Ecological theory suggests that habitat connectivity can stabilize spatially-connected habitat patches, called metacommunities, from disturbances such as climate change. Within a well-connected metacommunity, theory predicts that moderate amounts of dispersal of organisms between connected patches can maintain biodiversity and buffer the impacts of anthropogenic changes. However, this theoretical prediction has rarely been tested in real-world ecosystems.
California grasslands harbor high plant biodiversity and often occur in patchy landscapes, making them ideal for testing relationships between habitat connectivity and ecological stability. California grasslands face a suite of anthropogenic disturbances that can decrease their plant diversity, including climate change and invasive plant species. Due to their high biodiversity and vulnerability, these grasslands have become a conservation priority and a key study system for understanding ecosystem stability through connectivity.
Harrison, S. and Nelson, R.A. 2025. Testing whether connectivity stabilizes metacommunities and rescues declining diversity in a 25-y grassland study. Proceedings of the National Academy of Sciences 122(46): e2520768122. DOI: 10.1073/pnas.2520768122.
A new study analyzed data from a 25-year observational study of plant community composition across 80 grasslands sites in a northern California grassland. The data included two types of spatially-structured grassland habitats: non-serpentine grasslands and serpentine grasslands. Non-serpentine grasslands, which have nutrient-rich soils, are highly invaded by non-native grasses. However, these invasive grasses generally cannot invade serpentine grasslands due to the lack of basic nutrients and high amounts of heavy metals. Consequently, the serpentine grasslands have become ecological refuges for diverse, native plant communities. For each of the 80 grassland sites, habitat connectivity was measured as the amount of same grassland habitat type that fell within an ecologically-relevant radius.
The results showed that contrary to ecological theory, habitat connectivity was not associated with ecological stability in California grasslands. For both serpentine and non-serpentine grasslands, the stability of the plant community over time did not correlate with the level of habitat connectivity. In serpentine grasslands, plant diversity metrics did not correlate with habitat connectivity. In non-serpentine grasslands, plant species turnover increased with increasing habitat connectivity, but this correlation was negated once differences in livestock grazing history were accounted for.
Grassland plant diversity declined over time irrespective of habitat connectivity. Tall, invasive grasses increased as plant species richness decreased over time, a change associated with increased warming under climate change. This finding suggests that climate change and plant invasions are acting as widespread anthropogenic changes across the landscape.
Ultimately, habitat connectivity did not appear to rescue plant diversity from pervasive anthropogenic changes. Future studies could apply this finding to testing relationships between habitat connectivity and stability under anthropogenic changes in other ecosystems. This study has implications for conservation efforts: restoring habitat connectivity alone may not be enough to buffer biodiversity from climate change. Additional conservation actions that directly mitigate anthropogenic changes may be warranted.
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