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Integrating occupancy models and structural equation models to understand species occurrence

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https://ir.library.oregonstate.edu/concern/articles/xw42n958z

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  • Understanding the drivers of species occurrence is a fundamental goal in basic and applied ecology. Occupancy models have emerged as a popular approach for inferring species occurrence because they account for problems associated with imperfect detection in field surveys. Current models, however, are limited because they assume covariates are independent (i.e., indirect effects do not occur). Here, we combined structural equation and occupancy models to investigate complex influences on species occurrence while accounting for imperfect detection. These two methods are inherently compatible because they both provide means to make inference on latent or unobserved quantities based on observed data. Our models evaluated the direct and indirect roles of cattle grazing, water chemistry, vegetation, nonnative fishes, and pond permanence on the occurrence of six pond-breeding amphibians, two of which are threatened: the California tiger salamander (Ambystoma californiense) and the California red-legged frog (Rana draytonii). While cattle had strong effects on pond vegetation and water chemistry, their overall effects on amphibian occurrence were small compared to the consistently negative effects of nonnative fish. Fish strongly reduced occurrence probabilities for four of five native amphibians, including both species of conservation concern. These results could help to identify drivers of amphibian declines and to prioritize strategies for amphibian conservation. More generally, this approach facilitates a more mechanistic representation of ideas about the causes of species distributions in space and time. As shown here, occupancy modeling and structural equation modeling are readily combined, and bring rich sets of techniques that may provide unique theoretical and applied insights into basic ecological questions.
  • KEYWORDS: cattle grazing, indirect effects, structural equation model, latent variable, imperfect detection, occupancy model
  • This is the publisher’s final pdf. The article is copyrighted by the Ecological Society of America and published by John Wiley & Sons, Inc. It can be found at: http://esajournals.onlinelibrary.wiley.com/hub/journal/10.1002/%28ISSN%291939-9170/
  • This is the publisher’s final pdf. The article is copyrighted by the Ecological Society of America and published by John Wiley & Sons, Inc. It can be found at: http://esajournals.onlinelibrary.wiley.com/hub/journal/10.1002/%28ISSN%291939-9170/
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  • Joseph, M. B., Preston, D. L., & Johnson, P. T. (2016). Integrating occupancy models and structural equation models to understand species occurrence. Ecology, 97(3), 765-775. doi:10.1890/15-0833.1
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  • 97
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  • 3
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  • This work used the Janus supercomputer, which is supported by the National Science Foundation (award number CNS-0821794) and the University of Colorado Boulder. The Janus supercomputer is a joint effort of the University of Colorado Boulder, the University of Colorado Denver and the National Center for Atmospheric Research. We thank Joseph Mihaljevic and Helen McCreery for comments on the manuscript. We also thank Travis McDevitt-Galles and Katherine Richgels for assistance in the field. This work was directly funded by grants from NSF (DEB-1311467, DEB-1149308, and DEB-0841758) and NIH (R01GM109499). Maxwell Joseph and Daniel Preston received support from the NSF Graduate Research Fellowship Program.
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