoring purposes should comprise one primary period per year, conducted in the summer-autumn season, and consisting of three capture sessions. If gaining insight into the ecology of the investigated species is the prime objective and sufficient resources are available, the optimal plan should include two primary periods (in spring and the summerautumn season) of five capture sessions each. Capture sessions need to be separated by roughly 2-week intervals in order to avoid the strong, but short-term, negative effect of capturing crayfish on their recapture chances. As the model without heterogeneity in capture probabilities ensures better estimate precision we recommend that data collected for both sexes are analysed separately. Taking into consideration higher male catchabilities and sex ratio being invariably 1:1, it also seems beneficial to estimate only male numbers and double them to achieve total population sizes.

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Estimating Animal Abundance: Review III

Abstract: The literature describing methods for estimating animal abundance and related parameters continues to grow. This paper reviews recent developments in the subject over the past seven years and updates two previous reviews.

Cited by 412 publications

References 337 publications

Field surveys of capercaillie (Tetrao urogallus) in the Swiss Alps underestimated local abundance of the species as revealed by genetic analyses of non-invasive samples

Field surveys of capercaillie (Tetrao urogallus) in the Swiss Alps underestimated local abundance of the species as revealed by genetic analyses of non-invasive samples

Process and measurement errors of population size: their mutual effects on precision and bias of estimates for demographic parameters

Monitoring crayfish using a mark-recapture method: potentials, recommendations, and limitations

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