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Faculty & Research

Michael Reed
Avian ecology and conservation biology


Vital Rate Sensitivity Analysis Program:

Recommendations for use of VRSA (PDF)
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Fefferman, N., and J. M. Reed. 2006. A vital rate sensitivity analysis that is valid for non-stable age distributions and for short-term planning. Journal of Wildlife Management 70: 649-656.
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There are multiple approaches to sensitivity analysis used to identify which vital rate most affects population growth, all of which involve evaluating effects on l, the dominant eigenvalue of the Leslie matrix. Management recommendations generated by these approaches can be difficult to determine, in part because results are valid only for populations with stable age distributions. Although these analyses identify the quickest way to increase population size to carrying capacity, they cannot identify best management options for short-term goals such as increasing population size above some critical value. We present a perturbation analysis, vital rate sensitivity analysis (VRSA), to identify the vital rate that most limits population growth over any specified time period by determining which vital rate has the greatest effect on population growth. VRSA is effective for stable and non-stable age distributions, differentiates optimal short- and long-term management options, can incorporate stochasticity in vital rates, and can differentiate efficacy of alternative management strategies. Along with being able to compare effects of incremental or specific changes in vital rates, VRSA can be used to compare specific management alternatives that affect single or multiple vital rates. We also present a method for measuring robustness of VRSA results. We illustrate VRSA for multiple greater prairie-chicken (Tympanuchus cupido) and red-cockaded woodpecker (Picoides borealis) populations. For greater prairie-chickens, we found juvenile survival to be the most sensitive vital rate for the specific comparisons made. For red-cockaded woodpeckers, reproductive rate was the most sensitive vital rate, but confidence was higher for larger populations and longer management horizons. Results for both might change with conditions and age structure. VRSA should be an effective tool for wildlife managers who want to compare alternative management strategies to increase population size.

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