SGA tool – Survey Gap Analysis

SGA - Survey Gap Analysis tool helps to design a biodiversity survey that will best complement the existing survey effort by identifying those areas least well surveyed in terms of environmental conditions.1

Description

The Survey Gap Analysis application enables a user to utilise locations of existing specimen records and mapped environmental variables to create a mapped complementarity surface indicating the relative priority for additional survey or collection effort throughout the region of interest (ROI). The priority being based on the potential for an area (based on climatic conditions) to complement existing survey effort in the region of interest.2

This excerpt from Funk et al 2005 briefly describes the Survey Gap Analysis tool:3

“… it analyses the survey coverage of a region in relation to the underlying continuous environmental and geographical space, rather than in terms of arbitrary classes. Faith & Walker's (1996)4 environmental diversity (ED) measure, based on the p-median criterion, was developed for selecting sets of sites that represent regional biodiversity by providing best possible coverage of regional environmental variation. It functions by measuring how well a set of sites covers the continuous environmental space and evaluating the potential improvement that any given site would make if added. The technique, based on the finding that sampling different parts of the overall environmental space yields a good representation of the biological diversity of a region (Faith & Walker, 1996), can equally be applied to the problem of selecting survey sites."

The basic calculations can be described as follows. Given a partial set of survey sites, SGA identifies a new site that would be expected to contribute the greatest number of additional species. Note that this is not the same as finding a site that would have the greatest total number (richness) of species. Instead, it is the site with the greatest complementarity to the existing survey sites. Complementarity is widely used in biological conservation, and conventionally refers to some count of the number of additional species provided by a new site. In the SGA context, we cannot explicitly count such gains. Instead, these complementarity values are estimated using ED (providing ED-complementarity values; Faith et al 2004;5 Funk et al 2005).6

Developed by Simon Ferrier at NSW Department of Environment and Conservation.

Function

• Analysis tools
  • Complex – gap analysis
• User interface
  • The SGA tool works with raw data needing a front end to interface with users

Why use this tool?

Biodiversity surveys are expensive undertakings requiring careful planning, and specialized resources in terms of personnel skills and equipment. It is essential then that the data obtained through new surveys complements existing data and maximizes the usefulness of the new data for conservation planning purposes. Many, if not all, museum collections are characterized by biased sampling resulting from either ad-hoc collection techniques or from planning that is based on ease of access and which only considers geographic, rather than environmental, coverage when locating survey sites. Survey Gap Analysis can be instrumental in reducing bias and thereby more effectively answering the question "If one is interested in obtaining an overall knowledge of the biodiversity (or of a taxon) of an area, and if there are insufficient data, then where should survey data be gathered?" Funk et al 2005.7

Who will use this tool?

• Data users
  • Expert
• Special skills are required

How will the tool be used?

• The SGA tool is a C code program
• Requires a front end to interface to other programs or users

Where in the data chain could this tool be used?

• User’s machine

When could this tool be used?

• As a post process, after data is with the user

Availability

• Contact: Simon Ferrier Simon.Ferrier@csiro.au
• Licence: Negotiate with NSW Department of Environment and Conservation

Comments

This SGA tool is used within GBIF MAPA.

In GBIF MAPA the SGA tool produces a map showing the distribution of current ED complementarity values for all possible new sites. Darker colours indicate larger values; the red flag is the suggested choice for a new site, as it is the one sitting at the "highest peak". Using the complementarity surface as a guide the user can move the suggested site to take into account access constraints (using roads and rivers GIS layers). Once accepted as a new site the red flag turns green and cannot be moved again.

Once a site is accepted and the analysis run again to select another site, a new complementarity surface is created showing a different pattern of ED complementarity values based on the use of the original survey sites you started the analysis with and the new sites chosen by SGA. This highlights the dynamic nature of the survey gap analysis - the complementarity value of a site always depends on the set of sites already selected.8