Seasonal differences in extinction and colonization drive occupancy dynamics of an imperilled amphibian

PLoS One. 2015 May 18;10(5):e0127059. doi: 10.1371/journal.pone.0127059. eCollection 2015.

Abstract

A detailed understanding of the population dynamics of many amphibian species is lacking despite concerns about declining amphibian biodiversity and abundance. This paper explores temporal patterns of occupancy and underlying extinction and colonization dynamics in a regionally imperiled amphibian species, the Northern leopard frog (Lithobates pipiens) in Alberta. Our study contributes to elucidating regional occupancy dynamics at northern latitudes, where climate extremes likely have a profound effect on seasonal occupancy. The primary advantage of our study is its wide geographic scale (60,000 km2) and the use of repeat visual surveys each spring and summer from 2009-2013. We find that occupancy varied more dramatically between seasons than years, with low spring and higher summer occupancy. Between spring and summer, colonization was high and extinction low; inversely, colonization was low and extinction high over the winter. The dynamics of extinction and colonization are complex, making conservation management challenging. Our results reveal that Northern leopard frog occupancy was constant over the last five years and thus there is no evidence of decline or recovery within our study area. Changes to equilibrium occupancy are most sensitive to increasing colonization in the spring or declining extinction in the summer. Therefore, conservation and management efforts should target actions that are likely to increase spring colonization; this could be achieved through translocations or improving the quality or access to breeding habitat. Because summer occupancy is already high, it may be difficult to improve further. Nevertheless, summer extinction could be reduced by predator control, increasing water quality or hydroperiod of wetlands, or increasing the quality or quantity of summer habitat.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alberta
  • Amphibians*
  • Animals
  • Ecosystem*
  • Models, Theoretical
  • Population Dynamics
  • Rana pipiens
  • Seasons*

Grant support

This research was funded by Cenovus Energy Ltd. (http://www.cenovus.com), EnCana (http://www.encana.com), the Alberta Conservation Association (http://www.ab-conservation.com), the Alberta Society of Professional Biologists (http://www.aspb.ab.ca), the Canadian Wildlife Federation (http://www.cwf-fcf.org), TD Friends of the Environment (https://fef.td.com), Calgary Foundation (http://www.thecalgaryfoundation.org), and Husky Energy (http://www.huskyenergy.ca). Mike and Sherri Balm also made a significant individual donation. The authors confirm that Wildland Consultants Ltd. provided support in the form of salaries for authors DS, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the "author contributions" section.