SREL Reprint #3410

Effects of scale of movement, detection probability, and true population density on common methods of estimating population density

David A. Keiter1, Amy J. Davis2, Olin E. Rhodes, Jr.3, Fred L. Cunningham4, John C. Kilgo5, Kim M. Pepin2, and James C. Beasley1

1University of Georgia, Savannah River Ecology Laboratory,
D.B. Warnell School of Forestry and Natural Resources, PO Drawer E, Aiken, SC, 29802, USA
2United States Department of Agriculture, Animal and Plant Health Inspection Service,
Wildlife Services, National Wildlife Research Center, 4101 Laporte Avenue, Fort Collins, CO, 80521, USA
3University of Georgia, Savannah River Ecology Laboratory, Odum School of Ecology,
PO Drawer E, Aiken, SC, 29802, USA
4United States Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services,
National Wildlife Research Center, Mississippi Field Station, PO Box 6099, Mississippi State, MS, 39762, USA
5United States Department of Agriculture, Forest Service, Southern Research Station,
PO Box 700, New Ellenton, SC, 29809, USA

Abstract: Knowledge of population density is necessary for effective management and conservation of wildlife, yet rarely are estimators compared in their robustness to effects of ecological and observational processes, which can greatly influence accuracy and precision of density estimates. In this study, we simulate biological and observational processes using empirical data to assess effects of animal scale of movement, true population density, and probability of detection on common density estimators. We also apply common data collection and analytical techniques in the field and evaluate their ability to estimate density of a globally widespread species. We find that animal scale of movement had the greatest impact on accuracy of estimators, although all estimators suffered reduced performance when detection probability was low, and we provide recommendations as to when each field and analytical technique is most appropriately employed. The large influence of scale of movement on estimator accuracy emphasizes the importance of effective post-hoc calculation of area sampled or use of methods that implicitly account for spatial variation. In particular, scale of movement impacted estimators substantially, such that area covered and spacing of detectors (e.g. cameras, traps, etc.) must reflect movement characteristics of the focal species to reduce bias in estimates of movement and thus density.

SREL Reprint #3410

Keiter, D. A., A. J. Davis, O. E. Rhodes, Jr., F. L. Cunningham, J. C. Kilgo, K. M. Pepin, and J. C. Beasley. 2017. Effects of scale of movement, detection probability, and true population density on common methods of estimating population density. Scientific Reports 7(9446): 1-12.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).