As landscapes become increasingly more fragmented, individuals need to find ways to move through them. While increasing connectivity between habitat fragments benefits many species, it also has the potential to encourage the spread of diseases or invasive species. If we can better predict how species might spread through a fragmented landscape, we can use this information to improve conservation strategies and landscape design plans.
Rayfield, B., Baines, C.B., Gilarranz, L.J. and Gonzalez, A. 2023. Spread of networked populations is determined by the interplay between dispersal behavior and habitat configuration. Proceedings of the National Academy of Sciences 120: e2201553120.
Fragmented habitats can be thought of as large networks, with habitat patches acting as nodes and corridors acting as links between them. One key to understanding how populations might spread through these networks is linking information about dispersal behavior at a species-specific level with information about network configuration. By combining knowledge about how individuals move and how the landscape is structured, it may be possible to predict spatial processes and get a better sense of how species view connections in the landscape.
A new study combines a theoretical and experimental approach to predict population spread using network theory. Researchers used a model system of springtails (Folsomia candida), which are small arthropods commonly found in leaf litter and soil that are often used for movement studies. First, they generated a model to create predictions of how individuals would move based on dispersal kernel and habitat configuration. Next, they tested the model predictions by placing springtails in physical habitats of dishes and tubes that were the same configurations as the ones in the model. This allowed them to measure how springtails spread through different link configurations, and how long it took until the springtails occupied all patches in the network.
The results showed that populations spread can be predicted by habitat network configuration and dispersal, with the experiment supporting the model. The connectivity metric used – algebraic connectivity – encodes the link between network configuration and dispersal kernel. It was a stronger predictor of how long it took springtails to occupy every patch in the network than network configuration alone.
This means that the interaction between dispersal traits and habitat configuration can have a large impact on whether a landscape helps or hinders population spread. This interaction can alter which type of network configuration (i.e. how a landscape is connected) is best at promoting spread. For species who rarely disperse long distances, spread is likely to be slowest in networks with random links. However, for species that are more likely to disperse long distances, the network may flip so that spread occurs fastest in networks with random links. The same network can have different effects based on the movement traits of target species.
Understanding the interplay between spatial structure and dispersal can inform, for example, how conservation reserves are designed, or how invasive species are managed. While this complicates efforts to protect multiple species within the same landscape, understanding how species spread ultimately leads to better decisions about how and where landscapes should be connected.
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