Question Unoccupied Termite Mounds Provide Ecological Benefits to Tropical Rainforests

Unoccupied mounds of soil-feeding termites host diverse soil fauna both in primary and logged tropical forests
By Jiri Tuma, Kalsum M. Yusah & Tom M. Fayle
Published 26, June, 2025
Soil Ecological Letters, Springer
Note: Not Peer Reviewed
link.springer.com/article/10.1007/s42832-025-0329-8#data-availability


From the Article:

Abstract:
'We quantified soil fauna communities in unoccupied Dicuspiditermes spp. mounds.

Mounds supported up to nine times more soil fauna individuals than control soil.

Ants were the most abundant group with active colonies within the unoccupied mounds.'

' We found the unoccupied mounds support a range of invertebrate groups, with ants (Formicidae) having the highest abundances of any group across both habitats. Mounds supported significantly higher abundances of invertebrates overall in both primary forest (nine times more) and logged forest (five times more). However, the number of invertebrate taxa did not differ between mounds and control soils. Plant root mass was higher in control soils than in unoccupied mounds, possibly due to dominance of fine roots in the latter microhabitat. Using previous estimates of mound densities, we estimate that unoccupied Dicuspiditermes spp. mounds support >340 000 invertebrate individuals in primary forest and >17 000 individuals in logged forest per hectare.'

'Our results indicate that unoccupied mounds are an important, although ephemeral, microhabitat for a range of invertebrate groups, in both pristine and anthropogenically disturbed habitats.'

Methods:

Field Sites:
'Field sampling took place within the Stability of Altered Forest Ecosystems (SAFE) Project sites (Ewers et al., 2011
see the website of safeproject.net) in Sabah, Malaysian Borneo, in two types of forest.'

Sampling:
'We investigated the mounds of the soil-feeding termites Dicuspiditermes spp. (Isoptera: Termitidae).'

'We classified the mounds as being unoccupied if they had been unoccupied by termites for more than one year, as determined through
labelling and surveying for occupancy during a previous field season, in which plot-based mound turnover was estimated'

'We chose mounds unoccupied by Dicuspiditermes spp. termites, based on the following conditions: 1. the mound had fallen and was touching the soil
surface in a horizontal position, 2. when the mound material was gently investigated by digging two to three narrow holes, no termites were observed, and 3. the surface of the mound was covered by mosses. Note that the third condition was used only as supplementary evidence for mound status, since moss cover is not entirely reliable as an indicator of termite absence.'

'We collected whole mounds in the field into sealed plastic bags and transported these to the field laboratory within six hours.'

'We took the control samples 0.5 m away from the mound using a tubular soil corer of dimensions 4.0 cm in diameter and 5.0 cm in depth in a triangular layout, such that the three control samples were approximately 0.87 m apart from each other (see Supplement 1) in locations with no visible termite structures nearby.'

'In the laboratory we took three samples per mound using the same method as for control samples. The volume of soil searched for animals equalled 188.4 cm3 of mound or control soil material.'

Extraction of invertebrates from mound and control
samples:

'In the field laboratory, we placed three subsamples from each mound or control sample into a plastic tray with high 4 Unoccupied termite mounds host diverse soil fauna in tropical forests rims, and gently broke down the soil aggregates. During this time the samples were searched for invertebrates visible to the naked eye by a trained research assistant for ten minutes using a head torch. All invertebrates were collected using entomological tweezers and transferred into 96%
ethanol.'

'The animals were counted and identified to higher taxonomic levels.'

'They were further identified to species or morphospecies level.'

'When ants were found in the samples, we defined a colony as being present when there
were both workers of a particular species and brood or queen (dealate) from the same species.'

Measurement of Root Content:
'Root content was measured by collecting all plant roots visible to the naked eye in the mound or in the control soil samples during the search for invertebrates. The roots were cleaned of the soil particles, oven-dried at 60 °C for 24 h and weighted on analytical scales with 0.0001 g precision.'

Results:
'In total, we collected 911 invertebrate individuals, with 808 individuals in termite mounds and 103 in control samples
from 16 higher taxonomical groups (13 in mounds, 14 in controls; Fig. 1).'

Figure 1: Mean invertebrate abundances in unoccupied Dicuspiditermes spp. termite mounds and in control soil samples in primary and logged forest in Sabah, Malaysia showing the first eleven most abundant taxa for clarity. The full list of taxa is available in Supplement 1. (A) all recorded taxa; (B) the same dataset, without the data for ants (Formicidae) as this taxon obscured the patterns of the other taxa due to its high numerical dominance in the samples. Each individual sample comprises invertebrates sampled from 188.4 cm3 of material.

'The mean abundance of invertebrates was nine times higher in the mounds than in the controls in primary forest and five times higher in the mounds than in
the controls in logged forest.'

'there was no difference in the mean number of higher taxa between the mound and control or between habitats.'

'The mean abundance of ants was fourteen times higher in the mounds than in the controls in the primary forest and eleven times higher in the mounds than in the controls in the logged forest.'

Discussion:
'In this study, we showed that unoccupied mounds of soilfeeding termites in the genus Dicuspiditermes host a range of invertebrate taxa with mounds having five to nine times higher invertebrate abundance compared to the surrounding soil.'

'The difference that we found is probably caused by the properties of the mound itself since the mound is a pre-built, well-protected microhabitat which can serve as a suitable foraging or nesting space for a range of secondary inhabitants. However, as the
mound is constructed predominantly from termite faeces in this genus, it is rich in basic soil nutrients and it may also serve as a valuable food source for soilfeeding fauna.'

'The most abundant group in termite mounds were ants, comprising 79.3% of all individuals, and being present in 11 out of 12 mounds.'

'As there is a relatively high abundance of potential prey for ants, the unoccupied termite mounds may serve as suitable foraging spaces. However due to the high incidence of ant colonies (9 out of 12 mounds with at least one ant colony), the unoccupied mounds may primarily serve as a nesting space. This would correspond to the high pressure for nesting spaces in the rainforest in general.

Figure 3: 3 (A) Mean abundance of ant individuals per sample, (B) species richness of ants per sample and (C) mean number of
ant colonies of ants in unoccupied mounds of Dicuspiditermes spp. and in control soil in primary and logged forest in Sabah,
Malaysia. The presence of an ant colony was confirmed in cases when one termite mound contained workers of a particular
species with brood and/or a dealate queen. (D) Summary table of ant species found inhabiting mounds. The number of species
present in both mounds and the control samples in each habitat is marked as shared, while unique denotes the species which
were found only in either the mound or in the control soil. In graphs, medians are denoted by bold horizontal lines, the interquartile
range box represents the middle 50% of the data, and the whiskers represent full data ranges. Outliers are represented by full
points and are defined as values being more extreme than 1.5 times the interquartile range from the upper or lower quartiles.
LMM models were used to evaluate the effect of habitat or type of the samples and their interaction in (A) and (B) while a GLMM
model for zero-inflated data was used in the case of graph (C), with a 0.05 threshold of significance for all analyses. Each individual
sample comprises invertebrates sampled from 188.4 cm3 of material.