Given the high rate of global habitat fragmentation, being able to predict how species will respond to fragmentation is a key first step in conservation planning.
While models based on metapopulation theory can help develop these predictions, they they don’t always line up perfectly with reality. Often there’s a trade-off between model complexity and generality, and in many cases models must rely on oversimplified assumptions about space, structure, and environmental stochasticity.
Tao, Y., Hastings, A., Lafferty, K.D., Hanski, I. and Ovaskainen, O. 2024. Landscape fragmentation overturns classical metapopulation thinking. Proceedings of the National Academy of Sciences, 121(20), p.e2303846121.
To close this gap between theory and practice, a new model has been developed that links landscape ecology and metapopulation ecology by incorporating landscape fragmentation over time with metapopulation dynamics. Rather than relying on common assumptions, researchers incorporated both simple and complex landscape structures into a spatially explicit, individual-based model that more realistically predicts metapopulation persistence, abundance, and synchrony.
As a result, it upends several classical views about the consequences of habitat fragmentation. Most importantly, it shows that trends in metapopulation dynamics can shift or even reverse over space and time, and according to dispersal strategy.
For example, the model predicts that resident species (local or short-distance dispersers) are likely to go extinct faster in homogenous landscapes, but migrants (long-distance dispersers) are likely to go extinct faster in fragmented landscapes. Some metapopulations are able to persist longer in environments that are more stochastic, but this persistence can flip to extinction as landscape area decreases.
Fragmentation reduced abundance for all species, but in a time-dependent way: in early stages of fragmentation, resident species may decline more rapidly, but as fragmentation increases, migrant species may decline more rapidly. Over time as fragmentation increases, the ability to disperse long-distance to other patches may actually become maladaptive.
Fragmentation also had contrasting effects on population synchronization, or the way populations can “mirror” each other in their dynamics. Increasing fragmentation increases synchrony between migrant populations but reduces synchrony between resident populations. Overall, resident species were predicted to be more resilient to fragmentation than migrant species.
Two main points emerge. First, current models on metapopulation dynamics in fragmented landscapes may be more unrealistic than previously thought, in that they don’t completely capture the duality of change over time. Second, these model results have many implications for how we place value on the size, structure, and connectivity of patches of land. Management actions, such as adding on to protected area boundaries or creating aggregates of protected areas, may be effective only when considering factors such as landscape area, stochasticity, or species traits.
Species response to fragmentation is likely to be more context dependent than previously thought. While keeping populations connected remains a key conservation strategy to preserve biodiversity, having a better idea of where and when connectivity might be most effective can lead to better biodiversity outcomes. Embracing a more nuanced understanding of species response to fragmentation makes the conservation tools we do have more effective in the long run.
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