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Measurement error causes scale-dependent threshold erosion of biological signals in animal movement data

Bradshaw, Corey J. A., Sims, David W. and Hays, Graeme C. (2007). Measurement error causes scale-dependent threshold erosion of biological signals in animal movement data. Ecological Applications,17(2):628-638.

Document type: Journal Article
Citation counts: Scopus Citation Count Cited 55 times in Scopus Article | Citations

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IRMA ID A00003xPUB59
Title Measurement error causes scale-dependent threshold erosion of biological signals in animal movement data
Author Bradshaw, Corey J. A.
Sims, David W.
Hays, Graeme C.
Journal Name Ecological Applications
Publication Date 2007
Volume Number 17
Issue Number 2
ISSN 1051-0761   (check CDU catalogue open catalogue search in new window)
Scopus ID 2-s2.0-34247210804
Start Page 628
End Page 638
Total Pages 11
Place of Publication Washington DC, United States of America
Publisher Ecological Society of America
Field of Research 0501 - Ecological Applications
HERDC Category C1 - Journal Article (DEST)
Abstract Recent advances in telemetry technology have created a wealth of tracking data available for many animal species moving over spatial scales from tens of meters to tens of thousands of kilometers. Increasingly, such data sets are being used for quantitative movement analyses aimed at extracting fundamental biological signals such as optimal searching behavior and scale-dependent foraging decisions. We show here that the location error inherent in various tracking technologies reduces the ability to detect patterns of behavior within movements. Our analyses endeavored to set out a series of initial ground rules for ecologists to help ensure that sampling noise is not misinterpreted as a real biological signal. We simulated animal movement tracks using specialized random walks known as Levy flights at three spatial scales of investigation: 100-km, 10-km, and 1-km maximum daily step lengths. The locations generated in the simulations were then blurred using known error distributions associated with commonly applied tracking methods: the Global Positioning System (GPS), Argos polarorbiting satellites, and light-level geolocation. Deviations from the idealized Levy flight pattern were assessed for each track after incrementing levels of location error were applied at each spatial scale, with additional assessments of the effect of error on scale-dependent movement patterns measured using fractal mean dimension and first-passage time (FPT) analyses. The accuracy of parameter estimation (Levy mu, fractal mean D, and variance in FPT) declined precipitously at threshold errors relative to each spatial scale. At 100-km maximum daily step lengths, error standard deviations of >= 10 km seriously eroded the biological patterns evident in the simulated tracks, with analogous thresholds at the 10-km and 1-km scales (error SD >= 1.3 km and 0.07 km, respectively). Temporal subsampling of the simulated tracks maintained some elements of the biological signals depending on error level and spatial scale. Failure to account for large errors relative to the scale of movement can produce substantial biases in the interpretation of movement patterns. This study provides researchers with a framework for understanding the limitations of their data and identifies how temporal subsampling can help to reduce the influence of spatial error on their conclusions.
Keywords Argos satellites
first-passage time
fractal dimension
Levy flight
random walk
spatial scale
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