Claims of Potential Expansion throughout the U.S. by Invasive Python Species Are Contradicted by Ecological Niche Models

Abstract

BackgroundRecent reports from the United States Geological Survey (USGS) suggested that invasive Burmese pythons in the Everglades may quickly spread into many parts of the U.S. due to putative climatic suitability. Additionally, projected trends of global warming were predicted to significantly increase suitable habitat and promote range expansion by these snakes. However, the ecological limitations of the Burmese python are not known and the possible effects of global warming on the potential expansion of the species are also unclear.Methodology/Principal FindingsHere we show that a predicted continental expansion is unlikely based on the ecology of the organism and the climate of the U.S. Our ecological niche models, which include variables representing climatic extremes as well as averages, indicate that the only suitable habitat in the U.S. for Burmese pythons presently occurs in southern Florida and in extreme southern Texas. Models based on the current distribution of the snake predict suitable habitat in essentially the only region in which the snakes are found in the U.S. Future climate models based on global warming forecasts actually indicate a significant contraction in suitable habitat for Burmese pythons in the U.S. as well as in their native range.Conclusions/SignificanceThe Burmese python is strongly limited to the small area of suitable environmental conditions in the United States it currently inhabits due to the ecological niche preferences of the snake. The ability of the Burmese python to expand further into the U.S. is severely limited by ecological constraints. Global warming is predicted to significantly reduce the area of suitable habitat worldwide, underscoring the potential negative effects of climate change for many species.

Weighing empirical and hypothetical evidence for assessing potential invasive species range limits: a review of the case of Burmese pythons in the USA

“…The January 2010 cold spell offered the first rigorous independent test data for assessing performance of bioclimatic models predicting the potential range of Burmese pythons. The most conservative model (Pyron et al 2008) corresponded best to the empirical observations.…”

“…Thus, it is essential to accurately define the appropriate native climate data to use in range predictions. Different models have been used to infer possible limits of Burmese python distribution in the continental USA and have produced widely divergent range predictions (Jacobson et al 2012;Pyron et al 2008;Rodda et al 2009;Van Wilgen et al 2009). …”

“…Three of these modeling efforts (Pyron et al 2008;Rodda et al 2009;Van Wilgen et al 2009) based their analyses on climate information from localities within and near the combined native distribution of the Burmese python and the closely related Indian python (P. molurus molurus). It should be noted that even though the Burmese python has been considered a subspecies of the same species as the Indian python, the two were distinguished legally, with the Indian python having been listed as an endangered species since 1976 (USDI/U.S.…”

“…As an example, the efforts of Pyron et al (2008) could be considered as an iterative update of the existing model efforts by Rodda et al (2009), which was originally published online in 2008 (hence the dates of the cited papers), as they stated that their efforts were motivated in part to correct some of the native climate issues found in Rodda et al (2009). Pyron et al (2008) did this by basing their analyses only on the actual locality presence information (for Burmese and Indian pythons combined), rather than the data from weather stations presumed to be within the envelope of their native range(s) as applied by Rodda et al (2009).…”

“…Various range predictions for the Burmese python in the USA have been far from concordant (Jacobson et al 2012;Pyron et al 2008;Rodda et al 2009;Van Wilgen et al 2009). Here, we use the case of the Burmese python in Florida to examine issues concerning disparities among modeling results and between model predictions and available empirical information as well as concepts for making cogent choices in model development and for deciding among alternative range predictions.…”