In a study published in Nature Ecology and Evolution, researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences have provided strong support for this central prediction by examining phytochemical diversity and herbivory in 60 tree communities ranging from species-rich tropical rainforests to species-poor subalpine forests.

The researchers investigated tree communities in Yunnan, one of the world's floristic hotspots, which contains an elevation gradient from tropical rainforest to subtropical forest to subalpine forest within a relatively short distance. In 2011 and 2012, they established 60 long-term forest inventory plots ranging from species-rich tropical rainforest to species-poor subalpine forest along the gradient.

Using community metabolomic approaches, they tested the predictions that phytochemical diversity is higher within and among communities in tropical forests as compared to less species-rich subtropical and subalpine forests. They also measured herbivore damage and leaf specialization.

Combining these data, they tested the prediction that these variables are higher in the tropics. They then quantified the phylogenetic signal in the phytochemical similarity between species to test whether closely related species diverged more in their phytochemicals than expected.