Traits, environmental stress and Malesian mints

As lockdown put paid to all our planned fieldwork – members of the Kew Asia team decided to look for data to gather and analyse despite being housebound.

We have just published (link here) our analysis of how species traits interact with environmental stress to shape the distribution of mint (Lamiaceae) species across the islands of Malesia. This was possible because in 2019 Gemma Bramley and co-authors had published the mint account for Flora Malesiana which gave us reliable, well delimited, data on where species occur and what traits they have.

We first calculated the major axes of variation for mint species traits – there were two: (1) an axis of increasing leaf and fruit size and (2) an axis of decreasing height but increasing flower size.

Then we calculated a measure of environmental stress. This was a variable that represented increasing metal-rich ultramafic soils, drought and high elevation areas. All these stressors have been shown to separately impact vegetation and species distributions. We wanted to identify if there were any general trait coping strategies that help explain species distribution when faced with these stressors in unison.

What we found was that for mints those species with smaller leaves and fruit were more likely to be widely distributed and more likely to be found in areas of high environmental stress. This suggests that the trait strategy of small leaves and fruit benefits occurrence across the islands of Malesia. The benefits of small leaves is unsurprising given that high stress environments often have low SLA species. The advantages of small fruits however is less immediately obvious perhaps having a lower energy requirement supports reproduction in stressful environments.

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