Seedling recruitment in a semi‐arid Patagonian steppe: Facilitative effects of refuse dumps of leaf‐cutting ants

Question: What is the influence of refuse dumps of leaf‐cutting ants on seedling recruitment under contrasting moisture conditions in a semi‐arid steppe? Location: Northwestern Patagonia, Argentina. Methods: In a greenhouse experiment, we monitored seedling recruitment in soil samples from refuse dumps of nests of the leaf‐cutting ant Acromyrmex lobicornis and non‐nest sites, under contrasting moisture conditions simulating wet and dry growing seasons. Results: The mean number of seedling species and individuals were higher in wet than in dry plots, and higher in refuse dump plots than in non‐nest soil plots. The positive effect of refuse dumps on seedling recruitment was greater under low moisture conditions. Both the accumulation of discarded seeds by leaf‐cutting ants and the passive trapping of blowing‐seeds seems not explain the increased number of seeds in refuse dumps. Conversely, refuse dumps have higher water retention capacity and nutrient content than adjacent non‐nest soils, allowing the recruitment of a greater number of species and individual seedlings. Conclusions: Nests of A. lobicornis may play an important role in plant recruitment in the study area, allowing a greater number of seedlings and species to be present, hence resulting in a more diverse community. Moreover, leaf‐cutting ant nests may function as nurse elements, generating safe sites that enhance the performance of neighbouring seedlings mainly during the driest, stressful periods.     

Moisture enhances the positive effect of leaf‐cutting ant refuse dumps on soil biota activity

Soil biota activity in arid lands is often limited by the availability of water and organic matter. We experimentally explored whether small changes in soil moisture affect the activity of soil biota in external refuse dumps of the leaf‐cutting ant Acromyrmex lobicornis, one of the most important sources of organic matter in a semi‐arid land of north‐western Patagonia. We estimated CO₂ consumption in refuse dumps and in adjacent, non‐nest soil samples at two moisture levels, after 48 and 72 h. Soil biota activity, estimated by respiration rates, was up to 160 times greater in refuse dumps than in adjacent, non‐nest soils. Activity of soil biota in non‐nest soil did not change through time and was not affected by moisture. Conversely, soil biota increased their activity in refuse dump samples only at high moisture condition after 72 h. As the activity of microorganisms is key for soil nutrient generation and availability, refuse dumps may be considered as ‘islands of fertility’ for plants. This effect may be especially important after sporadic spring rainfalls, when the beneficial effect of refuse dumps on soil biota is enhanced. In addition, as refuse dumps generate several times more CO₂ than non‐nest soils, nest areas may be considered also as hot spots of CO₂ emissions. These results illustrate the potential importance of ant nests for nutrient cycling, maintenance of plant cover and carbon balance in arid ecosystems.     

Refuse attracts? Effect of refuse dumps of leaf‐cutting ants on floral traits

The nutrient‐rich organic waste generated by ants may affect plant reproductive success directly by enhancing fruit production but also indirectly, by affecting floral traits related with pollinator attraction. Understanding how these soil‐nutrient hot spots influence floral phenotype is relevant to plant–pollination interactions. We experimentally evaluated whether the addition of organic waste from refuse dumps of the leaf‐cutting ant Acromyrmex lobicornis (Hymenoptera: Formicidae: Attini) alters floral traits associated with pollinator attraction in Eschscholzia californica (Ranunculales: Papaveraceae), an entomophilous herb. We analysed flower shape and size using geometric morphometric techniques in plants with and without the addition of refuse‐dumps soil, under greenhouse conditions. We also measured the duration of flowering season, days with new flowers, flower production and floral display size. Plants growing in refuse‐dumps soil showed higher flower shape diversity than those in control soil. Moreover, plants in refuse‐dumps soil showed bigger flower and floral display size, longer flowering season, higher number of flowering days and flower production. As all these variables may potentially increase pollinator visits, plants in refuse‐dumps soil might increase their fitness through enhanced attraction. Our work describes how organic waste from ant nests may enhance floral traits involved in floral attraction, illustrating a novel way of how ants may indirectly benefit plants.     

Relocation of Croton sonderianus (Euphorbiaceae) seeds by Pheidole fallax Mayr (Formicidae): a case of post-dispersal seed protection by ants?

Although seed dispersal by ants might reduce seed predation near the parent plants, predation on discarded seeds clustered on nest refuse piles may reduce any initial benefit provided by seed removal. Here we examine the fate of Croton sonderianus seeds that were discarded by Pheidole fallax Mayr ants on their nest refuses in caatinga vegetation of northeast Brazil. We collected all seeds discarded in refuse piles of 20 nests and within a radius of 50 cm from their borders, and examined them for evidence of predation. A total of 3,017 seeds were recorded either located in the P. fallax refuse piles (89.1%) or nest vicinity (10.9%). Predation was three fold higher in nest vicinity as compared to refuse piles. By removing seeds from beneath parent plants and relocating then to refuse piles, P. fallax is possibly providing double protection services for C. sonderianus seeds. Our findings represent the first evidence for predator-avoidance as benefit for plants resulting from ant seed-dispersal in the neotropics.     

Small-scale disturbances spread along trophic chains: leaf-cutting ant nests, plants, aphids, and tending ants

Small-scale disturbances caused by animals often modify soil resource availability and may also affect plant attributes. Changes in the phenotype of plants growing on disturbed, nutrient-enriched microsites may influence the distribution and abundance of associated insects. We evaluated how the high nutrient availability generated by leaf-cutting ant nests in a Patagonian desert steppe may spread along the trophic chain, affecting the phenotype of two thistle species, the abundance of a specialist aphid and the composition of the associated assemblage of tending ants. Plants of the thistle species Carduus nutans and Onopordum acanthium growing in piles of waste material generated by leaf-cutting ant nests (i.e., refuse dumps) had more leaves, inflorescences and higher foliar nitrogen content than those in non-nest soils. Overall, plants in refuse dumps showed higher abundance of aphids than plants in non-nest soils, and aphid colonies were of greater size on O. acanthium plants than on C. nutans plants. However, only C. nutans plants showed an increase in aphid abundance when growing on refuse dumps. This resulted in a similar aphid load in both thistle species when growing on refuse dumps. Accordingly, only C. nutans showed an increase in the number of ant species attending aphids when growing on refuse dumps. The increase of soil fertility generated by leaf-cutting ant nests can affect aphid abundance and their tending ant assemblage through its effect on plant size and quality. However, the propagation of small-scale soil disturbances through the trophic chain may depend on the identity of the species involved.     

The Importance of Where to Dump the Refuse: Seed Banks and Fine Roots in Nests of the Leaf‐Cutting Ants Atta cephalotes and A. colombica1

The location of the nutrient‐rich organic refuse produced by a leaf‐cutting ant colony varies among ant species. Atta cephalotes locate their organic refuse in subterranean chambers, whereas A. colombica place their organic refuse on the soil surface near the nest. We studied the effect of the absence or presence of external organic refuse on the abundance of fine roots and seed bank composition in the superficial horizons of ant nests. We sampled soils from ant nests or dumps and adjacent areas of 15 adult nests of A. cephalotes at La Selva (LS), Costa Rica, and of 15 of A. colombica nests on Barro Colorado Island (BCI), Panama. Soils from A. cephalotes nests did not differ from adjacent soils in abundance of fine‐root and seed diversity. In contrast, organic refuse from A. colombica nests was less diverse in seed composition (due to the great abundance of Miconia argentea) and had a greater abundance of fine roots than adjacent areas. Thus the external location of the ant‐nest organic refuse is potentially important in determining the different types of plant recolonization in abandoned or dead ant nests. The relative abundance of these Atta species may influence the structure and/or composition of tropical forests.     

Foraging activity of leaf‐cutting ants changes light availability and plant assemblage in Atlantic forest

1. Leaf‐cutting ants (LCAs) have often been denoted as ecosystem engineers because of their multifarious effects on the vegetation, particularly via nest‐driven environmental changes. However, the non‐trophic impacts of LCAs on forest dynamics via foliage harvesting across sizeable foraging zones (so‐called associated ecosystem engineering) are still poorly investigated. 2. Here, light availability and sapling assemblages were assessed within foraging areas and ant‐free control zones of 16 Atta cephalotes colonies located in a large remnant of Atlantic forest in northeastern Brazil. 3. Canopy openness and total light transmission were 1.4 and 1.6 times higher in foraging zones than in control areas. In parallel, sapling density and species richness decreased constantly from control to foraging zone plots. Additionally, shade‐tolerant species exhibited reduced abundance across foraging zones. A non‐metric multidimensional scaling ordination based on taxonomic similarity primarily segregated foraging zone and control plots; foraging zone plots converged to be more similar to each other as well. Finally, some plant species emerged as indicators of LCA‐free zones. 4. These results suggest that LCA foraging activity in the forest canopy directly increases the light availability and indirectly affects the recruitment and the structure of local plant assemblages. 5. Such a biologically significant effect on the light environment and its cascades confirms LCAs as potent ecosystem engineers, particularly as a plant assembly force, which operates beyond the spatial reach of their well‐described nest effects.     

Waste Management in the Leaf-Cutting Ant <Emphasis Type="Italic">Acromyrmex lobicornis</Emphasis>: Division of Labour,Aggressive Behaviour,and Location of External Refuse Dumps

In leaf-cutting ants, the handling of waste materials from the fungus culture increases the risk of infection. Consequently, ants should manage their waste in a way that minimizes the spread of diseases. We investigated whether in Acromyrmex lobicornis, waste-worker ants (a) also perform roles in foraging or mound maintenance, (b) are morphologically different than other ant workers, and (c) are aggressively discriminated by other worker ants from the same colony. In addition, we investigated whether the location of external waste piles minimizes the probability that wastes spread to the ant nest. In the field, we (a) marked with different colours waste-workers, foragers and mound-workers and monitored whether these ants interchanged their tasks; (b) measured head width, head length, hind femur length and total length of waste-workers; foragers and mound-workers; (c) forced field encounters between waste-workers and foragers, and (d) measured the cardinal orientation of the waste piles in relation to the colony mound. Waste-worker ants did not perform other function outside the nest; neither foragers nor mound-workers managed the waste. Moreover, waste-workers were smaller than foragers and mound-workers, and were attacked if they tried to enter their nest using foraging entrances. The location of external refuse dumps also appears to reduce contamination risks. Waste piles always were down-slope, and often followed the prevailing wind direction. The importance of behaviours such as the division of labour, aggressions against waste-workers and nest compartmentalization (i.e., the orientation of external waste piles) to minimize the spread of pathogens is discussed.     

Influence of nests of leaf‐cutting ants on plant species diversity in road verges of northern Patagonia

Abstract. It has been suggested that ant nests are the most frequent small‐scale disturbance that affect vegetation patterns. However, their effects on plant diversity are little studied. We document effects of nests of the leaf‐cutting ant Acromyrmex lobicornis on physical‐chemical soil properties and their influence on plant diversity near road verges in a desert steppe in NW Patagonia, Argentina. We analysed nest soils and controls for nitrogen, phosphorus, organic matter, moisture retention capacity and texture. We also analysed the vegetation on 42 nests (30 active and 12 abandoned or without life) and 42 areas without nests. Soil around nests had a greater nutrient content and capacity to retain moisture than control soils, which is mainly due to the presence of organic waste that the ants deposit on the soil surface. We found no association between the occurrence of nests and specific groups of plants, but plant diversity was higher at nest‐sites than at nearby non‐nest sites. This increased diversity – which is also found on abandoned nests – is mainly due to the occurrence of a larger number of native and exotic plant species on nest‐sites that are uncommon elsewhere in the study area. The most abundant plant species showed similar cover values at nest and non‐nest sites. This suggests that changes in diversity are associated to edaphic changes caused by nests rather than by changes in competitive balance caused by dominant species exclusion. We propose that the nests of Acromyrmex lobicornis, through increasing the availability of resources, generate favourable microsites that can function both as ‘refuges’ for less frequent native species, and as‘stepping stones’ for less frequent exotic plant species.     

Pay it forward: refuse dump from leaf‐cutting ants promotes caterpillar digestive performance by increasing plant nitrogen content

1. The activity of soil‐disturbing animals that increase soil nutrients can affect the carbon : nitrogen (C : N) ratio of plants, which, in turn, may determine the transfer of energy and nutrients through higher trophic levels. However, the strength and sign of this indirect effect depend on whether enhanced nutrient substrates increase plant foliar nutrients and/or plant defensive traits. 2. We investigated how the nutrient‐rich refuse dumps of the leaf‐cutting ant Acromyrmex lobicornis, as a result of their direct effects on thistles, indirectly impact the growth rate and digestive performance of a generalist chewing herbivore. We also included the application of commercial fertilisers to test whether the enhanced soil nutrients comprises the mechanism behind the impact of refuse dumps on the upward cascade effects. 3. Thistles growing on nutrient‐rich substrates (i.e. ant refuse dumps and fertilised soil) had more and larger leaves, up to 80% lower C : N ratios, and higher physical defences compared to plants growing on steppe soil. Caterpillars showed an enhanced digestive performance and growth rate when feed on nutrient‐rich plants and were able to adjust the C : N ratio of their excretion to regulate the relative acquisition of nutrients. 4. The positive effect of nutrient‐rich substrates on caterpillar feeding efficiency suggest that the enhanced nutritional quality of the thistles could compensate for the negative effects of the increased physical defences. The results of the present study indicate how organisms that increase soil nutrient availability may diminish the stoichiometric constraints at the base of food chains, enhancing the development and growth rate of herbivores and, thus, indirectly mediating plant–herbivore interactions.     

Task partitioning in leafcutting ants

A task is said to be partitioned when it is split into two or more sequential stages and material is passed from one worker to another; for instance, one individual collects a material from a source and passes it to another for transportation back to the nest. In this study, we review the existence of task partitioning in leafcutting ants (Attini) and find that, across species, this form of work organisation occurs in all stages of leaf collection, leaf transportation, and leaf processing within the nest; in the deposition of refuse (leaves and spent fungal garden) to internal or external dumps; and in colony emigration. Thus, task partitioning is shown to be a very important component of work organisation in leafcutting ants. Examples mostly concern Atta but task partitioning is also known in Acromyrmex. The costs and benefits of task partitioning of the various stages are discussed and suggestions for further research are highlighted. Electronic Publication     

Leaf-cutting ant abundance and distribution under different agricultural practices in grassland biome

1. Leaf-cutting ants (LCA) frequently show positive associations with human disturbance in forest biome, explained by habitat opening and increase of pioneer vegetation. However, little is known about LCA response in grassland biome. Agriculture and commercial forestry typically introduce closed habitats and displace pioneer vegetation when occurring in grasslands. The aim of this study was to assess the response of LCA to different land use types developed in a grassland biome.
2. Semi-natural grassland remnants, soybean crops, cattle pastures and young and mature eucalypt plantations were sampled in Entre Ríos, Argentina. LCA nest abundance and occurrence of workers was obtained by hand sampling and baited pitfall traps.
3. LCA nest abundance significantly decreased in most land use types when compared with the grassland sites. All habitat types were characterized by the presence of different LCA species, which showed different associations with temperature, vegetation and soil structure.
4. Our results suggest that LCA response to human disturbance depends on the biome where it occurs; contrary to what was observed in forests, the LCA assemblage was negatively associated to human disturbance in grasslands. The response of the whole assemblage masked different responses of LCA species, possibly indicating differences in their ecological niche.

     

Leaf‐cutting ants,seasonal burning and nutrient distribution in Cerrado vegetation

Abstract Fire and herbivory are known to modify plant community structure. Many studies have suggested that fire ashes may increase soil nutrients in dystrophic soils. Herbivores may also change plant community structure through direct effects of herbivory and affecting nutrient cycling. Leaf‐cutting ants were traditionally viewed as herbivores, although their role may be more complex, because their nests affect both chemical and physical soil properties, thus affecting plants indirectly. We investigated the effects of frequent burning and of leaf‐cutting ants on the nutrient status of an herbaceous and a shrub species occurring in the Brazilian Cerrado, a habitat that is characterized by natural burnings. The proximity of ant nests resulted in an increase of nutrients in the leaves of both vegetation strata, whereas burning sometimes resulted in a decrease of nutrients. Our results do not lead to a possible positive effect of fire on plant nutrient content. On the other hand, ant nests may represent an important source of nutrients for plants on the nutrient‐depleted Cerrado soils and may accelerate vegetation recovery after burning.     

Aphid‐tending ants on introduced fennel: can resources derived from non‐native plants alter the trophic position of higher‐order consumers?

1. Although plant invasions often reduce insect abundance and diversity, non‐native plants that support phytophagous insects can subsidise higher trophic levels via elevated herbivore abundance. 2. Here ant–aphid interactions on non‐native fennel on Santa Cruz Island, California are examined. Fennel hosts abundant, honeydew‐producing fennel aphids. The patchiness of fennel and the relative lack of honeydew‐producing insects on other plants at our study sites suggest that assimilation of fennel‐derived honeydew would increase the abundance and decrease the trophic position of the omnivorous, aphid‐tending Argentine ant. 3. To assess the strength of the ant–aphid interaction, a comparison of ant abundance on and adjacent to fennel prior to and 3 weeks after experimental aphid removal was performed. Compared with control plants with aphids, ants declined in abundance on and around fennel plants following aphid removal. At the habitat scale, pitfall traps in fennel‐dominated habitats captured more ants than in fennel‐free scrub habitats. 4. To determine if assimilation of aphid‐produced honeydew reduces the ant's trophic position, variation in δ¹⁵N values among ants, plants and other arthropods was analysed. Unexpectedly, δ¹⁵N values for ants in fennel‐dominated habitats were higher than those of arthropod predators from the same sites and also higher than those of ants from fennel‐free habitats. 5. Our results illustrate how introduced plants that support phytophagous insects appear to transfer energy to higher trophic levels via elevated herbivore abundance. Although assimilation of fennel‐derived honeydew did not appear to reduce consumer trophic position, spatial variation in alternative food resources might obscure contributions from honeydew.     

Divergent effects of leaf-cutting ant herbivory and soil engineering on the reproductive success of plants in a Caatinga dry forest

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Refuse dumps of leaf‐cutting ants as a deterrent for ant herbivory: does refuse age matter?

Leaf‐cutting ants often avoid contact with their waste because it harbors microorganisms that are dangerous to the ants and their symbiotic fungus. Therefore, the use of ant waste (i.e., refuse dumps) has been proposed as a deterrent method against leafcutter attack. We tested experimentally whether the age of the refuse dump (fresh vs. old) affects the herbivory‐deterrent effect against the leaf‐cutting ant Acromyrmex lobicornis Emery (Hymenoptera: Formicidae). Refuse placed around seedlings significantly delayed the initiation attacks of leaf‐cutting ants, and this deterrent effect decreased gradually over a period of 30 days. The initial strength of this decrease was the same for newly‐discarded ( ‘new’) refuse and refuse from the bottom of the ants’ waste pile (‘old’ refuse). However, the loss of deterrent effect over time was more rapid for new than old refuse. A further experimental manipulation, replacement of refuse every 3 days, had no effect on the deterrent effect for old refuse, but increased this effect for new refuse, although the amount of this increase gradually weakened over the course of the 30‐day experiment. We speculate on the possible causes of these effects, their consequences for the hygienic behavior of leaf‐cutting ants, and on the use of ant debris as short‐term control method against leaf‐cutting ants.     

Simple rules based on pile slope are used in the self organization of sand pile formation by <Emphasis Type="Italic">Pheidole oxyops</Emphasis> ants

We tested the hypothesis that slope influences where worker ants deposit excavated soil on piles near the nest entrance. We predicted that ants will deposit their load near the top of a pile where the slope changes from upward to downward, to prevent material rolling back towards the entrance. We tested this hypothesis by studying five natural colonies of Pheidole oxyops ants at a field site at S?o Sim?o, Brazil. At this site, each colony was dumping sandy soil excavated from its underground nest in a crescent-shaped pile c. 13 cm from and perpendicular to the nest entrance. Each nest was given an experimental sand pile of symmetrical curved cross section on a plywood platform that could be tilted 15 degrees up or down. From videos, the locations where individual ants dumped their soil loads were measured in relation to the inner (position = 0) and outer (position = 1) edges of the pile. When the platform was tilted down the ants deposited their loads significantly closer to the inner edge (0.458 ± 0.007) than when not tilted (0.530 ± 0.006). When the platform was tilted up the ants deposited their loads significantly further from the inner edge (0.626 ± 0.006) than when not tilted (0.522 ± 0.006). These results support the hypothesis that ants use pile slope in deciding where to dump their load. A similar rule is probably used in other ant species that place excavated soil in steep piles near the nest entrance. Received 5 February 2007; revised 10 June 2007; accepted 9 October 2007.     

Do Leaf Cutting Ants Cut Undetected? Testing the Effect of Ant-Induced Plant Defences on Foraging Decisions in Atta colombica

Leaf-cutting ants (LCAs) are polyphagous, yet highly selective herbivores. The factors that govern their selection of food plants, however, remain poorly understood. We hypothesized that the induction of anti-herbivore defences by attacked food plants, which are toxic to either ants or their mutualistic fungus, should significantly affect the ants' foraging behaviour. To test this "induced defence hypothesis," we used lima bean (Phaseolus lunatus), a plant that emits many volatile organic compounds (VOCs) upon herbivore attack with known anti-fungal or ant-repellent effects. Our results provide three important insights into the foraging ecology of LCAs. First, leaf-cutting by Atta ants can induce plant defences: Lima bean plants that were repeatedly exposed to foraging workers of Atta colombica over a period of three days emitted significantly more VOCs than undamaged control plants. Second, the level to which a plant has induced its anti-herbivore defences can affect the LCAs' foraging behaviour: In dual choice bioassays, foragers discriminated control plants from plants that have been damaged mechanically or by LCAs 24 h ago. In contrast, strong induction levels of plants after treatment with the plant hormone jasmonic acid or three days of LCA feeding strongly repelled LCA foragers relative to undamaged control plants. Third, the LCA-specific mode of damaging leaves allows them to remove larger quantities of leaf material before being recognized by the plant: While leaf loss of approximately 15% due to a chewing herbivore (coccinelid beetle) was sufficient to significantly increase VOC emission levels after 24 h, the removal of even 20% of a plant's leaf area within 20 min by LCAs did not affect its VOC emission rate after 24 h. Taken together, our results support the "induced defence hypothesis" and provide first empirical evidence that the foraging behaviour of LCAs is affected by the induction of plant defence responses.     

Nutrient transfer supports a beneficial relationship between the canopy ant,Azteca trigona,and its host tree

1. Energy fluxes between ants and plants have been a focal point for documenting mutualistic behaviour. Plants can provide resources to ants through the production of extrafloral nectaries. In exchange, ants can fertilise plants through their nutrient‐ and microbe‐rich refuse. 2. Here, we test a potential facultative mutualism between the carton‐nesting canopy ant, Azteca trigona, and their host trees. Through observational and experimental approaches, this study documents how nutrient transfer provides a basis for this beneficial ant–plant relationship. 3. In a greenhouse experiment, fertilisation with sterilised refuse (i.e. nutrients only) increased seedling growth three‐fold, while the refuse with its natural microbial community increased growth 11‐fold. 4. Total root density was doubled in refuse piles compared with the surrounding area in situ. On average, refuse provides host trees and the surrounding plant community with access to a > 800% increase in N, P and K relative to leaf litter. 5. Azteca trigona preferentially nests in trees with extrafloral nectaries and on large, longer‐lived tree species. 6. Given the nutrient‐poor nature of the Neotropics, host trees probably experience significant benefits from refuse fertilisation. Conversely, A. trigona benefit from long‐term stable structural support for nests and access to nutrient‐rich extrafloral nectaries. Without clear costs to either A. trigona or host trees, it is proposed that these positive interactions are preliminary evidence of a facultative mutualism.     

Utilization of harvester ant nest sites by Persian goitered gazelle in steppes of central Iran

Ants are among the most important elements in many ecosystems and known as famous ecosystem engineers. By changing physical and chemical properties of soil, ants may provide suitable habitats for other species. Based on previous observations, we hypothesized that Persian goitered gazelles (Gazella subgutturosa subgutturosa) exhibit a preference for utilizing sites close to seed harvester ant (Messor spp.) nests. We tested our hypothesis by (1) mapping the occurrence of harvester ant nests and aggregated gazelle pellet groups along 31 strip transects, (2) monitoring pellet group accumulation bimonthly at 56 pairs of permanent plots established on ant nests and at adjacent control sites for a complete year, and (3) comparing vegetation and soil parameters between ant nest sites used by gazelles and paired control plots without ant nests. Although the area of Messor spp. nest sites covered only about 0.29% of the sampled transects, 84% of the gazelle pellet group aggregation sites were positioned upon ant nests, suggesting that gazelles actively selected Messor spp. nest sites. Pair-wise comparisons between ant nest plots and paired control plots also confirmed higher use of ant nest sites by gazelles compared to sites without ant nests in all time periods. Percent soil organic matter, percent cover of gravel, and annual herb vegetation significantly differed between ant nest and paired control plots in all the vegetation communities. We suggest that the alterations brought about by harvester ants on soil and vegetation make these sites attractive to gazelles. Gazelle territoriality behaviour and use of ant nests as bedding sites may be the reasons for selection of ant nest sites by gazelles.