How reliable are harvesting data for analyses of spatio-temporal population dynamics?

Ranta, E., Lindstrom, J. , Lindén, H. and Helle, P. (2008) How reliable are harvesting data for analyses of spatio-temporal population dynamics? Oikos, 117(10), pp. 1461-1468. (doi: 10.1111/j.0030-1299.2008.16879.x)

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Harvest data are commonly used as proxy for count data, especially in studies of long-term temporal and spatial patterns of population fluctuations. However, usually the concurrence of the conclusions based on different types of data is impossible to verify due to the lack of count data. Here, we use annual (1964–2004) harvest and population census data for capercaillie, black grouse and hazel grouse from 14 game management districts covering Finland, and demonstrate some mismatch in the information that these data sets provide. Overall, linear regressions of annual harvest against population count give a reasonable fit, but the slopes are less than 1 in every species. Harvest bags have been proportionally larger in north and eastern Finland than in southwestern Finland, with marked species-specific differences. Considering population variation, the CV% in the census data (30–50%) is consistently smaller than it is in the harvest data (60–70%). Most importantly, conclusions on the spatio-temporal patterns of the population dynamics are different if based on harvest rather than count data. In capercaillie, synchrony decreases faster with distance according to the harvest data, while in black grouse and hazel grouse the census data show the steeper decline. In addition, the autocorrelation coefficients in the census time series are higher in capercaillie and black grouse than in harvest data, but in hazel grouse the opposite is true. Finally, the parameter estimates for a second order autoregressive model using different data sets differ, and these differences are species-specific. Despite the fact that annual harvest is a positive and linear function of annual grouse population density, the pattern of population dynamics derived from the bag data is different from that shown by the census data. This result urges caution in using wildlife bag data as reliable indices of population dynamics.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Lindstrom, Dr Jan
Authors: Ranta, E., Lindstrom, J., Lindén, H., and Helle, P.
College/School:College of Medical Veterinary and Life Sciences > School of Life Sciences
Journal Name:Oikos
Publisher:Wiley-Blackwell Publishing, Inc.
ISSN (Online):1600-0706
Published Online:12 August 2008

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