You eat what you find – Local patterns in vegetation structure control diets of African fungus‐growing termites

Abstract

Fungus‐growing termites and their symbiotic Termitomyces fungi are critically important carbon and nutrient recyclers in arid and semiarid environments of sub‐Saharan Africa. A major proportion of plant litter produced in these ecosystems is decomposed within nest chambers of termite mounds, where temperature and humidity are kept optimal for the fungal symbionts. While fungus‐growing termites are generally believed to exploit a wide range of different plant substrates, the actual diets of most species remain elusive. We studied dietary niches of two Macrotermes species across the semiarid savanna landscape in the Tsavo Ecosystem, southern Kenya, based on carbon (C) and nitrogen (N) stable isotopes in Termitomyces fungus combs. We applied Bayesian mixing models to determine the proportion of grass and woody plant matter in the combs, these being the two major food sources available for Macrotermes species in the region. Our results showed that both termite species, and colonies cultivating different Termitomyces fungi, occupied broad and largely overlapping isotopic niches, indicating no dietary specialization. Including laser scanning derived vegetation cover estimates to the dietary mixing model revealed that the proportion of woody plant matter in fungus combs increased with increasing woody plant cover in the nest surroundings. Nitrogen content of fungus combs was positively correlated with woody plant cover around the mounds and negatively correlated with the proportion of grass matter in the comb. Considering the high N demand of large Macrotermes colonies, woody plant matter seems to thus represent a more profitable food source than grass. As grass is also utilized by grazing mammals, and the availability of grass matter typically fluctuates over the year, mixed woodland‐grasslands and bushlands seem to represent more favorable habitats for large Macrotermes colonies than open grasslands.

Mound architecture and season affect concentrations of CO2, CH4 and N2O in nests of African fungus‐growing termites

“…Brauman et al (2015) found that workers of termite species relying on relatively nitrogen‐rich diets emitted more N 2 O than those having N poor diets. Thus, also dietary differences, which can significantly alter fungus comb N content and C:N stoichiometry (Vesala, Rikkinen, et al, 2022), could potentially induce both spatial and intra‐annual variations in N 2 O concentrations within Macrotermes mounds. However, more information is needed about sources and sinks of N 2 O in termite nest ecosystems to draw more definite conclusions about nest internal N 2 O levels.…”

“…For example, in East African arid and semi‐arid savannas, the biomass of grass harvested by the fungus‐growing termites corresponds roughly to that consumed by grazing mammal herbivores (Lepage, 1979, 1981a), and wood litter degraded in their nests may represent even 90% of the dead wood formed in the ecosystem (Buxton, 1981). Fungus‐growing termites collect dead plant matter, including litter from grasses, trees and shrubs (Boutton et al, 1983; Lepage et al, 1993; Vesala, Rikkinen, et al, 2022) and translocate the material into their climatically controlled nest chambers. There, the plant cell walls are broken down into simple sugars by actions of the Termitomyces symbionts in well‐aerated fungus combs and by the intestinal bacterial flora during two subsequent passages through guts of termite workers (Badertscher et al, 1983; Nobre & Aanen, 2012; Poulsen et al, 2014; Vesala, Arppe, & Rikkinen, 2022).…”

Assessing CO2 and CH4 fluxes from mounds of African fungus-growing termites

“…Termite nest temperature measurements were used from an earlier study (Vesala et al, 2019b) where small temperature sensors (iButton Thermochron DS1922L) were placed next to the first fungus combs that were encountered by digging small hole to the mound. The CO2 and CH4 fluxes measured for each mound were correlated with above ground biomass (AGB) assessed using airborne laser scanner data and field measurements (Amara et al, 2020;Pellikka et al, 2018) applying the logic that fluxes may vary with the amount woody vegetation in the environment (Vesala et al, 2022b).…”

“…For soil and wood-feeding termites the relationship between mound CO2 and CH4 fluxes has been species-specific (Jamali et al, 2013). With the assistance of Termitomyces symbionts, fungus-growing termites can utilize widely different types of plant matter including grasses, leaf litter, and dead wood (Collins 1981;Lepage 1981a) and the proportion of utilized food sources may vary both geographically and seasonally (Boutton et al, 1983;Lepage et al, 1993;Vesala et al, 2022b). Alternative food sources may also differ in their nutritional value with potential consequences to the gas fluxes.…”

“…Alternative food sources may also differ in their nutritional value with potential consequences to the gas fluxes. For example, a lower nitrogen content associated with grass-based compared to woody plantbased fungus combs found in Vesala et al, (2022b) could necessitate relatively higher CO2 and CH4 emissions, as more carbon needs to be eliminated to gain sufficiently protein from the N deficient diet (Higashi et al, 1992;Eggleton and Tayasu, 2001).…”