Hot Climate Specialists Research Articles

Diversity and Abundance of Ants from Tehsil Nerwa of District Shimla, Himachal Pradesh, India

The present study focused on diversity, abundance and functional groups of ants from Tehsil Nerwa of District Shimla, Himachal Pradesh. A total of 693 ant specimens representing 33 species belonging to 22 genera of 4 subfamilies were collected. Myrmicinae is the most diverse and abundant subfamily. Dolichoderinae is the least diverse subfamily while Ponerinae is the least abundant subfamily. During this study also reports range extension of 3 invasive species. 2 Species are endemic to the region. In this study seven functional groups of ants were identified. These are: “Generalized Myrmicinae”, “Opportunists”, “Subordinate Camponotini”, “Hot climate Specialists”, “Cold climate Specialists”, “Cryptic Species”, and “Specialist Predators”. The area is very susceptible to anthropogenic activity, as indicated by the prevalence of invasive species there. Therefore, some stringent measures should be taken to preserve the deteriorating ecosystem of the study area.

Old‐field restoration improves habitat for ants in a semi‐arid landscape

Many old fields are undergoing ecological restoration aiming to return lost biodiversity and ecosystem functions. However, there is scant evidence that this outcome is achieved. Here we investigate the effects of tree planting following cessation of cropping on ant communities. Ants are a dominant faunal group, functionally important for ecosystem recovery and widely used as indicators of ecosystem restoration. Using a space‐for‐time approach, we surveyed eight fallow croplands, 10‐year‐old planted old fields, and reference woodlands in semi‐arid south‐western Australia. We tested the extent ant communities in planted old fields diverged from those of fallow cropland and converged with those of reference woodlands, distinguishing areas under tree canopies and open patches to account for a direct tree effect. We analyzed ant community data at species, genus, and functional‐group levels. Ant species composition in planted old fields substantially converged from fallow croplands toward reference woodlands. Abundance and richness of genera in the tree‐associated functional group Subordinate Camponotini was higher under trees than in open areas in planted old fields and reference woodlands. Unlike in reference woodlands, abundance and richness of Hot Climate Specialists was not higher in open areas than under trees in planted old fields, indicating that planted trees did not yet strongly impact the microclimate beneath them. Although old field restoration had positive effects on ant assemblages, full convergence to reference woodlands had not been achieved after 10 years. This was particularly evident for functional groups. Research on older plantings is needed to test if and when full convergence occurs.

Effects of Habitat Conversion on Ant Functional Groups: A Global Review

Conversion of natural to anthropogenic environments affects biodiversity, and the understanding of these impacts may be improved by assessing how different functional groups respond to such land conversion. We studied land conversion impacts on ant functional groups, as ants are ecologically important and respond well to various environmental changes. We hypothesized that conversion of natural to anthropogenic environments modifies the composition of functional groups, fostering generalist and opportunistic groups over specialist ones, with more responses of this type in tropical than in temperate regions. We recovered 412 papers from ISI Web of Science, of which we selected 17 studies, published between 1993 and 2018, that addressed our study’s question. We assessed whether each functional group responded positively or negatively to conversion of natural habitat into anthropogenic land uses and used Monte Carlo tests to assess significance. Ants were affected by natural habitat conversion into monoculture and polyculture and by the conversion of savannas and of tropical and subtropical forests. Land conversion affected six of the 13 functional groups assessed here. In the temperate zone, cryptic species, predators, subordinate Camponotini, cold-climate specialists and tropical-climate specialists were impaired, whereas hot-climate specialists were favored. In the tropics, land conversion negatively impacted fungus-growers and predators. In both climatic zones, several functional groups, mainly those with broad ecological niches, did not respond to land conversion. Our results corroborate that land conversion effects vary among ant functional groups and indicate that the ant fauna of temperate ecosystems may be more susceptible than that of tropical regions.

Ant functional structure and diversity changes along a post-grazing succession in Mediterranean oak woodlands

Grazing exclusion may be used to promote the recovery of disturbed ecosystems. A promising way for the evaluation of its effectiveness is through the monitoring of key biological groups, particularly those more responsive to disturbance and playing key roles in ecosystem functioning. Ants have been used as ecological indicators as they are abundant, diverse and sensitive to environmental changes. Here, we aimed to evaluate changes in ant taxonomic and functional structure and diversity, using functional groups, along a post-grazing succession in a Mediterranean oak woodland and to understand which environmental variables drive them. The post-grazing succession comprised a chronosequence of grazing excluded sites for 8, 12 and 18 years and a grazed control site. We found that ant species richness, functional structure and diversity increased with years since grazing exclusion: Generalist/Opportunist and the Hot Climate specialists increased in the 18 years grazing excluded site, while the Cryptic Species group increased in the 12 years grazing excluded site. Yet, their responses were not linear over time. Time since grazing exclusion and vegetation structure explained differences in ant taxonomic and functional structure and diversity. The Invasive/Exotic group dominated in all sites, except in the longest excluded site, where it occurred in the lowest proportion. The invasive Argentine ant dominated the grazed site, where it may have led to ant taxonomic and functional homogenization. Our results suggest that the time and changes in habitat structure may favour the recovery of ant biodiversity, although the presence of the invasive Argentine ant species may have slowed it down.

Ants respond more strongly to grazing than changes in shrub cover

AbstractIncreases in the cover or density of woody plants (encroachment) and overgrazing by European livestock are 2 major drivers of ecosystem structure and function in drylands and are often associated with land degradation. Although the effects of encroachment and overgrazing on vascular plants are relatively well known, little is known about their effects on arthropods such as ants. We examined ant community composition at sites ranging in shrub cover in a wooded dryland in eastern Australia, testing the notion that increasing shrub cover and grazing intensity would alter ant assemblages and functional group composition. We used ants because they are abundant, diverse, and respond to small‐scale environmental changes. Increasing shrub cover had no effect on ant richness, diversity, or evenness but increased the abundance of Subordinate Camponotini. Larger shrubs tended to have greater ant richness, and abundance of Cold Climate Specialists, but fewer Generalized Myrmicinae and Hot Climate Specialists. More intense grazing was associated with greater ant richness, diversity, and evenness; a greater abundance of Hot Climate Specialists and Dominant Dolichoridae; and lower abundance of Subordinate Camponotini. Our study indicates that changes in grazing intensity had stronger effects on ant richness than any increase in shrub cover. The effects of grazing likely resulted from changes in soil surface complexity such as barer ground associated with grazing‐induced degradation.

Variability of ant community composition in cork oak woodlands across the Mediterranean region: implications for forest management

Abstract: We evaluated the potential use of ants as a powerful tool for environmental monitoring, together with the applicability of the functional group approach as an alternative method for studying ant communities in cork oak woodlands. Variations in ant community composition, diversity and functional groups were studied in two cork oak forested sites across the Mediterranean region. Ants were sampled using pitfall traps placed along linear transects at 12 sites located in the main cork districts of Italy and Morocco (Gallura in Sardinia, and Maâmora, east of Rabat). A total of 13.501 specimens were collected, belonging to 38 species (five shared species). A distinct separation in the NMDS plots between Gallura and Maâmora ant assemblages was clearly visible. Ant species composition was widely different between the two districts and significant differences were detected within the Gallura district at the species level. Opportunist species were well represented in Gallura (about 27% of average Bray-Curtis similarity) as well as cryptic species (over 23%). In the Maâmora forest, generalized Myrmicinae, hot climate specialists and opportunists contributed equally to the average similarity (together about 53%). Multi-scale ant diversity showed that the true turnover was higher in Gallura than in Maâmora. These findings support the idea that the functional group approach, rather than species diversity per se, could be considered as a valuable tool to detect the response of the ant community to environmental changes in Mediterranean cork oak woodlands. Using ants as bioindicators could help not only in detecting early warning signs of habitat disturbance, but also in defining a useful management strategy to increase the resilience of agroforestry systems under future global change scenarios.

Biodiversity impacts of an invasive grass: ant community responses to Cenchrus ciliaris in arid Australia

Buffel grass (Cenchrus ciliaris) is a highly invasive species that thrives in semi-arid environments and has the capacity to transform native vegetation outside its native range. However, there is limited information on the effects of buffel grass invasion on native fauna. We used an experimental approach to investigate the impact of buffel grass on the native ant fauna near Alice Springs in semi-arid central Australia. A series of plots where buffel grass was removed and native vegetation had regenerated (B−), paired with adjacent control plots heavily invaded by buffel grass (B+), were used to assess the impact of buffel grass on ant diversity and composition, and on rates of seed dispersal by ants. Differences in ant diversity were also compared between two microhabitat types: bare ground and under cover, to examine the extent to which any impacts were a simple function of change in vegetation cover. Ant abundance and richness were approximately 50 % higher in B− compared with B+ plots, and higher abundance was especially pronounced for the very thermophilic Hot-Climate Specialists. Ant species composition varied significantly between plot types. B− plots supported more species and individuals in both bare and covered microhabitats, which suggests that the differences in ant diversity was not simply through changes in vegetation cover. Rates of seed removal by ants were marginally higher in B− plots. Our findings indicate that buffel grass has a major impact on a dominant faunal group of arid Australia, and possibly reduces the delivery of an important ecosystem service. In addition, our study demonstrates the potential for ecosystem recovery following effective buffel grass management.

Multi-century dynamics of ant communities following fire in Mediterranean-climate woodlands: Are changes congruent with vegetation succession?

As vegetation recovers after disturbances such as fire its composition and structure systematically changes, affecting the availability of resources for fauna and mediating physical conditions. According to the habitat accommodation model, these changes drive a succession of animal species, which enter and leave according to their habitat requirements. While the response of ants to fire has been extensively studied, studies of ant communities in biomes with long fire-return intervals have been overwhelmingly short-term in nature. Here, we explore the response of ant species, functional groups and communities to time since fire using a uniquely long-term (>300years) chronosequence in eucalypt woodlands of south-western Australia. Marked non-monotonic vegetation structural changes occur in non-resprouting Eucalyptussalubris-dominated woodlands following fire, with tree and ground fuel cover peaking at intermediate periods post-fire. Hence, we predicted that changes in the occurrence of Dominant Dolichoderinae, Hot-Climate Specialist and Cold-Climate Specialist functional groups would mirror the non-monotonic changes in habitat complexity, as predicted by the habitat accommodation model. Overall ant species richness and composition did not show clear post-fire successional patterns, with extensive spatial turnover a likely factor. However, richness and abundance of ant functional groups broadly responded as predicted, with Dominant Dolichoderinae and Hot-Climate Specialists more prominent in more-open recently-burnt and long-unburnt habitat, and Cold-Climate Specialists more prominent in less open habitat at an intermediate time since fire. This matching, non-monotonic temporal pattern of changes in ant functional groups and vegetation structure suggests that ant functional group occurrence is mediated through changes in habitat, as posited by the habitat accommodation model, and not simply time since disturbance. Current fire management in E. salubris woodlands aims to minimise wildfire occurrence, which is consistent with the maintenance of ant functional diversity at a regional scale given the long time periods over which changes occur post-fire. The combination of recent large wildfires and predicted fire-facilitating climate changes suggest that future shifts in the relative dominance of ant functional groups are likely if fire management is unsuccessful in limiting wildfires occurring in mature woodlands.

Response of ants to grazing disturbance at the central Monte Desert of Argentina: community descriptors and functional group scheme

Livestock ranching is one of the main productive activities in arid regions of the world. Grazing produces changes in animal as well as plant communities (e.g. richness, abundance and species dominance relationships). Ants are good biological indicators due to the environmental fidelity of some of their community parameters. We described the functional structure of the ant community in the central Monte of Mendoza, Argentina, and examined the effect of grazing using richness, diversity and the functional group scheme. We used pitfall traps to sample ants at a reserve with 30-year cattle exclusion and at an adjacent ranch. Eleven of the 27 recorded species showed significant differences in their abundance and two species were absent at the ranch. While richness and diversity did not reflect these differences, functional groups did. Hot Climate Specialists were more abundant at the ranch while Cryptic Species and Generalized Myrmicinae increased at the reserve. This study supports the utility of the functional group scheme to study the effects of grazing disturbance in ant communities of arid regions.

Distinctive life traits and distribution along environmental gradients of dominant and subordinate Mediterranean ant species

For most animal and plant species, life traits strongly affect their species-specific role, function or position within ecological communities. Previous studies on ant communities have mostly focused on the role of dominant species and the outcome of interspecific interactions. However, life traits of ant species have seldom been considered within a community framework. This study (1) analyses life traits related to ecological and behavioural characteristics of dominant and subordinate ant species from 13 sites distributed throughout the Iberian Peninsula, (2) determines how similar the ant species are within each of the two levels of the dominance hierarchy, and (3) establishes the distribution patterns of these different groups of species along environmental gradients. Our results showed that the differences between dominants and subordinates fall into two main categories: resource exploitation and thermal tolerance. Dominant species have more populated colonies and defend food resources more fiercely than subordinates, but they display low tolerance to high temperatures. We have identified different assemblages of species included within each of these two levels in the dominance hierarchy. The distribution of these assemblages varied along the environmental gradient, shifting from dominant Dolichoderinae and cryptic species in moist areas, to dominant Myrmicinae and hot climate specialists mainly in open and hot sites. We have been able to identify a set of life traits of the most common Iberian ant species that has enabled us to characterise groups of dominant and subordinate species. Although certain common features within the groups of both dominants and subordinates always emerge, other different features allow for differentiating subgroups within each of these groups. These different traits allow the different subgroups coping with particular conditions across environmental gradients.

Selective logging in public pine forests of the central Iberian Peninsula: Effects of the recovery process on ant assemblages

Pine forests on the northern plateau of the Iberian Peninsula have a long history of use, exploitation, and management. Current management practices consist of selective logging with relatively short periods of time between logging events. The main objective of this study is to detect changes in ant assemblages in the short time periods between selective logging activities. Ants were sampled at 44 sites considering three grouping categories of time periods after the last timber extraction: short (<4 years), medium (4–8 years) and long (>8 years). After selective logging the number of ant species increases as the forest recovers. A look at the differences between the assemblages when the analysis shifts from the species-specific level to functional groups showed differences between the short and long categories. This indicates that in certain circumstances the functional groups may be more informative of the functional restructuring of the ant assemblages in a disturbed habitat. Ant species from three functional groups display significant indicative values (Opportunist, Hot Climate Specialists and Subordinate Camponotini) in the medium- and long-time-after-logging categories: Messor capitatus (HCS) for medium-time category sites; and Aphaenogaster iberica (Op), Camponotus cruentatus (SC) and, Cataglyphis velox (HCS) for long-time category sites. No indicator species were found for the early stages of recovery. This information may also be of interest to managers because it reduces the number of data elements of the recovery status of these forests, and can be translated into monitoring protocols. The continued exploitation of these forests leads to an ant fauna that reflects this change. The results show that ant assemblages need at least 8 years to recover since only after that much time there is an emergence of Subordinate Camponotinae, a behaviorally dominant and low stress-tolerant functional group. This selective logging maintains the relative diversity and structure of ant assemblages.

Habitat and Grazing Influence on Terrestrial Ants in Subtropical Grasslands and Savannas of Argentina

AbstractThe maintenance of species diversity in modified and natural habitats is a central focus of conservation biology. The Iberá Nature Reserve (INR) protects highly diverse ecosystems in northeastern Argentina, including one of the largest freshwater wetlands in South America. Livestock grazing is one of the major disturbances to these ecosystems; however, its effect on ant diversity is poorly known. The objective of this work was to study the effect of savanna versus grassland and grazing on the structure and composition of subtropical terrestrial ants focusing on the particular response of the native red imported fire ant, Solenopsis invicta Buren. Unbaited pitfall traps were used to capture worker ants in 25 grazed and 20 nongrazed sites. Fifty ant species were collected. The savanna showed more species, individuals, biomass, and functional groups of ants than the grassland. S. invicta was the most frequently captured (61.4%) and numerically dominant species; however Camponotus punctulatus punctulatus Mayr showed the highest biomass. Grazing simplified vegetation structure in both habitats, but its impact on vegetation seemed only to promote a higher total biomass especially in the grassland, and/or functional groups, favoring occurrence of hot-climate specialists in the savanna. This study revealed that habitat type strongly affected the organization of the terrestrial ant assemblages at the INR. However, as in other studies, we did not find clear evidence that habitat modification by grazing significantly affected terrestrial ant assemblages. The weak grazing influence could be the consequence of the short enclosure time as to recover the original ant communities, the differential response of ant species to habitat type, and/or the resilience of ants.

Composition and functional groups of epiedaphic ants (Hymenoptera: Formicidae) in irrigated agroecosystem and in nonagricultural areas

The objective of this work was to evaluate the species composition and functional groups of ants in nonagricultural (NA) and in irrigated areas (S, seasonal irrigation; P, irrigation with well water; W, irrigation with wastewater) in an arid agricultural region in central Mexico, throughout 2005 and 2006. A total of 52,358 ants belonging to 6 subfamilies, 21 genera and 39 species was collected using pitfall traps. The species best represented in all plots were: Forelius pruinosus, Pheidole obtusospinosa, Monomorium minimum and Dorymyrmex spp. NA plots recorded the highest density of ants. The highest values for diversity (H') and equitativity (J') were recorded in NA and P plots, while the lowest were recorded in W plots. Cluster analysis showed two different groups regarding species composition: NA-S and W-P. Functional groups recorded were: dominant Dolichoderinae, three species; subordinate Camponotini, five species; hot climate specialists, three species; tropical climate specialists, seven species; cold climate specialists, five species; cryptic species, one species; opportunists, six species; generalized Myrmicinae, nine species. Agricultural activity affects the structure of the ant community with epiedaphic forage, and the constant use of irrigation wastewater in conjunction with intense agricultural practices has negative effect upon species richness of epiedaphic ants.

Community structure and functional group classification of litter ants in the montane evergreen and deciduous forests of Wayanad region of Western Ghats, Southern India

Community structure of litter ants based on feeding guilds and the more recent functional group classification, and also the role of abiotic factors in determining the community structure have been analyzed following ‘Ants of Leaf Litter’ protocol in a montane evergreen (shola) and deciduous forests in the Wayanad region of Western Ghats, southern India. Distinct variations in the guild structure of litter ant communities in shola and deciduous forests have been recorded. Predators dominated deciduous and omnivores in the shola forests. Cryptic species was the dominant functional guild in both litter stands, although hot-climate specialists have not been recorded from the shola forests. Rank-abundance plots attributed the difference in diversity between the forests to the dominance of Tapinoma sp. and Myrmicaria brunnea in deciduous forest. Physical characteristics of the habitat critically influenced ant abundance in both forest types. Functional group model classification was found to be a better model for the classification of litter ants than the conventional feeding-guild categorization as it enabled a meaningful comparison in relation to physical factors.

Biogeography and diversity of ants in Purnululu (Bungle Bungle) National Park and Conservation Reserve, Western Australia

We describe the diversity, composition, functional group organisation and biogeography of ants in Purnululu National Park (128°19′E, 17°19′S) in Western Australia’s Kimberley region, located at a semi-arid/tropical zone boundary. Pitfall trapping collected a representative sample of ants from three main habitats within the park: spinifex, sandplain and gorges. In total, 154 species from 25 genera were collected. The richest genera were Melophorus, Iridomyrmex and Monomorium. Iridomyrmex was the most abundant genus, accounting for 80% of all individuals recorded in traps. Functional group composition was dominated by Dominant Dolichoderinae (41% of individuals collected) and Hot Climate Specialists (26%). Biogeographical composition was typical of semi-arid zone assemblages located on the overlap between Eyrean and Torresian zones: 50% of the species recorded represented Eyrean taxa, followed by 33% with Torresian affinities, and 10% Widespread. Differences in ant species richness, abundance and assemblage composition between the three habitat types were attributed to a combination of variation in vegetation structure and microhabitat composition. This paper provides baseline data on local ant communities in the semi-arid Kimberley, enabling a greater understanding of the conservation value of reserves within the Kimberley, one of Australia’s least studied bioregions.

Community organization and species richness of ants (Hymenoptera/Formicidae) in Mongolia along an ecological gradient from steppe to Gobi desert

AbstractAim Ants (Hymenoptera/Formicidae) have strong influences on ecosystems especially in arid regions. However, little is known about ants of the vast steppe and desert regions of Central Asia. Here we provide the first comprehensive study of ant communities in Mongolia, conducted along a north‐to‐south gradient in climate. We examined ants’ distribution patterns, assessed the impact of climatic parameters on community structure and species diversity and investigated the influence of the corresponding communities of plants.Location Mongolia (Central Asia).Methods We observed 31,956 ants at seed baits at 11 study sites along a transect from steppe to Gobi desert for which we attained meteorological data (mean yearly precipitation: 197 to 84 mm). Extra sampling was conducted at sugar and protein baits and by the inspection of different microhabitats. Vegetation patterns of each plot were recorded. Statistical evaluation comprised ordination and correlation.Results We observed 15 species of ants at seed baits. Three faunal complexes of ants could be distinguished by detrended correspondence analysis (DCA): (1) in steppe baits were dominated byFormica‐ andMyrmica‐species, (2) in semi desert we found mostly species ofTetramorium,Myrmica,Proformica,Plagiolepis, andLeptothorax, and (3) in desertCataglyphis aenescensandMessor aciculatusdominated, andLasiuswas exclusively found there. Another 11 rare ant species were sampled by hand and at sugar baits. Altogether five ant species were new to the Mongolian fauna:Cardiocondyla koshewnikovi,Myrmica koreana,Myrmica pisarskii,Polyergus nigerrimus, andProformica kaszabi. Assignment of taxa to functional groups showed that in steppe cold climate specialists dominated, in semi desert we found mainly opportunists, and in desert hot climate specialists. Several functional groups know from arid zones in other parts of the world were missing. In desert certain species were highly dominant. First DCA scores of ant‐ and plant‐communities were highly correlated with each other and with climatic parameters. While plant species diversity was positively correlated with increasing northern latitude, ant diversity and ant species richness were not correlated with latitude and responded neither to precipitation, nor to any other climatic parameter. Semi desert was a transition zone between steppe and desert, with high species richness. Ant genus composition of the ecotone overlapped with both other regions. However, beta diversity between pairs of plots within this zone was low, indicating a small‐scale mosaic pattern.Main conclusions The ant communities in the Mongolian steppe and desert zones were strongly influenced by low temperatures and differed in many aspects from the ant fauna in other arid ecosystems, especially in terms of species richness, diversity of feeding guilds, and richness of functional groups.

Responses of ants to disturbance in Australia, with particular reference to functional groups

Abstract Ants are widely used as bioindicators in environmental assessment in Australia, partly because the responses of ant communities to disturbance are relatively well understood. In particular, the use of functional groups has provided a predictive framework for analysing ant community responses to disturbance in the absence of reliable information on the responses of individual species. Here we review 45 studies of the responses of Australian ant communities to disturbance, in order to: (i) identify individual species or species‐groups that respond consistently to disturbance; and (ii) examine the usefulness of the functional group scheme as a framework for predicting ant community responses under different disturbance regimes in different biogeographical regions. The most common forms of disturbance in our studies were fire (17 studies), mining (12; mostly studies of minesite restoration) and grazing (7), with other disturbances including clearing, logging, flooding, recreation, urbanization and farming. Responses of individual species were inevitably variable because of differences in vegetation type, severity of disturbance and time since disturbance. However, we identified a range of widespread species that showed predictable responses, including species of the metallica group of Rhytidoponera in temperate Australia (‘increasers’ in relation to disturbance), species of the terebrans and denticulatus groups of Camponotus (increasers), the aeneovirens group of Melophorus (increasers) from the arid zone, and Iridomyrmex pallidus (increaser) from the monsoonal region. The functional group scheme assessed here was not designed specifically in the context of disturbance, but nevertheless in some situations provides a useful framework for analysing ant community responses. Three distinct syndromes of functional group responses can be recognized. First, Dominant Dolichoderinae and Hot Climate Specialists are groups that prefer open environments, and tend to be favoured by low levels of disturbance in well‐forested habitats. Second, Opportunists and often also Generalized Myrmicinae are broadly adapted taxa with wide habitat tolerances, but are particularly sensitive to competitive interactions such that their responses oppose those of Dominant Dolichoderinae. Finally, Cryptic Species and Specialist Predators have highly specialized requirements that make them especially sensitive to disturbance. Functional groups are of most use in situations where disturbance causes substantial change in habitat structure, particularly in the ground‐layer. Functional groups are of least use in very open habitats, where disturbance merely increases what is already extensive bare ground, and has relatively little impact on microclimate. The ant functional group scheme can play an important role in assessing disturbance in mesic Australia, but may be of more limited use for this in the arid zone.

Short Note

Using process‐orientated parameters to assess degradation.

Structure of ground-foraging ant assemblages in relation to land-use change in the northwestern Mediterranean region

The abandonment by humans of marginal and less productive zones signifies an important change in land use in North Mediterranean agroecosystems. Human perturbations have led to a highly diversified landscape, with a mosaic made up of patches of land at different stages of succession, from cultivated fields to closed forest. Our aim here is to characterize ant assemblages and their functional groups in response to these land-use changes. This progressive abandonment results in an initial increase in ant richness and abundance, which can reach high levels if the succession proceeds as far as woodland. In terms of the ant functional groups, this land-use change implies: (1) the appearance of Subordinate Camponotini; (2) an increase in Generalized Myrmicinae, Cryptics and Cold-climate specialists in terms of ant species richness, overall abundance and, for Generalized Myrmicinae and Cryptics, an increase in abundance percentage; (3) a decrease in percentage abundance of Opportunists; (4) a progressive decrease in species richness as well as overall and percentage abundance of Hot-climate Specialists throughout the transformation from crops to woodlands; and (5) an initial increase of Dominant Dolichoderinae followed by a decrease in ant species richness, overall abundance and percentage abundance. Using the ant functional group approach for the clearly separate stages of the regeneration process is a promising method for comparing responses of ant communities to human land use.

Changes in ant species composition and community organisation along grazing gradients in semi-arid rangelands of the Northern Territory.

The impact of cattle grazing on ant diversity, species composition and community organisation was investigated in the Victoria River District of the Northern Territory, using distance from water as a surrogate of grazing intensity. Two gradients were sampled, one on red earth at Kidman Springs (5 plots), the other on black cracking clay at Mount Sanford (6 plots). Sites were sampled in April (both sites) and October (Kidman Springs only)1998. The two sites supported distinctly different ant communities, with 70 species at Kidman Springs and 36 at Mount Sanford. Species richness and total abundance did not change significantly with distance from water, although species richness was always greatest at the most distant plot. However, multivariate analysis showed that ant species composition changed markedly. Despite large changes in species composition, the abundance of only six of the 24 most common species (two at Kidman Springs and four at Mount Sanford) were significantly correlated with grazing intensity. The abundance of Bassian taxa was promoted by grazing, whereas the species richness of Torresian taxa and the abundance and species richness of Widespread taxa were suppressed. Ant functional group analysis showed community organisation was resilient, with slight changes being primarily driven by Hot Climate Specialists and dependent on the season. However, the relative richness of five functional groups correlated significantly with grazing intensity, all negatively. Ant variables suppressed by grazing were positively associated with patch cover variables and litter, and negatively correlated with annual grass and bare ground, and may serve as indicators of rangeland condition. Key words: biodiversity, cattle grazing, indicators, piosphere, rangeland management, semi-arid, tropical savannas