Effects of ants on water and soil losses from organically-managed citrus orchards in eastern Spain

Ants can play a key role in the erosion processes on agriculture land by modifying soil properties and increasing macropore flow. Ants are abundant in organically-managed orchards in the Mediterranean region due to climate conditions, no-till practices, no pesticide use, and the resulting vegetation cover. In order to determine the effect of ants on soil and water losses from these orchards growing on moderately-sloped land (4–8%), forty 1.0 m² plots (20 with ants mounts and 20 without ants — controls) were established during the summer of 2007. A rainfall simulator was used to apply 78 mm of water to each plot over a one-hour period, equivalent to a 20-year return-period thunderstorm. Runoff was collected at 1-minute intervals and sediment concentration measured every 10 minutes. Sediment concentrations were 300% higher on plots with ant mounds, but runoff rates were similar to the plots without ants. Average soil erosion rates averaged 41 kg ha⁻¹ h⁻¹ on the ant plots and 13 kg ha⁻¹ h⁻¹ on the control plots. The low erosion rates are due to the effect of the vegetation and litter cover in this organically-managed soil, which were little impacted by ant activity at the pedon scale.     

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.     

Organic mound-building ants: their impact on soil properties in temperate and boreal forests

Ants are important components of most soil invertebrate communities, and can affect the flow of energy, nutrients and water through many terrestrial ecosystems. The vast majority of ant species build nests in the mineral soil, but a small group of ants in temperate and boreal forests of Eurasia and North America build large parts of their nests above‐ground using organic materials collected from the surrounding soil. Many studies have shown that ants nesting in mineral soil can affect water infiltration rates, soil organic matter (OM) content, and nutrient cycling, but much less is known on how mound‐building ants influence soil physical and chemical properties. In this paper we summarize what is known on the soil impacts of organic mound‐building ants in temperate and boreal forests, and how these ants could be affected by ecosystem disturbance and future climate change. Much of this information comes from studies on Formica rufa group ants in Europe, which showed that CO₂ emissions and concentrations of C, N, and P are usually higher in ant mounds than in the surrounding forest soil. However, ant mounds are a minor component of total soil C and nutrient pools, but they do increase spatial heterogeneity of soil water and available nutrients. Mound‐building ants can also impact tree growth, which could change the quantity and quality of OM added to soil. Forest management, fire, and projected climate change, especially in boreal forests, could affect mound‐building ant population dynamics, and indirectly, soil properties.     

Ecosystem engineering and predation: the multi-trophic impact of two ant species

1. Ants are ubiquitous ecosystem engineers and generalist predators and are able to affect ecological communities via both pathways. They are likely to influence any other terrestrial arthropod group either directly or indirectly caused by their high abundance and territoriality. 2. We studied the impact of two ant species common in Central Europe, Myrmica rubra and Lasius niger, on an arthropod community. Colony presence and density of these two ant species were manipulated in a field experiment from the start of ant activity in spring to late summer. 3. The experiment revealed a positive influence of the presence of one ant colony on densities of decomposers, herbivores and parasitoids. However, in the case of herbivores and parasitoids, this effect was reversed in the presence of two colonies. 4. Generally, effects of the two ant species were similar with the exception of their effect on Braconidae parasitoid densities that responded positively to one colony of M. rubra but not of L. niger. 5. Spider density was not affected by ant colony manipulation, but species richness of spiders responded positively to ant presence. This effect was independent of ant colony density, but where two colonies were present, spider richness was significantly greater in plots with two M. rubra colonies than in plots with one colony of each ant species. 6. To test whether the positive ecosystem engineering effects were purely caused by modified properties of the soil, we added in an additional experiment (i) the soil from ant nests (without ants) or (ii) unmodified soil or (iii) ant nests (including ants) to experimental plots. Ant nest soil on its own did not have a significant impact on densities of decomposers, herbivores or predators, which were significantly, and positively, affected by the addition of an intact nest. 7. The results suggest an important role of both ant species in the grassland food web, strongly affecting the densities of decomposers, herbivores and higher trophic levels. We discuss how the relative impact via bottom-up and top-down effects of ants depends on nest density, with a relatively greater top-down predatory impact at higher densities.     

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.     

Camponotus ants mine sand for vertebrate urine to extract nitrogen

The ability of some ant species (including Camponotus spp.) to forage on vertebrate urine to extract urea may extend their niche in competitive and strongly nitrogen‐limited environments. We examined the preference of Camponotus terebrans, a sand‐dwelling ant widespread in southern Australia, for baits including urine, and the duration of their foraging on those baits. We baited ants with liquid stains of urine (human and kangaroo), urea in water (2.5%. 3.5%, 7.0%, 10.0%) and sucrose in water (20% and 40%) poured directly on the ground, as well as hard baits in plots drawn on sandy soil (Kangaroo Island, South Australia). We counted individuals of this mostly nocturnal species to determine their attraction to different baits for one month. We checked plant growth on the plots after nine and 13 months. Ants collected insects and meat; they foraged for at least 29 days on stains. Ants were most numerous on 10% urea, followed by 7% urea, 3.5% urea, urine (which contains ~2.5% urea) and 2.5% urea, 40% sucrose and 20% sucrose; sucrose was less attractive to them than equimolar urea bait. Ants were attracted to human, kangaroo, and unidentified urines, and they collected bird guano. Baits and ant foraging did not affect plant recruitment in plots. We observed incidentally Camponotus consobrinus foraging on urine, which may be a common resource for this genus at the site. The remarkable ability of C. terebrans to extract nitrogen from dry sand over weeks explains partly its success on sandy soils. Foraging on urine may be an important strategy to address nitrogen limitation on sandy soils and exploit commensally niches in which hosts are kangaroos, wallabies and other vertebrates. The understanding of plant–vertebrate interactions must factor in the role of ants as commensal organisms. Such ants could also reduce greenhouse gas emissions from urine.     

CO2 efflux from subterranean nests of ant communities in a seasonal tropical forest,Thailand

Many ant species construct subterranean nests. The presence of their nests may explain soil respiration “hot spots”, an important factor in the high CO₂ efflux from tropical forests. However, no studies have directly measured CO₂ efflux from ant nests. We established 61 experimental plots containing 13 subterranean ant species to evaluate the CO₂ efflux from subterranean ant nests in a tropical seasonal forest, Thailand. We examined differences in nest CO₂ efflux among ant species. We determined the effects of environmental factors on nest CO₂ efflux and calculated an index of nest structure. The mean CO₂ efflux from nests was significantly higher than those from the surrounding soil in the wet and dry seasons. The CO₂ efflux was species‐specific, showing significant differences among the 13 ant species. The soil moisture content significantly affected nest CO₂ efflux, but there was no clear relationship between nest CO₂ efflux and nest soil temperature. The diameter of the nest entrance hole affected CO₂ efflux. However, there was no significant difference in CO₂ efflux rates between single‐hole and multiple‐hole nests. Our results suggest that in a tropical forest ecosystem the increase in CO₂ efflux from subterranean ant nests is caused by species‐specific activity of ants, the nest soil environment, and nest structure.     

Does the morphology of animal foraging pits influence secondary seed dispersal by ants?

Secondary seed dispersal by ants (myrmecochory) is an important process in semi‐arid environments where seeds are transported from the soil surface to an ant nest. Microsites from which ants often remove seeds are the small pits and depressions made by native and exotic animals that forage in the soil. Previous studies have demonstrated greater seed retention in the pits of native than exotic animals, but little is known about how biotic factors such as secondary seed dispersal by ants affect seed removal and therefore retention in these foraging pits. We used an experimental approach to examine how the morphology of burrowing bettong (Bettongia lesueur), greater bilby (Macrotis lagotis), short‐beaked echidna (Tachyglossus aculeatus) and European rabbit (Oryctolagus cuniculus) foraging pits and ant body size influenced ant locomotion and seed removal from pits along an aridity gradient. Ants took 3.7‐times longer to emerge from echidna pits (19.6 s) and six‐times longer to emerge from bettong pits (30.5 s) than from rabbit pits (5.2 s), resulting in lower seed removal from bettong pits than other pit types. Fewer seeds were removed from pits when cages were used to exclude large body‐sized (>2 mm) ants. Few seeds were removed from the pits or surface up to aridity values of 0.5 (humid and dry sub‐humid), but removal increased rapidly in semi‐arid and arid zones. Our study demonstrates that mammal foraging pit morphology significantly affects ant locomotion, the ability of ants to retrieve seeds, and therefore the likelihood that seeds will be retained within foraging pits.     

Überlebensstrategien von Regenwaldameisen

Survival strategies of rainforest ants The heavy rainfall in the humid tropics pose special challenges to plants and animals. Ants have developed a variety of adaptations to flooding. Measures against floods range from raft formation to various methods of nest drainage. In the intertidal zone nests are sealed watertight, while the ants react with physiological adaptations to the oxygen deficiency. In an obligate symbiosis between a carnivorous pitcher plant and a carpenter ant a unique coexistence has developed, in which the partner ant dives and forages unharmed in the digestive pitcher fluid for mosquito larvae and drowned prey.     

Colony Dehydration and Water Collection by Specialized Caste in the Leaf-Cutting Ant <Emphasis Type="Italic">Atta Sexdens Rubropilosa</Emphasis>

Social organization enables leaf-cutting ants to keep appropriate micro-ecological nest conditions for the fungus garden (their main food), eggs, larvae and adults. To maintain stability while facing changing conditions, individual ants must perceive destabilising factors and produce a proper behavioral response. We investigated behavioral responses to experimental dehydration in leaf-cutting ants to verify if task specialization exists, and to quantify the ability of ant sub-colonies for water management. Our setup consisted of fourteen sub-colonies, ten of which were randomly assigned to different levels of experimental dehydration with silica gel, whereas the remaining four were controls. The ten experimental sub-colonies were split into two groups, so that five of them had access to water. Diverse ant morphs searched for water in dehydrated colonies, but mainly a caste of small ants collected water after sources had been discovered. Size specialization for water collection was replicable in shorter experiments with three additional colonies. Ants of dehydrated colonies accumulated leaf-fragments on the nest entrance, and covering the fungus garden. Behaviors that may enhance humidity within the nests were common to all dehydration treatments. Water availability increased the life span of dehydrated colonies.     

Ants on the Move: Resource Limitation of a Litter‐nesting Ant Community in Costa Rica1

The leaf litter of tropical wet forests is replete with itinerant ant nests. Nest movement may help ants evade the constraints of stress and disturbance and increase access to resources. I studied how nest relocation and environmental factors may explain the density, size, and growth of leaf litter ant nests. I decoupled the relationships among litter depth, food abundance, and nest availability in a 4‐mo manipulation of food and leaf litter in a community of litter‐nesting ants in a lowland wet forest in Costa Rica. Over 4 mo, 290 1 m² treatment and control plots were sampled without replacement. Nest densities doubled in response to food supplementation, but did not decrease in response to litter removal or stress (from litter trampling). The supplementation of food increased the utilization of less favored nesting materials. In response to food supplementation and litter trampling, arboreal ants established nests in the litter, and growth rates of the most common ants (Pheidole spp.) increased. Colony growth was independent of colony size and growth rates of the most abundant ants. In general, I conclude that litter‐nesting ant density is driven primarily by food limitation, that nest relocation behavior significantly affects access to resource and the demographic structure of this community, and that nest fission may be a method to break the growth–reproduction trade‐off.     

Response of the foraging behaviour of red wood ants (Formica rufa group) to exclusion from trees

Abstract 1 Because of the large numbers within a colony and their aggressive nature, red wood ants (Formica rufa group) have a potential to greatly influence the cold‐temperate forest ecosystem. Wood ants are omnivorous and hunt in trees as well as on the forest floor. 2 A field experiment in a mixed forest in central Sweden was carried out to examine (i) the foraging behaviour of wood ants on the forest floor and (ii) the impact of increased numbers of wood ants on the soil fauna. The foraging behaviour of wood ants was manipulated by excluding the ants from their food resources in the tree canopy, with the intention to increase ant activity on the forest floor. To estimate this activity, the number of trees with foraging ants, the numbers of ants going to and from their nests and the prey carried by home‐running wood ants were determined during the summer period. Pitfall traps were placed in the soil to determine effects on mobile soil invertebrates. 3 When excluded from local trees, wood ants searched other trees further away from the nests rather than searching more intensively for prey on the forest floor. By contrast to the initial hypothesis, more soil‐living prey were caught by ants in the control plots than in the plots where the local trees were not accessible to the wood ants. The proportion of soil‐living to tree‐living prey tended to be greater in the control plots. 4 In the treated plots (no access to the trees), wood ants had a negative effect on the activity of Linyphiidae spiders. There was little effect of wood ants on other soil invertebrates. 5 This study suggests that the role of wood ants as top predators in the forest soil food‐web in central Sweden is limited.     

枝条覆盖对半干旱黄土丘陵区平茬柠条林地土壤水分的影响

为了研究枝条覆盖对林地土壤水分的影响,提高土壤水分利用效率。2013年5—9月,以半干旱黄土丘陵区平茬柠条林为对象,采用中子水分仪对未覆盖和枝条覆盖林地土壤水分进行定位观测,研究了枝条覆盖对林地土壤水分的影响。研究期间共观测到降雨28次,总降雨量达495.9 mm。未覆盖和覆盖林地降雨补给量与降雨量之间均呈极显著正相关关系。枝条覆盖使林地降水入渗补给系数由0.50增加至0.70,明显提高了林地次降水补给量和入渗深度。覆盖林地各月土壤水分消耗量均高于对照林地,整个生长季,前者比后者多消耗了37.56 mm土壤水分,仅相当于所增加的降雨补给量的1/3。在丰水年,覆盖一直表现出对林地土壤水分的正效应,剖面0—260 cm范围内土壤水分条件有明显改善。     

Horizontal transfer of insecticides in laboratory colonies of the Argentine ant (Hymenoptera: Formicidae)

Five insecticides used by urban pest management professionals for ant control and three experimental insecticides were tested to determine whether these insecticides were horizontally transferred among individuals in colonies of Argentine ants, Linepithema humile (Mayr) (Hymenoptera: Formicidae). Ants were exposed to insecticide-treated sand for 1 min and then placed in a colony of untreated ants. Ants exposed to 20 and 40 ppm fipronil readily transferred the insecticide to other individuals in the colony, resulting in high mortality. Most of the transfer and subsequent mortality occurred within 4 d after exposure to treated ants. The other insecticides were not transferred, and ants exhibited mortality rates similar to that of the controls. Experiments in large foraging arenas demonstrated that necrophoresis was an important behavior facilitating the horizontal transfer of fipronil. When ants contacted contaminated corpses in the process of removing them to refuse piles, they received a lethal dose of fipronil and subsequently died. Fipronil-contaminated dead ants that were placed in the vicinity of the nest resulted in significantly higher mortality than did corpses placed in a distant foraging arena (30 cm away). Most of the dead ants accumulated in the vicinity of the nest rather than in the foraging arena, workers retrieving dead ants to refuse piles from the foraging arena. The position effect of insecticide-contaminated corpses relative to the nest and its implication for Argentine ant control are discussed.     

The influence of ants and water availability on oviposition behaviour and survivorship of a facultatively ant-tended herbivore

1. The lycaenid butterfly Hemiargus isola associates facultatively with the ant species Formica perpilosa in arid areas of south-western North America. Ants solicit liquid food rewards from butterfly larvae as larvae feed on the host plant, Acacia constricta . Previous studies have shown that tending by F. perpilosa enhances larval growth and pupal survivorship.
2. The effects of ants and plant water content on oviposition behaviour and survivorship to the last larval instar were tested by excluding ants and supplementing water to host plants in a two-way factorial experiment.
3. Butterflies, which lay eggs singly on host plant inflorescences, laid significantly higher egg numbers and densities (eggs/inflorescence) on plants with ants than on plants without ants. This is the first report of a facultative, generalized ant-associate using ants as oviposition cues. Water supplements increased the number, but not the density, of eggs laid on plants. Therefore, it appears that egg-laying butterflies responded to number of inflorescences, rather than plant tissue water per se .
4. Plants with ants had significantly greater numbers of inflorescences during the experiment than plants without ants. Water supplements increased number of inflorescences slightly, but not significantly.
5. Ants increased larval survivorship. Twice as many fourth-instar larvae survived per egg laid on plants with ants than on plants without ants. Ants did not reduce the number of predators present on acacias, but may have reduced predator effectiveness. Ants also did not reduce the numbers of potential H. isola competitors present.
6. Water supplementation affected neither the survivorship of H. isola larvae, nor the intensity of ant tending. Water supplementation did not affect the abundance of predators on plants, but did increase the abundance of several herbivorous insect taxa.     

Effects of harvester ants on plant species distribution and abundance in a serpentine grassland

Seed harvesting ants can have important effects on the composition and structure of plant communities. We investigated two effects of Messor andrei, the black seed-harvesting ant, on a serpentine grassland plant community in northern California. First, to determine if selective seed predation by ants affects plant community composition, we excluded harvester ants from 1-mediameter circular plots of grassland. Abundances of all species on these plots and on control plots were measured before and after exclosure. Second, to determine if M. andrei nest mounds affect plant community composition, we compared plant species abundances on and off nest mounds. M. andrei deposit large amounts of organic matter on their nest mounds over a foraging season, so mounds may alter the edaphic environment. The exclusion of seed-harvesting activity did not cause changes in the plant community. Nest mounds had a strong effect on plant communities: there were many more grasses and fewer forbs on ant mounds, although at least one forb, Lepidium nitidum, produced twice as many seeds when it grew on nest mounds. We found that nest mounds formed islands of higher-temperature soil in the serpentine grassland. Received: 31 March 1997 / Accepted: 6 May 1997     

Strong but taxon‐specific responses of termites and wood‐nesting ants to forest regeneration in Borneo

Land use change is accelerating globally at the expense of biodiversity and ecosystem functioning. Invertebrates are numerically dominant and functionally important in old growth tropical rain forests but highly susceptible to the adverse effects of forest degradation and fragmentation. Ants (Formicidae) and termites (Blattodea: Termitoidae) perform crucial ecosystem services. Here, the potential effects of anthropogenic disturbance on ant and termite communities in dead wood are investigated. Community composition, generic richness, and occupancy rates of ants and termites were compared among two old growth sites (Danum Valley and Maliau Basin) and one twice‐logged site (the Stability of Altered Forest Ecosystems’ (SAFE) Project), in Sabah, Malaysian Borneo. Occupancy was measured as the number of ant or termite encounters (1) per deadwood items, and (2) per deadwood volume, and acts as surrogates for relative abundance (or generic richness). Termites had a lower wood‐occupancy per volume in logged forest. In contrast, there were more ant encounters, and more ant genera, in logged sites and there was a community shift (especially, there were more Crematogaster encounters). The disruption of soil and canopy structure in logged forest may reduce both termite and fungal decay rates, inducing increased deadwood residence times and therefore favoring ants that nest in dead wood. There is an anthropogenic‐induced shift of dead wood in ants and termites in response to disturbance in tropical rain forests and the nature of that shift is taxon‐specific.     

The harvester ant (Pogonomyrmex badius) midden: refuse or boundary?

Abstract. 1. P.badius Latreille, a harvester ant of the southern U.S.A., surrounds its nest mound with small bits of charcoal, previously believed to be incidental refuse, along with other components of the colony's midden.
2. Charcoal middens were removed from the nest mounds of colonies in northern Florida. These colonies collected new charcoal and replaced the middens within 7 days.
3. Activity rhythms, use of space, and interspecific aggression were compared in experimental and control colonies. When middens were removed, the frequency of invasions of the nest mounds by other species of ants increased. Foreign ants circled the nest mound and interfered with colony activities. Increased numbers of invading ants led to an increase in patrolling and defensive behaviour by the P.badius colonies.
4. The charcoal midden is not merely refuse. Instead, it acts as a boundary that deters ants of other species from coming onto the P.badizls nest mound. Ants may use charcoal bits as a repository of a chemical substance functioning as a territorial marker.     

The effect of predation of western widow spiders (Araneae: Theridiidae) on harvester ants (Hymenoptera: Formicidae)

Summary Spiders have been shown to be important predators on ant populations, although ant mortality may be low. Western widow spider (Latrodectus hesperus) predation on Pogonomyrmex rugosus ant nests is slight, less than 0.2% of the nest population per day. Yet, the ants respond by halting foraging temporarily and may even close the nest entrace with pebbles. If spiders are removed from such nests, the ants become active within 24 h and within five days foraging activity reaches higher levels than at any previous time of the year.Ants have at least four responses to spiders predation: 1) Moving the nest entrace; 2) posting of guards; 3) attacking the spiders; 4) halting foraging. Pogonomyrmex rugosus practices the fourth response, although it results in losses of food intake into the nest. This is apparently the only option available. If the ants continue to forage, the spider density may increase, resulting in heavy mortality of the ants.