ber that even a well-parameterized model based on high-quality data can
give volatile results, especially if it is based on parameters programmed to
vary randomly in time and space or if it incorporates nonlinear process
functions with chaotic properties. The following sections discuss methods of
obtaining data and the issues that should be considered when using each
type of data collection.
10.3.1 Previous Data Collection Efforts
Obtaining data from existing sources can be a cost- and time-efficient
method, provided that the data are appropriate for the ecological model
being constructed. With the advances in Internet and file-sharing technology and increases in monitoring programs (Beard et al. 1999), existing data from a variety of sources have become increasingly available and
inexpensive. However, available data are not always appropriate data. The
following concerns should be considered when obtaining data from an existing source: species appropriateness, temporal and spatial scale appropriateness, previous manipulations or analysis of the data, and measurement
error.
10.3.1.1 Species Appropriateness
Are the existing data representative of the species being modeled? Existing data may be available for the same or a similar species as the one being
modeled. A surrogate indicator species has characteristics, such as population density or demographic parameters, that can be used, with caution,
as an index of attributes for the species of interest (Landres et al. 1988).
However, as models increase in complexity, it is more difficult to find surrogate species that will accurately represent all of the characteristics of the
species of interest. Species that are close in taxonomy to the species of interest are generally the best candidates for surrogate species. Even if the existing data were collected for the species of interest, intraspecific variability is
a concern. Species characteristics, such as habitat and forage preferences,
can vary across the geographic range of the species. For species with a large
geographic range or large variation within their range, the similarity of the
ecosystem’s and species’ traits between the existing data and those of the
species being modeled should be particularly examined.
10.3.1.2 Temporal and Spatial Scale Appropriateness
Care regarding temporal and spatial variability is particularly advised when
the variability is large. Two factors to consider when deciding whether to
use existing data for the model are the extent and resolution of the data.
Extent of the data is determined by the total spatial area of the data collection and the total length of time over which the data were collected. Resolution of the data is measured by the smallest spatial area for which data
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give volatile results, especially if it is based on parameters programmed to
vary randomly in time and space or if it incorporates nonlinear process
functions with chaotic properties. The following sections discuss methods of
obtaining data and the issues that should be considered when using each
type of data collection.
10.3.1 Previous Data Collection Efforts
Obtaining data from existing sources can be a cost- and time-efficient
method, provided that the data are appropriate for the ecological model
being constructed. With the advances in Internet and file-sharing technology and increases in monitoring programs (Beard et al. 1999), existing data from a variety of sources have become increasingly available and
inexpensive. However, available data are not always appropriate data. The
following concerns should be considered when obtaining data from an existing source: species appropriateness, temporal and spatial scale appropriateness, previous manipulations or analysis of the data, and measurement
error.
10.3.1.1 Species Appropriateness
Are the existing data representative of the species being modeled? Existing data may be available for the same or a similar species as the one being
modeled. A surrogate indicator species has characteristics, such as population density or demographic parameters, that can be used, with caution,
as an index of attributes for the species of interest (Landres et al. 1988).
However, as models increase in complexity, it is more difficult to find surrogate species that will accurately represent all of the characteristics of the
species of interest. Species that are close in taxonomy to the species of interest are generally the best candidates for surrogate species. Even if the existing data were collected for the species of interest, intraspecific variability is
a concern. Species characteristics, such as habitat and forage preferences,
can vary across the geographic range of the species. For species with a large
geographic range or large variation within their range, the similarity of the
ecosystem’s and species’ traits between the existing data and those of the
species being modeled should be particularly examined.
10.3.1.2 Temporal and Spatial Scale Appropriateness
Care regarding temporal and spatial variability is particularly advised when
the variability is large. Two factors to consider when deciding whether to
use existing data for the model are the extent and resolution of the data.
Extent of the data is determined by the total spatial area of the data collection and the total length of time over which the data were collected. Resolution of the data is measured by the smallest spatial area for which data
188
David Hohler et al.