Use and Interpretation of Climate Envelope Models: a Practical Guide

Use and Interpretation of Climate Envelope Models: A Practical Guide James I. Watling, University of Florida Laura A. Brandt, U.S. Fish and Wildlife Service Frank J. Mazzotti, University of Florida Stephanie S. Romañach, U.S. Geological Survey Preface This guidebook is intended to provide a practical overview of climate envelope modeling for conservation professionals and natural resource managers. The material is intended for people with little background or experience in climate envelope modeling who want to better understand and interpret models developed by others and the results generated by such models, or want to do some modeling themselves. This is not an exhaustive review of climate envelope modeling, but rather a brief introduction to some key concepts in the discipline. Readers interested in a more in-depth treatment of much of the material presented here are referred to an excellent book, Mapping Species Distributions: Spatial Inference and Prediction by Janet Franklin. Also, a recent review (Araújo & Peterson 2012) provides an excellent, though more technical, discussion of many of the issues dealt with here. Here we treat selected topics from a practical perspective, using minimal jargon to explain and illustrate some of the many issues that one has to be aware of when using climate envelope models. When we do introduce specialized terminology in the guidebook, we bold the term when it is first used; a glossary of these terms is included at the back of the guidebook. We have written the guidebook from the perspective of a natural resource manager attending a national conference, reading scientific articles or viewing webinars on climate change science related to species and habitat. That manager would likely read or hear about research from across the United States or the world, including many talks in which different groups are using climate envelope models to forecast species responses to future climate change. As is often the case in real life, the different research groups presenting at the conference may be addressing broadly similar questions, but the details of their approaches differ. Some may be working with endangered species, others with invasive species, and some with migratory species. Some researchers may work with plants, and others with animals (one of the great things about climate envelope modeling is that the approach is the same regardless of the species of interest). They probably use different methods to create their models, the spatial extent of their modeling may vary, and they may use different approaches to validate their models. How would a non-expert compare such seemingly disparate models? Are there ‘best practices’ to keep in mind when evaluating climate envelope models? How would you know if someone is making a reasonable inference, or violating a major assumption of the modeling? We attempt to deal with some of these issues and other important concepts related to climate envelope modeling throughout the guidebook. The guidebook is structured as a series of questions that might result from hearing about work with climate envelope models at a conference, webinar, or in the primary literature. We begin with some general aspects of models and relevant background information. We then examine different components of the models, including species and climate data. We illustrate key concepts with examples from our own work developing climate envelope models for Florida’s threatened and endangered species, as well as work of others in the field of distribution modeling. 2 We urge readers of this guidebook to keep in mind that models are one part of a natural resource manager’s toolbox, but they are not the only, or even the most important tool. It can’t be repeated enough that ‘all models are wrong, but some models are useful’. Models are abstractions of reality and cannot, by definition, include all the relevant or interesting parts of a system. Models can help guide our thinking by describing plausible outcomes of different conditions or management decisions and they help to suggest hypotheses to be tested with additional research. Models do not provide all the answers and should not be accepted uncritically—all models make simplifying assumptions and abstract reality in different ways. It is our hope that this guidebook helps identify some of the key assumptions and uncertainties underlying climate envelope modeling while providing useful insights that will help users interpret the results of climate envelope models. We gratefully acknowledge support for our work from the U.S. Fish and Wildlife Service, the National Park Service and the U. S. Geological Survey Greater Everglades Priority Ecosystem Sciences. Funding from the National Park Service was made possible by Everglades and Dry Tortugas National Park through the South Florida and Caribbean Cooperative Ecosystem Studies Unit. We thank Ronnie Best, Bob Ford, Kurt Johnson, Leonard Pearlstine and Steve Traxler for their support of our work. Robert Fletcher, Nancy Green, Lori Miller, Scott Sanders and Mark Shaffer made helpful comments on earlier drafts of this document that helped to shape the final product, and we thank them for the time they took to help improve this guidebook. The work presented here would not have been possible without assistance from Robin Bijlani, Yesenia Escribano, Ikuko Fujisaki, Rebecca Harvey, Emily Pifer, Joy Vinci and Sara Williams. Finally, we thank Allison Benscoter, David Bucklin and Carolina Speroterra for their substantial contributions to all aspects of our research group’s work. The views expressed here do not necessarily reflect the views of the U.S. Fish and Wildlife Service. Use of trade, product, or firm names does not imply endorsement by the U.S. Government. Contact information for authors: • James I. Watling, Ft Lauderdale Research and Education Center, 3205 College Avenue, Ft Lauderdale, FL 33314 USA. E-mail: [email protected] • Laura A. Brandt, U. S. Fish and Wildlife Service, Ft Lauderdale Research and Education Center, 3205 College Avenue, Ft Lauderdale, FL 33314 USA. E-mail: [email protected] • Frank J. Mazzotti, Ft Lauderdale Research and Education Center, 3205 College Avenue, Ft Lauderdale, FL 33314 USA. E-mail: [email protected] • Stephanie S. Romañach, U. S. Geological Survey, Southeast Ecological Science Center, 3205 College Avenue, Ft Lauderdale, FL 33314 USA. E-mail: [email protected] Suggested citation: Watling JI, LA Brandt, FJ Mazzotti & SS Romañach. 2013. Use and Interpretation of Climate Envelope Models: A Practical Guide. University of Florida, 43 pp. For comments or questions on any of the material in this document, please contact James Watling at the University of Florida, [email protected]. 3 Table of Contents Preface . 2 I. Introduction to Climate Envelope Modeling . 5 What is a climate envelope model? ......................................... 5 What are climate envelope models designed to do? . 5 What are the limitations of climate envelope models? . 6 How are climate envelope models created? ................................... 8 How is model performance evaluated? . 11 How are continuous probabilities converted to presence-absence? . 16 What algorithms are used to model the species-climate relationship? . 16 What are some of the assumptions underlying climate envelope modeling?......... 18 II. Selection of Input Data.................................................. 21 Species Occurrences . 21 What is the effect of erroneous occurrence data on models? . 21 What about the effects of small sample size?.............................. 22 How are pseudo-absence data obtained? . 23 Climate Data . 24 Which climate data should be used for models? . 24 Which individual variables should be used for modeling? .................... 26 How does the climate dataset input influence model outputs? . 30 III. Interpreting Model Outputs.............................................. 32 To what extent can model results be extrapolated to other contexts? . 32 What are ‘no-analog’ conditions?.......................................... 32 IV. Appendix I ............................................................ 35 V. Glossary .............................................................. 36 VI. Helpful Resources ...................................................... 39 VII. Literature Cited........................................................ 40 4 I. INTRODUCTION TO CLIMATE ENVELOPE MODELING What is a climate envelope model? What are climate envelope models designed to do? Throughout this document we use the term ‘climate envelope model’ to refer to a subset of Climate envelope models delineate areas of species distribution models that use climate climate suitability for plant or animal species variables to make spatial predictions of environmental of interest by correlating georeferenced species suitability for a species. Species distribution models occurrences (presences and absences) with observed (also called ‘niche models’) use rules or mathematical climate conditions at occurrence sites. Climate functions to describe associations between species envelope models are spatially-explicit, and modelers occurrence and environmental conditions. On generally use maps of species occurrences and climate the basis of these rules, users can extrapolate an conditions to describe species-climate relationships index of environmental suitability or probability within individual grid cells of those maps. According of occurrence for the modeled species from a map to our definition, climate envelope

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