Maintaining connectivity between protected areas is a key conservation strategy. However, there are some concerns that greater connectivity can have unintended negative consequences. One of these concerns is that connectivity could encourage population synchrony – the idea that local populations can all start to change in the same way, or “sync up.” This could potentially make them more vulnerable to an antagonistic event like disturbance or invasion.
Spatial synchrony is common in population dynamics, but identifying the cause and scale of synchrony is often a challenge. Recent research takes a step toward doing so, focusing specifically on how shared resources between ecosystems might cause those ecosystems to synchronize.
Walter, J.A., Emery, K.A., Dugan, J.E., Hubbard, D.M., Bell, T.W., Sheppard, L.W., Karatayev, V.A., Cavanaugh, K.C., Reuman, D.C. and Castorani, M.C. 2024. Spatial synchrony cascades across ecosystem boundaries and up food webs via resource subsidies. Proceedings of the National Academy of Sciences 121(2): e2310052120.
Evidence comes from California’s Santa Barbara coastal region, where giant kelp forests dominate the marine environment and leave large deposits of dead kelp (wrack) along the shore each year. This wrack supports a diversity of microbes and detritivores, which in turn act as food for shorebirds that live on the beach.
Given this cross-ecosystem connection, just how tightly synchronized are kelp populations to shorebird populations? To answer this question, over a decade of surveys of live kelp, kelp wrack, and shorebirds were combined with data about wave intensity and beach width. These variables were compared over multiple timescales to determine the extent of cross-ecosystem synchronization.
The results show that fluctuations in the amount of kelp wrack were spatially synchronous among all five beaches that were surveyed. This was due to a combination of synchronous fluctuations in live kelp biomass and wave action, and also fluctuations in beach width. The influence of these different drivers varied over time. For example, at short time scales, wrack lagged behind kelp biomass (because kelp must grow before it can become detritus), but that lag disappeared over longer time scales.
Synchrony also cascaded up the food web, with synchrony in kelp wrack producing synchrony in shorebird abundance. This type of synchrony is unique, in that it’s caused by one ecosystem providing resources to another ecosystem, rather than by environmental factors such as shared climate fluctuations. In this case, the beach ecosystem only exists because of the kelp provided by the marine ecosystem, making the connectivity between them that much more important to preserve.
Cross-ecosystem synchronization means that disruptors to connectivity could have substantial large-scale impacts on overall stability for more than one ecosystem. Given the predicted impacts of climate change, environmental conditions are likely to contribute to synchrony along with other factors like resource sharing. Maintaining connectivity in the face of these factors will be key to successfully protecting threatened ecosystems.
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