MMaauurreerr SScchhooooll ooff LLaaww:: IInnddiiaannaa UUnniivveerrssiittyy DDiiggiittaall RReeppoossiittoorryy @@ MMaauurreerr LLaaww Articles by Maurer Faculty Faculty Scholarship 2010 TThhee LLeeggaall CChhaalllleennggee ooff PPrrootteeccttiinngg AAnniimmaall MMiiggrraattiioonnss aass PPhheennoommeennaa ooff AAbbuunnddaannccee Robert L. Fischman Indiana University Maurer School of Law, [email protected] Jeffrey B. Hyman Indiana University Maurer School of Law, [email protected] Follow this and additional works at: https://www.repository.law.indiana.edu/facpub Part of the Animal Law Commons, and the Environmental Law Commons RReeccoommmmeennddeedd CCiittaattiioonn Fischman, Robert L. and Hyman, Jeffrey B., "The Legal Challenge of Protecting Animal Migrations as Phenomena of Abundance" (2010). Articles by Maurer Faculty. 112. https://www.repository.law.indiana.edu/facpub/112 This Article is brought to you for free and open access by the Faculty Scholarship at Digital Repository @ Maurer Law. It has been accepted for inclusion in Articles by Maurer Faculty by an authorized administrator of Digital Repository @ Maurer Law. For more information, please contact [email protected]. ARTICLE THE LEGAL CHALLENGE OF PROTECTING ANIMAL MIGRATIONS AS PHENOMENA OF ABUNDANCE Robert L. Fischman* and Jeffrey B. Hyman** ABSTRACT Animal migrations are as familiar as geese in the sky on a fall afternoon and as mysterious as the peregrinationso f sea turtles across thousands of miles of open ocean. This article discusses the distinguishing attributes of animal migrations, why they are important to biodiversity conservation, and the legal challenges posed by migration conservation. In particu- lar, the articlef ocuses on those aspects of migration conserva- tion that existing law, dominated by imperiled species protection, fails to address. It consequently suggests law reforms that would better conserve animal migrations. A step toward serious legal efforts to protect the process and func- tion of migration would represent significant broadening of the current framework for biodiversity protection policy. This article begins by describing animal migrations and explaining the common threats that raise conservation con- cerns. Any successful strategy for protecting migration will need to address habitat destruction, human-created obstacles, overexploitation (i.e., hunting and fishing), and climate change. The article examines the four key legal elements of a conservation strategy. The first is the establishment of differ- ential thresholds of action responsive to the different abun- dance goals for a migration. Second is transboundary coordination, which may involve internationalo r interstate * Professor, Indiana University Maurer School of Law and School of Public and Envi- ronmental Affairs. The authors are grateful for the research support of the Indiana Uni- versity Maurer School of Law. Comments from Alejandro Camacho, Holly Doremus, Julie Lurman Joly, and the participants of the Indiana University Institute for Advanced Study animal migration conservation seminar significantly aided the authors. The authors thank Elizabeth Baldwin, Lindsey Hemly and Jeremiah Williamson for their meticulous research assistance. ** Staff Attorney, Conservation Law Center and Adjunct Professor, Indiana University Maurer School of Law. 174 Virginia Environmental Law Journal [Vol. 28:173 agreements, depending on the scale of the migration. Third is the protection of migration connectivity. Effective connectiv- ity requires designation of corridors. Within the corridors, legal activity should concentrate on acquisition of habitat as well as activity-based regulation of habitat-disturbingp rac- tices. Fourth is controlling commercial and recreationalh ar- vests of migrating animals or the species on which the migrations rely. Finally, the article presents a theoretical model that tailors a place-based legal response to both migra- tory population abundance and the ecological importance of habitat. Application of the model would result in variable levels of legal protection to minimize unnecessary costs and optimize the benefit of conservation efforts. Existing attempts to conserve migrations using variable levels of protection compose a mixed record from which we extract lessons. I. INTRODUCTION ........................................ 175 II. ANIMAL MIGRATIONS: CHARACTERISTICS AND THREATS ............................................... 180 A. Common Threats.. ................................. 183 B . Illustrations ......................................... 186 III. ELEMENTS OF A LEGAL RESPONSE TO THREATS ...... 189 A. Defining and Determining Population Triggers for M igration Protection. .............................. 190 1. Defining Thresholds of Abundance ............ 194 2. Applying Thresholds to Trigger Conservation A ctions ........................................ 200 B. Transboundary Considerations .................... 203 1. Crossing Agency Jurisdictions ................. 205 2. Crossing State Boundaries ..................... 206 3. Crossing National Borders ..................... 208 4. Sewing It Together ............................. 210 C. Protecting Migration Connectivity ................. 211 1. CorridorD esignation and Habitat A cquisition .................................... 212 2. Land Use Controls to Protect Habitat ......... 217 3. Standards to Reduce and Mitigate Barriers. ... 222 D . Harvest Controls. .................................. 227 E . Sum m ary .......................................... 228 IV. CONCEPTS FOR A COMPREHENSIVE MIGRATION PROTECTION LAW ..................................... 228 A. Migration Protection Model ....................... 229 2010] Animal Migrations as Phenomena of Abundance 175 B. Existing Approaches Using Variable Protection L evels .............................................. 232 C. Limitations of a Multiple-Threshold Approach .... 234 V . CONCLUSION ........................................... 236 I. INTRODUCTION The current legal approach to maintaining and restoring biodiversity has many shortcomings. One of the chief problems is that imperiled species on the brink of extinction consume almost all attention (and resources). This "emergency room" response to the biodiversity crisis is necessary to begin reversing the disturbing decline in biodiversity. However, its predominance in the public mind, the courts, and administrative procedure eclipses other important conservation objectives. One of the overlooked issues in biodiversity protection is con- serving animal migrations as phenomena of abundance. Animal migrations are as familiar as the geese in the sky on a fall afternoon and as mysterious as the peregrinations of sea turtles across thousands of miles of open ocean. This article discusses the distin- guishing attributes of animal migrations, why they are important to biodiversity conservation, and the legal challenges posed by migra- tion conservation. In particular, the article focuses on those aspects of migration conservation that existing law, dominated by endangered species protection, fails to address. It consequently suggests law reforms that would better conserve animal migrations. Though species diversity dominates the popular conception of biodiversity, the term is actually much broader. The scientific and policy literature embraces within "biodiversity" all biotic composi- tional elements of the world, from genes to large assemblages, such as habitats.' Limiting the definition of biodiversity to just the com- positional elements of nature has the practical merit of making the concept relatively concrete, specific, and measurable. However, such a limitation excludes some of the most emotionally resonant and ecologically important spectacles of nature.2 Intellectual his- 1 E.g., NAT'L RESEARCH COUNCIL, PERSPECTIVES ON BIODIVERSITY: VALUING ITS ROLE IN AN EVERCHANGING WORLD 20-21 (1999). 2 Such spectacles include millions of wildebeest, zebras, gazelles and buffalos semiannu- ally crossing the Serengeti; a hundred thousand caribou and hundreds of thousands of birds traversing the Arctic National Wildlife Refuge; and shoals of fish miles long migrating along South Africa's east coast. See MONTE HUMMEL & JUSTINA C. RAY, CARIBOU AND THE NORTH 53 (2008) (discussing the ecological significance of caribou as nutrient distribu- tors and food source); NAT'L RESEARCH COUNCIL, CUMULATIVE ENVIRONMENTAL EFFECTs OF OIL AND GAS ACTIVITIES ON ALASKA'S NORTH SLOPE (2003) (discussing all 176 Virginia Environmental Law Journal [Vol. 28:173 torians have noted that the term "biodiversity" answers the evolv- ing needs of the conservation community to describe what to value in nature.3 Animal migrations certainly qualify under this elastic definition. Indeed, most scholarly definitions of biodiversity include ecological processes and functions,4 such as migration. But, with the exception of birds, there is scant systematic legal concern about conserving migrations. A step toward serious legal efforts to protect the process and function of migration would represent significant broadening of the current framework for biodiversity protection policy. Alas, migrations are already greatly diminished from their historic profusion. Though lawmakers may support migration conservation as a matter of Leopoldian aesthet- ics6 or other ethics,7 protection is also a matter of enlightened self- interest: the ecosystem services that migrations provide, such as nutrient cycling and pest control, are valuable for human flourish- ing.8 Furthermore, the opportunity to observe large numbers of migratory animals using the refuge); Robert J. M. Crawford, Influence of Food on Numbers Breeding, Colony Size and Fidelity to Localities of Swift Terns in South Africa's Western Cape, 1987-2000, 26 INT'L J. WATERBIRD BIOLOGY 44 (2003) (discussing the ecological importance of sardines as a food source for Swift Terns); Jeremy David & Patti Wickens, Management of Cape Fur Seals and Fisheries in South Africa, in MARINE MAMMALS 116, 120 (Nick Gales et al. eds., 2003) (discussing the importance of South African sardine shoals as a food source for ocean mammal populations); John Pastor et al., The Roles of Large Herbivores in Ecosystem Nutrient Cycles, in LARGE HERBIVORE ECOLOGY, Ecosys- TEM DYNAMICS AND CONSERVATION 289, 293-318 (Kjell Danell et al. eds., 2006) (discuss- ing the role of migrating ungulates in cycling nutrients in the Serengeti grazing ecosystem). 3 See, e.g., TIMOTHY J. FARNHAM, SAVING NATURE'S LEGACY: ORIGINS OF THE IDEA OF BIOLOGICAL DIVERSITY 3 (2007). 4 Id. at 5. An intermediate step in the inclusiveness continuum of biodiversity involves consideration of ecological structures such as standing dead trees (snags), which helped make the case for conservation of old-growth forests. See, e.g., DAVID B. LINDENMAYER & JERRY F. FRANKLIN, CONSERVING FOREST BIODIVERSrrY: A COMPREHENSIVE MULTIS- CALED APPROACH (2002). Reed Noss has usefully characterized biodiversity as having compositional, structural, and functional components. See Reed F. Noss, Indicators for Monitoring Biodiversity: A HierarchicalA. pproach, 4 CONSERVATION BIOLOGY 355, 356 (1990); see also REED F. Noss & ALLEN Y. COOPERRIDER, SAVING NATURE'S LEGACY: PROTECTING AND RESTORING BIODIVERSITY (1994). 5 See generally Lincoln P. Brower & Stephen B. Malcolm, Animal Migrations: Endan- gered Phenomena, 31 AM. ZOOLOGIST 265 (1991); Grant Harris et al., Global Decline in Aggregated Migrations of Large Terrestrial Mammals, 7 ENDANGERED SPECIES RES. 55 (2009). 6 ALDO LEOPOLD, A SAND CoUNTY ALMANAC 262 (Ballantine Books 1970) (1949) ("A thing is right when it tends to preserve the integrity, stability, and beauty of the biotic community. It is wrong when it tends otherwise."). 7 See, e.g., JOHN PASSMORE, MAN'S RESPONSIBLrTY FOR NATURE (2d ed. 1980) (describing an environmental ethic based on stewardship, which has roots in the Judeo- Christian tradition). A helpful survey of the ethical bases for biodiversity protection is BRYAN G. NORTON, WHY PRESERVE NATURAL VARIETY? (1987). 8 See generally NAT'L RESEARCH COUNCIL, VALUING ECOSYSTEM SERVICES (2005). 2010] Animal Migrations as Phenomena of Abundance 177 animals migrating together has important psychological value to humans.9 Yet, to date, these concerns have failed to translate into effective legal action. Though imperiled species legislation covers some migrating spe- cies, such as right whales and piping plovers, most migrations receive no special legal protection. This is largely because migra- tion is generally a "phenomenon of abundance."1 Many migrating animal populations require large numbers to instigate migration or to succeed in their journeys,11 and to fulfill their ecological func- tions.12 Imperiled species laws, such as the U.S. Endangered Spe- cies Act (ESA), focus instead on species whose populations are 9 See, e.g., DAVID S. WILCOVE, No WAY HOME: THE DECLINE OF THE WORLD'S GREAT ANIMAL MIGRATIONS 12, 40 (2007) ("[A]lmost every aspect of migration inspires awe: the incredible journeys migratory animals undertake and the hardships they face along the way; the complex mechanisms they use to navigate across the land and through the skies and seas .... ") ("I first witnessed the shorebird congregation in Delaware Bay in 1987 .... What I encountered was extraordinary .... The sex and gluttony were both there, along with great beauty. I felt as though I had stepped into the shoes of John James Audubon, back into an era of wilderness and abundant wildlife .... "); D. J. Aidley, Questions About Migration, in ANIMAL MIGRATION 1, 7 (D. J. Aidley ed., 1981) ("But perhaps the main reason for the interest of zoologists in migration is less logical but more pervasive. Migrants are often beautiful, they may journey great distances to faraway places, they act as though they were adventurous, intrepid, free, as though they solved their problems by taking action. They stir the imagination."); Doug Perrine, South Africa, Sardine Run, in DIVING WITH GIANTS 74, 74-75 (Jack Johnson ed., 2006) (discussing human fascination with and emotional attraction to sardine migrations off the South African coast); see also Sergio Cristancho & Joanne Vining, Culturally Defined Keystone Species, 11 Hum. ECOL- OGY REV. 153 (2004) (discussing conservation priorities based on spiritual or symbolic value). See generally PETER H. KAHN, JR., THE HUMAN RELATIONSHIP WITH NATURE: DEVELOPMENT AND CULTURE 13-17 (1999) (summarizing research demonstrating improvements in psychological well-being resulting from exposure to natural landscapes and affiliation with animals); Lawrence St. Leger, Health and Nature-New Challenges for Health Promotion, 18 HEALTH PROMOTION INT'L 173, 174 (2003) (explaining that viewing flora and fauna and exposure to nature can enhance psychological health). 10 WILCOVE, supra note 9, at 10. 11 See, e.g., Kristine L. Grayson & Henry M. Wilbur, Sex- and Context-Dependent Migra- tion in a Pond-Breeding Amphibian, 90 ECOLOGY 306 (2009); Caz M. Taylor & D. Ryan Norris, Predicting Conditions for Migration: Effects of Density Dependence and Habitat Quality, 3 BIOLOGY LETTERS 280 (2007). 12 Among the important ecological functions are transporting nutrients (e.g. from the ocean to forests through salmon migration) and regulating prey populations (e.g. leaf-eat- ing insects through bird migration). See David S. Wilcove, Animal Migration: An Endan- gered Phenomenon?, 24 ISSUES ScI. & TECH. 71 (2008), available at www.plosbiology.org; see also Joseph E. Merz & Peter B. Moyle, Salmon, Wildlife, and Wine: Marine-Derived Nutrients In Human-Dominated Ecosystems Of Central California,1 6 ECOLOGICAL APPLI- CATIONS 999 (2006); Gary A. Polis, Wendy B. Anderson & Robert D. Holt, Toward an Integration of Landscape and Foodweb Ecology: The Dynamics of Spatially Subsidized Food Webs, 28 ANN. REV. ECOLOGY & SYSTEMATICS 289 (1997); Oystein Varpe, 0yvind Fiksen & Aril Slotte, Meta-Ecosystems and Biological Energy Transport from Ocean to Coast. The Ecological Importance of Herring Migration, 146 OECOLOGIA 443 (2005). 178 Virginia Environmental Law Journal [Vol. 28:173 diminished almost to the point of disappearance. For preventing extinctions, scarcity generally triggers a legal reaction. Conserving migration as a phenomenon of abundance, in contrast, will require a different set of thresholds for initiating action - once the popula- tions are scarce, most of the values of migration are already lost. Using rarity to trigger legal protection is not the only paradigm in biological conservation. The sustained-yield principle that guided the Progressive Movement's conservation program prom- ised perpetual abundance of nature's bounty.13 And, in the United States, the monumental scenery that prompted the creation of the national parks more than a century ago'4 illustrates a preservation tradition that values the inspirational in nature. 5 Creating a new set of legal tools to maintain abundant animal migrations may tap into these deep currents of American identity. International com- mitments to conserve migrations will likely emerge from the lingua franca of science and valuation of ecological services. 6 Any one of these principles can support the conservation of animal migrations as phenomena of abundance. This paper focuses on how law could be designed to succeed in such an effort. While we concentrate on the key difficulties of drawing up a blueprint for migration conservation, the aim of this article is to provide a broad, comprehensive review of the essential elements of a plan. In doing so, our aim is to explain the difficul- ties of animal migration conservation and to identify the key tools for addressing them. It is beyond the scope of this current effort to resolve all the questions involving implementation of the tools. Many animal migrations do not have the high-flying prowess of the trans-Himalayan bar-headed goose, 7 the spectacular global sweep of the Arctic tern, which travels almost from pole to pole,'8 13 SAMUEL P. HAYS, CONSERVATION AND THt GOSPEL OF EFFICIENCY: THE PROGRES- SIVE CONSERVATION MOVEMENT 1890-1920 (1959). 14 ALFRED RUNTE, NATIONAL PARKS: THE AMERICAN EXPERIENCE 5 (2d ed. 1987). 15 JOSEPH L. SAX, MOUNTAINS WITHoUT HANDRAILS 7 (1980). 16 Robert L. Fischman, The Significance of National Wildlife Refuges in the Development of U.S. Conservation Policy, 21 J.-LAND USE & ENVTL. L. 1, 21 (2005). 17 Bar-headed geese migrate over the Himalayan mountains twice a year between wintering grounds in southern Asia and nesting grounds on the Tibetan plateau. The geese have been observed at altitudes over 30,000 feet. Stella Y. Lee et al., Have Wing Morphol- ogy or Flight Kinematics Evolved for Extreme High Altitude Migration in the Bar-Headed Goose?, 148 COMp. BIOCHEMISTRY & PHYSIOLOGY PART C: TOXICOLOGY & PHARMACOL- OGY 324, 324 (2008); Lily Whiteman, The High Life, AUDUBON, Nov.-Dec. 2000, at 106, available at http://www.audubonmagazine.org/birds/birds0011.html. 18 See generally Carsten Egevang et al., Tracking of Arctic Terns Sterna Paradisaea Reveals Longest Animal Migration, 107 PRoC. NAT'L ACAD. SCI. U.S. AM. 2078; see also WILCOVE, supra note 9, at 139. 2010] Animal Migrations as Phenomena of Abundance 179 or the grandeur of the 1.3 million wildebeest tramping around the Serengeti.19 Some reptiles and amphibians experience the peril of migration merely in crossing a road. Other significant migrations, such as pronghorn movement from winter to summer range, occur entirely within a single state.2' The scales vary enormously and any attempt to address migration conservation needs to account for the significant spatial differences. What all migrations share is an unu- sual adaptive behavior.21 This unifying characteristic further distin- guishes migration conservation from imperiled species protection, since the only thing that imperiled species necessarily share is their imperilment. Protecting migrations typically involves some sort of inter-juris- dictional challenge. Within a state or watershed, such challenges may be driven by divisions of authority between, say, a road-main- taining agency and a wetlands regulating agency. At larger scales, many challenges to migration require international coordination. Notwithstanding the 1979 Convention on the Conservation of Migratory Species of Wild Animals (Bonn Convention),22 there currently exists no strong framework for identifying and protecting transboundary migrations. However, projects aimed at particular species that generate widespread enthusiasm, such as birds, point the way to a legal .foundation for stronger migrations that will sus- tain ecological integrity across great distances. Part II of this article describes animal migrations and explains common threats that raise conservation concerns. Any successful strategy for protecting migration will need to address habitat destruction, human-created obstacles, overexploitation (i.e., hunt- ing and fishing), and climate change. Part III examines the four key legal elements of a conservation strategy. The first is the estab- lishment of differential thresholds of action responsive to different social objectives reflected in various abundance goals. Exploring different population thresholds helps to disaggregate these differ- ent social objectives that are often confounded. This allows us to 19 Id. at 82. 20 Id. at 121-24. 21 See Mark S. Ogonowski & Courtney J. Conway, Migratory Decisions in Birds: Extent of Genetic Versus Environmental Control, 161 OECOLOGIA 199 (2009); see also Wolfgang Fiedler et al., Using Large-Scale Data from Ringed Birds for the Investigation of Effects of Climate Change on Migrating Birds: Pitfalls and Prospects, in BIRDS AND CLIMATE CHANGE 49, 51-52 (Anders P. Moller et al. eds., 2006). 22 Convention on the Conservation of Migratory Species of Wild Animals, June 23, 1979, 19 I.L.M. 15, 1651 U.N.T.S. 28395, available at http://www.cms.int/pdf/convtxt/cms- convtxt-english.pdf. Virginia Environmental Law Journal [Vol. 28:173 explain what it means to protect migrations "as phenomena of abundance." Second is transboundary coordination, which may involve international or interstate agreements, depending on the scale of the migration. Third is the protection of migration connec- tivity. Effective connectivity requires designation of corridors. Within the corridors, legal activity should concentrate on acquisi- tion of habitat as well as activity-based regulation of habitat-dis- turbing practices. Fourth is controlling commercial and recreational harvests of migrating animals or the species on which the migrations rely. Part III surveys existing legal approaches to protecting migration and discusses the ways in which they fall short of effectiveness. It also highlights some tools that can be strength- ened or extended to improve conservation outcomes for migrating animals. Part IV presents a new design for comprehensive migration pro- tection laws and programs. We describe a conceptual model that tailors a place-based legal response to both migratory population abundance and the ecological importance of habitat. Application of the model would result in variable levels of legal protection to minimize unnecessary costs and optimize the benefit of conserva- tion efforts. Existing attempts to conserve migrations using varia- ble levels of protection compose a mixed record from which we extract lessons. We conclude with some general thoughts about how to improve that record. Climate change complicates the path toward law reform, but many actions that would safeguard migrations also improve the resilience of ecosystems to adapt to climatic instabil- ity. There are many details of a new legal program over which rea- sonable minds can differ. But the existing neglect of migration conservation provides tremendous potential for significant gains. A vigorous effort to conserve migrations in abundance rather than as faint echoes of past glory would also prompt fresh debate over objectives for biodiversity policy. II. ANIMAL MIGRATIONS: CHARACTERISTICS AND THREATS A wide variety of nearly ten thousand bird, fish, mammal, rep- tile, amphibian, insect, and other invertebrate species move rela- tively long distances in search of favorable resources for feeding, sheltering, and breeding.23 Both environmental and internal cues 23 UNITED NATIONS ENV'T PROGRAMME [UNEP], CONVENTION ON MIGRATORY SPE- CIES, CONSERVING ANIMALS ON THE MOVE 1 (2003), available at http://www.cms.int/pdf/ 2010] Animal Migrations as Phenomena of Abundance 181 trigger these long-distance movements. Animals display an aston- ishing array of migratory behaviors. But one common attribute stands out as the most important feature of migration: an abun- dance of animals moving during the same time period.24 The yearly round-trip movements of birds, ungulates, and whales, and the periodic return of sea turtles to beaches for egg laying are among the most familiar migrations. Some animals complete only a single migration cycle in their lifetime (e.g., Pacific salmon), and others complete only part of a cycle (e.g., monarch butterflies).26 In general, migration involves periodic movements and recurrent destinations for at least part of the journey. Move- ments known as ranging or dispersal, in contrast, generally cease once a suitable new home range is found - for example, young birds and mammals range to find space away from their parents to avoid competition and inbreeding.27 Both migration and dispersal are distinguished from the typically shorter-distance and shorter- time scale movements known as foraging.28 Climate change has raised the conservation prospect of moving certain endemic species that are isolated by mountains, roads, and other human developments. As their existing habitats become inhospitable for their needs, some isolated species will disappear if not translocated to more suitable habitat. This translocation had been called "assisted migration. '29 But it is not migration in the sense we use the term in this article because there is no return en/CMSBrochure-en.pdf. Migration is an adaptation driven by the transitory availability and changing location of resources, and involves movement of populations of animals between areas where conditions are alternately favorable or unfavorable for feeding, shel- tering, and reproducing. Hugh Dingle & V. Alistair Drake, What is Migration?, 57 BIOS- CIENCE 113, 114 (2007). 24 David S. Wilcove, Animal Migration:A n Endangered Phenomenon?, 24 IssuEs ScI. & TECH. 71 (2008); David S. Wilcove & Martin Wikelski, Going, Going, Gone: Is Animal Migration Disappearing?,6 PLoS BIOLOGY 1361 (2008), available at www.plosbiology.org. 25 Dingle & Drake, supra note 23 (describing many familiar migrations). 26 Id. at 115. 27 Id. at 116. 28 Not all foraging movements are short distance, however. An extended foraging behavior called commuting involves relatively long journeys to spatially separated resources. Dramatic examples include the mass daily vertical movements of plankton through the water column and the several-thousand-kilometer foraging round trips extending over several days made by albatrosses (Diomedea spp.) and other seabirds between nesting islands and food locales. Id. 29 Julie Lurman Joly & Nell Fuller, Advising Noah: A Legal Analysis of Assisted Migra- tion, 39 ENVTL. L. REP. 10413 (2009); Jason S. McLachlan et al., A Frameworkf or Debate of Assisted Migration in an Era of Climate Change, 21 CONSERVATION BIOLOGY 297 (2007).