December 2012 Number 1 - Utah Native Plant Society

Utah Native Plant Society
The habitat suitability maps also varied between the
models (Figure 2). The full model (Figure 2a) and the
pruned model (Figure 2b) clearly show a smaller range
than the topo model (Figure 2c). The area of suitable
habitat for the full model was 919,973 acres, the pruned
model 1,386,261 acres and the topo model 47,110,640
acres.
The spatial comparison of models found 571,307
acres of suitable habitat agreement between the models
(Figure 2d). Disagreement analysis of the three models
shows 47,081,482 acres (Figure 2e) and suggests that
the topo model generated the most disagreement between
models.
DISCUSSION
Alternative Suitability Models
The use of alternative models can offer a better understanding
of how environmental variables play a role
in a species distribution. The comparison of the three
models may provide a deeper knowledge of speciesenvironment
relationships and lead to a more rigorous
assessment of potential distributions. The alternative
models may also identify needs in data to further understand
species-environment relationships.
The three models used in this analysis all performed
better than random. The full and pruned models performed
the best (highest AUC scores) while the topo
model over predicted suitable habitat. The jackknife
analysis provided a way to understand variable importance
for the use in the pruned model. This may help
eliminate redundant variables and an overly large
model.
Most pruned models showed a larger area of suitable
habitat when compared with the full models. This suggests
two possible interpretations: 1) the full model may
be over fit, and not predicting all potential suitable habitat,
or 2) the pruned model may be over predicting. Another
interesting aspect of using alternative models was
the use of only topographic variables in the topo model.
Although this model over predicted suitable habitat for
Mesa Verde cactus, other species models show a closer
fit. This model may provide a way to analyze a species
distribution when only elevation data are available, as
Parolo and others (2008) found with Arnica montana.
Spatial Comparison
The spatial comparison of habitat suitability map
output from the three models provides quantification of
uncertainty in the model predictions of suitable habitat.
Levels of uncertainty have important management implications.
Areas with high model agreement that a species
is present but without known occurrences of that
species are target areas for field surveys. Areas of disagreement
may provide insight into variables that con-
tribute to uncertainty that could be better resolved
through additional field work.
Final Habitat Maps and Use
The goal of this project was to identify potential suitable
habitat for species by using alternative models
evaluated with AUC scores and a spatial comparison.
When comparing the three models, the AUC scores
range from good to excellent for Mesa Verde cactus.
The spatial comparison identified the full and pruned
models as having similar predicted areas, while the area
predicted by the topo model was larger. This technique
provides a more rigorous analysis of the potential distribution
of suitable habitat.
The methods described above provide a more
straightforward ecological interpretation of how the environment
affects a species’ distribution. This modeling
technique can also provide a better understanding of
endemic plant distributions. These models can be used
for future field investigations to find new populations
and to identify relationships between climate, geology
and topography with endemics.
ACKNOWLEDGEMENTS
This project was supported by the Gloria Barron Wilderness
Society Scholarship and NSF grant 0753163.
Comments from Dr. Deana Pennington and Daniela
Roth greatly improved the manuscript and many thanks
to those who have shared their data and time to improve
this project.
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