A conversion proposal for biomass estimates in termites

Abstract

Termites (Isoptera) constitute a considerable fraction of the global animal biomass. Conventionally, termite dry biomass estimates (g) range between 1:3 and 1:6 of fresh biomass (g). But estimates are often based on a few species or coarse taxonomic resolution. In this study, we (1) calculated the fresh and dry mass of 15 widely distributed Neotropical termite species (three families) and (2) established the conversion ratio for dry mass, which is indispensable for biomass estimates. Workers and soldiers were sampled in their colonies and quickly weighed in the laboratory to obtain the fresh mass. Then, the individuals were placed in 80% alcohol for 5 days and weighed. Finally, the samples were dried at 60°C for 24 h and weighed again. Our results suggest an average ratio of 1:4.2 (dry-to-fresh mass), with a mean (±SE) conversion ratio of 0.24 ± 0.06, for estimating termite biomass at local, regional, and global scales. Moreover, our results demonstrate that values from termites preserved in alcohol could still be used to estimate biomass. Specifically, after insertion in alcohol, the termites lost 16.9%–56% of their water content, with an average of 26.5%. While this represents a source of bias in estimates using samples from biological collections, dry mass was significantly related to fresh mass ($R_{\mathrm{adj}}^2$ = 0.99; dry mass = 0.000055 + 0.22 × fresh mass), and to the mass of termites in alcohol ($R_{\mathrm{adj}}^2$ = 0.97; dry mass = 0.00014 + 0.26 × mass in alcohol). Applying our results to data from the literature indicates that global termite dry biomass ranges from 89 to 106 Mt.