While reviewing the literature for another study in 2021 (https://teelabntu.wixsite.com/home/post/new-publication-isopod-mouthpart-traits), Weng Ngai noticed a surprising gap that was begging to be filled. Standardized feeding experiments have been used to determine the consumption rates of detritivorous animals such as isopods and millipedes since the 1950s. This wealth of data provided an excellent opportunity to investigate how different factors affect the rate at which detritivorous invertebrates consume leaf litter, and thus perform the ecosystem function of decomposition. This realization ultimately led to a publication last week in Functional Ecology: https://doi.org/10.1111/1365-2435.14520, co-authored by Weng Ngai, Eleanor and David Wardle.
Using data on consumption, assimilation and growth rates of isopods and millipedes in laboratory experiments conducted over the past 70 years, and leaf trait data obtained from the TRY global leaf trait database, the study found that leaf traits had strong effects on all three rates. Soft and thin leaves were preferentially consumed by isopods and millipedes, and leaves with high nitrogen contents led to higher assimilation and growth rates. Furthermore, isopods and millipedes always preferred to consume leaves that had been first colonised by microbes, suggesting that they may eat very few freshly fallen leaves in nature, where microbe-colonised leaves are almost always present. These results thus show that microbes have a strong positive effect on invertebrates and invertebrate-assisted leaf decomposition, and that leaf traits affect nutrient recycling rates through their effects on the invertebrates that feed on dead leaves.
The giant flat millipede, Platyrhacus lineatus (Polydesmida: Platyrhacidae) feeding on dead leaves. This species is commonly found in forests in Singapore, and likely contributes to nutrient cycling by consuming dead leaves on the forest floor. Photo 2023 Lam Weng Ngai.