Estimating Landscape Resistance to Movement: a Review Katherine A. Zeller, Kevin Mcgarigal & Andrew R. Whiteley
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Estimating landscape resistance to movement: a review Katherine A. Zeller, Kevin McGarigal & Andrew R. Whiteley Landscape Ecology ISSN 0921-2973 Volume 27 Number 6 Landscape Ecol (2012) 27:777-797 DOI 10.1007/s10980-012-9737-0 1 23 Your article is protected by copyright and all rights are held exclusively by Springer Science+Business Media B.V.. This e-offprint is for personal use only and shall not be self- archived in electronic repositories. If you wish to self-archive your work, please use the accepted author’s version for posting to your own website or your institution’s repository. You may further deposit the accepted author’s version on a funder’s repository at a funder’s request, provided it is not made publicly available until 12 months after publication. 1 23 Author's personal copy Landscape Ecol (2012) 27:777–797 DOI 10.1007/s10980-012-9737-0 LANDSCAPE ECOLOGY IN REVIEW Estimating landscape resistance to movement: a review Katherine A. Zeller • Kevin McGarigal • Andrew R. Whiteley Received: 19 January 2012 / Accepted: 24 March 2012 / Published online: 11 April 2012 Ó Springer Science+Business Media B.V. 2012 Abstract Resistance surfaces are often used to fill functions; point (n = 16), matrix (n = 38), home gaps in our knowledge surrounding animal movement range (n = 3), step (n = 1), and pathway (n = 1). We and are frequently the basis for modeling connectivity found a general lack of justification for choice of associated with conservation initiatives. However, the environmental variables and their thematic and spatial methods for quantifying resistance surfaces are varied representation, a heavy reliance on expert opinion and and there is no general consensus on the appropriate detection data, and a tendency to confound movement choice of environmental data or analytical approaches. behavior and resource use. Future research needs We provide a comprehensive review of the literature include comparative analyses on the choice of envi- on this topic to highlight methods used and identify ronmental variables and their spatial and thematic knowledge gaps. Our review includes 96 papers that scales, and on the various biological data types used to parameterized resistance surfaces (sometimes using estimate resistance. Comparative analyses amongst multiple approaches) for a variety of taxa. Data types analytical processes is also needed, as well as trans- used included expert opinion (n = 76), detection parency in reporting on uncertainty in parameter (n = 23), relocation (n = 8), pathway (n = 2), and estimates and sensitivity of final resistance surfaces, genetic (n = 28). We organized the papers into three especially if the resistance surfaces are to be used for main analytical approaches; one-stage expert opinion, conservation and planning purposes. one-stage empirical, and two-stage empirical, each of which was represented by 43, 22, and 36 Keywords Connectivity Á Cost/friction surface Á papers, respectively. We further organized the empir- Landscape permeability Á Corridors Á Resistant kernel Á ical approaches into five main resource selection Landscape pattern Á Wildlife Electronic supplementary material The online version of Introduction this article (doi:10.1007/s10980-012-9737-0) contains supplementary material, which is available to authorized users. Understanding animal movement is crucial for devel- K. A. Zeller (&) Á K. McGarigal Á A. R. Whiteley oping effective landscape-level conservation initia- Department of Environmental Conservation, University tives. Successful movement of animals across the of Massachusetts, Amherst, MA 01003, USA landscape may fulfill a number of biological pro- e-mail: [email protected] cesses, including foraging, mating, migration, dis- K. A. Zeller persal and gene flow, and is especially critical in Panthera, 8 West 40th Street, New York, NY 10018, USA allowing individuals and populations to adjust (e.g., 123 Author's personal copy 778 Landscape Ecol (2012) 27:777–797 redistribute) to a changing environment. However, Moreover, no general consensus has been reached animal movement is one of the most difficult behav- regarding the most accurate data sources and analyt- iors to observe and quantify. When movement can be ical methods for modeling resistance surfaces (Spear assessed, the number of individuals being studied is et al. 2010). A summary of the methods used and their often small, and/or there may be large gaps of time pros and cons is needed in order to frame the current between successive point locations along a movement state of knowledge surrounding resistance surface path. Resistance to movement values are typically modeling and provide guidance for future research. used to fill this gap in movement knowledge by Here, we provide a comprehensive literature review of providing a quantitative estimate of how environmen- the data sources and analytical methods used for tal parameters affect animal movement. In this con- deriving resistance surfaces. We discuss common text, ‘resistance’ represents the willingness of an techniques, highlight unique approaches, and consider organism to cross a particular environment, the the strengths and weaknesses of these methods. physiological cost of moving through a particular Finally, we discuss directions for future research and environment, the reduction in survival for the organ- methodological improvement. ism moving through a particular environment, or an integration of all these factors. Resistance estimation is most commonly accomplished by parameterizing Methods environmental variables across a ‘resistance’ or ‘cost’ to movement continuum, where a low resistance We focused our literature review on papers that dealt denotes ease of movement and a high resistance explicitly with estimating resistance to movement denotes restricted movement, or is used to represent an values for wildlife. We searched for papers in the ISI absolute barrier to movement. ‘Friction’ and ‘imped- Web of Science (ISI 2011) with the following search ance’ to movement or their inverse, ‘permeability’ and criteria from January 2000 to June 2011: Topic = ‘conductivity’ to movement are also terms used to (resistance OR cost OR effective distance OR lands- describe these travel surfaces (Singleton et al. 2002; cape permeability)AND(corridor*ORconnect* Chardon et al. 2003; Sutcliffe et al. 2003). For OR wildlife OR linkage); this resulted in 1,343 simplicity, the term ‘resistance surface’ will be used papers. We refined our results by restricting the search to describe these movement surfaces for the remainder to the following subject areas: Genetics and Heredity, of the paper. Biochemistry and Molecular Biology, Ecology, Envi- The use of resistance surfaces in landscape ecology ronmental Sciences, Multidisciplinary Sciences, Envi- and conservation biology has increased over the last ronmental Studies, Zoology, Biology, Evolutionary decade. In particular, resistance surfaces are used in Biology, Veterinary Sciences, Biodiversity Conserva- metapopulation and corridor studies to represent the tion, Forestry, Agriculture, Dairy and Animal Science, landscape between populations or habitat patches. Management, Marine and Freshwater Biology, Ento- These studies have matured from simple ‘isolation- mology, Geography, Fisheries, Oceanography, by-distance’ or ‘isolation-by-barrier’ hypotheses to Remote Sensing, and Ornithology. This restricted the recognizing that animal movement between popula- result to 693 papers, which we further refined by tions is influenced by the varying environmental excluding papers which were simulation exercises conditions an individual encounters as it moves only, did not deal explicitly with wildlife, and/or did through a landscape (Ferreras 2001; Adriaensen not estimate resistance values. This resulted in our et al. 2003). This is typically referred to as ‘isola- final sample of 96 papers distributed across 26 tion-by-resistance’ (McRae 2006). Resistance sur- different journals. We purport that, although this is faces are a quintessential element to contemporary not a full census of papers on resistance, the final set of landscape genetics studies focused on assessing how papers we reviewed represent a comprehensive survey landscape structure affects the flow of genes across the of current methods used to estimate resistance to landscape (Manel et al. 2003; Spear et al. 2010). movement for wildlife. Myriad methods have been used to model land- To summarize each paper, we recorded the follow- scape resistance to movement. Techniques range from ing information: taxonomy and number of target very basic and data-light to complex and data-heavy. species, number and type of environmental variables, 123 Author's personal copy Landscape Ecol (2012) 27:777–797 779 grain and extent of analysis, type of biological input home range selection function (HSF), (3) matrix data, analytical approach, type of resource selection selection function (MSF), (4) step selection function function (RSF), and final range of resultant resistance (SSF), and (5) path selection function (PathSF), as values (Appendix 1 in electronic supplementary defined below (‘‘Resource selection functions’’ sec- material). We distinguished among five types of tion). Lastly, although we reviewed 96 papers, several biological input data: (1) expert opinion, (2) detection papers used more than one biological input data type data, (3) relocation data, (4) pathway data, and (5) or analytical approach. Consequently, we refer to the genetic data, as defined below (‘‘Biological data’’ number of ‘instances’