Abstract
Nest architecture plays a fundamental role in the adaptation of ants to their habitat, favoring the action of economically important species. Ectatomma ruidum sp. 2 (ruidum species complex) is a biological control agent in Neotropical agroecosystems, exhibiting high bioturbation impact due to high nest densities. The architecture and composition of 152 nests were studied in two Andean populations of southwestern Colombia, 24 of them being cast using the paraffin wax technique. Nest entrance was a single, circular, 4 mm hole at ground level, without any special external structure, connected to a single vertical tunnel communicating with successive half ellipsoidal chambers. Nests were extremely shallow (depth range: 28.7-35.4 cm), with an average of six chambers and an overall volume of 92.2 cm3 per nest. The deeper the chamber, the smaller its volume. Nest building was independent of plants or roots, and no surface or underground physical connections were found between neighboring nests. Few nests possessed a queen, and neither ergatoids nor microgynes were recorded. Despite significant interactions between localities and the number of both males and workers, queen presence had an overall highly positive effect on the number of workers and larvae and a negative one on the number of gynes. Overall, the studied Colombian populations of E. ruidum sp. 2 retained the simple nest structure described for other species of this species complex and for colonies of the same species from other geographical areas, though they constrasted in their extreme shallowness. Our data suggest that E. ruidum sp. 2, at the local level, does not follow the usual monodomic pattern of this species with facultative polygyny but, rather, has a polydomic pattern with monogyny, perhaps related to the extreme shallowness of the nests due to soil structure, which could significantly enhance the queen's reproductive inhibition previously reported for this species.
Highlights
Ants are considered ecosystem engineers [1] and their functional role on soil dynamics is directly related to both their key impact as soil modifiers and their considerable bioturbation activity through nest-building [2,3,4,5,6]
Nest densities recorded in ‘Cali’ (1828 and 3768 nests ha-1) tended to be higher than the range of densities previously reported in Colombia (360 to 3020 nests ha-1 [40, 57]) and, in particular, that found in paddocks adjacent to ‘Cauca’, which had previously been estimated between 568 and 1945 nests ha-1 [40]
Our data did not allow us to determine the exact causes of these high rates of nest relocation and new nest building, they did highlight that E. ruidum sp. 2 nest-building activity in this geographic area is apparently not limited to a period of only two months as recently suggested [6] but, rather, is spread over several months of the year
Summary
Ants are considered ecosystem engineers [1] and their functional role on soil dynamics is directly related to both their key impact as soil modifiers and their considerable bioturbation activity through nest-building [2,3,4,5,6]. Nest architecture and nesting material choice play a fundamental role in the adaptation of ant colonies to their habitat and their survival through changes in soil physical properties and the resulting effects on both flooding resistance and thermal and humidity regulation [3, 7]. Humidity and temperature conditions can vary according to both the location of the nest and the insulation properties of the nest material [9, 10] and according to the depth of the chambers. Adults position themselves within the nest according to a temperature gradient according to their physiological state and age [11, 12]. Immature individuals are distributed in the chambers according to their developmental stage and the thermal requirement ensuring ideal conditions for their development [11, 13]
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