Landscape connectivity

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In landscape ecology, landscape connectivity is, broadly, "the degree to which the landscape facilitates or impedes movement among resource patches". [1] Alternatively, connectivity may be a continuous property of the landscape and independent of patches and paths. [2] [3] Connectivity includes both structural connectivity (the physical arrangements of disturbance and/or patches) and functional connectivity (the movement of individuals across contours of disturbance and/or among patches). [4] [5] Functional connectivity includes actual connectivity (requires observations of individual movements) and potential connectivity in which movement paths are estimated using the life-history data. [6]

Contents

A similar but different concept proposed by Jacques Baudry, landscape connectedness, refers to structural links between elements of spatial structures of a landscape, which concerns the topology of landscape features and not ecological processes. [7]

Definition

The concept of "landscape connectivity" was first introduced by Dr. Gray Merriam in 1984. Merriam noted that movement among habitat patches was not merely a function of an organism's attributes, but also, a quality of the landscape elements through which it must move. [8] To emphasize this fundamental interaction in determining a particular movement pathway, Merriam (1984), defined landscape connectivity as "the degree to which absolute isolation is prevented by landscape elements which allow organisms to move among habitat patches." [9] Nine years later, Merriam and colleagues, revised the definition to "the degree to which the landscape impedes or facilitates movement among resource patches. [1] Although this definition has undoubtedly become the most accepted and cited meaning within the scientific literature, many authors have continued to create their own definitions. With et al (1997), presented their interpretation as "the functional relationship among habitat patches, owing to the spatial contagion of habitat and the movement responses of organisms to landscape structure", [10] and Ament et al. (2014) defined it as "the degree to which regional landscapes, encompassing a variety of natural, semi-natural, and developed land cover types, are conducive to wildlife movement and to sustain ecological processes." [11] Thus, although there have been many definitions of landscape connectivity over the past 30 years, each new description emphasizes both a structural and a behavioural element to the landscape connectivity concept. The physical component is defined by the spatial and temporal configuration of the landscape elements (landform, landcover and land use types), and the behavioural component is defined by the behavioural responses, of organisms and/or processes, to the physical arrangement of the landscape elements. [12] [13] [8]

Importance

Habitat loss and habitat fragmentation have become ubiquitous in both natural and human modified landscapes, resulting in detrimental consequences for local species interactions and global biodiversity. [14] Human development now modifies over 50% of the earth's landscape, leaving only patches of isolated natural or semi-natural habitats for the millions of other species we share this planet with. [15] Loss of natural habitat and fluctuations in landscape patterns is one of the many problems in biogeography and conservation biology. [16] Patterns of biodiversity and ecosystem functions are changing worldwide resulting in a loss of connectivity and ecological integrity for the entire global ecological network. [17] Loss of connectivity can influence individuals, populations and communities through within species, between species, and between ecosystem interactions. These interactions affect ecological mechanisms such as nutrient and energy flows, predator-prey relationships, pollination, seed dispersal, demographic rescue, inbreeding avoidance, colonization of unoccupied habitat, altered species interactions, and spread of disease. [18] [19] [20] Accordingly, landscape connectivity facilitates the movement of biotic processes such as animal movement, plant propagation, and genetic exchange, as well as abiotic processes such as water, energy, and material movement within and between ecosystems. [11]

Types of animal movement

Daily movements

Within their home range or territory most animals must move daily among multiple primary habitat patches to forage for food and obtain all the resources they need. [11]

Migration

Some species travel to different locations throughout the year to access the resources they need. These movements are usually predictable and are due to changes in the environmental conditions at the primary habitat site, or to facilitate access to breeding grounds. [11] Migratory behaviour is seen in land animals, [21] birds [22] and marine species, [23] and the routes they follow are usually the same year after year. [11]

Dispersal

Is the once in a lifetime movement of certain individuals from one population to another for the purpose of breeding. [24] These exchanges maintain genetic and demographic diversity among populations. [25]

Disturbance movement

Is the unpredictable movement of individuals or populations to new locations of suitable habitat due to an environmental disturbance. Major disturbances such as fire, natural disasters, human development, and climate change can impact the quality and distribution of habitats and necessitate the movement of species to new locations of suitable habitat. [11]

Incidental movement

Movement of species in areas that are typically used by humans. These include greenbelts, recreational trail systems, hedgerows, and golf courses. [11]

Connectivity conservation

Preserving or creating landscape connectivity has become increasingly recognized as a key strategy to protect biodiversity, maintain viable ecosystems and wildlife populations, and facilitate the movement and adaptation of wildlife populations in the face of climate change. [26] The degree to which landscapes are connected determines the overall amount of movement taking place within and between local populations. This connectivity has influences on gene flow, local adaptation, extinction risk, colonization probability, and the potential for organisms to move and adapt to climate change. [11] [27] [28] With habitat loss and fragmentation increasingly deteriorating natural habitats, the sizes and isolation of the remaining habitat fragments are particularly critical to the long-term conservation of biodiversity. [11]

Thus, connectivity among these remaining fragments, as well as the characteristics of the surrounding matrix, and the permeability and structure of the habitat edges are all important for biodiversity conservation and affect the overall persistence, strength and integrity of the remaining ecological interactions. [29]

Quantifying landscape connectivity

Since the definition of landscape connectivity has both a physical and a behavioural component, quantifying landscape connectivity is consequently organism-, process- and landscape-specific. [1] According to (Wiens & Milne, 1989), the first step in the quantification process of landscape connectivity is defining the specific habitat or habitat network of the focal species, and in turn, describe the landscape elements from its point of view. [30] The next step is to determine the scale of the landscape structure as perceived by the organism. This is defined as the scale at which the species responds to the array of landscape elements, through its fine-scale (grain), and large-scale (extent), movement behaviours. [31] Lastly, how the species responds to the different elements of a landscape is determined. This comprises the species' movement pattern based on behavioural reactions to the mortality risk of the landscape elements, including habitat barriers and edges. [8]

Landscape networks can be constructed based on the linear relationship between a species home range size and its dispersal distance. [32] For example, small mammals will have a small range and short dispersal distances and large ones will have larger range and long dispersal distances. In short this relationship can help in scaling & constructing landscape networks based on a mammals body size. [33]

For many organisms, particularly marine invertebrates, the scale of connectivity (usually in the form of larval dispersal) is driven by passive transport through ocean currents. [34] Dispersal potential tends to be considerably higher in water than air due its higher density (and therefore higher buoyancy of propagules). [35] It is therefore sometimes possible to quantify potential connectivity for marine organisms through process-based models such as larval dispersal simulations. [36]

Connectivity metrics

Although connectivity is an intuitive concept, there is no single consistently-used metric of connectivity. Theories of connectivity include consideration of both binary representations of connectivity through "corridors" and "linkages" and continuous representations of connectivity, which include the binary condition as a sub-set [2] [3]

Generally, connectivity metrics fall into three categories: [37]

  1. Structural connectivity metrics are based on the physical properties of landscapes, which includes the idea of patches (size, number of patches, average distance to each other) and relative disturbance (human structures such as roads, parcellization, urban/agricultural land-use, human population).
  2. Potential connectivity metrics are based on the landscape structure as well as some basic information about the study organism's dispersal ability such as average dispersal distance, or dispersal kernel.
  3. Actual (also called realized, or functional) connectivity metrics are measured based on the actual movements of individuals along and across contours of connectivity, including among patches (where these exist). This takes into account the actual number of individuals born at different sites, their reproduction rates, and mortality during dispersal. [38] Some authors make a further distinction based on the number of individuals that not only disperse between sites, but that also survive to reproduce. [39]

Data structures

Connectivity can usually be described as a graph or network, i.e. a set of nodes (possibly representing discrete populations or sampling sites) connected by edges (describing the presence or strength of connectivity). [40] Depending on the type of connectivity being described, this could range from a simple undirected and unweighted graph (with edges perhaps representing the presence or absence of a shared species), to a directed, weighted, layered or temporal graph (with edges perhaps representing flows of individuals through time). Representing connectivity as a graph is often useful, both for data visualisation purposes, and analyses. For instance, graph theory algorithms are often used to identify central populations that maintain connectivity (betweenness centrality), [41] or clusters of populations with strong intra-connectivity and weak inter-connectivity (modularity optimization). [42]

Various data structures exist for storing and operating on graph data. [43] Of particular note are array representations, often called connectivity matrices for two-dimensional arrays (as is usually the case for graphs without temporal variability). For example, the time-mean potential connectivity between a set of populations could be represented as a matrix , with each element giving the dispersal ability from population to population . [44] Many ecological models rely on this matrix representation. For instance, the matrix product may represent the likelihood of dispersal from population to population over steps of dispersal and, when combined with other demographic processes, the eigenvalues of may represent the metapopulation growth rate. [45]

Software

Typically, the "natural" form of connectivity as an ecological property perceived by organisms is modeled as a continuous surface of permeability, which is the corollary to disturbance. This can be accomplished by most geographic information systems (GIS) able to model in grid/raster format. A critical component of this form of modeling is the recognition that connectivity and disturbance are perceived and responded to differently by different organisms and ecological processes. This variety in responses is one of the most challenging parts of attempting to represent connectivity in spatial modeling. Typically, the most accurate connectivity models are for single species/processes and are developed based on information about the species/process. [46] There is little, and often no evidence that spatial models, including those described here, can represent connectivity for the many species or processes that occupy many natural landscapes. The disturbance-based models are used as the basis for the binary representations of connectivity as paths/corridor/linkages through landscapes described below.

Circuitscape

Circuitscape is an open source program that uses circuit theory to predict connectivity in heterogeneous landscapes for individual movement, gene flow, and conservation planning. Circuit theory offers several advantages over common analytic connectivity models, including a theoretical basis in random walk theory and an ability to evaluate contributions of multiple dispersal pathways. Landscapes are represented as conductive surfaces, with low resistances assigned to habitats that are most permeable to movement or best promote gene flow, and high resistances assigned to poor dispersal habitat or to movement barriers. Effective resistances, current densities, and voltages calculated across the landscapes can then be related to ecological processes, such as individual movement and gene flow. [47]

Graphab

Graphab is a software application devoted to the modelling of landscape networks. It is composed of four main modules: graph building, including loading the initial landscape data and identification of the patches and the links; computation of the connectivity metrics from the graph; connection between the graph and exogenous point data set; visual and cartographical interface. Graphab runs on any computer supporting Java 1.6 or later (PC under Linux, Windows, Mac...). It is distributed free of charge for non-commercial use. [48]

See also

Related Research Articles

<span class="mw-page-title-main">Ecology</span> Study of organisms and their environment

Ecology is the natural science of the relationships among living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overlaps with the closely related sciences of biogeography, evolutionary biology, genetics, ethology, and natural history.

<span class="mw-page-title-main">Theoretical ecology</span>

Theoretical ecology is the scientific discipline devoted to the study of ecological systems using theoretical methods such as simple conceptual models, mathematical models, computational simulations, and advanced data analysis. Effective models improve understanding of the natural world by revealing how the dynamics of species populations are often based on fundamental biological conditions and processes. Further, the field aims to unify a diverse range of empirical observations by assuming that common, mechanistic processes generate observable phenomena across species and ecological environments. Based on biologically realistic assumptions, theoretical ecologists are able to uncover novel, non-intuitive insights about natural processes. Theoretical results are often verified by empirical and observational studies, revealing the power of theoretical methods in both predicting and understanding the noisy, diverse biological world.

<span class="mw-page-title-main">Landscape ecology</span> Science of relationships between ecological processes in the environment and particular ecosystems

Landscape ecology is the science of studying and improving relationships between ecological processes in the environment and particular ecosystems. This is done within a variety of landscape scales, development spatial patterns, and organizational levels of research and policy. Concisely, landscape ecology can be described as the science of "landscape diversity" as the synergetic result of biodiversity and geodiversity.

<span class="mw-page-title-main">Urban ecology</span> Scientific study of living organisms

Urban ecology is the scientific study of the relation of living organisms with each other and their surroundings in an urban environment. An urban environment refers to environments dominated by high-density residential and commercial buildings, paved surfaces, and other urban-related factors that create a unique landscape. The goal of urban ecology is to achieve a balance between human culture and the natural environment.

<span class="mw-page-title-main">Biological dispersal</span> Movement of individuals from their birth site to a breeding site

Biological dispersal refers to both the movement of individuals from their birth site to their breeding site, as well as the movement from one breeding site to another . Dispersal is also used to describe the movement of propagules such as seeds and spores. Technically, dispersal is defined as any movement that has the potential to lead to gene flow. The act of dispersal involves three phases: departure, transfer, settlement and there are different fitness costs and benefits associated with each of these phases. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population genetics, and species distribution. Understanding dispersal and the consequences both for evolutionary strategies at a species level, and for processes at an ecosystem level, requires understanding on the type of dispersal, the dispersal range of a given species, and the dispersal mechanisms involved. Biological dispersal can be correlated to population density. The range of variations of a species' location determines expansion range.

<span class="mw-page-title-main">Ecosystem engineer</span> Ecological niche

An ecosystem engineer is any species that creates, significantly modifies, maintains or destroys a habitat. These organisms can have a large impact on species richness and landscape-level heterogeneity of an area. As a result, ecosystem engineers are important for maintaining the health and stability of the environment they are living in. Since all organisms impact the environment they live in one way or another, it has been proposed that the term "ecosystem engineers" be used only for keystone species whose behavior very strongly affects other organisms.

<span class="mw-page-title-main">Population ecology</span> Study of the dynamics of species populations and how these populations interact with the environment

Population ecology is a sub-field of ecology that deals with the dynamics of species populations and how these populations interact with the environment, such as birth and death rates, and by immigration and emigration.

<span class="mw-page-title-main">Habitat fragmentation</span> Discontinuities in an organisms environment causing population fragmentation.

Habitat fragmentation describes the emergence of discontinuities (fragmentation) in an organism's preferred environment (habitat), causing population fragmentation and ecosystem decay. Causes of habitat fragmentation include geological processes that slowly alter the layout of the physical environment, and human activity such as land conversion, which can alter the environment much faster and causes the extinction of many species. More specifically, habitat fragmentation is a process by which large and contiguous habitats get divided into smaller, isolated patches of habitats.

<span class="mw-page-title-main">Metapopulation</span> Group of separated yet interacting ecological populations

A metapopulation consists of a group of spatially separated populations of the same species which interact at some level. The term metapopulation was coined by Richard Levins in 1969 to describe a model of population dynamics of insect pests in agricultural fields, but the idea has been most broadly applied to species in naturally or artificially fragmented habitats. In Levins' own words, it consists of "a population of populations".

<span class="mw-page-title-main">Intermediate disturbance hypothesis</span> Model proposing regional biodiversity is increased by a moderate level of ecological disturbance

The intermediate disturbance hypothesis (IDH) suggests that local species diversity is maximized when ecological disturbance is neither too rare nor too frequent. At low levels of disturbance, more competitive organisms will push subordinate species to extinction and dominate the ecosystem. At high levels of disturbance, due to frequent forest fires or human impacts like deforestation, all species are at risk of going extinct. According to IDH theory, at intermediate levels of disturbance, diversity is thus maximized because species that thrive at both early and late successional stages can coexist. IDH is a nonequilibrium model used to describe the relationship between disturbance and species diversity. IDH is based on the following premises: First, ecological disturbances have major effects on species richness within the area of disturbance. Second, interspecific competition results in one species driving a competitor to extinction and becoming dominant in the ecosystem. Third, moderate ecological scale disturbances prevent interspecific competition.

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<span class="mw-page-title-main">Community (ecology)</span> Associated populations of species in a given area

In ecology, a community is a group or association of populations of two or more different species occupying the same geographical area at the same time, also known as a biocoenosis, biotic community, biological community, ecological community, or life assemblage. The term community has a variety of uses. In its simplest form it refers to groups of organisms in a specific place or time, for example, "the fish community of Lake Ontario before industrialization".

Source–sink dynamics is a theoretical model used by ecologists to describe how variation in habitat quality may affect the population growth or decline of organisms.

<span class="mw-page-title-main">Cross-boundary subsidy</span>

Cross-boundary subsidies are caused by organisms or materials that cross or traverse habitat patch boundaries, subsidizing the resident populations. The transferred organisms and materials may provide additional predators, prey, or nutrients to resident species, which can affect community and food web structure. Cross-boundary subsidies of materials and organisms occur in landscapes composed of different habitat patch types, and so depend on characteristics of those patches and on the boundaries in between them. Human alteration of the landscape, primarily through fragmentation, has the potential to alter important cross-boundary subsidies to increasingly isolated habitat patches. Understanding how processes that occur outside of habitat patches can affect populations within them may be important to habitat management.

<span class="mw-page-title-main">Wildlife corridor</span> Connecting wild territories for animals

A wildlife corridor, habitat corridor, or green corridor is an area of habitat connecting wildlife populations separated by human activities or structures. This allows an exchange of individuals between populations, which may help prevent the negative effects of inbreeding and reduced genetic diversity that often occur within isolated populations. Corridors may also help facilitate the re-establishment of populations that have been reduced or eliminated due to random events. This may moderate some of the worst effects of habitat fragmentation, whereas urbanization can split up habitat areas, causing animals to lose both their natural habitat and the ability to move between regions to access resources. Habitat fragmentation due to human development is an ever-increasing threat to biodiversity, and habitat corridors serve to manage its effects.

Patch dynamics is an ecological perspective that the structure, function, and dynamics of ecological systems can be understood through studying their interactive patches. Patch dynamics, as a term, may also refer to the spatiotemporal changes within and among patches that make up a landscape. Patch dynamics is ubiquitous in terrestrial and aquatic systems across organizational levels and spatial scales. From a patch dynamics perspective, populations, communities, ecosystems, and landscapes may all be studied effectively as mosaics of patches that differ in size, shape, composition, history, and boundary characteristics.

Ecological traps are scenarios in which rapid environmental change leads organisms to prefer to settle in poor-quality habitats. The concept stems from the idea that organisms that are actively selecting habitat must rely on environmental cues to help them identify high-quality habitat. If either the habitat quality or the cue changes so that one does not reliably indicate the other, organisms may be lured into poor-quality habitat.

Seascape ecology is a scientific discipline that deals with the causes and ecological consequences of spatial pattern in the marine environment, drawing heavily on conceptual and analytical frameworks developed in terrestrial landscape ecology.

<span class="mw-page-title-main">Landscape genetics</span> Combination of population genetics and landscape ecology

Landscape genetics is the scientific discipline that combines population genetics and landscape ecology. It broadly encompasses any study that analyses plant or animal population genetic data in conjunction with data on the landscape features and matrix quality where the sampled population lives. This allows for the analysis of microevolutionary processes affecting the species in light of landscape spatial patterns, providing a more realistic view of how populations interact with their environments. Landscape genetics attempts to determine which landscape features are barriers to dispersal and gene flow, how human-induced landscape changes affect the evolution of populations, the source-sink dynamics of a given population, and how diseases or invasive species spread across landscapes.

<span class="mw-page-title-main">Lenore Fahrig</span> Biologist

Lenore Fahrig is a Chancellor's Professor in the biology department at Carleton University, Canada and a Fellow of the Royal Society of Canada. Fahrig studies effects of landscape structure—the arrangement of forests, wetlands, roads, cities, and farmland—on wildlife populations and biodiversity, and is best known for her work on habitat fragmentation. In 2023, she was elected to the National Academy of Sciences.

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