Spatial patterns and life histories of Macrotermes michaelseni termite mounds reflect intraspecific competition: insights of a temporal comparison spanning 12 years

Abstract

Termite mounds contribute to the heterogeneity and productivity of many semi-arid ecosystems worldwide. Regular spatial patterns of termite mounds are well documented but the underlying pattern-building mechanisms remain to be clarified.This study analysed a comprehensive data set of Macrotermes michaelseni mound metrics, spatial patterns and dynamics, recorded 12 years apart within 1 km 2 of Namibian thornbush savanna. We used both unmarked and marked point pattern analyses to assess spatial distributions of termite mounds.We recorded 485 termite mounds in 2007 and 2019. Out of the investigated 142 active termite mounds in 2007, 81 were active 12 years later. Only 2% (n = 3/129) of remnant mound sites in 2007 were newly colonised in 2019. All mounds were distributed at regular distances. Mounds higher than 2 m and long-term active mounds (active in 2007 and 2019) showed high regularity. Mounds up to 0.7 m height and new mounds occurred in clusters and showed a spatial repulsion to large and long-term active colonies. The spatial distribution of Boscia albitrunca trees generally clustered around termite mounds, but did not cluster around young colonies.The results contradict the hypothesis of preferred colony settlement on previously inhabited mound sites. Remnant mounds are relatively unlikely to be recolonised when recently abandoned. The observed spatial patterns show that intraspecific competition between large colonies is the decisive factor for regular spatial patterns of termite colonies, whereas small and young colonies are limited to unoccupied patches. Surrounding trees are a pattern-building factor of only secondary importance.The spatio-temporal scale in our study reveals general trends of termite mound life histories and spatial pattern-building mechanisms. Availability of not previously inhabited sites form the patterns of founding new colonies. Well-established mounds are highly regulated by intraspecific competition. This highlights that termites contribute to ecosystem heterogeneity through self-organised spatial regularity.

Carbon dioxide and methane fluxes from mounds of African fungus-growing termites

“…An average lifespan of a Macrotermes bellicosus colony is thought to be around 4 years, whereas the mounds that they build persist typically for much longer (Pomeroy, 1976). However, a recent long-term monitoring study in Namibia found that 57 % of initially active M. michaelseni mounds were still active after 12 years (Wildermuth et al, 2022), demonstrating that some colonies can live much longer. These authors also found that small mounds were more likely to be dead than large mounds after 12 years, showing that large well-established colonies are less vulnerable to disruptions.…”

“…The stable diurnal flux variability is in line with the stable humidity and temperature conditions within mounds of fungus-growing termites. Constant temperature and high humidity are of key importance for the fungal Termitomyces symbionts, which have a relatively narrow range of optimal microclimatic conditions (Lüscher, 1961;Thomas, 1981;Wood and Thomas, 1989).…”

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

“…Macrotermes bellicosus colony is thought to be around four years, whereas the mounds that they build persist typically much longer (Pomeroy, 1976). However, a recent long-term monitoring study in Namibia found that 57% of initially active M. michaelseni mounds were still active after 12 years (Wildermuth et al, 2022), demonstrating that some colonies can live much longer. These authors also found that small mounds were more likely to be dead than large mounds after 12 years, showing that large well-established colonies are less vulnerable to disruptions.…”

Need for shared internal mound conditions by fungus-growing Macrotermes does not predict their species distributions, in current or future climates

“…Through their mound-building activities, Macrotermes change the distribution of water [33] and nutrients [34] in soils. Active mounds can be regularly spaced [35][36][37][38][39], creating habitat heterogeneity that contributes to plant [40][41][42], invertebrate [43], bird [3], mammal [4] and functional group diversity [44,45], patterns of grazing and browsing [14,46,47], productivity [48], drought amelioration [49,50], and the interplay between top-down and bottom-up processes in ecosystems [51]. Were termites to disappear, consequences for other biota may only unfold slowly, but would ultimately cascade through the ecosystem.…”