Improving habitat suitability index models

Abstract

The use of Habitat Suitability Index (HSI) models and the associated Habitat Evaluation Procedures (HEP) to assess habitat quality for a spectrum of wildlife species is widespread. They are some of the most influential management tools in use. Results of these assessments are applied daily by natural resource managers and decision-makers (Cole and LeFebvre 1989). I suspect that more wildlife is influenced by application of HSI models and HEP than most other management methods. Yet, if one peruses the peer-reviewed literature, it would appear that no further discussion about the process or refinement of HSI models is needed. Articles on HSI models and HEP are surprisingly scarce (Lancia et al. 1982, Thomasma et al. 1991), and only a few papers have appeared in the literature since the comprehensive book edited by Verner et al. (1986). Based on my experience with model development and testing, I suspect that limited publication of results over the past decade does not reflect a lack of interest in or need for this information among natural resource managers. Biologists engaged in environmental impact assessment (EIA) and regulatory permit reviews make daily decisions about managing wildlife and their habitats. HEP and HSI models provide (and were intended to provide) a rapid assessment method to assist these practitioners. Managers and biologists on the front line seldom have the time or the incentives to present the results of their work in print. On the few occasions that they do seek to publish their findings in peer-reviewed journals, editors and referees apply a typically rigorous review process that apparently fails to find value in the development and use of HSI models and HEP. Only models tested with independent data based on population densities appear to be worthy of publication. I call this the all-or-nothing syndrome. The outcome should concern every wildlife ecologist, biologist, and manager. The biologist conducting ELAs must use the method whether it is tested or not; their jobs, and sometimes environmental regulations, demand it. Research-oriented scientists are critical of HSI models and virtually ignore the application of HEP unless it is tested with independent data and population estimates. The result is that little if any progress is being made in improving either the models or their application. This paper seeks to remedy this situation by describing a series of stages in HSI development and testing that should be recognized. Incremental improvements could be made by publishing interim models that have not been fully validated. Completion of any stage in the process after initial development is a worthwhile accomplishment, published or not. Provided that authors are explicit about the stage of model development reported, valuable information could be exchanged through peer-reviewed publications about HSI models in progress. Surely, a well-designed HSI model, tested or not, should be on par with descriptive notes on a species' life history that are frequently published in peer-reviewed literature. We could engage in lengthy discussions questioning the use of HSI-type models with regard to the bias of best professional judgment, the danger of