《森林生态学》课程教学资源（生态学热点）Issues in ecology - 16 景观连通性在规划和实施保护中的作用 The Role of Landscape Connectivity in Planning and Implementing Conservation and Restoration Priorities

ISSUES IN ECOLOGY Published by the Ecological Society of America The Role of Landscape Connectivity in Planning and Implementing Conservation and Restoration Priorities Deborah A.Rudnick,Sadie J.Ryan,Paul Beier,Samuel A.Cushman,Fred Dieffenbach, Clinton W.Epps,Leah R.Gerber,Joel Hartter,Jeff S.Jenness,Julia Kintsch, Adina M.Merenlender,Ryan M.Perkl,Damian V.Preziosi,and Stephen C.Trombulak Fall 2012 Report Number 16 esa

esa Published by the Ecological Society of America esa The Role of Landscape Connectivity in Planning and Implementing Conservation and Restoration Priorities Deborah A. Rudnick, Sadie J. Ryan, Paul Beier, Samuel A. Cushman, Fred Dieffenbach, Clinton W. Epps, Leah R. Gerber, Joel Hartter, Jeff S. Jenness, Julia Kintsch, Adina M. Merenlender, Ryan M. Perkl, Damian V. Preziosi, and Stephen C. Trombulak Fall 2012 Report Number 16 The Role of Landscape Connectivity in Planning and Implementing Conservation and Restoration Priorities Issues inin Ecology Ecology

ISSUES IN ECOLOGY NUMBER SIXTEEN FALL 2012 The Role of Landscape Connectivity in Planning and Implementing Conservation and Restoration Priorities SUMMARY ent to which a landscape facilitates them increase the resilience of re including decreased carrying capacity,population declines,loss of genetic variation,and ultimately species extinction. ectivity is facilitated by a to mitigate t anagers must confront and overcome several challenges inherent in evaluating and planning for con- .characterizing the biology of focal species .understanding the strengths and the limitations of the models used to evaluate connectivity: considering spatial and temporal extent in connectivity planning; using caution in extrapolating results outside of observed conditions .considering non-linear relationships that can complicate assumed or expected ecological responses; .accounting and planning for anthropogenic change in the landscape; usi I goals and objectiv drive the selection of methods used for evaluating and connectivity .and communicating to the uhlic in cle age the importance of Several ast ecrs of connectivity science deserve additional attention in order to improve the effectiveness of design and imple mentation.Research on species pe associated with connectiv ating and hepreof dvancementhor elinopt humn Cover photo Photos credits:a)NASA Goddar's Scientific Visli Sdio.b)Admna Merenlender.c)Flickrser Abeerd)Flickr uer Danid Lane. The Ecological Society of Americaesahq@esa.org esa 1

© The Ecological Society of America • esahq@esa.org esa 1 ISSUES IN ECOLOGY NUMBER SIXTEEN FALL 2012 The Role of Landscape Connectivity in Planning and Implementing Conservation and Restoration Priorities SUMMARY L andscape connectivity, the extent to which a landscape facilitates the movements of organisms and their genes, faces critical threats from both fragmentation and habitat loss. Many conservation efforts focus on protecting and enhancing connectivity to offset the impacts of habitat loss and fragmentation on biodiversity conservation, and to increase the resilience of reserve networks to potential threats associated with climate change. Loss of connectivity can reduce the size and quality of available habitat, impede and disrupt movement (including dispersal) to new habitats, and affect seasonal migration patterns. These changes can lead, in turn, to detrimental effects for populations and species, including decreased carrying capacity, population declines, loss of genetic variation, and ultimately species extinction. Measuring and mapping connectivity is facilitated by a growing number of quantitative approaches that can integrate large amounts of information about organisms’ life histories, habitat quality, and other features essential to evaluating connectivity for a given population or species. However, identifying effective approaches for maintaining and restoring connectivity poses several challenges, and our understanding of how connectivity should be designed to mitigate the impacts of climate change is, as yet, in its infancy. Scientists and managers must confront and overcome several challenges inherent in evaluating and planning for con￾nectivity, including: •characterizing the biology of focal species; •understanding the strengths and the limitations of the models used to evaluate connectivity; •considering spatial and temporal extent in connectivity planning; •using caution in extrapolating results outside of observed conditions; •considering non-linear relationships that can complicate assumed or expected ecological responses; •accounting and planning for anthropogenic change in the landscape; •using well-defined goals and objectives to drive the selection of methods used for evaluating and planning for connectivity; •and communicating to the general public in clear and meaningful language the importance of connectivity to improve awareness and strengthen policies for ensuring conservation. Several aspects of connectivity science deserve additional attention in order to improve the effectiveness of design and imple￾mentation. Research on species persistence, behavioral ecology, and community structure is needed to reduce the uncertainty associated with connectivity models. Evaluating and testing connectivity responses to climate change will be critical to achieving conservation goals in the face of the rapid changes that will confront many communities and ecosystems. All of these potential areas of advancement will fall short of conservation goals if we do not effectively incorporate human activities into connectivity planning. While this Issue identifies substantial uncertainties in mapping connectivity and evaluating resilience to climate change, it is also clear that integrating human and natural landscape conservation planning to enhance habitat connectivity is essential for biodiversity conservation. Cover photos: Examples of ways different species move through landscapes and depend on connectivity. Clockwise starting on the upper left: a) The interconnection of ocean surface current patterns provides pathways for dispersal of larvae between coral reefs. b) A network of riparian corridors used by wildlife to move through an agri￾cultural landscape. c) Continuous grasslands are used by migrating wildebeest in eastern Africa. d) Intact lowland forest is used by endemic forest birds for dispersal between mountain ranges. Photos credits: a) NASA Goddard's Scientific Visualization Studio. b) Adina Merenlender. c) Flickr user Abeeeer. d) Flickr user Daniel Lane

ISSUES IN ECOLOGY NUMBER SIXTEEN FALL 2012 The Role of Landscape Connectivity in Planning and Implementing Conservation and Restoration Priorities Deborah A.Rudnick,Sadie J.Ryan,Paul Beier,Samuel A.Cushman,Fred Dieffenbach,Clinton W.Epps Leah R.Gerber,Joel Hartter,Jeff S.Jenness,Julia Kintsch,Adina M.Merenlender,Ryan M.Perkl, Damian V.Preziosi,and Stephen C.Trombulak Introduction What Is Landscape Connectivity and How Does It Affect Conservation cape. Objectives populations to move among Connectivity is the extent to which move aciate by ane.A landscape's conncctivity is defined ing humans is occurring at an unprece. convert or r s,and as our impacts on global elimate continus to ace patems providing path change the physical educe the o move through an agricultural landscape; amount of a habitat or fragment it,breaking it oomgating photos).Each of these examples demonstrates seascape ften time ame and over Connectivity has th str and fumnc atur physical characteristics of a land- daptand ap movement,incding amdoowdah gy,vege ve cover,and ma ules,individu habitat lossar the dominant hanisms by e way ism.such as habitat preference and dispersal the subdivision of habitat into smaller or more pecies move through and depend on the and- ciated with habitat loss.However,fragmenta- scape and demonstrate bot nctional and 2 esa The Ecological Society of Americaesahq@esa.org

2 esa © The Ecological Society of America • esahq@esa.org Introduction What Is Landscape Connectivity and How Does It Affect Conservation Objectives? Connectivity is the extent to which move￾ments of genes, propagules (pollen and seeds), individuals, and populations are facilitated by the structure and composition of the land￾scape. A landscape’s connectivity is defined relative to the requirements of the organisms that live within it and move through it. Therefore, connectivity is species and context dependent. Consider the interconnection of ocean surface current patterns providing path￾ways for dispersal of larvae between coral reefs; a network of riparian corridors used by wildlife to move through an agricultural landscape; the continuity of grasslands used by migrating wildebeest; intact lowland forest through which endemic forest birds move (see cover photos). Each of these examples demonstrates that connectivity is measured relative to the ease or difficulty with which a particular species is able to move across a particular land or seascape. Connectivity has both structural and func￾tional components. Structural connectivity describes the physical characteristics of a land￾scape that allow for movement, including topography, hydrology, vegetative cover, and human land use patterns. Functional connectivity describes how well genes, propagules, individu￾als, or populations move through the landscape. Functional connectivity results from the ways that the ecological characteristics of the organ￾ism, such as habitat preference and dispersal ability, interact with the structural characteris￾tics of the landscape. The examples provided on the cover depict the ways that different species move through and depend on the land￾scape and demonstrate both functional and structural connectivity, whereby ecological requirements of individual species interact with the composition and configuration of the land￾scape. These interactions influence the ability of individuals and populations to move among locations to find key resources, such as food, water, appropriate substrates for sessile organ￾isms, or breeding partners. The destruction and degradation of natural habitats on which all organisms rely – includ￾ing humans – is occurring at an unprece￾dented rate across most regions of our planet. As humans convert land for resource extrac￾tion and for urban and agricultural uses, and as our impacts on global climate continue to grow, we profoundly change the physical, chemical, and biological character of these landscapes. Land use changes may reduce the amount of a habitat or fragment it, breaking it up into smaller or differently arranged units. This process changes not only the size of habi￾tat patches but also other landscape features, such as patch geometry or the amount of edge habitat, that may be of fundamental impor￾tance to species, communities, and ecological functions. Because human-caused disturbances often occur in shorter timeframes and over larger areas than do natural disturbances, eco￾logical communities face challenges of how to adapt and respond to novel rates and scales of disturbances that are quite different from those with which they may have evolved. Fragmentation, habitat degradation, and habitat loss are the dominant mechanisms by which connectivity is reduced or lost, and are widely recognized as major drivers of the pre￾sent global biodiversity crisis. Fragmentation, the subdivision of habitat into smaller or more isolated remnants, can directly impact species persistence and accelerate local extinction rates. Habitat fragmentation is frequently asso￾ciated with habitat loss. However, fragmenta￾tion can also eliminate dispersal or gene flow without causing impacts on a population’s core The Role of Landscape Connectivity in Planning and Implementing Conservation and Restoration Priorities Deborah A. Rudnick, Sadie J. Ryan, Paul Beier, Samuel A. Cushman, Fred Dieffenbach, Clinton W. Epps, Leah R. Gerber, Joel Hartter, Jeff S. Jenness, Julia Kintsch, Adina M. Merenlender, Ryan M. Perkl, Damian V. Preziosi, and Stephen C. Trombulak ISSUES IN ECOLOGY NUMBER SIXTEEN FALL 2012

ISSUES IN ECOLOGY NUMBER SIXTEEN FALL 2012 habitat-for example,a highway bisecting may be more releva movement corridor. s;for e such as food,breeding habtat,or refuge from or a heterogeneous assemblage of meadow the land ms to ecological requirements becomes even sidermaoinngPCeicorghoaoiCYoe tate moveme beween patches,are fre. that contribute to andscape connectivity for tion of corridors can maintain connectivity for s or large views the impor Corridors n rovide structural conpectivity rent science-based for mitigating the and are consistent with the functional con- negative ecological effects of fragmentation, at can take dis a ga opportunities for developing policies and man The growing movement toward ecosystem-based management.including ne orks of no-take zones in marine ecosvstems (marine ed areas or MPA sI re uires that these conservation areas be deli and adequately spaced to allow for conn into h functionlly and structurally linked to each other by both biological (e.g. dispersal of organisms)and physical (e.g..currents ld become genetically isolated if populations cannot reach each othe dermining the viability of populations in the MPA should include MPAs and other conservation and managen ent ar reas that support each other by taking advantage of oceanic currents ween the a is a critic rvation areas that are d d critical to marine ation ectives,whic cover 26%of the ecoregion en put are used to track species'dispersal from site to site as well as movement through the matrix(for example satellite trac g and the For example.sea turtle and whale shark tagging programs are already underway in the ecoregion,and ity in marine spatia The Ecological Society of America.esahg@esa.ord esa 3

© The Ecological Society of America • esahq@esa.org esa 3 ISSUES IN ECOLOGY NUMBER SIXTEEN FALL 2012 habitat – for example, a highway bisecting a movement corridor. For any given species, some parts of the landscape provide better opportunities than others to fulfill its ecological requirements, such as food, breeding habitat, or refuge from predation. Fragmentation and degradation can further increase the patchiness of the land￾scape in terms of meeting a species’ needs. Conserving connectivity in this context requires identifying, maintaining, and possibly enhancing the linkages between suitable patches of habitat in the landscape. Corridors, which are generally linear spaces that facili￾tate movement between patches, are fre￾quently used as a tool for conserving or enhancing linkages. The creation or protec￾tion of corridors can maintain connectivity for mobile species, such as ungulates or large felines that typically have large territories. Corridors provide structural connectivity and are consistent with the functional con￾nectivity needs of animals that can take advantage of linear spaces to move among dis￾parate habitat patches. However, landscape connectivity is highly diverse and species￾dependent, and other forms of connectivity may be more relevant to other types of organ￾isms; for example, a linked mosaic of small wetlands for breeding populations of amphib￾ians, continuity of vegetated intertidal rocky substrate along a coastline for a marine snail, or a heterogeneous assemblage of meadow plant communities with different flowering times for a population of pollinators. The challenge of matching connectivity patterns to ecological requirements becomes even greater when we expand our thinking to con￾sider maintaining or restoring connectivity for multiple species or entire communities. Many populations and ecosystem functions are dependent on extensive, well-connected habitats; however, understanding the factors that contribute to landscape connectivity for specific populations, species, or communities is challenging. This Issue reviews the impor￾tance of habitat connectivity, summarizes cur￾rent science-based strategies for mitigating the negative ecological effects of fragmentation, explores data gaps and limitations of connec￾tivity models, and describes obstacles and opportunities for developing policies and man￾agement approaches that improve connectiv￾ity and reach conservation goals. Case Study 1. Managing for Marine Connectivity: Marine Protected Areas in the Gulf of California, Mexico The growing movement toward ecosystem-based management, including networks of no-take zones in marine ecosystems (marine protected areas, or MPAs) requires that these conservation areas be deliberately and adequately spaced to allow for connectivity. The performance of a network of sites designed with the two-fold purpose of protecting commercial species and allowing for spillover effects (movement of organisms from protected areas into harvestable areas) will largely depend on whether sites in a network are functionally and structurally linked to each other by both biological (e.g., dispersal of organisms) and physical (e.g., currents) processes. Although the number and extent of MPAs has increased recently, studies have shown that, on a global scale, average dis￾tance between neighboring MPAs exceeds the distance of reef organism propagule dispersal. This distance suggests that some taxa could become genetically isolated if populations cannot reach each other, undermining the viability of populations in the MPAs. The conservation of species, habitats, and ecoregions depends on developing practical, efficient, and effective planning strategies. This is especially true in the marine realm, where threats are diffuse and difficult to both identify and quantify. Well-designed networks should include MPAs and other conservation and management areas that support each other by taking advantage of oceanic currents and movement/migration capabilities of species. They also provide much-needed resilience against a range of threats. Because estab￾lishment of isolated marine reserves may not alone suffice for the conservation of biodiversity, identifying the level of connectivity between the areas is a critical aspect in network design. In the Gulf of California, Mexico (GOC), two organizations, Comunidad y Biodiversidad and The Nature Conservancy, recently com￾pleted a marine ecoregional assessment to identify priority conservation sites and establish a network of conservation areas. This analysis identified 54 conservation areas that are deemed critical to marine conservation objectives, which cover 26% of the ecoregion. An important step towards implementing the assessment will be to account for connectivity between putative sites. To move from con￾nectivity assessments based exclusively on structural attributes of connectivity to a detailed assessment of actual connectivity, mod￾els are used to track species’ dispersal from site to site as well as movement through the matrix (for example, satellite tracking and the development of oceanographic models for the entire ecoregion). Pop-up satellite archival tags are being used globally for many marine species (e.g., the Tagging of Pacific Predators Program, http://www.topp.org/) and can greatly enhance knowledge of the dispersal of focal species. For example, sea turtle, cetacean, and whale shark tagging programs are already underway in the ecoregion, and expanded versions of these programs are expected to provide a more complete understanding of connectivity throughout the ecore￾gion. Integrating data from these tagging programs into the GOC ecoregional assessment is an important priority in understanding the role of connectivity in marine spatial planning

ISSUES IN ECOLOGY NUMBER SIXTEEN FALL 2012 How Fragmentation Affects ent:From Genes to long-term ecological Landscape fragmentation affects ecological ceebiecplorcethfihand gene flow within and between populations to climate change sinc the mate shifts;rather,species responded individu itats,and nate 1 ies for mental tole .dispersal abilities.and migra chang tions change throughout the year.Habitat frag- required by many species (their niches)may mentation can disrupt migration ting t ster can adapt mati habitat patches may act as filters or conditions encountered by srecies in their tions,are c mpounded by cesful movement.Last,the composition and nge, to such an extent that many species could be driven to mence lity of extinction. gmentation impedes seasonal migration, Effects of Connectivity on urces Disease and Biotic Invasions spe The extent to which landsc when trying to disp eacompleiew e,or they may be or fragmented may also affect the rate and pat. ding to unsustainably tem of disease spread and in asion byno pe mal dise aswelascompetitors and predator flow and lead to Ger he against wh ommunities may not have genetic variation and s d onsider how chan olation may inluence the spread of disease can be a me he creation of nev ant pop ather depe nd the par icular species and land n tion,whi inquestion. Inta connec and lead to local extinctions.Retaining or ways to native speciesn tive effects of genetic provid arge areas(connectivity across ecoregions o sions.For exan ple the recent asian can continents is critical for some species)and over long timeframes (connectivity over many godon ( er carp (Hypop 4 esa The Ecological Society of America esahq@esa.org

ISSUES IN ECOLOGY NUMBER SIXTEEN FALL 2012 How Fragmentation Affects Movement: From Genes to Species Landscape fragmentation affects ecological communities at multiple levels of organiza￾tion. Here, we briefly explore these effects, ranging from the movement of individuals and gene flow within and between populations to shifts in species range and species persistence. Landscape connectivity is important for dis￾persing or migrating individuals. Dispersal increases resilience to disturbances by allowing organisms to track their shifting habitats, and it promotes the spread and expansion of popu￾lations. In some species – for example, wilde￾beest in Africa, bison in North America, a wide variety of bird species – seasonal migra￾tion has evolved as a means of maximizing access to critical resources as ecological condi￾tions change throughout the year. Habitat frag￾mentation can disrupt dispersal and migration in several ways. First, edges of the remnant habitat patches may act as filters or barriers that discourage or impede movement. Second, increased distances between suitable habitat patches may influence the likelihood of suc￾cessful movement. Last, the composition and structure of the intervening landscape mosaic may influence the permeability of the land￾scape to movements by different organisms. If fragmentation impedes seasonal migration, wildlife may be cut off from seasonal resources. If dispersal routes are blocked or altered, organ￾isms may experience higher rates of mortality when trying to disperse, or they may be stopped completely, leading to unsustainably high densities of organisms in remnant patches, resulting in increases in mortality. Habitat fragmentation may impede gene flow and lead to genetic isolation. Gene flow is critical to population viability, as it helps maintain local genetic variation and spreads potentially adaptive genes. Genetic isolation can be a mechanism for the creation of new populations and even species; however, small remnant populations inhabiting fragmented landscapes are more likely to suffer from inbreeding and low genetic variation, which can increase vulnerability to other stressors and lead to local extinctions. Retaining or restoring connectivity counteracts these nega￾tive effects of genetic isolation. Landscape connectivity is essential across large areas (connectivity across ecoregions or continents is critical for some species) and over long timeframes (connectivity over many years or generations) to allow species’ range shifts in response to long-term ecological change. Projected climate change over the next few decades will change ecosystem struc￾ture, species composition, and diversity. Changes in biophysical conditions will likely lead to species replacement in communities (community turnover) and latitudinal and ele￾vational shifts in geographic ranges. During episodes of climate change since the Pleistocene, vegetation zones or communities did not move as a whole in response to cli￾mate shifts; rather, species responded individu￾ally to climate change, according to their own individual and largely independent environ￾mental tolerances, dispersal abilities, and responses to biotic interactions. Current cli￾mate change appears to be occurring substan￾tially faster than in the pre-historical record, meaning that the ecological conditions required by many species (their niches) may be shifting faster than species can adapt. These pressures, caused by changes in climatic conditions encountered by species in their current distributions, are compounded by habitat loss and fragmentation. The resulting obstacles to migration may impede species’ abilities to adapt to climate change, to such an extent that many species could be driven to extinction. Effects of Connectivity on Disease and Biotic Invasions The extent to which landscapes are connected or fragmented may also affect the rate and pat￾tern of disease spread and invasion by non￾native species. Species introductions, which can radically alter ecosystems, include plant and ani￾mal diseases as well as competitors and predators against which native communities may not have evolved defenses. It is important for managers to consider how changes in connectivity and frag￾mentation may influence the spread of diseases and invasive species, and to recognize that these influences are not necessarily unidirectional, but rather depend on the characteristics of the par￾ticular species and landscape in question. Intact, well-connected landscapes can serve as conduits for many invasive species if they disperse in similar ways to native species. In other cases, processes that fragment habitats for native species may simultaneously provide connections that can facilitate biotic inva￾sions. For example, the recent Asian carp invasion (including grass carp (Ctenopharyn￾godon idella), silver carp (Hypophthalmichthys 4 esa © The Ecological Society of America • esahq@esa.org

ISSUES IN ECOLOGY NUMBER SIXTEEN FALL 2012 Box 1.Habitat Fragmentation and Increased Disease Transmissivity a to be m for ulatio land bacte that c rum (Bon urg ely resul bined with release from natural e found ins ts.pthe nay those near larger forest fragments Area (ha) gm b)Pe apugceieshe Source: risk. ecteodwt pathogens and parasites for which the host d,and their porential constitute the true x D).Ho "across which both fragment the ter estrial environment and host subpopulations.which then may bec ome en aquatic syst habitats,they can simultaneous e as cor scape fragme tation ma duits for some invasive species,such as cheat from lisease.For example mia pestis ow star thistl n orado prairie dog (C that benefit from the onenin. more closely grouped together. ion and Measuring,Analyzing and increased host connectivity,it does not neces. Designing Landscape Connectivity ect Mea host abundance and alter host distributior and these changes can increase connectivity for and policy makers,as Geographic Information The Ecological Society of America.esahg@esa.org esa 5

© The Ecological Society of America • esahq@esa.org esa 5 ISSUES IN ECOLOGY NUMBER SIXTEEN FALL 2012 molitrix), and bighead carp (H. nobilis)) in the Mississippi River watershed, and their potential spread into the Great Lakes, illustrate how human-constructed connections (canals) can both fragment the terrestrial environment and provide new corridors between aquatic systems. Similarly, while roads can fragment vegetated habitats, they can simultaneously serve as con￾duits for some invasive species, such as cheat￾grass (Bromus tectorum), yellow star thistle (Centaurea solstitialis), and other invasive species that benefit from the openings created by roads. Connectivity for pathogens and parasites is largely a function of host distribution and abun￾dance. While disease persistence benefits from increased host connectivity, it does not neces￾sarily follow that these conditions are optimized only in well-connected landscapes. Landscape disturbance and fragmentation can increase host abundance and alter host distribution, and these changes can increase connectivity for pathogens and parasites for which the hosts constitute the true “landscape” across which movement occurs (Box 1). However, fragmen￾tation may also lead to the isolation of smaller host subpopulations, which then may become more susceptible to disease or invasions. In other situations, isolation resulting from land￾scape fragmentation may protect a population from disease. For example, plague (Yersinia pestis) in Colorado prairie dog (Cynomys ludovicianus) populations was shown to be less prevalent in more remote, isolated populations than in those more closely grouped together. Measuring, Analyzing and Designing Landscape Connectivity Measuring structural connectivity has increas￾ingly become a routine objective of researchers and policy makers, as Geographic Information Box 1. Habitat Fragmentation and Increased Disease Transmissivity An important consequence of fragmentation in forested habitats is the loss of species diversity. Those species that thrive in fragmented habitats tend to be more generalist or opportunistic, or have traits such as smaller home range require￾ments and tolerance for higher densities. Fragmentation can actually increase connectiv￾ity from the perspective of a disease-causing pathogen. Higher densities of hosts increase opportunities for transmissivity, and the host population is the true “landscape” across which pathogen movement occurs. This is the case for the tick-transmitted bacterium (Borrelia burgdor￾feri) that causes Lyme disease. Its host, the white-footed mouse (Peromyscus leucopus), has become increasingly common in small forest fragments (<2 ha) in New England, likely result￾ing from its small home range requirements combined with release from competitors and predators in smaller forest patches. P. leucopus is the principal natural reservoir for Lyme dis￾ease. Higher densities of ticks infested with B. burgdorferi are found in smaller forest fragments (Figure 1), which may result from higher densities of white-footed mouse in these smaller frag￾ments, presenting more opportunities for ticks to feed on the mice. Consequently, humans living near these small forest fragments may have a higher risk of exposure to Lyme disease relative to those near larger forest fragments. Figure 1. Relationship between measures of Lyme disease risk and forest patch area in a frag￾mented landscape in New York state. a) Density of nymphal ticks is higher in smaller forest fragments. b) Percentage of nymphal ticks infected with the bacterium Borrelia burgdorferi is higher in smaller forest fragments. c) Density of nymphal ticks infected with the B. burgdorferi is higher in smaller forest fragments. (Source: Allan, B.F., F. Keesing, and R.S. Ostfeld. 2003. Effect of forest fragmentation on Lyme disease risk. Conservation Biology. 17: 267–272). Image used with permission of John Wiley and Sons. (a) (b) (c)

ISSUES IN ECOLOGY NUMBER SIXTEEN FALL 2012 System(GIS)and remote sensing tools needs.Thus,recent developments in connec affordable,and ne a s isms can be logistically complicated. with a functional approach that highlights scan rac only rela t requirements controlled experiments addressing movements Modeling Approaches for dispersal at relevant Quantifying may more accurately and efficiently reflect across large emented in a GlS env s of tracking individual animals and inte grate only those mo vements that produce approach has specific data meaning popu tion impacts ispe require input from b s to help C. comine of this anpr isthat current geneti ns may not reflect the impact of current ally for species wit comes. Least-cost analysis identifics the least human perse by past epidemics by oal adaptation.which can drive etic where ost"may reflect the actual energ 0ecradland expended to move over the area,mortality risk cting or impact on A common product of connectiv ity analysis e of habitat.Habitats that the anima hil n D nThe le tion of cells that has the lowest cumulative unique strengths as the path as a pa w popu sistance (an indica of how well a land patch)to the other endpoint. cape can be traversed by a giv species),a can 1 of information about s hahitat nrefer can be lysts lon methods to rig sly n in red in the r anel o -specific resistar om at e which is a swath of cells expected to provide a ow,genetic at use, ow-co r movemen ance.hased on the extent to which land patchesa esults in higher costs.This latte cover,in hay be y ar mpacts measures may be useful for some gen cale of perc ption andh may not be able to cor sider total 1.C ing species-specific movements and so referred to as 6 esa The Ecological Society of America.esahg@esa ora

ISSUES IN ECOLOGY NUMBER SIXTEEN FALL 2012 6 esa © The Ecological Society of America • esahq@esa.org System (GIS) and remote sensing tools become more widely available, affordable, and scalable. However, measuring functional con￾nectivity using the movements of individual organisms can be logistically complicated. Even the largest studies using the most appro￾priate technologies can track only relatively few individuals over modest time periods, and controlled experiments addressing movements and dispersal at relevant scales are extremely difficult to implement. One way to address this difficulty is to measure gene flow, which may more accurately and efficiently reflect functional connectivity across large landscapes. Genetic studies avoid the logistic and financial costs of tracking individual animals and inte￾grate only those movements that produce meaningful population impacts – dispersals that result in breeding or emigration. A short￾coming of this approach is that current genetic patterns may not reflect the impact of current landscape features, especially for species with large population sizes or long generation times, or species affected by unobserved events, such as genetic bottlenecks caused by past epidemics or human persecution. In addition, genetic connectivity may be masked in some instances by local adaptation, which can drive genetic distinctiveness even in a well-connected land￾scape, by selecting for particular characteristics of the local environment. A common product of connectivity analysis is a map of predicted core areas, linkage zones, or barriers. Such maps often become the basis for management actions. Several tools can be used to map these features, and each has unique strengths and weaknesses. All of the approaches described in the next section depend on accurately defining landscape resistance (an indication of how well a land￾scape can be traversed by a given species), a challenging task when only a limited amount of information about species habitat prefer￾ences is available. Furthermore, connectivity models can be difficult to validate. Several research teams are working to develop methods to rigorously estimate species-specific resistance from data on gene flow, genetic distances, habitat use, and movement paths. Simple estimates of resis￾tance, based on the extent to which land￾scapes are impacted by roads, loss of natural land cover, increased edge effects, spread of invasive species, and other direct human impacts measures may be useful for some gen￾eralist species, but are insufficient for address￾ing species-specific movements and habitat needs. Thus, recent developments in connec￾tivity modeling combine a structural land￾scape approach, identifying both the potential for and obstacles to long-term habitat shifts, with a functional approach that highlights the specific connectivity needs of species with restricted habitat requirements. Modeling Approaches for Identifying and Quantifying Landscape Connectivity We describe five widely-used analytical approaches, all implemented in a GIS envi￾ronment, to assist planners in mapping and prioritizing landscape connections. Each approach has specific data requirements that often require input from biologists to help define model parameters. In addition, each approach is designed to meet different objec￾tives and will, therefore, produce different out￾comes. Least-cost analysis identifies the least costly route that an animal can take from one area to another. The method assumes that the animal incurs a cost as it moves over an area, where “cost” may reflect the actual energy expended to move over the area, mortality risk, or impact on future reproductive potential. In practice, cost is usually estimated simply as the inverse of habitat suitability. Habitats that the animal favors are assigned low cost while unsuitable habitats are assigned high cost. The least-cost path is the contiguous collec￾tion of cells that has the lowest cumulative cost as the path crosses from one endpoint (such as a park, natural area, or known popu￾lation; sometimes referred to as a node or patch) to the other endpoint. Computers using GIS software can easily identify this path. Because the least-cost path is only one cell wide (for example, the center panel in Figure 2), it is often not a realistic area to pro￾pose for conservation. Therefore, analysts usu￾ally identify the least-cost corridor (shown in red in the panel on the right in Figure 2), which is a swath of cells expected to provide a low-cost route for movement. Increased distance between two nodes or patches also results in higher costs. This latter assumption is important, in that some species may be able to identify and take advantage of shorter linkages, while others operate at a finer scale of perception and therefore may not be able to consider total corridor length. Correctly assigning these cost values (also referred to as

ISSUES IN ECOLOGY NUMBER SIXTEEN FALL 2012 W2Aeascostpah 50 15 5 717 andscape Defined in Cost Unit Least-Cost Pat Least-Cost Corridor resistance or permeability values)is the mo poorly-connected habitat patches problematic a of least-cost analysis and the might ha constrictions and bottlenecks, factorial least cost paths address one Current maps (Figure 4)can be a useful major limitation of traditional least-cost path way to visualize a circuit-theoretic analysis lyses in that they en single sources and single destinations or habitat patches.Current maps can be diffi in west cost route ctonepibieherure nay occur in a ce require a more comprehensive analysis of con are forced through that area because of high nectivity.For example,co elsewhere. may need to s spa all d n blue) hundreds of sources and hundreds of destina may imply either high resistance in the underlying layer,or simply that many e there are y go inte ae move network of connectivity ac ss large and com- oximate how organisms m scapes,suck torial least-cos analysis among paths are shown in a gradient from yellow to ng paths with the servation action.In Figure 4a,where the rce areas (green points on among least Circuit the the lands cells in the landscape can support movement en this and other m nat whi tional processing),they are most useful in ana be.gi connecred habitat parches have wide.contin uous habitat between them,while paths The Ecological Society of America.esahg@esa.oro esa 7

© The Ecological Society of America • esahq@esa.org esa 7 ISSUES IN ECOLOGY NUMBER SIXTEEN FALL 2012 resistance or permeability values) is the most problematic aspect of least-cost analysis and the other approaches described here. Factorial least-cost paths address one major limitation of traditional least-cost path and least-cost corridor analyses in that they are limited to predictions of connectivity between single sources and single destinations. While this may be ideal in the case where one is interested in the lowest cost routes between two focal conservation areas, many situations require a more comprehensive analysis of con￾nectivity. For example, corridor connectivity may need to be calculated between thousands of sources and a single destination, or between hundreds of sources and hundreds of destina￾tions distributed across a complex landscape. A factorial implementation of least-cost paths integrates a vast number of paths to show a network of connectivity across large and com￾plex landscapes, such as a factorial least-cost path analysis among hundreds of points across a resistance surface (Figure 3). Densities of paths are shown in a gradient from yellow to red, with red paths representing routes that are predicted to contain the least-cost paths between many pairs of source and destination points. Additionally, while factorial approaches are most common among least￾cost approaches, they can also be integrated into graph and circuit analysis as well. Circuit theory treats the landscape as if it were a large electrical circuit, in which all cells in the landscape can support movement. An important distinction between this and other methods is that while circuit approaches can be used to delineate corridors (with addi￾tional processing), they are most useful in ana￾lyzing and describing how well connected source and destination habitat patches may be, given multiple movement pathways. Well￾connected habitat patches have wide, contin￾uous habitat between them, while paths between poorly-connected habitat patches might have constrictions and bottlenecks, each of which can be identified using a circuit based approach. Current maps (Figure 4) can be a useful way to visualize a circuit-theoretic analysis. Current strength reflects the predicted proba￾bility of movement between the two points or habitat patches. Current maps can be diffi￾cult to interpret: higher current (usually depicted in yellow) may occur in a cell because resistance is low, because most paths are forced through that area because of high resistance elsewhere, or because the analysis is spatially constrained (Figure 4a). Lower current (usually depicted in blue), in turn, may imply either high resistance in the underlying layer, or simply that there are many equally good alternate paths for move￾ment. In this way, circuit models may more accurately approximate how organisms move through real landscapes. Despite their rela￾tive complexity, these maps are useful for evaluating connectivity and identifying con￾strained areas (bottlenecks) for possible con￾servation action. In Figure 4a, where the Figure 2. A least cost path analysis. Figure 3. A factorial least-cost path analysis, evaluating least￾cost paths (lines in blue to red, with red showing paths with the lowest costs) among many source areas (green points)

ISSUES IN ECOLOGY NUMBER SIXTEEN FALL 2012 Current High es. of these patches as points o connec instance by evaluating how r many potentia connection rely on each r node or edge.Thi pproac when mo laees of patches.parks.or). Figure 4.Current maps reserve sets within the c curre landscape,evaluaing into a narrow space.In Figure 4b,where the of los ot c areas have higher surrent due to lower resis TheesistakceeP oach to con The Graph theory combined with least-cost habitat patches modeling or circuit theory provides several persing individua in the of the other sround 拉eee cach has a numbe of adv ntages for assesing population co e me predictio tion and mapping of expected migration rates I in the st 8 esa The Ecological Society of Americaesahq@esa.org

ISSUES IN ECOLOGY NUMBER SIXTEEN FALL 2012 8 esa © The Ecological Society of America • esahq@esa.org model was confined to a particular habitat corridor, high current values clearly indicate a bottleneck where movement is funneled into a narrow space. In Figure 4b, where the analysis was conducted in a different land￾scape and not constrained to a corridor, few major bottlenecks are apparent but some areas have higher current due to lower resis￾tance or proximity to the nearest edges of the habitat patches, which are shown in beige. Graph theory combined with least-cost modeling or circuit theory provides several useful enhancements to landscape connectiv￾ity assessment and modeling. The landscape itself can be likened to an interlaced web or network that is composed of habitat patches (graph theory modeling uses centers, or “nodes,” of these patches as points of connec￾tion) and the connections between these patches (the linear representations of which are described in graph theory language as “edges”) (Figure 5). Once identified, nodes and edges can be prioritized based on their overall contribution to the landscape network, for instance by evaluating how many potential connections rely on each node or edge. This approach allows for multiple least-cost path￾ways to be evaluated for their contribution to the configuration of the overall network. This approach is particularly useful when modeling connectivity between large reserve sets (assem￾blages of patches, parks, or protected areas), identifying isolated reserve sets within the con￾text of the modeled landscape, evaluating the robustness of multiple connections within the landscape network, node/connection prioritiza￾tion, and evaluating the consequences of los￾ing nodes due to competing factors such as development pressure or fiscal constraints. The resistant kernel approach to con￾nectivity modeling is based on least-cost dis￾persal from a defined set of sources. The model calculates the expected relative density of dis￾persing individuals in each cell around the source, given the dispersal ability of the species, the nature of the dispersal function, and the resistance of the landscape. Once the expected density around each source cell (the smallest unit of space that is modeled contain￾ing individuals dispersing to other parts, or cells, in the landscape) is calculated, the ker￾nels surrounding all sources are summed to give the total expected density at each cell. The results of the model are surfaces of expected density of dispersing organisms at any location in the landscape, in contrast to the physical delineation of linkages or corridors. The resistant kernel approach has a number of advantages for assessing population connec￾tivity. First, unlike most corridor prediction efforts, but similar to circuit-based approaches, it is spatially comprehensive, provides predic￾tion and mapping of expected migration rates for every cell in the study area extent, and can do so for large geographic extents rather than only for a few selected linkage zones. Second, this approach allows assessment of how species with different movement patterns and disper￾Figure 4. Current maps, illustrating a) a landscape where analysis was confined to a corridor and b) a different landscape where the analysis was not confined to a corridor. Figure 5. A graph theory model depicting connectivity between habitat patches. (a) (b)

ISSUES IN ECOLOGY NUMBER SIXTEEN FALL 2012 sal abilities are affected by a range of land- coarse to inform specific conservation action Figu not identify Connectivity.Two Countries-One Forest (Cas and utan a)a single r Comp cumulative resistant kemnel surface created analysis and mapping are the identification and delineation of core as are ed to have rom th while blue areas are predicted to experience mining which pairs or set of blocks can feasib Case Stdy 2 provide be connected in a way that promotes functional an exam in aAamphibanpophtioms tions (or lin among t Design eory,or indi Finer-grained linkage designs can guide site which connecti ty is eco conserve connectivity g ider the a bo In raac ss the landscape. sign plans. ape mea ive maps (thou by le tion (for the hundreds of meter Califomia (South Coast Miss ject,ava t www serve as decision-support tools for managers,or ccoridorndcsNgm.orgasdcsigneig provide a high-leve ision of landscape co al species includ. They may meet the needs of severalf ervation opportunities pecies,specics with short or habitat However,these types of maps are often too restricted dispersal movements,and species The Ecological Society of Americaesahq@esa.org esa 9

© The Ecological Society of America • esahq@esa.org esa 9 ISSUES IN ECOLOGY NUMBER SIXTEEN FALL 2012 sal abilities are affected by a range of land￾scape change and fragmentation scenarios. This approach is useful for characterizing con￾nectivity across continuous surfaces but does not identify individual linkages or corridors without additional analyses. Figure 6 shows an individual resistant kernel around a) a single source cell and b) the cumulative resistant kernel surface created from summing all individual kernels for all habitat cells. Red areas are predicted to have high frequency of occupancy by dispersers, while blue areas are predicted to experience low rates of dispersal. Case Study 2 provides an example of the use of the resistant kernel approach in evaluating fragmenting effects of roads on amphibian populations. Considering Resolution and Focus in Connectivity Design The resolution at which connectivity is ecolog￾ically meaningful varies enormously, depending on the species in question. For example, con￾sider the scale of connectivity relevant to a bee￾tle versus a bison. In practice, we tend to design and plan for connectivity at a human scale, meaning that we visualize connectivity in terms of landscape management units in a policy framework. Spatially extensive maps (thou￾sands of kilometers), with coarse grained resolu￾tion (for example, in the hundreds of meters per pixel or measurement unit) can depict a network of numerous habitat blocks and the connections among them. Such maps may serve as decision-support tools for managers, or provide a high-level vision of landscape con￾nectivity. They may be used to alert decision￾makers to potential threats to large-scale con￾nectivity as well as conservation opportunities. However, these types of maps are often too coarse to inform specific conservation action plans. Examples include the Yellowstone to Yukon initiative, Arizona Wildlife Linkage Assessment, California Essential Habitat Connectivity, Two Countries-One Forest (Case Study 3), Washington Connected Landscapes, and the Bhutan Biological Corridor Complex. The two largest challenges for coarse-grained analysis and mapping are the identification and delineation of core habitat blocks (areas whose conservation value derives from the species and ecological processes within them) and deter￾mining which pairs or sets of blocks can feasibly be connected in a way that promotes functional connectivity and meets conservation goals. Once habitat blocks have been identified, vari￾ous techniques may be used to map the connec￾tions (or linkages) among them, including least-cost path analysis, graph theory, or indi￾vidual-based movement models. Finer-grained linkage designs can guide site￾specific actions to conserve connectivity between specific habitat areas that are rele￾vant to the distances and ways in which species of interest move across the landscape. To develop maps for these plans, landscape connectivity planners typically select a suite of focal species and use the union of their corri￾dors or movement pathways (usually produced by least-cost modeling) to serve as a prelimi￾nary linkage design for the entire biota. For instance, each of the 27 linkage plans in California (South Coast Missing Linkages pro￾ject, available at www.scwildlands.org) and Arizona (the Arizona Missing Linkages pro￾ject, www.corridordesign.org) was designed to meet the needs of several focal species includ￾ing mammals, reptiles, amphibians, plants, and invertebrates. Focal species included area￾sensitive species, species with short or habitat￾restricted dispersal movements, and species Figure 6. Resistance kernel modeling: a) single-kernel analysis and b) the cumulative resistance surface of all kernels across the landscape. (a) (b)