Posted on May 7th, 2013

Back to School – Ecological Modeling

A researcher at the University of Kansas conducted a study to determine 34 species’ ecological niches. One species he took into consideration was the Brown Thrasher. Using GIS, the author completed a Gap Analysis to examine species distribution, land use and protection information to paint a picture of how best to manage species’ habitats. Citing ecologists as far back as a century, Peterson gave consideration to the difference between fundamental and realized niches – the former contemplates a range of theoretical management possibilities, and the latter being applied or practiced manners of management. Species distribution was measured using North American Breeding Bird Surveys. 30 U.S. states were randomly chosen for model development of migration patterns, while the remaining 20 were set aside for statistical testing of the model.

brown_trasher_mapAbove is a map of geographic predictions for the Brown Thrasher. Black areas predict areas of presence, open circles indicate model development point, and dotted circles indicate test-points for model accuracy.

The aforementioned Brown Thrasher was modeled to focus its distribution in relatively warm, yet dry portions of the states. There were 741 test-points for the thrasher, and 715 were accurately predicted with the model. Prior to this study, there were several models in existence for predicting fundamental ecological niches; most notably the BIOCLIM method, though it has been criticized for over-prediction and is not widely considered as the best model for avian niche prediction. The Genetic Algorithm for Rule-set Prediction (GARP) has also been applied to produce component rules. It has been found to be more successful in predicting distribution patterns within or without key niche.

There are two key types of error which often enter into Gap Analysis. First, there can be omissions of key representative areas that leads the model to not consider all ecological conditions under which a species can maintain populations. Second, there can be commission where areas that are uninhabitate are included in the models. This is actually two-pronged in that you can find real commission errors (where ecological conditions not within the species’ niche are included in models) and also apparent commission errors (where species’ absence is due to factors such as speciation patterns, local extinction or historical considerations but the ecological conditions would actually be ideal otherwise).

Peterson’s model, built on the successes of GARP, was able to accurately predict species pattern and niche through 34 native avian fauna in the United States. It was then tested on 25 varieties of tropical birds in Mexico with great success. The mapping of key niche areas for the survival and sustainability of species aided land and wildlife management agencies in documenting migration and critical habitat necessities.

Justin Harmon
Staff Writer

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