• Explore more than 100 years of PNAS content!
  • Sign-up for PNAS eTOC Alerts

Spatial scale modulates the strength of ecological processes driving disease distributions

  1. Jason R. Rohra
  1. aDepartment of Integrative Biology, University of South Florida, Tampa, FL 33620;
  2. bKey Laboratory of Animal Ecology and Conservation Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, People’s Republic of China

  1. Edited by Andrea Rinaldo, Laboratory of Ecohydrology, Ecole Polytechnique Federale Lausanne, CH-1015 Lausanne, Switzerland, and approved April 21, 2016 (received for review November 3, 2015)

Significance

For four decades, ecologists have hypothesized that biotic interactions predominantly control species’ distributions at local scales, whereas abiotic factors operate more at regional scales. Here, we demonstrate that the drivers of three emerging diseases (amphibian chytridiomycosis, West Nile virus, and Lyme disease) in the United States support the predictions of this fundamental hypothesis. Humans are contributing to biodiversity loss, changes in dispersal patterns, and global climate change at an unprecedented rate. Our results highlight that common single-scale analyses can misestimate the impact that humans are having on biodiversity, disease, and the environment.

Abstract

Humans are altering the distribution of species by changing the climate and disrupting biotic interactions and dispersal. A fundamental hypothesis in spatial ecology suggests that these effects are scale dependent; biotic interactions should shape distributions at local scales, whereas climate should dominate at regional scales. If so, common single-scale analyses might misestimate the impacts of anthropogenic modifications on biodiversity and the environment. However, large-scale datasets necessary to test these hypotheses have not been available until recently. Here we conduct a cross-continental, cross-scale (almost five orders of magnitude) analysis of the influence of biotic and abiotic processes and human population density on the distribution of three emerging pathogens: the amphibian chytrid fungus implicated in worldwide amphibian declines and West Nile virus and the bacterium that causes Lyme disease (Borrelia burgdorferi), which are responsible for ongoing human health crises. In all three systems, we show that biotic factors were significant predictors of pathogen distributions in multiple regression models only at local scales (∼102–103 km2), whereas climate and human population density always were significant only at relatively larger, regional scales (usually >104 km2). Spatial autocorrelation analyses revealed that biotic factors were more variable at smaller scales, whereas climatic factors were more variable at larger scales, as is consistent with the prediction that factors should be important at the scales at which they vary the most. Finally, no single scale could detect the importance of all three categories of processes. These results highlight that common single-scale analyses can misrepresent the true impact of anthropogenic modifications on biodiversity and the environment.

Footnotes

  • ↵1To whom correspondence should be addressed. Email: jcohen9{at}mail.usf.edu.

  • ↵2A.J.B., E.M.F., C.N.O., J.C.R., and E.L.S. contributed equally to this work.

  • Author contributions: J.M.C., D.J.C., A.J.B., E.M.F., C.N.O., J.C.R., E.L.S., X.L., and J.R.R. designed research; J.M.C. performed research; J.M.C., D.J.C., and J.R.R. analyzed data; and J.M.C. and J.R.R. wrote the paper.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission.

  • This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1521657113/-/DCSupplemental.

Online Impact