DOI: 10.5061/dryad.zpc866tbz
title: Data from: Density-dependence produces spurious relationships among demographic parameters in a harvested species

description: 1. Harvest of wild organisms is an important component of human culture,
 economy, and recreation, but can also put species at risk of extinction.
 Decisions that guide successful management actions therefore rely on the
 ability of researchers to link changes in demographic processes to the
 anthropogenic actions or environmental changes that underlie variation in
 demographic parameters.  2. Ecologists often use population
 models or maximum sustained yield curves to estimate the impacts of
 harvest on wildlife and fish populations. Applications of these models
 usually focus exclusively on the impact of harvest and often fail to
 consider adequately other potential, often collinear, mechanistic drivers
 of the observed relationships between harvest and demographic rates. In
 this study, we used an integrated population model and long-term data
 (1973-2016) to examine the relationships among hunting and natural
 mortality, the number of hunters, habitat conditions, and population size
 of blue-winged teal (Spatula discors), an abundant North American dabbling
 duck with a  relatively fast-paced life history strategy. 3. Over
 the last two and a half decades of the study, teal abundance tripled,
 hunting mortality probability increased slightly (&lt; 0.02), and
 natural mortality probability increased substantially (&gt; 0.1) at
 greater population densities. We demonstrate strong density-dependent
 effects on natural mortality and fecundity as population density
 increased, indicative of compensatory harvest mortality and compensatory
 natality. Critically, an analysis that only assessed the relationship
 between survival and hunting mortality would spuriously indicate
 depensatory hunting mortality due to multicollinearity between abundance,
 natural mortality, and hunting mortality.  4. Our findings
 demonstrate that models that only consider the direct effect of hunting on
 survival or natural mortality can fail to accurately assess the
 mechanistic impact of hunting on population dynamics due to
 multicollinearity among demographic drivers. This multicollinearity limits
 inference and may have strong impacts on applied management actions
 globally.
description: Adult female blue-winged teal (n = 112,639) were captured in
 traps and nets prior to the hunting season (July-September) in the prairie
 potholes and aspen parklands of the North American midcontinent from 1973
 to 2016 (Figure 1). Teal were ringed with uniquely engraved metal markers,
 and some marked individuals were killed by hunters. A portion of these
 markers were retrieved and reported to the USGS Bird Banding Lab (n =
 2,518; USGS Patuxent Wildlife Research Center). From 1974-2016, waterfowl
 breeding population and habitat surveys were flown at the beginning of the
 breeding season over the same area by the U.S. Fish and Wildlife Service
 and the Canadian Wildlife Service to estimate the total number of breeding
 pairs of teal (y_n,t) and other ducks, and the number of ponds (y_p,t), a
 landscape scale measure of habitat suitability for breeding waterfowl
 (Walker et al. 2013, U.S. Fish & Wildlife Service 2018). We
 downloaded the ringing and recovery data from the GameBirds Database CD
 (Bird Banding Lab, USGS Patuxent Wildlife Research Center), and the
 Waterfowl Breeding Population and Habitat Survey data from the USFWS
 Migratory Birds Data Center. We retained females marked in Canada and the
 United States in Waterfowl Breeding Population and Habitat Survey strata
 20-49 (U.S. Fish & Wildlife Service 2018), and we restricted
 re-encounters to harvested individuals recovered and reported by hunters
 in the United States and Canada from September through early February,
 with half of all reported hunting mortality occurring in September. We
 excluded recoveries in Mexico, Central and South America, and the
 Carribean (n = 316) due to the inclusion of band reporting probabilities
 (r = r_1973, ... , r_2016) in our analyses, which were not available for
 Latin America. Mark-recovery data were downloaded from the USGS Bird
 Banding Lab Celis-Murillo et al. 2020. We accessed estimates of teal
 abundance and pond abundance from the Waterfowl Breeding Population and
 Habitat Survey (U.S. Fish & Wildlife Service 2018), as well as
 data on federal duck stamp sales, which are required to hunt for waterfowl
 in the United States. Third party data were used for this study,
 collection of which followed appropriate ethical guidelines. No additional
 ethical approval was required from our respective insitutions. We
 formatted the capture-recovery data into a multinomial array to reduce
 computational requirements. Please contact the authors
 for additional information about data processing.
description: The open-source programs R and JAGS are required to run the
 integrated population model described in this manuscript.