ANTS

Ants belong to the family Formicidae, super family Vespoidea, order Hymenoptera. Among the social insects ants are placed in the category of “eusocial insects” or “truly insects”, where individual of the same species cooperate in caring for the brood, there is a reproductive division of labour with more or less sterile individuals working on behalf of the fertile individuals in the colony and there is an overlap of at least 2 generations in the life cycle capable of contributing to colony labour, so that offspring’s assist the parents during some period of their lifetime. Ants tend to be very aggressive and have great ability to dominate themselves because of which direct interactions between them and plants and also with other arthropods and insects are distinctly seen. They are usually separated from the other Hymenopterans by the one or two-segmented node (modified II and III abdominal segments), connecting the alitrunk (thorax plus I abdominal segment fused, that is known as propodeum or mesonoma) and the gaster (abdomen proper minus II or III segments) and a metapleural gland invariably present in ants (Wilson, 1971).

Together with Homo sapiens, ants are one of the few animal groups that commonly manipulate and modify their surroundings to suit their needs and it’s a truism that they occupy a position among terrestrial invertebrates equivalent to that occupied by our species in/among the vertebrates (Bolton 1995).They offer a lot to people who are interested in long-term monitoring, inventory and ecology.

Ants Diversity
Ants show tremendous diversity, numerical and biomass dominance in almost every habitat throughout the world. Ants constitute upto 15% of the total animal biomass in a Central Amazonian rainforest (Fittkau and Klinge, 1973). Ants can be called as herbivores as they harvest nearly 15% of the herbivory in tropical forests. Studies carried out by Erwin (1989) at Peru showed that 69% of the total insect specimens collected by fogging the forest canopy were ants. Wilson (1987) has reported that a single tree in Peruvian tropical lowland forest yielded 26 genera and 43 species of ants. Agosti et al (1994) have reported a collection of 104 ant species representing 41 ant genera in a 20 m2 of leaf litter and rotting logs at Malaysia. Anderson and Clay (1996) have recorded ants under 248 species from 32 genera in a 18 sq km semiarid area in Australia. Anderson’s work in semiarid north-western Victoria reports the presence of 105 species of ants in a 0.1 ha mallee plot, 100 species of ants from a 0.05 ha plot in tropical savanna at the Northern Territory, which are undoubtedly the richest local ant fauna of the world. Talbot (1975) has recorded 87 species under 23 genera of ants in a 5.6 sq km area in temperate Michigan. Fogging of 2 canopies of Gouupis glabra in the Central Amazonia revealed 100 species of ants representing 21 genera and 5 subfamilies. An overlapping of 28% was also recorded (Haraa and Adis 1997). Sampling in 33, one hectare plots from 12 habitats at the Western Ghats, Gadagkar et al report the collection of 120 species from 31 genera.

Ants are highly variable in their morphology, measuring anywhere between less than 1 mm to 40 mm. Colony sizes of ants range from less than a 100 to several million individuals. Ants exhibit a high degree of variability in their feeding habits, reflecting their temperament, which are docile to highly aggressive. Food preference is extreme in ants – exhibiting a high degree of variability in food selection. They survive on both animal and vegetable matter and there are very few of those ants that are highly specific in their diet. Having exceptions as leaf cutter ants and some harvester ants most of the ants live in part at least by predation (Dumpert 1978). A lot of inconsistency is seen in the diets of ants as one species of the African army ant Anomma molesta not only bring back captured preys to their nest but also feed on bananas. A forest dwelling Ponerine species Odontomachus, a jumping ant, which was considered to be exclusively flesh-eater is known to take honeydew (Evans and Leston, 1971). Members of Rhytidoponera a Ponerine collect and utilize seed kernels (Haskins, 1970). Oecophylla smaragdina a Formicine has diverse diets, tuna fish in baits, coconut, honey, other ants (Pheidole sp) and termites. Members of most of the primitive genera are carnivores which chiefly hunt insects (Veeresh and Ali 1991). Members belonging to the primitive genera of Amblyopone sustain mainly on centipedes (Dumpert 1978). Leptogenys processionalis and L.chinensis are seen to be highly specific and exclusively feed on specific forms of insect diet as termites (Shivshankar 1985). Ants belonging to the genera of Strumigenys, Cerapachys, Proceratium are specialised predators that feed on restricted set of arthropods. Species belonging to Strumigenys are regarded as Collembolan specialists (Kaspari 2000 Ants). Eciton burcelli consumes more than 10000 captured animals per day, a majority of which are insects (Dumpert 1978). Though not specific Harpegnathos saltator preys on wolf spiders, Diacamma rugosm preys on other ants, spiders and termites. Some ants survive on plant exudates (Tennant and Porter 1991). The exudates are however got directly by harvesting nectar from flowers and extra floral nectarines or they are derived as ‘honey dew’, a secretion of homopterans (Veeresh and Ali 1991) (Huxley and Cutler 1991). Some cultivate fungus gardens to meet their food requirements, some are accomplished scavengers and necrophagous while a majority of species serve as general predators on other insect groups exerting enormous pressure on other invertebrate populations in their habitats.

The diversity seen in ant fauna globally suggests that they have attained the ability to survive in various biotopes, which means that they have specialised nesting structures to suit different environmental conditions. Anthills and ant nests are a maze of internal subdivisions wherein they conceal their inhabitants in a highly ordered manner. Accurate and intelligent construction and positioning of the nest and its chambers and passages internally suffices for the specific temperature and moisture levels necessities of the eggs, larvae at different instars, the queen and the different classes of workers (Dumpert 1978). Ant nests are highly diverse taking a variety of forms and shapes. Ground nests are usually associated with most of the Ponerines as Harpegnathos, Streblognathos, Paraponera, Dinoponera, Megaponera and Odontoponera and majority of Myrmicines (Dumpert 1978). However, all their ground nests are not homogeneous and show variations. The nests would have a brood chamber, the queens chamber, a chamber wherein the young ones’ are kept. In most of the cases the brood chamber and the queen would be found at the deepest point of the nest. A refuse-dumping pit is also present at the most inhabitable passage of the nest where the wastes from the colonies as dead nest mates, inedible parts of prey, are dumped (Dumpert 1978). Cataglyphis bicolor builds hill nests or crater nests usually seen in steppes and steppe regions (Schneider 1971). Dietary habits also determine nesting sites for instance Crematogaster auberti follows the tree roots with their passages to reach their diet ¾ the root lice (Soulie, 1961). Nests of Formica sp are 70 cm deep into the ground (Brian and Downing 1958), nests of Veromessor pergandei attains a depth of 3 m and Pogonomyrmex barbatus nests may be over 5 m deep (Wray 1983). The shape of the ant hill can vary from being a flat nest to a steep dome shaped nest in accordance with the available moisture and exigencies of heat in the local environment (Dumpert 1978). In deciduous forests the nests are not very large but the colonies could be very large (Lange 1959). Breathtaking anthills are built by wood ants that are over 1 m in height and 9 m in circumference (Stammer 1938). Ants also nest under the stones which is seen exclusively on higher mountains as the stones lose less heat because of their faster drying out in summer and in addition to this, in these areas frosty nights occur in summer and nesting underneath the stone is an advantage as the temperature of a stone increases immediately at the onset of sunlight (Dumpert 1978). The largest ground nests are constructed by leafcutter ants that run 4 m deep and can penetrate to 8 m of ground with passages and chambers (Eidmann 1932; Jacoby 1953). Some ants belonging to the genera of Crematogaster and Lasius (Maschwitz and Holldobler 1970) build carton nests, which consist of fine sawdust, held together with a cementing material. Members of Crematogaster genus also divide tree hollows with carton nests (Soulie 1961). Ant plants or myrmecophytes support and provide nesting sites for ants belonging to the genera of Crematogaster, Tetraponera, Monomorium, and others. Plants provide hollow structures (Humboltia sp - Crematogaster) thorns (Bull horn Acacia - Azteca ants), pocket like structures with differing forms (Cocoa genus - Azteca ants) for nesting. Strumigenys and Allomerus colonies are seen on several South American species as Maieta, Microphysca, Calophysca, Myrmidone, Tococoa, Hirtella that have swellings on their petiole or at the base of the leaf (Wilson 1971). Very conspicuous swollen and cavernous trunks or stems are seen in trees and shrubs belonging to the dicotyledon families which always act as nesting sites for ants (Wilson, 1971). The silk nest constructed by Oecophylla smaragdina, the weaver ant, use the silk from their larvae and stitch living leaves together to get huge tent like nests (Green 1896; Holldobler and Wilson 1990). 

Status
At present there are about 9000 species of ants described from world-over representing 296 genera and 16 subfamilies (Agosti et al, 2000). Ants have repeatedly turned up in fossils, so far 61 extinct genera of the living subfamilies have been recognized in addition to 14 genera which are grouped under 4 extinct subfamilies (Bolton 1995). The Indian subcontinent records ant species under 8 subfamilies representing 600 species and 92 genera. The subfamilies are Aenictinae, Dolichoderinae, Dorylinae, Formicinae, Leptanillinae, Myrmicinae, Ponerinae and Pseudomyrmicinae (Bingham 1903; Veeresh and Ali 1991). Ants belonging to 7 subfamilies represented by 125 species and 44 genera are known to occur in Karnataka. The subfamilies are Dorylinae, Ponerinae, Myrmicinae, Formicinae, Pseudomyrmicinae, Cerapachyinae and Dolichoderinae  (Ali 1991; Ali 1992).

The Indicator Approach
Identification of robust indicators in the ecological systems for their incorporation into land monitoring and assessment programmes is an interest expressed by most of the conservation biologists. The invertebrate group gets showered with a lot of focus because of their dominant biomass, exceedingly high diversity and intricate relations in the functioning of the ecosystem. Bioindicators are used to assess any kind of environmental perturbation that is generating a response from an ecosystem. The perturbation is often linked with human land use (Noss, 1990, Spellerberg, 1992). The bioindicator approach sometimes can also address (depending on the indicator used) the total species diversity, which would have very important implications in the field of conservation (Anderson 1997). Positive correlation between ants and invertebrate fauna (Majer, 1983), ants and plant species richness at uranium mine site (Anderson et al 1996) and ants with soil microbial biomass (Anderson and Sparling, in press) highlight the significance of essential studies on ants, while addressing issues of biological diversity and conservation.

Ant communities have been used as indicators in determining restoration process at mine sites; changes in soil microbial regimes, monitoring programmes associated with fire, in relation to environmental disturbance and stress. Ants have the potential to be used as indicators since they are sensitive and also because of the rapidity at which they adapt to changes brought about in the environment (Anderson 1990). A functional group concept put forward by Greenslade, which looks into behavior of the species instead only by taxonomic affinity, provides an acceptable system for habitat evaluation to detect environmental changes.

One of the most important studies done on ant communities was classifying 94 Australian ant communities similar to the way vegetation is classified according to predominating life forms by keeping their functional groups as attributes (Anderson, 1995). This study went further to classify that Dominant Dolichoderinae are analogous to trees, Generalised Myrmicinae to shrubs, and ruderal opportunists to grasses in terms of their responses to stress and disturbance. This study showed how these functional groups vary across vegetation types, such as open woodlands, forest, plantation, and treeless plant communities. It showed that abundance of dominant group of ants (a combination of Dominant Dolichoderines and Generalised Myrmicines) was positively correlated to species richness, while poor correspondence was seen between ant plant community structure types.

Ant communities when used as indicators of ecosystem restoration at mining sites have shown excellent successional patterns over a period of time thus proving that understanding of the functional groups and their signals that respond directly to any kind of stress and disturbance can lead to accurate prediction of ecosystem restoration. Monitoring ant communities for a 20-year period in Australia and changes in their composition has been used as an indication of restoration success following mining. The patterns in their changes reflect ecological changes at the mine site that is undergoing restoration Anderson (1997) showed that for the initial 5 years the species richness increases after which it stabilises, with the species varying from year to year depending on vegetation and other ecological factors. Ants have shown to be excellent indicator taxa to detect restoration of bauxite mines by long term work done by Majer and Nichols (1998). On planting seeds of mixed plant species in a mine pit, the first 2 years showed a rapid attainment of forest like ants.

A similar kind of work done in Brazil to see ant recolonisation at bauxite mines was carried out by Majer (1996). Rehabilitated bauxite sites ranged from 0 – 11 years; rehabilitation done by planting mixed native forest tree species. Of the 206 species of ants collected, 26.21% were confined in rehabilitation areas, 39.80% exclusive in native vegetation and 33.98% were found in both the situations. Sampling done also in a Eucalyptus and Acacia plantation showed ant species richness as high as in native vegetation. The rehabilitated areas compared to the forest had proportionally more of generalists of soil and litter and fewer specialists. Extensive work done near Richards Bay, South Africa by Majer and Kock (1992) in 8 rehabilitated sand mined areas and 3 coastal dune forests showed that species richness increased for the first 2 years, declined and later again started increasing following rehabilitation for 8 years. Sampling ant fauna by Biserac and Majers (1997) in 7 rehabilitated (2 – 20 yr old) and 3 native healthlands at Western Australia recorded 96 species of ants compared to the 46 species got 17 years earlier. Ant species richness plotted against rehabilitation age showed a logarithmic curve indicating an improvement in conditions. Although there was an increase in species richness the ant composition and functional groups varied from 1980 to 1997. This gives an insight into ecological community as it seems that even after 17 years of rehabilitation which should have facilitated the rapid return of ant species, the composition of the original health land fauna has not yet been regained.

Work done in the Brazilian rain forest of Amazon basin in three 1ha, two 100ha and one 1ha lot revealed that ant species increased as forest area increased (Anonymous, 2000). This study also strongly suggests that forest fragmentation affect the structure of ground dwelling ant communities. At Venezuela it was seen that the densities of nests of Atta sp increased in small and medium islands (5.6 and 2.3 colonies per ha) compared to large islands (0.72 colonies per ha) and main land (0 nests in 5.5 ha). The incipient colonies however showed a reverse trend with number of colonies increasing in large islands. However, on a comparative basis their survival decreased in larger land areas (Rao, 2000). Greenslades’ (1991) work in Tasmanian temperate rain forests showed that richness and abundance of ant fauna is very low.

Vanderwoude et al, (1997), used ants as indicators in forest monitoring programs to determine the impacts of different fire regimes on ant communities. Of the total 88 species of ants recorded under 43 genera in South East Queensland (Vanderwoude et al, 1997), the annually burned site recorded 74 species, the periodically burned site 63 species and 43 from the unburned site. The annually burned site recorded a relatively high abundance of 36% of the arid taxa and 8% of the cool temperate taxa with the opposite being true for the unburned site. The relative abundance of Dominant Dolichoderinae increased with fire frequency. 65% of the ants at the unburned sites were Opportunists, but they reduced to 16% at the annually burned site. Thus, reflecting on the potential of utilising the sensitivity of ant communities in fire management practices.

Majer et al (2001) examined the influence of decreasing latitude and elevational changes on richness and abundance of arboreal ants. This study was done in cool temperate forests, notophyll vine forests, high elevation notophyll vine forest, complex notophyll vine forest, complex mesophyll vine forest and mixed dipterocarp forests. Species richness was negatively correlated with both latitude and elevation. Majer’s (1990) earlier work showed that richness of arboreal ants, tree ants and ground dwelling ants in Australian rain forests is very low compared to other tropical rain forests and was occasionally lower even when compared to the neighboring Eucalyptus plantation. Oecophylla smaragdina and Crematogaster sp were dominating in the tropical and sub tropical rain forests.

Galle et al (1998) described the species composition, diversity, population interactions and external correlates of ant assemblages in different successional plots of a sand-dune area in the Kampinos National Park, Poland. An increase in the species diversity was contradicted with a decrease in the last phase, which could be explained by the presence of red wood ant species, which are dominant in the interference competition. The Architecture of vegetation, number and condition of dead twigs on soil surface and temperature seem to be correlated with the composition of the ant assemblages. In the competitive network of the early successional ant communities, Formica cinerea and Myrmica rugulosa have the same rank.

A unique study was done at Mount Isa, Australia to detect responses of ant communities to dry sulphur deposition (Benjamin et al, 2000). Few species of ants showed a positive correlation with sulphur deposition, which were those, found in the disturbed sites of Australia. Species richness however reduced with soil SO₄ concentration. High and medium sulphur zone levels showed less abundance of ants.

Sampling for ants in a Mediterranean grassland by Cerda and Retana (1990) fetched 13 species of ants, with Pheidole pallidula being the most dominant, followed by Tapinoma nigerrium and Aphaenogaster senilis. Kondoh (1990) studied the ant communities at Mt Fuji and came up with interesting communities of ants with particular vegetation types. The scoria grassland vegetation corresponds with Myrmica kuroki – Formica lemani community, deciduous woodland with Myrmica kuroki – Formica lemani – Leptothorax acervorum community, coniferous evergreen forest of Abies with monospecies community of Myrmica kuroki and shrub with Myrmica kuroki – Formica lemani – Leptothorax acervorum – Formica sanguinea community. Coniferous evergreen forest which is disturbed by scoria drift and its marginal vegetation corresponds with 2 communities; one is Myrmica kuroki – Camponotus sachalinensis – Leptothorax acervorum – Formica sanguinea – Lasius niger; the other being Formica lemani – Leptothorax acervorum – Formica sanguinea – Camponotus sachalinensis.

Anderson and Majer (1991) report that several of the rainforest species as Oecophylla, Oligomyrmex, Quadristruma, certain Leptogenys, Crematogaster and Polyrhachis provide biogeographic links with the east coast of Australia. They also point out that most of the cryptic species of the rain forest are areas with moist litter only in dry seasons. The most common ants found in their study were Pheidole, Monomorium and Tetramorium. This study also differentiates ants based on their foraging strata as whether they forage on litter, vegetation or ground.

Remote sensing and GIS
Remote sensing in the field of conservation and management of natural resources has had varied applications. It has been used for census of wildlife especially marine mammals, and carnivores in savannas. It is also used in monitoring the movement of wildlife. But the increasing applications of remote sensing have been primarily in the area of plant sciences. Practically most of the work done in remote sensing revolves around vegetation classification, crop monitoring and harvesting, mapping patterns in different forests, range lands, agricultural lands and diseases detection in crops (James, 1996). GIS along with remote sensing data help in inventorying, monitoring and assessing the natural resources on both spatial and temporal scale.