Ground-dwelling Ant Assemblages Research Articles

Can environmental complexity predict functional trait composition of ground-dwelling ant assemblages? A test across the Amazon Basin

Environmental gradients may influence species distributions by filtering their functional traits, resulting in a correspondence between community functional composition and local environmental conditions. We used a vegetation gradient as an indicator for environmental complexity to test whether it predicted the morphological composition of ground-dwelling ant assemblages across geographic extents. The sampling design covered 126 plots distributed across eight sampling sites along a broad environmental gradient in the Amazon Basin. Plots covered different phytophysiognomies that have a strong relation with forest biomass and, consequently, litter production. We selected six morphological traits related to ant foraging strategies and behavior. Generalized linear mixed models were used to predict how environmental complexity affects trait composition of ground-dwelling ant assemblages. Structurally less complex environments (eg. Amazonian savannah) harboured more species of smaller ants, with relatively smaller mandibles and relatively larger eyes. In more complex environments (eg. dense ombrophylous forest), there were more ant species of larger size, with relatively larger mandibles and relatively smaller eyes. No relationship was detected between relative femur length and the environmental gradient investigated. The functional approach focused on individual traits may illuminate which ant foraging strategies are best adapted to a particular habitat. Our data reveal that the morphological composition of ground-dewelling ant assemblages responds clearly to environmental complexity suggesting that certain ant characteristics offer ecological advantages to particular species in particular habitats.

Ants as indicators of environmental change and ecosystem processes

Environmental stressors and changes in land use have led to rapid and dramatic species losses. As such, we need effective monitoring programs that alert us not only to biodiversity losses, but also to functional changes in species assemblages and associated ecosystem processes. Ants are important components of terrestrial food webs and a key group in food web interactions and numerous ecosystem processes. Their sensitive and rapid response to environmental changes suggests that they are a suitable indicator group for the monitoring of abiotic, biotic, and functional changes. We tested the suitability of the incidence (i.e. the sum of all species occurrences at 30 baits), species richness, and functional richness of ants as indicators of ecological responses to environmental change, forest degradation, and of the ecosystem process predation on herbivorous arthropods. We sampled data along an elevational gradient (1000–3000m a.s.l.) and across seasons (wetter and drier period) in a montane rainforest in southern Ecuador. The incidence of ants declined with increasing elevation but did not change with forest degradation. Ant incidence was higher during the drier season. Species richness was highly correlated with incidence and showed comparable results. Functional richness also declined with increasing elevation and did not change with forest degradation. However, a null-model comparison revealed that the functional richness pattern did not differ from a pattern expected for ant assemblages with randomly distributed sets of traits across species. Predation on artificial caterpillars decreased along the elevational gradient; the pattern was not driven by elevation itself, but by ant incidence (or interchangeable by ant richness), which positively affected predation. In spite of lower ant incidence (or ant richness), predation was higher during the wetter season and did not change with forest degradation and ant functional richness. We used path analysis to disentangle the causal relationships of the environmental factors temperature (with elevation as a proxy), season, and habitat degradation with the incidence and functional richness of ants, and their consequences for predation. Our results would suggest that the forecasted global warming might support more active and species-rich ant assemblages, which in turn would mediate increased predation on herbivorous arthropods. However, this prediction should be made with reservation, as it assumes that the dispersal of ants keeps pace with the climatic changes as well as a one-dimensional relationship between ants and predation within a food-web that comprises species interactions of much higher complexity. Our results also suggested that degraded forests in our study area might provide suitable habitat for epigaeic, ground-dwelling ant assemblages that do not differ in incidence, species richness, functional richness, composition, or predation on arthropods from assemblages of primary forests. Most importantly, our results suggest that the occurrence and activity of ants are important drivers of ecosystem processes and that changes in the incidence and richness of ants can be used as effective indicators of responses to temperature changes and of predation within mega-diverse forest ecosystems.

Ground-dwelling ant assemblages (Family: Formicidae) in six coconut (Cocos nucifera L. 1753) plantations in Sri Lanka

The contribution of six well-established coconut plantations to the conservation of biodiversity, specifically of ants, was investigated using soil sifting, timed hand collection and honey baiting along five, 100 m transects established in each plantation. Twenty honey-baited pitfall traps were set throughout each sampling area of each plantation. Collected worker ants were preserved in 70% ethanol and sorted and identified to the furthest possible taxonomic levels under a low-power stereo-microscope. The ant species observed at the five transects in each plantation were tabulated and species richness and proportional abundance of each species at each plantation were recorded. The Shannon-Wiener Diversity index for the ant assemblage at each plantation was calculated. Air and soil temperature, soil humidity and soil pH at each locality were also measured. A diverse ant assemblage occurred at each plantation, where between 19 and 29 species in 4 or 5 subfamilies were recorded; the Shannon-Wiener diversity index values were determined. Higher proportions of formicines and myrmicines than those of other subfamilies were observed. Two or more species in higher proportions than the rest of the ants occurred in each assemblage. Also, the six plantations shared three species and five plantations shared nine species in common. The considerable diversity of ants indicated a healthy environment and provided insight into the presence of other animals in the well-established coconut plantations.

Annual fire resilience of ground-dwelling ant communities in Hiraodai Karst Plateau grassland in Japan

The fire resilience of ground-dwelling ant assemblages in grassland subjected to annual fire management was investigated. Study sites consisted of three burnt sites and three unburnt sites in grasslands on the Hiraodai Karst Plateau in Fukuoka Prefecture, Japan. Ground-dwelling ants were sampled by Winkler extraction and collected at 10 days and 1, 2, 3 and 6 months post-fire. In total 33 ant species belonging to 25 genera in six subfamilies were collected from the burnt and unburnt sites. Eight of the 29 ant species collected at burnt sites were restricted to burnt sites, while four of the 25 ant species collected at unburnt sites were restricted to unburnt sites. Non-metric multidimensional scaling and analysis of similarities revealed that the ant assemblages in the burnt sites at 10 days and 1 month post-fire were clearly separated from the assemblages observed at 2, 3 and 6 months post-fire. The results suggested that the ground-dwelling ant fauna in the study area were highly resilient to fire at 2 months post-fire and that the annual fire regime did not have a marked effect on species richness.

The importance of remnants of natural vegetation for maintaining ant diversity in Brazilian agricultural landscapes

Brazil is one of the leading producers of soybeans and other annual crops, and in several regions landowners are required by law to maintain 20 % of their lands with natural vegetation (i.e. as “legal reserves”). However, there is a growing concern that some of these reserves will be subject to increased levels of disturbance or even be lost as a result of the ongoing legislation reforms. In this sense, studies that evaluate the conservation potential of retaining natural habitats within agricultural areas are of great importance. We assessed the efficiency with which remnants of natural vegetation conserve the native ant fauna in a context of intensive agriculture. We compared the structure of ground-dwelling ant assemblages between crop fields and reserves located in different farms. Ant species richness was much higher in the reserves than in the crops, and this pattern was consistent in spite of variations in the type of crop planted in each field, and in the size (39–149 ha) and vegetation (open or closed savanna) of the reserves. From 41.4 to 76.4 % of all species recorded within each farm were exclusively found in the reserves. Differences in species composition were strong not only because the reserves had much more species, but also because the species that were present in both habitats showed contrasting patterns of abundance in each habitat. Overall, our results highlight that even small remnants of natural vegetation can have a significant potential to maintain a higher diversity of ants within an agriculturally dominated landscape.

Soil properties only weakly affect subterranean ant distribution at small spatial scales

Physico-chemical properties of soils have an indirect effect on ground-dwelling ant assemblages at regional scale. By contrast, little is known on their effect at the scale of the meter, at which direct interactions between subterranean ants and their environments occur.We aimed to study the effect of soil properties on the small-scale distribution of highly diverse subterranean ant assemblages. We expected ant species to be differentially associated with soil variables.This study was conducted in Bombuscaro and Copalinga (Ecuador), two premontane tropical forests 2km apart, sharing the same climate and altitude. In each site, we delineated a 100m line transect and every meter collected a sample of mineral soil (15cm×15cm×10cm) and the associated ant fauna. Compared with traditional baiting this method should provide a relatively unbiased measure of subterranean ant diversity. Organic matter content, pH, electrical conductivity, degree of humification, soil texture and land slope were measured at each sampling point.Soil attributes of the two sites were contrasting and strongly spatially autocorrelated. The two ant assemblages shared only 12% of their 76 species. Ant diversity was higher in Bombuscaro (Fisher-α=21.7 vs. 16 in Copalinga). Species turnover was remarkably high at both regional (intersite) and local (intrasite) scales. Ant species richness was not correlated with any of the measured variables. Soil properties were not associated with the occurrence of any ant species in Copalinga. In Bombuscaro, Hypoponera sp.01RI was correlated with lower pH values, and Acropyga fuhrmanni to higher clay content. A. fuhrmanni did not show correlation with this variable in Copalinga, where it is the dominant species (present in 48% of the samples). However, this species is associated with higher clay content at Copalinga (36.7±6% SD) compared with Bombuscaro (6.5±2%).Although weakly explained by the soil factors investigated, a high ant species turnover was observed at both small (1m) and regional (2km) spatial scales. The latter observation stresses the importance of designing large nature reserves including mosaics of habitats to conserve subterranean ant diversity in the Andes.

Trade-offs between complementarity and redundancy in the use of different sampling techniques for ground-dwelling ant assemblages

Sampling ground-dwelling ants in the field is relatively fast, but sorting and identifying in the laboratory is costly and time-consuming. Using sub-samples collected in 25km2 grids, we surveyed ant assemblages using sardine baits, pitfall traps and Winkler extraction in three Amazonian vegetation types. Combining all three techniques detects the greatest number of species, but may be inefficient. Therefore, we compared the pooled results from the three techniques to results using one or two techniques combined. We evaluated whether the extra information acquired by adding a sampling technique compensates for the time and money associated with the extra processing. We also evaluated the consequences of the reduced effort on the retention of ecological information captured by the three techniques, using soil clay content, terrain slope and altitude as predictor variables in an ecological analysis. Pitfall traps captured the largest number of species and had the highest congruence with ant assemblages recorded by other techniques. Redundancy analysis indicated that pitfall-trapping is the most efficient technique, allowing reduction of 48% in cost and 43% in time. The loss of information about species richness when using only pitfall traps is apparently compensated by the saving of cost and time in the field and laboratory, because use of this technique alone was sufficient to detect all the responses of the ant assemblage to environmental variables that were detected by other techniques. These results indicate that considerable gains in efficiency can be obtained in most Amazonian-forest monitoring programs for ants by using only pitfall traps.

Cerrado ground-dwelling ants (Hymenoptera: Formicidae) as indicators of edge effects

Large-scale agricultural production in Brazil preferentially occupies plateaus reclaimed from areas originally covered by Cerrado (savanna). Depending on the region, a percentage of the pristine vegetation coverage must be preserved by law, resulting in the creation of fragmented legal Cerrado reserves. The geometry of these relatively small legal reserves creates new habitat edges and ecotones, whose effects on the invertebrate fauna are poorly understood. This study aimed to assess the effects of abrupt edges resulting from soy production on ground-dwelling ant assemblages in the Brazilian Cerrado. The study sites are located within the Amazon region, in the state of Maranhão, northern Brazil, but were covered by Cerrado on a relatively low plateau, irregularly inter-spaced with gallery forests along streams. We compared species richness and species composition of ground-dwelling ants along eight transects set 0, 50, 100, 150, 200, and 250 m into the sensu stricto Cerrado and 50 and 100 m into the soy field. The collecting periods covered the wet and dry seasons. Effects on ant species richness were non-significant, although composition of the assemblages was significantly affected by edge effects, which were, in part, found to be species specific. We hypothesize that edge effects are probably greater than estimated because of the shape and complexity of reserves. Consideration of edge effects in the Cerrado Biome should enable the design of appropriate reserve sizes and shapes to meet conservation goals.

Spatio-temporal patterns of ground-dwelling ant assemblages in a lowland rainforest in southeast Cameroon

We studied the spatio-temporal patterns of ground-dwelling and -foraging ant assemblages in a continuous mixed secondary lowland rainforest on the northern periphery of the Dja Biosphere Reserve in southeast Cameroon. The effect of season and of the interaction of season with vegetation type on ant species density, activity and composition were investigated. We also checked for a possible impact of army ant activity on the ant assemblage. Ants were collected by pitfall trapping in seven vegetation types in each of three seasons during 12 months in 2003 and 2004–2005. Season significantly influenced the ground-dwelling ant assemblage. The late wet season had the lowest ant species density and a different species composition than the early wet and the dry season. Also inter-annual variation in ant species density and composition was detected and could partly be explained by an influence of Dorylus activity. In general, vegetation type and inter-annual variation had a larger influence on the ground-ant assemblage than season. Significant effects of interactions between season, year, vegetation type and army ants on the ant assemblage confirm that also in African rainforests ant assemblages are extremely dynamic and depend on a complex combination of availability of food resources, nest sites and predators.