Diversity and Organization of the Ground Foraging Ant Faunas of Forest, Grassland and Tree Crops in Papua New Guinea

Home , Acropyga acutiventris, Cardiocondyla nuda, Iridomyrmex, Meranoplus, Odontomachus, Oecophylla smaragdina

- - -- Aust. J. Zool., 1975, 23, 71-89

P. M. Room Department of Agriculture, Stock and Fisheries, Papua New Guinea; present address: Cotton Research Unit, CSIRO, P.M.B. Myallvale Mail Run, Narrabri, N.S.W. 2390.

Abstract Thirty samples of ants were taken in each of seven habitats: primary forest, rubber plantation, coffee plantation, oilpalm plantation, kunai grassland, eucalypt savannah and urban grassland. Sixty samples were taken in cocoa plantations. A total of 156 species was taken, and the frequency of occurrence of each in each habitat is given. Eight stenoecious species are suggested as habitat indicators. Habitats fell into a series according to the similarity of their ant faunas: forest, rubber and coffee, cocoa and oilpalm, kunai and savannah, urban. This series represents an artificial, discontinuous succession from a complex stable ecosystem to a simple unstable one. Availability of species suitably preadapted to occupy habitats did not appear to limit species richness. Habitat heterogeneity and stability as affected by human interference did seem to account for inter-habitat variability in species richness. Species diversity was compared between habitats using four indices: Fisher et al.; Margalef; Shannon; Brillouin. Correlation of diversity index with habitat heterogeneity plus stability was good for the first two, moderate for Shannon, and poor for Brillouin. Greatest diversity was found in rubber, the penultimate in the series of habitats according to heterogeneity plus stability ('maturity'). Equitability exceeded the presumed maximum in rubber, and was close to the maximum in all habitats. The mosaic dispersion pattern found among ants elsewhere also appeared to be present in each habitat. The mean maximum number of territories possible to be overlapping is about 4.6; the number in a particular case probably being a function of the specialization of the dominant ant present. Ecological isolating mechanisms among ants are probably similar to those among birds; size and structure of mouthparts in ant communities warrant further study. Introduction The importance of ants in many tropical ecosystems has long been recognized (Wheeler 1910), and there have been a number of cases in which ants have been used to control pests of tropical crops (Groff and Howard 1925; Meer Mohr 1927; Bruneau de Mire 1969; Stapley 1971). Recently, interest has developed in the general principles governing interactions between ants and tropical tree crops, and ways in which those interactions can be manipulated (Room 1972; Leston 1973). The study reported here was concerned with description and analysis of the ground- foraging components of the ant faunas of a variety of habitats ranging from primary forest to urban grassland. Its principal objective was to examine the extent to which ant faunal diversity was a function of habitat heterogeneity as affected by human interference.

Study Area and Habitats Study Area Field work was carried out around Popondetta (148'14'E., 8'45's.) in the Northern District of Papua New Guinea. Fig. 1 shows the major localities in the area, and P. M. Room

the position of the area in relation to the whole of the island of New Guinea. All samples were taken within or very close to the triangle subtended by Saiho, Lego and Girua with the exception of those taken in the eucalypt savannah grassland in the hills immediately to the south of Oro Bay. The above triangle is located on the gently sloping outwash plain to the north of Mt Lamington. Numerous steep- sided stream valleys dissect this plain, and the black sandy soil is very well drained.

0 30 -kilometres

Solomon

Afore

Fig. 1. Map of the Popondetta area in the Northern District of Papua New Guinea, showing roads and mountains.

Much of the primary, evergreen rain forest is still standing in the Northern District. Dotted about on the outwash plain are a number of quite extensive grassland 'islands', while near human settlements and particularly along roads there is a patchwork of secondary forest, food garden clearings, and cocoa, coffee and rubber plantings. Popondetta has an average annual rainfall of 2425 mm. Monthly mean rainfall and daily sunshine are given by Room and Smith (1974). June, July and August of each year are usually relatively dry, but not so dry that lack of water limits plant growth. Rainfall increases inland towards Mt Lamington and the Wharton Range, and decreases towards the coast. No figures are available, but residents believe that Saiho has a little more rain than Popondetta, while Oro Bay has a great deal less. Mean maximum and minimum temperatures at Popondetta are 32 and 22°C I2"C (7-y means). Haantjens (1964) gives more detailed information on geology, soils, climate and vegetation in the study area. Ground-foraging Ant Faunas of Papua New Guinea

Habitats Primary forest. Anisoptera kostermansiana Dilmy-Pometia pinnata Forst. F. association (Taylor 1964). A, B and C storey trees were present, with great diversity of species. The herb layer was sparse and contained many tree seedlings. Leaf litter and rotting wood were abundant on the ground. Light intensity was generally less than 1 % of outside light and the microclimate was warm, humid and stable. Rubber plantation. The rubber trees were between 15 and 25 y old and most had a low C storey of young cocoa trees, bananas or rubber saplings beneath them. Light penetration through the rubber canopy was greater than in the forest and consequently there was a denser layer of herbs on the ground. Pathways were kept clear along the rows of rubber trees for tapping, and periodically bush regrowth between rows was cut back. Leaf litter was present on the ground, but not to such a depth as in the forest. Cocoa plantation. The cocoa trees and the most commonly used shade tree, Leucaena leucocephala (Lam.) de Wit, formed a single C storey canopy in most of the plantations, but in a few others Erythrina spp., coconuts or thinned forest trees formed a thin B or A storey above the cocoa. Light penetration to the ground was generally less than in the rubber but more than in the forest. A thick layer of leaf litter was usually present, and in places where the canopy was thin there was a moderately dense herb layer. Room and Smith (1974) give a detailed account of this cocoa ecosystem. CofSee plantation. Most of the robusta coffee formed a dense C storey canopy beneath scattered Albizia falcataria (L.) Fosberg or Leucaena leucocephala shade trees. Light penetration was very low and the herb stratum consisted almost entirely of seedling coffee trees. A thick layer of wet leaf litter was usually present. Oilpalm plantation. Oilpalm is grown without top shade, and, though more light penetrates the canopy than in cocoa plantations, the ground in the two oilpalm blocks sampled was mostly bare because of frequent weeding. Each block was 19 by 17 palms in size and it is probable that microclimatic conditions within the blocks were not as stable as they would be in more extensive plantings. Kunai grassland. Imperata cylindrica (L.) Beauv.-Saccharum spontaneum L. alliance (Taylor 1964) is maintained as a disclimax by annual burning. Mature stands are up to 3 m in height. Temperatures in full sunlight are very high at 1 m, but lower on the ground due to shading by the tall grasses which tend to lodge. Soil between the grass stems is usually bare. Eucalypt savannah grassland. This is a Themeda australis (R. Br.) Stapf.-Imperata cylindrica alliance (Taylor 1964) which is regularly burned. There are some scattered thin stands of Eucalyptus tereticornis Sm. and the grass is generally below 1.5m in height. The rainfall in this habitat is significantly less than in the others. Urban mown grassland. This is dominated by Chrysopogon aciculatus (Retz.) Trin. and repeatedly cut down to 2 cm in height. Playing fields, an airstrip and garden lawns were sampled. Table I summarizes the main components of each of the above habitats, and for the purpose of later discussion indicates the comparative diversity of the ground ant fauna to be expected in each. These latter projections are based on the hypothesis that faunal diversity is a function of habitat : age by area by heterogeneity by microclimatic stability. The first two factors, and a factor 'availability of suitably preadapted P. M. Room

species' which could not be estimated, relate to the number of species successfully invading a habitat. The latter two factors relate to the carrying capacity of the habitat, and themselves vary as some inverse function of the 'degree of repeated human interference'. With the exception of the forest, each of the habitats is maintained as a disclimax by man: rubber, cocoa and coffee by infrequent bush regrowth clearance; oilpalm by regular weeding; kunai and savannah grassland by annual burning; urban grassland by frequent mowing.

Table 1. Comparison of factors affecting faunal diversity in eight habitats in Papua New Guinea For 'Strata of vegetation' the numeral indicates the stratum; T, tree; H, herb. Other factors are rated on a five-point scale: I, very low, very young or very small; 11, low, etc.; 111, moderate; IV, high, old or large; V, very high, etc.

Factor Primary Rubber Cocoa Coffee Oilpalm Kunai Savannah Urban forest grassland grassland grassland

Strata of 3T 1H 2T 1H 1T 1H 1-2T 1T 1H 1H 1H 1H vegetation 1H Tree species Many 1-2 2-3 2-3 1 0 0 0 Herb diversity 111 111 I11 I1 I1 111 111 I Leaf litter Much Some Much Much None None None None Microclimate stability IV IV IV IV 111 I1 I1 I Human interference I 111 111 I11 V IV IV IV Age of habitat V I1 I1 I1 I I11 111 I1 Area of habitat V n I1 I1 I I11 I11 I Expected ground ant faunal diversity V IV IV IV I1 I1 I1 I

Sampling Methods Thirty samples were taken in each of the habitats except cocoa plantation, in which 60 were taken as part of a more detailed study of the ground and canopy ant faunas. For the sake of the present study these 60 have been split into two groups of 30 each (cocoa 1 and cocoa 2) so that nine sets each of 30 samples were taken in all. In order to minimize the effects of variables extrinsic to the various habitats, each sample was taken: (1) between 0900 and 1100 h; (2) when the sun was shining; (3) well away from the edges of habitats; (4) only in areas of mature habitat. To ensure independence of each sample, no two samples were taken closer together than 30 m and, with the exception of samples in the oilpalm habitat, no more than five were taken in the same discrete area of habitat. There were only two blocks of mature oilpalm present in the Northern District, so 15 regularly spaced samples were taken in each. Samples were taken by placing a 1-m2 quadrat on the ground. Specimens were collected of every ant species seen on the ground, among loose dead leaves on the ground, or climbing on the herb stratum within the quadrat, in a 10-min period. Many specimens of easily confused species were taken, and if a recognized species was missed in the first 10 min an extra 2 min were allowed for its possible capture. All specimens were killed by dropping into 70% alcohol and were identified in the laboratory by use of a reference collection. A list was made of the species present in each sample. All names, letters and numbers used to designate ant species in this paper are those in current use by the Papua New Guinea Department of Agriculture, Stock and Fisheries (D.A.S.F.) Central Insect Collection, and the Australian National Insect Collection.

Results The frequencies of occurrence in the various habitats of the 156 species of ant taken in the 270 samples are shown in the Appendix. Those species which occurred in one-third or more of the samples from any habitat are (asterisk indicates dominant species) : Ground-foraging Ant Faunas of Papua New Guinea

Forest Aphaenogaster perplexus* Rubber Paratrechina ?stigmatica Cocoa 1 Brachyponera croceicornis*, Anoplolepis longipes* Cocoa 2 Brachyponera croceicornis*, Anoplolepis longipes*, Odontomachus simillimus*, Techno- myrmex albipes* Coffee Brachyponera croceicornis* Oil palm Anoplolepis longipes*, Paratrechina ?stigmatica Kunai Brachyponera croceicornis*, Anoplolepis longipes*, Iridomyrmex cordatus*, Polyrhachis sp. R281 Savannah Anoplolepis longipes*, Iridomyrmex cordatus*, Polyrhachis sp. R281 Urban Iridomyrmex cordatus*, Iridomyvmex sp. R349, Meranoplus sp. 1, Cardiocondyla nuda, Paratrechina ?minutula Some of these were restricted to a single habitat or group of habitats, and could be used as indicator species, as follows: Forest Aphaenogaster perplexus Rubber None Cocoa Technomyrmex albipes Coffee None 1 Odontomachus simillimus Oilpalm None Anoplolepis longipes Kunai Polyrhachis sp. R281 Savannah Iridomyrmex cordatus Urban Meranoplus sp. 1 Cardiocondyla nuda J Faunas considered as whole units may be compared according to a number of criteria. The results of several different analyses of similarities and differences between the faunas of the habitats are reported below under separate headings.

Table 2. Numbers of ant species occurrences common to different habitats, and the percentage similarity of habitats Occurrences, upper right; percentages, lower left, expressed as 100 x [(2 x number of occurrences common to both)/(sum of occurrences present in each)]. Abbreviations: F, forest; R, rubber; C1 and C2, cocoa; Cf, coffee; 0, oilpalm; K, kunai; S savannah; U, urban

Species Composition The frequency of occurrence of a species in the 30 samples from a habitat was taken as the importance value for that species in that habitat. Habitat faunas were P. M. Room

compared by summing the importance values common to a pair of habitats, multi- plying by 200, and dividing by the sum of all the importance values for the two habitats. Table 2 shows importance values common to all pairs of habitats, total importance values for each habitat (on the diagonal), and calculated percentage similarities.

Fig. 2. Web diagram of those habitats which had ground-foraging ant faunas more than 25% similar in Table 2.

The cocoa 1 and cocoa 2 faunas had a similarity of 54%, suggesting that faunas with a similarity of more than about 50% under the conditions of the study were essentially identical. Thus, faunas having a similarity of 25 % or more were more similar to each other than dissimilar. Fig. 2 shows faunas more than 25% similar as linked together. There was a gradation in faunal composition between the forest habitat and the eucalypt savannah, while the urban grassland fauna was linked to no other fauna.

Table 3. Indicators of species richness according to habitat Thirty samples each from 1 mZof ground were taken in each habitat. For abbreviations, see Table 2

No. of species F R C1 C2 Cf 0 K S U per sample

Mean No. of species per sample 4.57 4.07 3.93 4.37 3.27 3.07 5.93 5.27 3.50 Total No. of species in 30 samples (N) 49 49 45 45 41 29 39 40 18 Sum of importance values(1) 137 121 118 131 98 92 177 158 105 NII 35.8 40.5 38.1 34.4 41.8 31.5 22.0 25.3 17.1

Species Richness Three kinds of species richness could be defined for the data gathered: the mean number of species present in l m2; the total number of species present in 30 in- dependent 1-m2 samples; and the total number of species present in 30 samples Ground-foraging Ant Faunas of Papua New Guinea

divided by the total importance values for the samples. Table 3 shows these measures of species richness for each habitat. The habitats rank into different orders depending on the expression of species richness used. Only the differences between the mean number of species per sample can be checked for significance (Table 4). Habitats having no significant differences between their means in Table 4 are shown linked in Fig. 3 (mean for the cocoa habitat taken as 4.15).

Table 4. Levels of significance below 5 % for the differences between mean number of species per sample shown in Table 3 For abbreviations, see Table 2

Fig. 3. Habitats linked together which have no significant difference between mean number of species per sample in Table 4.

Diversity Species richness and the distribution of individuals among species are the two components of indices of diversity. Some indices assume the form of the distribution of individuals among species and utilize the number of species (S) and the number of individuals (N) only as inputs for calculation: the a of Fisher et al. (1943) and the D' of Margalef (1968). Other indices are based on the information content of a sample and incorporate the observed distribution of individuals among species in their calculation: the H' of Shannon (1948) and the H of Brillouin (1962). There is some doubt as to the practical value of some diversity indices (Gillon and Pernes 1970; Bullock 1970), so it was decided to calculate each of the above indices for each of the habitats (Table 5). a was estimated using fig. 94 in Southwood (1966), while the other indices were found using the equations: D' = (S- l)/exp N ;

where c = 3.321928 (the conversion factor to change the base of logarithms from 10 to 2) and ni = the importance value of the ith species. Table 1 in Lloyd et al. (1968b) was used to assist calculation of H' and H. P. M. Room

Equitability The evenness or equitability of the apportionment of importance values among species in the different habitats was compared by finding for each habitat (Table 5) the ratio E = S'IS, where Stis the number of species in a MacArthur's broken stick model with maximum equitability necessary to give a species diversity equivalent to the observed one, and S is the actual number of species in the habitat. S' was found by substituting the information function H' calculated previously into table 22 in Southwood (1966), which shows the diversity in terms of the information content associated with different numbers of species in MacArthur's model.

Table 5. Indices of diversity and index of equitability calculated for the ground ant faunas of eight different habitats

Habitat Fisher Margalef Shannon Brillouin Equitability index index index index index

Forest 28 0.8980 Rubber 31 1.1030 Cocoa 1 25 0.9111 Cocoa 2 24 0.8668 Coffee 25 0.9757 Oilpalm 15 0.8966 Kunai 16 0.9486 Savannah 17 1 .oooo Urban 7 0.9443

Dominance Pattern There are always a few species present in the ant fauna of a tropical tree crop canopy which dominate all the others in terms of density of foraging individuals. Colonies of these dominant ants generally maintain foraging territories exclusively free from individuals from other colonies of the same or different species of dominant ant, though some cases of codominance are known (Strickland 1951; Way 1953; Greenslade 1971; Room 1971; Majer 1972; Leston 1973). To test whether a similar mosaic pattern of ant territories was present on the ground in the habitats investigated, associations between species taken five times or more in each habitat were analysed using an unmodified x2 method (Room 1971). Positive associations found to be significant are shown in Fig. 4, and significant negative associations in Fig. 5.

Discussion The D.A.S.F. collection of Papua New Guinea ants contains more than 570 recognized species at the time of writing. Most of these were collected in the Central, Northern, Morobe and Manus Districts over a 2-month period by B. B. Lowery and over an 18-month period by the author. Species new to the collection continue to be discovered regularly in the above Districts, while more than half the country remains to be covered by collecting. It seems likely that the ant fauna of Papua New Guinea totals over 1000 species, so that the 156 species taken in the present study represent less than 20 % of it. Ground-foraging Ant Faunas of Papua New Guinea

Forest

Polyrhachis sp. R251 Odontornachus sp.1------Pheidole irnpressiceps

Rubber

Aphaenogaster perplexus Tapinorna melanocephalurn

Oecophylla srnaragdina Pheidole sp. R672

Brachyponera croceicornis Paratrechina ? stigrnatica

Cocoa

Brachyponera croceicornis ------Rhytidoponera araneoides I ~heidolo~eton? australis Coffee

Brachyponera croceicornis Pheidologetori ? australis

Oilpalm

B. croceicornis Paratrechina ? stigmatica Anoplolepis longipes

Kunai

Rhytidoponera araneoides ------Polyrhachis sp. R274 A, longipes------Paratrechina sp.R217------Iridornyrmex sp. R313

Savannah

A. longipes Polyrhnchis sp. R90 Iridomyrmex sp. R655 Iridornyrrnex cordatus ------Polyrhachis sp. R281

Urban

lridornyrrnex cordatus Meranoplus sp.1

Fig. 4. Positive associations between ground-foraging ants in different habitats, significant at less than the 10 % (- - -) and 5 % (-) levels. P. M. Room

Forest

Pheidologeton ? australis ------Pheidole impressiceps

Aphaenogaster perplexus Brachyponera croceicornis

Rubber

A, perplexus ------B. croceicornis ------Pheidole sp. R679

Cocoa

Monornorium floricola ------Technomyrmex albipes

Odontornnchus B. croceicornis simillimus I I I Rhytidoponera Pheidole megacephala araneoides-. .. --..- . / Anoplolepis longipes I I Oecophylla srnaragdina

Coffee

Brachyponera croceicornis ------Hypoponera sp. 2

Odontornnchus simillimus ------Anoplolepis longipes

Kunai

Iridomyrmex nitidus A. longipes Polyrhachis sp. R274

5. croceicornis ------Paratrechina sp. R217 Pnlyrhachis sp. R281 I I Calornyrrnex nlbertisi

Savannah

Polyrhachis sp. R90 - - - - -I. cordatus A. longipes Carnponotus sp. R148 Paratrechina longicornis ------Polyrhachis sp. R129 Acantholepis sp.1 I I Polyrhachis sp. R281 Iridornyrrnex sp. R655

Fig. 5. Negative associations between ground-foraging ants in different habitats, significant at less than the 10 % (- - -) and 5 % (-) levels. Ground-foraging Ant Faunas of Papua New Guinea

Urban

Monornoriurn floricola Paratrechina ? rninutula

I. cordatus Pheidole rnegacephala lridornyrrnex sp. R349 I I I I Meranoplus sp.1 Cardiocondyla nuda Fig. 5 (Continued)

The great majority of species listed in the Appendix nest at ground level, usually in dead wood, and forage at ground level only. Some species such as Oecophylla smaragdina and Crematogaster spp. R117, R118 and R136, nest arboreally and forage to some extent on the ground. Ground-nesting species which forage in trees were generally absent, as recorded by Wilson (1959). A notable exception was Anoplolepis longipes, which nested under leaf litter or in holes in the ground, and foraged over the surface of everything within its territories, including forest trees if present. Sampling was of presence or absence over a period of time, so frequencies in the Appendix refer to foraging territories rather than to individuals. It may be helpful to think of ant colonies as 'superorganisms' for the remanider of this discussion. The list on p. 75 shows that some of the common species of ant, such as Brachy- ponera croceicornis, were euryecious, while others, such as Aphaenogaster perplexus, were stenoecious. Strictly stenoecious species which are abundant in the habitat in which they occur make useful indicators of the nature of the habitat from which a collection was made. The secondlist shows strictly stenioecous species, and combinations of less stenoecious species, which could be used as indicators for the habitats, or combinations of habitats, investigated. Few of the species which act as dominants are stenoecious and this supports the contention (Room 1971) that lack of ecological specialization and dominance are correlated. Table 2 and Fig. 2 show that the order of the habitats arranged according to similarity of faunal composition closely resembles the order of the habitats ranked according to expected ant diversity (Table 1). These orders can best be interpreted as showing the relative positions of the habitats along an artificial, discontinuous succession from a simple unstable ecosystem (urban grassland) to a complex stable one (rain forest). The number of species taken in a sample may be considered to be determined by sample size and the factors affecting diversity mentioned earlier. Sample size was constant throughout, so values for the mean number of species per m2 and the total number of species in 30 samples (Table 3) are measures of species richness at different size scales comparable between habitats. The forest habitat, for example, with its large size, old age and presumed saturation of ant niches, had a mean of 4.57 species per m2. This should be a measure of mean ant niche hypervolume available, or heterogeneity, on the small scale in the forest. It is not strictly a measure of heterogeneity in 1 m2 of the habitat, because heterogeneity of the surroundings will have partly determined the species taken. Since tropical rain forest is the one habitat in which all the factors presumed to affect diversity are maximal, this figure of 4.57 should also be an estimate of the P. M. Room

mean maximum number of ant foraging territories it is possible to have overlapping at one point in space and time. Additional evidence for this hypothesis is the mean number of 4.65 for overlapping territories in the canopy of 'cocoa forest' (sensu Leston 1970) in Ghana (Room 1971). The term 'mean maximum' is used because the actual number of non-dominant species able to forage in the territory of a particular dominant ant appears to be correlated with the specialization of the dominant (Room 1971). However, Table 3 shows that both kunai and savannah grasslands had a higher mean number of species per m2 than did forest. Though the same 1-m2 quadrat was used in all habitats, sample size in the kunai and savannah could be considered larger than in the other habitats because of the additional foraging area provided by the tall grasses. In addition, when the grasses lodged two separate microhabitats were effectively formed: the shaded, relatively cool and humid soil surface, and the insolated, hot, dry, horizontal grass stems and leaves. Polyrhachis spp. R90, R110, R129 and R281 were rarely taken on the ground, for example, while Iridomyrmex cordatus was almost never taken climbing grass stems. Hence the unexpectedly high values for kunai and savannah may have resulted from the unintentionally greater volume of samples, and the two microhabitats, rather than one, sampled. If the component of diversity, 'availability of preadapted species', were maximal for each of the habitats as for the forest, then comparison of the order of habitats ranked by the other assumed components of diversity with the order of the habitats ranked by ant species richness (Table 4 and Fig. 3) might suggest which of the other components was most important. Comparison of Fig. 3 with Table 1 does not suggest association of species richness with any single component of diversity even if the positions of kunai and savannah are ignored. The linkage of forest, rubber and cocoa (Fig. 3) suggests that the lesser age and area of the rubber and cocoa do not significantly reduce species richness as compared with forest. That is, heterogeneity plus stability (or ant niche hypervolume) and availability of preadapted species must be very similar for the floors of primary forest and cocoa and rubber plantations. The linking of oilpalm, coffee and urban habitats does not correlate with any of the components in Table 1 except herb diversity, which is low in all three. Diversity of herb species may affect ant diversity through diversity of honeydew sources such as extrafloral nectaries and relatively host-specific Homoptera. The link between rubber and urban is inexplicable except to suggest that availability of preadapted species may be independently similar for both habitats. The age of the grasslands in the Northern District is not definitely known, but they probably originated with the arrival of man many thousands of years ago. Because of this, the availability of species to invade the new urban grassland habitat might be greater than the availability of species to invade the new coffee and oilpalm habitats. Further, the age and large extent of the grasslands might partly account for the positions of kunai and savannah in Fig. 3. The total numbers of species taken in each habitat (Table 3) enable a comparison to be made between the total species richness of the various habitats. The values for kunai and savannah may be erroneously high, but even so the agreement between the order of habitats ranked by large-scale species richness and by expected ant diversity (Table 1) is striking. This suggests that availability of preadapted species is not a significant factor in determining species richness at the larger scale, while Ground-foraging Ant Faunas of Papua New Guinea

habitat heterogeneity plus stability are. Further, the equal values for forest and rubber, and the high values for cocoa, in Table 3 suggest that tree diversity is not a major factor in determining ground ant diversity. The ratio of the total species in 30 samples to the sum of importance values com- pares heterogeneity plus stability at the 1-m2 scale with that at the larger scale if other factors affect species richness at both scales equally. Thus, the coffee habitat has the greatest range of floor microhabitats from place to place, while the urban grassland has the least. The relative values given in Table 3 correlate well enough with subjective impressions of the variability of the habitats: coffee, rubber and cocoa seem to have less uniform floor coverings than forest; forest appears to have a less uniform floor than the weeded ground under oilpalms; this seems less uniform than annually burnt grassland; and this is less uniform than regularly mown grassland. The indices of diversity in Table 5 allow the habitats to be ranked into different orders (Table 6). Each index gives rubber the highest, urban the lowest, and oilpalm the next to lowest diversity. Between the extremes of rubber and oilpalm the orders of habitats according to the Fisher and Margalef indices agreed best; the only difference being in the relative positions of cocoa and coffee. The order according to the Shannon index differed from the Margalef index order in the positions of savannah and cocoa 2, and from the Fisher index order in the positions of savannah, coffee and cocoa 2. The order according to the Brillouin index differed greatly from all the other three orders.

Table 6. Habitats ranked according to the indices of diversity shown in Table 5

Fisher Margalef Shannon Brillouin Equitability index index index index index

Rubber Rubber Rubber Rubber Rubber Forest Forest Forest Savannah Savannah Cocoa 1 Cocoa 1 Cocoa 1 Forest Coffee Coffce Sa~annah Kunai Kunai Cocoa 2 / El;:: Coffee Cocoa 1 Urban Savannah Savannah Cocoa 2 Cocoa 2 Cocoa 1 Kunai Kuna~ Kuna~ Coffee Forest Oilpalm Oilpalm Oilpalm Oilpalm Oilpalm Urban Urban Urban Urban Cocoa 2

Comparison of Table 6 with Table 1 shows that the Fisher and Margalef indices arrange the habitats into the most readily comprehensible order. The lesser diversity of the forest fauna compared with the rubber fauna was not entirely unexpected. Margalef (1968) noted that species diversity is sometimes greater in the less mature stages than in the final stage of a succession. The Shannon and Brillouin indices do not rank the habitats into orders which are completely sensible in terms of any of the information in Tables 1 and 3. It can only be assumed that the MacArthur's broken stick model basis for these indices is not entirely appropriate to the present P. M. Room

study, and that the Brillouin index suffers from some additional impediment to its usefulness. Both Gillon and Pernes (1970) and Bullock (1971) concluded that the Fisher index was useful and the Shannon index useless in their cases. The former authors did, however, find the index of equitability derived from the Shannon index to be of value. Clearly, if the MacArthur model is to some extent inappropriate, values of the equitability index in Table 5 and the ranking of habitats in Table 6 should be regarded with suspicion. It is noteworthy that the value of 1.103 for the rubber habitat exceeds the conjectured 'ecological maximum' equitability of 1.0 of Lloyd and Ghelardi (1964). Also, the forest, which should have the greatest equitability because of its 'maturity' (Goulden 1966), is surpassed in Table 6 by most of the other habitats. Lloyd et al. (1968~)suggested that random, intense rainfall might have caused instability of a forest floor environment in Borneo, causing a low equitability value observed for herptiles. No such factor could possibly be suggested to account for the low position of forest in the last column of Table 6. However, if the basis for use of the equitability index is not entirely wrong, it could be that differences between the indices for the various habitats are not significant. In that case, the order in the last column of Table 6 is meaningless, and the high index value for all the habitats simply 'reflects the extreme efficiency of the Formicidae in utilizing even young disturbed habitats. The factors causing the mosaic-type dispersion of dominant ants might have given rise to the high equitabilities found in the study. In particular inter- and intraspecific territoriality might be involved. Tramer (1969) and Kricher (1972) found that equitability among bird populations increased during the breeding season when territoriality increased. Figs 4 and 5 give information on territoriality among ants in each habitat as described by the frequencies of joint occurrence in samples. Time did not allow greater numbers of samples to be taken from each habitat and the data gathered enabled positive and negative associations to be detected between particularly abundant species only. Nevertheless, such associations were found in every habitat, though they give but a glimpse of the true complexity of the organization believed to exist in the various ant communities. Sampling minimized, as far as possible, effects of variables extrinsic to the habitats. In a relatively uniform habitat the most important variable affecting the distribution of any species of ant is that of the (other) dominant ants in the habitat (Way 1953; Greenslade 1971 ; Room 1971 ; Majer 1972; Leston 1973). Figs 4 and 5 support this generalization in that almost every chain of negatively associated species contains at least two dominants, while every chain of positively associated species contains but one dominant. Fig. 5 confirms that dominant species have mutually exclusive distributions no matter in which habitat they come into contact. That is, their niches appear to overlap a great deal. It is pertinent to mention here the similarity between the results of recent work on relative distributions of tropical ants and of birds (Lack 1971). In both cases the animals occupy three-dimensional environments which they split into horizontal and vertical compartments. Nest sites do not seem to be limiting for the ants, nor for the birds (Edington and Edington 1972), but food supply does appear to be limiting for both. Temporal isolation of feeding among birds is not a common phenomenon, though it does occur as between hawks and owls; among ants temporal isolation is Ground-foraging Ant Faunas of Papua New Guinea

more widespread possibly because of lesser dependence on sight. The most important mechanisms reducing competition for food among birds have been radiation in size and beak shape. An analysis of the distribution by size and mouthpart structure of the ant species in communities associated with different dominants in the same habitat might clarify the nature of ant community structure. With reference to tree crops, their faunas contained elements from both of the older, more extensive habitats in the area: forest and grassland. Species richness and diversity fell between the extremes for forest and grasslands in the cases of cocoa and coffee. The oilpalm fauna seemed to be impoverished by the effects of intensive human interference, while the rubber fauna appeared to have the high diversity which has been observed before in immediately preclimax stages of ecological succession.

Acknowledgments Field work was partly carried out while the author was working for the Department of Agriculture, Stock and Fisheries of Papua New Guinea. Analyses and writing up were supported by a grant from the Cocoa, Chocolate and Confectionery Alliance. Dr R. W. Taylor identified the reference collection of ants as far as possible; valuable discussions were held with Dr D. Leston.

Reference Brillouin, L. (1962). 'Science and Information Theory.' 2nd Ed. (Academic Press: New York.) Bruneau de Mire, P. (1969). Une fourmi utilisee au Cameroun dans la lutte contre les mirides du cacaoyer Wassmannia auvopunctata Roger. Cafe' Cacao The' 13, 209-12. Bullock, J. A. (1970). The investigation of samples containing many species. 2. Sample comparison. Biol. J. Linn. Soc. 3, 23-56. Edington J. M. and Edington, M. A. (1972). Spatial patterns and habitat partition in the breeding birds of an upland wood. J. Aninz. Ecol. 41, 331-57. Fisher, R. A., Corbet, A. S., and Williams, C. B. (1943). The relation between the number of species and the number of individuals in a sample of an animal population. J. Anim. Ecol. 12, 42-58. Gillon, Y., and Pernes, J. (1970). Recherches ecologiques dans la savane de Lamto (CBte d'Ivoire): comparaison de plusieurs indices de diversite dans I'btude d'un peuplement de mantes. Terre Vie 1970(1), 54-61. Goulden, C. E. (1966). La Aguada de Santa Ana Vieja: an interpretative study of the Cladoceran microfossils. Arch. Hydrobiol. 62, 373-404. Greenslade, P. J. M. (1971). Interspecific competition and frequency changes among ants in Solomon Islands coconut plantations. J. Appl. Ecol. 8, 323-52. Groff, G. W., and Howard, C. W. (1925). The cultured citrus ant of South China. Lingnaam Agvic. Rev. 2, 108-14. Haantjens, H. A. (Ed.) (1964). General report on lands of the Buna-Kokoda area, Territory of Papua and New Guinea. Aust. CSIRO Land Res. Ser. No. 10. Kricher, J. C. (1972). Bird species diversity: the effect of species richness and equitability on the diversity index. Ecology 53, 278-82. Lack, D. (1971). 'Ecological Isolation of Birds.' (Blackwell: Oxford.) Leston, D. (1970). Entomology of the cocoa farm. Annu. Rev. Entomol. 15, 273-94. Leston, D. (1973). The ant mosaic-tropical tree crops and the limiting of pests and diseases. PANS (Pest Avtic. News Summ.) 19, 311-41. Lloyd, M., and Ghelardi, R. J, (1964). A table for calculating the equitability component of species diversity. J. Anim. Ecol. 33, 217-25. Lloyd, M., Inger, R. F., and King, F. W. (1968~).On the diversity of reptile and amphibian species in a Bornean rain forest. Am. Nut. 102, 497-515. P. M. Room

Lloyd, M., Zar, J. H., and Karr, J. R. (1968b). On the calculation of information-theoretical measures of diversity. Am. Midl. Nat. 79, 257-72. Majer, J. D. (1972). The ant mosaic in Ghana cocoa farms. Bull. Entomol. Res. 62, 151-60. Margalef, R. (1968). 'Perspectives in Ecological Theory.' (University of Chicago Press.) Meer Mohr, J. C. (1927). Au sujet du rBle de certaines fourmis dans les plantations coloniales. Bull. Agric. Congo Belg. 1927, 97-106. Room, P. M. (1971). The relative distributions of ant species in Ghana's cocoa farms. J. Anim. Ecol. 40, 735-51. Room, P. M. (1972). A rational approach to control by ants of pest situations in tropical tree crops. Abstr. 14th Int. Congr. Entomol., Canberra 1972, p. 329. Room, P. M., and Smith, E. S. C. (1974). Relative abundance and distribution of insect pests, ants and other components of the cocoa ecosystem in Papua New Guinea. J. Appl. Ecol. 11, in press. Shannon, C. E. (1948). A mathematical theory of communication. Bell Syst. Tech. J. 27, 379-423; 623-56. Southwood, T. R. E. (1966). 'Ecological Methods.' (Methuen: London.) Stapley, J. H. (1971). Field studies on the ant complex in relation to premature nutfall of coconuts in the Solomon Islands. Proc. Conf. Cocoa and Coconuts in Malaysia, Kuala Lumpur, 1971, pp. 345-54. Strickland, A. H. (1951). The entomology of swollen shoot of cacao. 11. The bionomics and ecology of the species involved. Bull. Entomol. Res. 42, 65-103. Taylor, B. W. (1964). In 'General Report on Lands of the Buna-Kokoda area, Territory of Papua and New Guinea'. (Ed. H. A. Haantjens.) Aust. CSIRO Land Res. Ser. No. 10. Tramer, E. J. (1969). Bird species diversity: components of Shannon's formula. Ecology 50, 927-9. Way, M. J. (1953). The relationship between certain ant species with special reference to biological control of the coreid Theraptus sp. Bull. Entomol. Res. 44, 669-91. Wheeler, W. M. (1910). 'Ants, their Structure, Development and Behaviour.' (Columbia University Press: New York.) Wilson, E. 0. (1959). Some ecological characteristics of ants in New Guinea rain forests. Ecology 40, 437-47.

Manuscript received 25 July 1974

Appendix

Frequency of occurrence of the 156 ant species taken in 30 samples from each of eight habitats Abbreviations: F, forest; R, rubber; C1, and C2 cocoa; Cf, coffee; 0, oilpalm; K, kunai; S, savannah; U, urban

Species F RClC2CfO K S U

Cerapachys ?krombeini (Donis.) 1 Cerapachys sp. 8 1 Cerapachys sp. 9 1 Rhytidoponera araneoides (Le Gillou) 1424 8 3 R. ?laciniosa Viehmeyer 311 R. ?inops Em. 2 Gnamptogenys sp. 2 1 Odontomachus nigriceps FSm. 4 1 0. simillimus F. Sm. 116126533 Odontomachus sp. 1 7 1 2 Anochetus graefei Mayr 11 3 2 Ground-foraging Ant Faunas of Papua New Guinea

Species

Anochetus sp. 1 1 Diacarnma rugosum (Le Gillou) Brachyponera croceicornis Em. Cryptopone motschylski Donis. Myopias sp. 6 Myopias sp. 19 Leptogenys sp. 9 Ectomomyrmex aciculatus Em. E. ?acutus Em. Ectomomyrmex sp. 2 Mesoponera sp. Hypoponera biroi Em. H. confinis Roger H. pruinosa Em. H. sororcula Wilson Hypoponera sp. 2 Hypoponera sp. R55 Aenictus ?doryloides Wilson Meranoplus spinosus (F. Sm.) Meranoplus sp. 1 Meranoplus sp. 2 Meranoplus sp. 3 Calyptomyrmex beccarii Em. Crematogaster sp. R114 Crematogaster sp. R115 Crematogaster sp. R117 Crematogaster sp. R118 Crematogaster sp. R136 Crematogaster sp. R307 Crematogaster sp. R377 Crematogaster sp. R432 Orectognathus velufinus Taylor Strumigenys chyzeri Em. S. lopotyle Brown S. loriae Em. S. mayri Em. S, sisyrata Brown S. szalayi Em. S. wallacei Em. Eurhopalothrix procera (Em.) Aphaenogaster perplexus M. R. Sm. A. dromedarius (Em.) Chelaner ?edentatus (Em.) Monomorium Jloricola (Jerdon) M. talpa Em. M. 'A' minutum group M. 'B' minutum group Tetramorium guineense (Fabr.) T. ?melanogynum Mann T. simillimum (F. Sm.) T, tonganum Mayr T. ?wilsoni Mann Tetramorium sp. 6 Tetramorium sp. 7 P. M. Room

Appendix (Cont.)

Species F R ClC2Cf 0 K S U

Tetramorium sp. 11 1 Triglyphothrix striatidens (Em.) 1 4 1 Myrmecina sp. 2 1 Myrmecina sp. 5 1 1 Lordomyrma sp. 2 1 Lordomyrma sp. 9 1 Cardiocondyla nuda Mayr 2 15 C. paradoxa Em. 1 1 C. ?wroughtoni (Forel) 167 3 Rhoptromyrmex melleus Em. 17 151 R. wroughtoni Forel 1 1 Solenopsis sp. 2 1 Solenopsis sp. R215 12 Pheidole impressiceps Mayr 71231 P. megacephala (Fabr.) 3 4 Pheidole sp. 2 1 Pheidole sp. R182 2 2 325 Pheidole sp. R208 11 11 Pheidole sp. R305 2 12 Pheidole sp. R453 1 Pheidole sp. R679 2 6 14 Pheidole sp. R698 P. (Pheidolacanthinus)sp. R124 1 P. (Pheidolacanthinus)sp. R261 1 P. (Pheidolacanthinus)sp. R318 1 2 P. (Pheidolacanthinus)sp. R449 12 311 P. (Pheidolacanthinus)sp. R450 12 211 P. (Pheidolacanthinus)sp. R467 2 P. (Pheidolacanthinus)sp. R672 2 6 3 Pheidologeton ?australis Fore1 914368 Pristomyrmex sp. R179 312 Monoceratoclinea tricornis (Em.) 2 Leptomyrmex fragilis (F. Sm.) 2 3 3 L. niger Em. 1 2 2 Tapinoma melanocephalurn (F) 6 3 124 T. minuturn Mayr 3 Technomyrmex albipes (F.Sm.) 3141763 Technomyrmex sp. 1 2 1 Zridomyrmex ?anceps Mayr 1 1 11 I. cordatus (F. Sm.) 1 1 14 17 18 I. nitidus Mayr 2 5 Zridomyrrnex sp. R313 5 Zridomyrmex sp. R320 3 Zridomyrmex sp. R349 2 4 10 Zridomyrmex sp. R434 222 Iridomyrmex sp. R441 Zridomyrmex sp. R607 Zridomyrmex sp. R655 6 Zridomyrmex sp. R701 3 Notoncus sp. 1 1 Plagiolepis exigua Fore1 1 1 P. ?ex@ua Fore1 3 1 Ground-foraging Ant Faunas of Papua New Guinea

Species F R C1 C2 Cf 0 K S U

Anoplolepis longipes (Jerdon) 3 3 16 14 4 17 18 11 Acropyga ?acutiventris (Rog.) 1 1 1 Pseudolasius ?breviceps Em. 2 1 Paratrechina bourbonica (Forel) 1 1 1 5 P. longicornis (Latr.) 6 P. ?minutula (Forel) 3 10 P. ?stigmatica Mann 10 7 8 114 5 2 P. ?vaga (Forel) 7 1 123 1 Paratrechina sp. 1 12 Paratrechina sp. 2 12 Paratrechina sp. 3 5 Paratrechina sp. R217 2 811 Paratrechina sp. R711 1 Acantholepis sp. 1 19 Oecophylla smaragdina F. 2 5 6 2 1 Opisthopsis respiciens (F. Sm.) 1 Calomyrmex albertisi Em. 7 2 Camponotus conithorax Em. 1 Camponotus sp. R132 13 1 3 Camponotus sp. R141 1 Camponotus sp. R148 6 Camponotus sp. R153 1 Camponotus sp. R158 2 1 Camponotus sp. R440 2 Polyrhachis 'Campomyrma' sp. R151 4 P. 'Chariomyrma' sp. R90 197 P. 'Chariomyrma' sp. Rl 10 1 124 P. 'Chariomyrma' sp. R129 18 P. 'Chariomyrma' sp. R251 P. 'Chariomyrma' sp. R281 2 24 17 P. 'Cyrtomyrma' sp. R107 1 P. 'Hagiomyrma' sp. R128 1 2 P. 'Hagiomyrrna' sp. R150 2 P. 'Hagiomyrma' sp. R273 4 1 P. 'Hedomyrma' sp. R274 8 P. 'Myrma' sp. R87 1 P. 'Myrma' sp. R247 1 2 P. 'Myrmhopla' sp. R89 3 P. 'Polyrhachis' sp. R86 1 1