Lomas microrefugia subject to random, but not function-based losses due to lowered rainfall

In many regions around the world, climate change is leading to decreased precipitation and increased aridity. Local microclimates may provide a buffer against this effect in some cases. These microclimates create habitat islands, wherein the vegetation is different and more varied than in the surrounding areas. However, decreased precipitation surrounding habitat islands can limit incoming propagules, potentially leading to population decline and loss of species.

One example of such a system is the isolated Lomas communities of the Atacama Desert in Chile, which are maintained by constant fog, but which exist along a precipitation gradient from semi-arid to hyper-arid. Plants in arid environments use different traits, such as small size, thicker leaves, or very tough, long-lived leaves to survive in their habitat.

In a new article published in Annals of Botany, lead author Gisela C. Stotz and colleagues set out to determine whether decreased precipitation results in a loss of functional diversity, if species losses are trait-based, or if functional diversity is maintained thanks to functional redundancy, which is expected when losses are stochastic, or random. The group studied six Lomas communities along a 500km precipitation gradient, determining the levels of functional diversity and redundancy of each community.

The researchers found that decreased precipitation was in fact associated with decreased species diversity and abundance. Despite this, no functional traits or strategies showed a consistent increase or decrease as precipitations levels changed, suggesting species loss occurred at random. Functional diversity at each site remained constant, though with lower functional redundancy at the more arid sites. This suggests that the species lost were functionally redundant, but that drier communities have less of a redundant buffer remaining to be lost. These findings show that lowered precipitation levels indirectly affect habitat islands through isolation and lowering incoming propagules, but that the loss is random rather than functionally-based, allowing the functional redundancy of species in the community to act as a buffer against functional diversity loss. “Results suggest that Lomas communities are resilient to environmental changes and thus would be able to preserve their functional diversity following the decreased precipitation expected under climate change in the region,” write the authors. “However, some declines in cloud cover have been documented in the study region, which could jeopardize the role of Lomas as habitat islands.”