As a result of climate change and changes in land-use, landscapes are being altered and taking new forms. This has consequences for species that inhabit the landscapes and are dependent on certain types of conditions. To find suitable conditions and surroundings they are now often forced to travel greater distances and altitudes, and manoeuvre through landscapes that have been modified by human activities.
In a recently published paper centre researcher Örjan Bodin and two colleagues present a network model developed to help researchers and practitioners assess, evaluate and plan for landscape connectivity that allows species to travel across fragmented landscapes.
An important journey
Constructions such as roads, railways or whole cities can function as barriers that many species of animals can not cross. Even insects that fly can have a difficult time travelling across if the distance to the next hospitable place is too big.
That is why "stepping stones" are needed, habitat patches in a landscape that are favourable to different species, and that offer them a refuge as they travel across, allowing them to move between other larger patches of habitat. Understanding the role of stepping stones and including them in management efforts is of great importance in conservation work.
The movements of species are vital to maintain many of the ecosystem services and functions that we depend upon.
"Making sure that species can travel through different types of human modified landscapes is vital for biodiversity given the current rate of change in different landscapes. This means, among other things, it is important that practitioners have access to adequate tools in their work"
Örjan Bodin, co-author
A stepping stone between models
In planning for landscape connectivity, researchers and practitioners can use computer-based models that give them critical information about how different species experience the connectivity of the landscape.
"One challenge is to find a model that produces reliable and relevant results. Many models previously used in research and planning are simpler and more static, they look only at the potential movement of single individuals and therefore generate limited results when the expansion of whole population is being at focus. However, the alternative has been complex models that require so much data that they become difficult to apply," Bodin explains.
"Our model looks at the number of individuals of a species in a population, the likelihood that they will travel long distances, the configuration of the landscape, and uses all this to assess how a population, over generations, could be able to move across a landscape. This way our model bridges the gap between simple and complex connectivity models. It gives us a better representation of the actual situation, while still being manageable in practice," he continues.
The authors tested the model against the 20-year dispersal pattern of the Black Woodpecker, and found that it provided a better explanation than other simpler models had done.
Stepping stones as vital connectors
Based on the results of the model the authors conclude that stepping stones are of vital importance for species to travel across landscapes. Inadequate stepping stone habitats, in size, location or number, is a determining factor for the distance that species can travel, and, contrary to previous assumptions, this cannot be compensated for by other factors such as the size of the population.
The authors conclude that stepping stones are important in reducing the isolation of large habitat blocks embedded in a landscape. In this way they contribute to the long-term survival and health of species as they allow species to colonize new areas; which might become a necessity in the face of climate change.
Saura, S., Ö. Bodin, M.-J. Fortin, J. Frair. 2013. Stepping stones are crucial for species' long-distance dispersal and range expansion through habitat networks, Journal of Applied Ecology doi:10.1111/1365-2664.12179
Örjan Bodin's research describes and models social, ecological and coupled social and ecological systems as complex and intricate webs of interactions between, and among, different ecological and/or social components.
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