In landscape ecology, landscape connectivity refers to how well a landscape helps or stops movement between areas that have resources. Another way to think about connectivity is as a feature of the whole landscape, not just specific areas or paths. Connectivity has two parts: structural connectivity, which is how parts of the landscape are physically arranged, and functional connectivity, which is how individuals move across areas affected by disturbances or between different patches. Functional connectivity includes actual connectivity, which is based on observations of real movements, and potential connectivity, which is estimated using information about how organisms live and move.
A related but different idea, called landscape connectedness, was introduced by Jacques Baudry. It focuses on how elements of a landscape's structure are linked, such as the arrangement of landscape features. This concept is about the shape and connections of landscape parts, not about how ecological processes, like animal movement, work.
Definition
The idea of "landscape connectivity" was first explained by Dr. Gray Merriam in 1984. Merriam observed that how animals move between areas depends not only on the animals themselves but also on the landscape around them. To highlight this important connection, Merriam (1984) described landscape connectivity as "how much the landscape prevents complete separation by allowing animals to move between areas where they live." In 1993, Merriam and others updated the definition to "how much the landscape makes it easier or harder for animals to move between areas with resources." This definition is now the most widely used and referenced in scientific studies, but many researchers have created their own versions. With et al. (1997) described it as "how habitat areas are connected based on how habitats are spread out and how animals respond to the landscape's structure." Ament et al. (2014) defined it as "how well landscapes with different types of land, such as natural areas, partially natural areas, and developed areas, support animal movement and natural processes." Over the past 30 years, many definitions of landscape connectivity have been proposed. Each one focuses on two main parts: the physical structure of the landscape and how animals or natural processes react to that structure. The physical part is determined by how land features, such as landforms, land types, and how land is used, are arranged over time and space. The behavioral part is determined by how animals or natural processes respond to how the landscape is arranged.
Importance
Habitat loss and habitat fragmentation are now common in both natural areas and places changed by humans. These changes harm how species interact locally and affect biodiversity worldwide. Human activities now change more than half of Earth's land, leaving only small, separated areas of natural or semi-natural habitats for the many other species that live here. Losing natural habitats and changes in how landscapes are arranged are major issues in the study of where species live and how to protect them. Biodiversity and how ecosystems function are changing around the world, which harms the connections and health of the global ecological system. Losing these connections can affect individuals, groups of animals, and entire communities by changing how species interact with each other and with ecosystems. These changes influence processes like the movement of nutrients and energy, predator-prey relationships, pollination, seed spreading, population recovery, avoiding inbreeding, moving into new areas, changes in how species relate to one another, and the spread of diseases. As a result, connecting landscapes helps support the movement of living processes, such as animal movement, plant growth, and the sharing of genes, as well as non-living processes like the movement of water, energy, and materials within and between ecosystems.
Types of animal movement
Many animals live in a specific area called their home range. To find food and other needed resources, they often move daily between different parts of this area.
Some animals travel to new places during different times of the year to find the resources they need. These trips usually happen in the same way each year and are caused by changes in their environment or the need to reach areas where they can breed. This type of movement, called migration, happens in animals, birds, and sea creatures. The paths they take are often the same each year.
Sometimes, individual animals move from one group to another to breed. This movement helps keep the groups genetically and demographically diverse.
When big changes, such as fires, natural disasters, human activities, or climate changes, harm their habitat, animals may move to new areas where conditions are better. These moves are not planned and happen because their old homes are no longer suitable.
Some animals live in areas that humans use, such as parks, trails, fences, and golf courses. These places are often part of their habitat.
Connectivity conservation
Preserving or creating connections between different areas of land has become an important method to protect wildlife, keep ecosystems healthy, and help animals move and adapt to changes in the environment. How well connected these areas are affects how much animals can move between groups living in different places. This connection influences how genes are shared between groups, how well animals can adjust to their environment, the chance that species might disappear, the possibility of new species moving into an area, and the ability of animals to survive and change as the climate changes. As natural habitats are lost and broken into smaller pieces, the size and how separated these pieces are become very important for keeping wildlife and ecosystems safe over time.
Therefore, the links between these smaller habitat areas, the features of the land around them, and how easy it is for animals to move through the edges of these areas all play a role in protecting wildlife. These factors also affect how long ecosystems can remain stable, how strong their relationships are, and how well they can continue to function.
Quantifying landscape connectivity
Landscape connectivity includes both physical features and how animals interact with their environment. Measuring landscape connectivity depends on the animal, the process being studied, and the specific landscape. According to Wiens and Milne (1989), the first step in measuring connectivity is identifying the habitat or network of the species being studied and describing the landscape from its perspective. Next, the scale of the landscape must be determined based on how the species perceives it. This scale includes how the animal moves at small distances (grain) and across larger areas (extent). Finally, scientists study how the species reacts to different parts of the landscape, such as how it avoids dangers like habitat barriers or edges.
Landscape networks can be created by linking the size of an animal's home range to how far it moves. For example, small mammals have small home ranges and short movement distances, while larger mammals have larger ranges and longer movement distances. This relationship helps scientists create and scale landscape networks based on an animal's body size.
For many animals, especially marine invertebrates, connectivity is often determined by the movement of larvae carried by ocean currents. Dispersal is more common in water than in air because water is denser, allowing larvae to float more easily. Scientists can sometimes measure connectivity for marine animals using models that simulate larval movement.
Connectivity metrics
Connectivity is a basic idea, but there is no one clear way to measure it. Scientists use different ways to describe connectivity. Some methods use simple yes-or-no ideas, like "corridors" or "linkages," while others use more detailed, continuous methods that include the yes-or-no ideas as part of their descriptions.
Connectivity measurements are usually divided into three groups:
- Structural connectivity looks at the physical features of a landscape, such as the size of areas, the number of areas, and how far apart they are. It also considers how human activities, like roads or cities, affect the environment.
- Potential connectivity considers the structure of the landscape and basic information about how animals or plants move, such as how far they can travel or how likely they are to move in certain directions.
- Actual connectivity (also called realized or functional connectivity) measures the real movement of living things between areas. This includes how many individuals are born in different places, how many survive, and how many reproduce after moving. Some scientists further divide this based on how many individuals not only move between areas but also survive to have offspring.
Connectivity is often shown as a graph or network. A graph has points (called nodes) that might represent groups of animals or places where samples are taken. These points are connected by lines (called edges) that show how strongly or weakly they are connected. The type of graph used depends on what is being studied. For example, a simple graph might only show whether a species is present in two areas, while a more complex graph might show directions, strengths, or changes over time. Using graphs helps scientists visualize data and perform calculations, such as finding which groups are most important for keeping populations connected or identifying groups that are closely connected within themselves but not with others.
There are many ways to store and use graph data. One common method is using a matrix, which is a table of numbers. For example, a matrix might show how likely animals are to move from one group to another. These matrices are used in many ecological models. For instance, multiplying the numbers in the matrix can show the chance of movement between groups over several steps, and special calculations from the matrix can help predict how quickly populations might grow or shrink.
Software
Connectivity in ecosystems is often modeled as a smooth surface showing how easy it is to move through different areas. This surface is related to disturbances, such as fires or human activities. Geographic information systems (GIS) can create these models using grid or raster formats. A key part of this method is understanding that different organisms and ecological processes see and react to connectivity and disturbances in different ways. This variety makes it difficult to create accurate models that apply to many species or processes. Most precise models focus on a single species or process, using specific information about that species or process. There is little evidence that these models can accurately represent connectivity for all species and processes in natural landscapes. Disturbance-based models form the basis for binary representations of connectivity, such as paths, corridors, or linkages through landscapes.
Circuitscape is a free program that uses circuit theory to predict how connected habitats are in diverse landscapes. It helps study individual movement, gene flow, and conservation planning. Circuit theory has advantages over other models, such as its foundation in random walk theory and its ability to consider multiple movement paths. Landscapes are shown as conductive surfaces, where areas with low resistance represent habitats that are easy to move through or support gene flow, and areas with high resistance represent barriers or poor habitats. Calculations of effective resistance, current density, and voltage across these surfaces can be linked to ecological processes like movement and gene flow.
Graphab is a software tool used to model landscape networks. It has four main parts: building a network map by loading landscape data and identifying patches and links; calculating connectivity metrics from the network; connecting the network to outside data points; and providing a visual and map-based interface. Graphab works on computers with Java 1.6 or later, including Windows, Mac, and Linux systems. It is available for free for non-commercial use.