Background and Purpose
 

Background

The Southwest Regional Gap Analysis Project predicted habitat for 819 vertebrate species that reside, breed, or use habitat in the five-state region for a substantial portion of the their life history.  The list of species to model was determined by identifying decision rules for taxon inclusion (These rules can be provided upon request).  To create the most accurate models possible we are engaging taxa experts to provide a review of these habitat models.

These models are based on the concept of Wildlife Habitat Relationships (WHRs).  We have defined WHRs as a statement describing resources and conditions present in areas where a species persists and reproduces or otherwise occurs.  Relationships can be modeled to predict habitat composition, and if the relationships are represented in a cartographic plane they can predict the presence of habitat spatially.  For each species, these relationships were identified by reviewing the available literature and then generating a spatial representation of habitat within the species known range.

An important factor for model implementation is understanding the objectives of the modeling effort and the assumptions of the models.  The objective of the habitat models are to: 1) Provide maps that predict the distribution of terrestrial vertebrate species in the project area to support analysis of conservation status; and 2) Develop a database of geographic range, wildlife habitat relationships, and predicted distribution of each vertebrate species for the long-term utility of GAP and its cooperators (Csuti and Crist 2000).  Along with these objectives are several assumptions associated with GAP vertebrate habitat models (Csuti and Crist 1998):

1.  Species are assumed to occur within a polygon representing potential habitat but are not predicted to occur at any particular point within that polygon.

2.  Species are assumed to be present within a polygon, but no assumptions are made about the abundance of the species in the polygon.

3.  Species are assumed to be present in a polygon at least once in the last 10 years but need not be present every year in the last decade.

4.  Species are assumed to be present during some portion of their life history, not necessarily during the entire year.

There are many challenges to creating habitat maps.  GAP uses expert review and a measure of agreement method in an effort to create the most accurate models possible.  This document describes the expert review process within SWReGAP.

We solicited habitat model review from knowledgeable individuals on the modeled terrestrial vertebrates across the five-state region.

Review Approach

The SWReGAP habitat models have three model components for review.  These are:  1), Wildlife habitat relationships (Report), 2) range extent and coding (Range); and 3) spatial depiction of predicted habitat (Model).  

Wildlife Habitat Relationships

Review of this section will either substantiate or refute the habitat relationships used in the model.  This process should include 1) review of each relationship used in the model, 2) concurrence with the relationships; and 3) review of references to ensure that important citations are not missed.  Questions to focus on this part of the review include:

1.  Are the habitat relationships (within the limits of available information) correctly identified?

2.  Are there additional relationships not identified, which should be included? Knowledge regarding the limitations of the habitat relationships are also requested.

Range Extent

The second component for the review is to ensure that the range extent accurately depicts the known range of the species.  The review should include an evaluation of: 1) extent, and 2) coding (this section is most relevant to migratory taxa, e.g., permanent resident, summer breeder).  Some considerations include:

1.  Does the range extent, as depicted by hydrologic units, reflect the known range of species?

2.  Are the hydrologic units correctly coded?

Spatial Map Depiction

Review of map depiction is a subjective review based on expert knowledge.  The review of this tier should focus on the following questions:

1.       Does the depiction look plausible?

2.       Does the depiction identify too much habitat?

3.       Does the depiction not identify enough habitat?

4.       Does the habitat identified appear to be spatially correct?

Rules for model modification

1. Modifications must be identified based on a reference with associated source code (Table 1).
2. Modifications should allow information to be regionally applied except in special cases. Special cases include species that have specific and relatively well-known habitat associations that can be represented in separate reasonably well-informed models. 

Table 1.  Categories of reference information.

* Though not a preferred reference, because of taxonomy changes this option may be applicable.

Literature Cited

Csuti, B. and P. Crist.  1998.  Methods for Assessing Accuracy of Animal Distribution Maps, Gap Analysis Program, University of Idaho, Moscow, Idaho.  http://www.gap.uidaho.edu/  Date Accessed: 02 July 2003.