Abstract
AbstractDecisions regarding endangered species recovery often face sparse data and multiple sources of uncertainty about the effects of management. Structured decision making (SDM) provides a framework for assembling knowledge and expert opinion and evaluating the tradeoffs between different objectives while formally incorporating uncertainty. The Atlantic Coast piping plover provides an illustrative case for the utility of SDM in endangered species management because its population growth is simple to model, most populations are monitored, decision alternatives are well defined, and many managers are open to recovery recommendations. We built a model to evaluate the decision to use nest exclosures to protect piping plover eggs from predators, where the objective was to maximize λ and the tradeoff was between nest survival and adult survival. The latter can be reduced by exclosures. We used a novel mixed multinomial logistic exposure model to predict daily nest fates and incorporated the results into a stochastic projection matrix that included renesting after nest failure, and adult mortality associated with abandonment. In our test data set (n = 329 nests from 28 sites over four years), the mean nest survival over 34 days was markedly higher for exclosed nests (0.76 ± 0.03 SE) than for unexclosed nests (0.37 ± 0.07). Abandonment rates were also higher for exclosed nests (0.092 ± 0.017) than for unexclosed nests (0.045 ± 0.017), but the difference was not statistically significant and the loss rate to “other sources” (mostly predators) was much lower for exclosed nests (0.15 ± 0.03) than for unexclosed nests (0.58 ± 0.07). Population growth rate (λ) was clearly improved by exclosure use at the sites with high background nest loss rates, but λ was still <1 with exclosure use. Where the background nest loss rates were low, the decision to use exclosures was ambiguous, and λ could benefit from reducing uncertainty in vital rates. Our process demonstrated that geographic and temporal variation in nest mortality determines whether exclosures will be useful in attaining positive population growth rates and that other management options must be considered where the background nest mortality rates are high.
Highlights
Management of endangered species often must proceed despite the significant uncertainty in abundance and vital rates and in how threats or limiting factors impact those quantities (Regan et al 2005)
We developed a nest survival model from nest monitoring data gathered across the breeding range
Plover biologists and managers worked with population modeling coaches to refine a projection model for piping plovers that could incorporate the potential positive and negative effects of nest exclosures
Summary
Management of endangered species often must proceed despite the significant uncertainty in abundance and vital rates and in how threats or limiting factors impact those quantities (Regan et al 2005). Key sources of uncertainty affecting the wildlife management include environmental stochasticity, partial observability (including measurement and sampling errors), partial controllability (factors outside of the manager’s control affect the population), and structural or model uncertainty (Williams et al 2002, Martin et al 2009). Failing to address and acknowledge uncertainty creates a false sense of confidence in the desired outcome (Marcot et al 2012). Mischaracterizing uncertainty can erode confidence in successful actions. Not addressing uncertainty can enable successful challenges from stakeholders dissatisfied with the decision (e.g., Mansfield and Haas 2006). Even evidence presented as “best available science” can be insufficient in preventing inconsistency in the implementation of listing and recovery procedures (Doremus 2004, Woods and Morey 2008)
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