The red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae), and ground-dwelling ant species native to Georgia were observed and studied in tree-canopied and open uncanopied habitats in two state parks in central Georgia. Population density, native species diversity, and interactions of native species with each other and with the invasive S. invicta were determined and compared in the two habitats. Sampling methods included pitfall traps, baits, collection of leaf litter, and visual searches. In comparison to the open uncanopied habitats, red imported fire ant population density was lower in tree-canopied habitats, and native ant species diversity was greater in the canopied habitats. We also observed native species competing with red imported fire ants more intensely in canopied than in open habitats primarily by foraging activity and by predation of S. invicta reproductives. Our results suggest that native ant species can suppress S. invicta population numbers and density and that competition by native ant species should be considered in approaches of managing red imported fire ant.

The red imported fire ant, Solenopsis invicta Buren, is native to South America where its home range extends north along the Guapore River into Brazil and south along the Paraguay River into northern Argentina (Buren et al. 1974; Rhoades 1977). It was accidentally introduced into North America on multiple occasions between 1933 and 1941 through the Mobile, AL area ports (Rhoades 1977). It has since expanded its range in the United States to include most of the Southeast and parts of the Southwest and southern California (Korzukhin et al. 2001).

Factors contributing to its successful range expansion in the United States include its reproductive strategies (Holldobler and Wilson 1990; Tschinkel 1998), its omnivorous feeding habits (Camilo and Phillips 1990), the relative lack of natural enemies to provide natural suppression in its expanded range (Wojcik 1983), and its aggressive behavior (Vinson 1994). Vinson (1994) noted that S. invicta rapidly establishes in disturbed areas such as grazed pasturelands, managed recreation areas, and areas cleared by fire, deforestation, or other events. Taber (2000) concurred, observing that in its expanded range, S. invicta occurs primarily in open and often disturbed areas rather than areas canopied with trees and other vegetation. Reasons for these observed responses to canopied versus open areas have not been delineated. Therefore, the study reported herein compares the occurrence of ground-dwelling ant species, foraging activity of ground-dwelling ant species, and the natural predation of S. invicta alates in canopied versus open habitats in central Georgia.

Study areas and habitats. The study areas selected for this study were within two Georgia state parks in central Georgia. High Falls State Park is approximately 20 km south of Jackson (Butts Co.), GA, is 178 m above sea level (m a.s.l.), and is characterized primarily by loamy/clay soils. Indian Springs State Park is approximately 5 km south of Jackson (Butts Co.), GA and is 193 m a.s.l. Its soils are primarily loamy/clays. Both parks contain over 100 ha of open uncanopied areas and more than 200 ha of wooded areas characterized as second-growth forests comprised primarily of oak and pine, Quercus spp. and Pinus spp., respectively.

One study area each was established in the canopied and open uncanopied habitats in each park. Each measured 1,000 m2 with plots within canopied habitats located at least 60 m from any adjacent right-of-way. The dominant plant species and amount of plant cover were characterized for each sample site using five, 20-m parallel linear transects established 10 m apart within each plot. Each transect served as a centerline for 200 quadrats of area, each 1 m2 in size. Plant species were identified, and the area covered by these species was estimated (Meyers and Shelton 1980).

Ant sampling. Ground-dwelling ant fauna were sampled using pitfall traps, baits, collection of leaf litter, and visual searching as described by Bestlemeyer et al. (2000). The combination of these methods is ideal for biodiversity monitoring programs and comparing ant fauna among different habitats (Bestlemeyer et al. 2000). In each plot, 20 pitfall traps were placed at 1-m intervals along the transect. These traps were 40-ml plastic vials containing propylene glycol (filled 2/3 capacity) as a nontoxic preservative. Each was inserted into the ground to a depth so that the upper rim of the vial was level with the soil surface. After 7 d, each trap was removed from the soil, capped, and returned to the laboratory.

Baits were placed in plastic Petri dishes (35 × 10 mm) containing a 25-mm-diameter grade 1 Whatman filter paper disk covered with a thin layer of tuna in oil as described by Brinkman et al. (2001). Bait dishes were placed at 2-m intervals along each transect in each plot. Dishes were placed at 9:00 a.m. (EST) during the warmer months and 12:00 p.m. (EST) during the colder months. These dishes remained exposed for 2 h, after which they were covered, sealed with transparent tape, and transported to the laboratory. If a bait dish was dominated by an individual ant species before the end of the 2-h time period, it was covered and sealed to collect as many ants as possible.

Litter samples were obtained at 5-m intervals along each transect. This involved hand collecting litter and humus in a 1-m2 area and placing it in large trash bags. These were sealed and transported to the laboratory where subsamples were placed into Berlese funnels. After 24 h, vials containing ants and other invertebrates were removed and ants were separated.

Each canopied sampling plot also was visually searched for three man-hours during each sampling date for ant fauna. Litter, bare ground, tree trunks, foliage, decaying wood, and other surfaces were searched. Representative ants were collected and placed in 70% ethyl alcohol for transport to the laboratory.

All ants collected by these methods were initially identified by comparison with specimens housed in the University of Georgia Natural History Museum (Athens, GA). Identifications were made with keys by Bolton (1994, 2000), Buren (1968), Creighton (1950), Cuezzo (2000), DuBois (1986), Gregg (1958), Holldobler and Wilson (1990), Johnson (1988), MacKay (2000), Smith (1957), Snelling (1988), Snelling and Longino (1992), Taylor (1967), Trager (1984, 1988), and Wilson (1955). Stefan Cover (The Museum of Comparative Zoology, Harvard University, Cambridge, MA) and Mark Deyrup (Archbold Biological Station, Lake Placid, FL) confirmed species identifications. Voucher specimens have been deposited in the University of Georgia Natural History Museum and the Museum of Comparative Zoology at Harvard University.

Each site was sampled at monthly intervals for 12 mo from September 2001 through August 2002. An analysis of variance (ANOVA) (Sokal and Rholf 1995) was used to determine differences in numbers of ants collected from the different sample sites by date. At each sample site location, the Shannon-Weaver's species diversity index (Southwood 1978) was used to measure ant species diversity based on species richness and evenness.

Fire ant reproductive mortality and predation.Solenopsis invicta reproductives (female alates) were placed individually in 20-ml plastic vials. The alates were collected from colonies maintained in the laboratory on the University of Georgia Griffin Campus and were used within 1 d after collection. The lid of each vial was modified by cutting a hole (≈2 cm diameter) through the center (Nichols and Sites 1991). Wire screen (1.66 mm2 mesh) was placed over each vial opening and secured with the modified lid. This screen allowed workers of most ant species as well as other small arthropods to enter the vial while preventing the escape of alates (Nichols and Sites 1991). Control vials were similar but contained an 0.8-mm2 mesh cover over the opening to exclude all arthropod predators. The bottom of each vial contained dental plaster that was moistened to prevent desiccation of the alate. Openings in the soil for the vials were created with a drill bit 24 h before vial placement to reduce arthropod activity in response to soil disturbance. Ten vials containing the 1.6-mm2 mesh and 10 vials containing the 0.8-mm2 mesh were placed in the center location within the 1,000 m2 plot. Each vial was placed vertically in the soil 2 m apart and 10 cm deep in the soil along a linear transect. Each was covered with a rock or piece of pinewood to simulate colony founding (Nichols and Sites 1991). Vials were checked each day for 7 d. After 7 d, alates that were not preyed upon were considered successful founders. Ants or other arthropods present in vials were collected, placed in 70% ethyl alcohol, and transported to the laboratory. Data were recorded as (a) preyed upon within 7 d (binomial distribution), and (b) the number of days until an alate was preyed upon within the 7-d period. Alates that perished due to adverse environmental conditions were not included in the analysis. All data were analyzed using Statistical Package for the Social Sciences (SPSS, version 19.0), Chicago, IL. A logistic regression (Sokal and Rholf 1995) was used to determine differences in alate mortality based on vial, habitat, location (state park), and sample date.

Foraging activity. Ant foraging activity within each habitat was estimated at monthly intervals for the duration of the study. On each sampling date, 10 baiting stations were placed at 2-m intervals along a 20-m transect in each plot. The baiting stations were individual 7.5 × 12.5-cm index cards staked in the ground using two wooden dowels (Saks and Carroll 1980). An individual termite worker obtained from decaying wood was firmly pressed to each card. After placement in the plot, cards were monitored for removal of prey items for 1 h. Ant species preying upon the termite on each card were recorded until the prey item was either removed or 1 h had elapsed, whichever occurred first. Once a prey item was removed, it was not replaced. All data were analyzed using SPSS. Data were analyzed using a logistic regression (Sokal and Rholf 1995) to determine differences in predation in relation to habitat (open versus canopied), location (state park), and sampling date. An ANOVA was used to determine differences in the amount of time for predation to occur from placement of prey.

Plant characterization. The dominant plant communities differed among the habitats sampled. The canopied area within High Falls State Park was a mature conifer forest dominated primarily by loblolly pine, Pinus taeda L., and short leaf pine, Pinus echinata Miller, with a few water oaks, Quercus nigra (L.), and other understory trees and shrubs (Table 1). The overstory and understory vegetation created 100% canopy coverage at a height of 5 m above the soil surface.

Table 1

Plant communities in canopied habitats at High Falls State Park and Indian Springs State Park in central Georgia, 2002.

Plant communities in canopied habitats at High Falls State Park and Indian Springs State Park in central Georgia, 2002.
Plant communities in canopied habitats at High Falls State Park and Indian Springs State Park in central Georgia, 2002.

The canopied area sampled in Indian Springs State Park was a second- to third-stage successional deciduous forest approaching climax community (Table 1). This community was dominated by southern red oak (Q. falcate Michaux), water oak (Q. nigra), American beech (Fagus grandifolia Ehrhart), yellow poplar (Liriodendron tulipifera L.), loblolly pine (P. taeda), dogwood (Cornus florida L.), and wild cherry (Prunus spp.). Due to the maturity of the forest and associated larger trees, this vegetative growth created 100% canopy coverage at a height of 8 m above the soil surface (Table 1). The open areas in each state park had no vegetative canopy above ground level and consisted completely of grasses, primarily fescue (Festuca arundinaceae Schreber) and common Bermuda grass (Cynodon dactylon L.).

Species diversity. A total of 93,834 ants representing 24 genera and 54 species were collected during this study (Table 2). The Shannon-Weaver index of diversity calculated a higher diversity of species in the canopied habitats than in uncanopied habitats at both locations (Table 3), while the total number of ants collected was significantly (P < 0.05) greater in the open habitats than in canopied habitats.

Table 2

Ant species collected in High Falls State Park and Indian Springs State Park from September 2001 through August 2002 in central Georgia.

Ant species collected in High Falls State Park and Indian Springs State Park from September 2001 through August 2002 in central Georgia.
Ant species collected in High Falls State Park and Indian Springs State Park from September 2001 through August 2002 in central Georgia.
Table 2

Continued.

Continued.
Continued.

During this study, S. invicta mounds were difficult to identify in all habitats and locations because S. invicta does not form mounds into dome structures in central Georgia during hot and dry weather. However, collections of S. invicta workers in pitfalls and on baits provided indications of activity. Data from these collections indicate that S. invicta workers did not forage between October 2001 and April 2002 (Fig. 1) with September 2001, May 2002, June 2002, July 2002, and August 2002 being the months of highest S. invicta activity (Fig. 2). Activity, as indicated by numbers of workers collected, increased from May 2002 through August 2002.

Fig. 1

Total numbers of Solenopsis invicta collected monthly in pitfall traps and bait dishes at High Falls State Park and Indian Springs State Park from September 2001 through August 2002 in central Georgia.

Fig. 1

Total numbers of Solenopsis invicta collected monthly in pitfall traps and bait dishes at High Falls State Park and Indian Springs State Park from September 2001 through August 2002 in central Georgia.

Close modal
Fig. 2

Numbers of Solenopsis invicta collected during months of high ant activity in pitfall traps and bait dishes at High Falls State Park and Indian Springs State Park.

Fig. 2

Numbers of Solenopsis invicta collected during months of high ant activity in pitfall traps and bait dishes at High Falls State Park and Indian Springs State Park.

Close modal

Over the entire study period, S. invicta was the most abundant species in terms of number of foragers collected from the open habitat at Indian Springs State Park, with 10,356 workers (88%) collected in August 2002 alone. However, over the entire study period, Monomorium viride Brown was the most active ant species collected in the open habitat at High Falls State Park, with 12,013 individuals collected for the duration of this study. Solenopsis invicta was not collected in canopied habitats for the duration of this study.

Numbers of native ant species collected at both state parks decreased in the winter months and increased in the spring and summer months (Fig. 3). The greatest numbers of native ant species were collected from the open habitat at High Falls State Park (Fig. 3). The two most dominant native ant species in that area were M. viride and Pheidole tysoni Forel, with a total of 12,013 and 7,146 workers collected, respectively. The greatest numbers of native ant species collected was in June 2002, when 4,707 individuals of M. viride were collected from bait dishes alone. While S. invicta occupied more baits, M. viride and Ph. tysoni occasionally recruited and occupied baits with greater numbers of workers than did S. invicta. At Indian Springs, Forelius analis (Andre) was the most abundant native ant species in the open habitat, with 6,166 individuals collected for the duration of this study, with September 2001, October 2001, April 2002, May 2002, June 2002, July 2002, and August 2002, being the months of greatest native ant activity (Fig. 4).

Fig. 3

Total numbers of native ants collected monthly in pitfall traps and bait dishes at High Falls State Park and Indian Springs State Park from September 2001 through August 2002 in central Georgia.

Fig. 3

Total numbers of native ants collected monthly in pitfall traps and bait dishes at High Falls State Park and Indian Springs State Park from September 2001 through August 2002 in central Georgia.

Close modal
Fig. 4

Numbers of native ants collected during selected months of high ant activity in pitfall traps and bait dishes at High Falls State Park and Indian Springs State Park.

Fig. 4

Numbers of native ants collected during selected months of high ant activity in pitfall traps and bait dishes at High Falls State Park and Indian Springs State Park.

Close modal

A greater diversity of species was collected from canopied habitats than from open habitats at both locations, with the canopied habitat at Indian Springs supporting the highest species diversity (Table 3). Prenolepis imparis (Say), the Aphaenogaster picea/rudis/texana Wheeler complex, and Ph. dentata Mayr were the three dominant species collected from the canopied habitats at each state park. During the colder months, Pr. imparis became the single most-dominant ant, but decreased in numbers during the warmer months when workers of the Aphaenogaster picea/rudis/texana complex became the most abundant.

Table 3

Numbers and species diversity of ground-dwelling ants occurring in canopied versus open habitats at High Falls State Park and Indian Springs State Park from September 2001 through August 2002 in central Georgia.

Numbers and species diversity of ground-dwelling ants occurring in canopied versus open habitats at High Falls State Park and Indian Springs State Park from September 2001 through August 2002 in central Georgia.
Numbers and species diversity of ground-dwelling ants occurring in canopied versus open habitats at High Falls State Park and Indian Springs State Park from September 2001 through August 2002 in central Georgia.

Numbers of ants in the canopied habitat at Indian Springs were substantially lower from September 2001 through March 2002 than from May 2002 through August 2002, with the greatest number of ants collected in August 2002 (Fig. 3). In the canopied habitat at High Falls, collections fluctuated slightly in September and October 2001 and from April 2002 through August 2002. The greatest number of ants was collected in September 2001. Collections of ants diminished in canopied habitats at both locations from November 2001 through March 2002.

Predation of alates. The logistic regression analysis detected significant differences in predation rates in relation to vial type, habitat, and sampling dates. Alates placed in the vials from which predators were excluded were not preyed upon. Some natural mortality of these alates occurred, ranging from a mean of 1.4–9.3%. Mortality data of these alates were not included in the analysis.

Percent predation of alates varied according to sampling date. Predation diminished in open and canopied habitats at both locations during the winter months (Fig. 5A). This was apparently due to lack of ant activity, as corroborated by the low numbers of ants collected during that period of time (Figs. 1, 3). For example, in September 2001, all of the alates were preyed upon in the canopied habitat at both locations. However, from December 2001 through May 2002, predation diminished significantly in those habitats. Predation of alates in the open habitat at High Falls State Park did not occur until May 2002, with the highest levels in July 2002 and August 2002. Similarly, at Indian Springs State Park, predation of alates in the open habitat occurred in September 2001, November 2001, December 2001, and June 2002, July 2002, and August 2002, with highest levels of predation occurring in the latter 2 mo.

Fig. 5

Percentage predation of Solenopsis invicta alates (A) and termite workers (B) in open and canopied habitats at High Falls State Park and Indian Springs State Park in central Georgia from September 2001 through August 2002.

Fig. 5

Percentage predation of Solenopsis invicta alates (A) and termite workers (B) in open and canopied habitats at High Falls State Park and Indian Springs State Park in central Georgia from September 2001 through August 2002.

Close modal

Predation of alates was significantly (P < 0.01) greater in canopied habitats than in open habitats (Fig. 5A). For example, in September 2001, all alates were preyed upon in the canopied habitat at High Falls State Park, while no predation of alates in the vials occurred in the open habitat at that same location. Similarly, all alates were preyed upon in the canopied habitat at Indian Springs State Park, while only 20% of alates were preyed upon in the open habitat at that location.

From September 2001 through August 2002, predation of the alates remained significantly (P < 0.01) greater in the canopied habitats than in the open habitats at each location. During this period, a mean (± standard error of the mean [SEM]) of 54.1 ± 5.4% of the alates were preyed upon in the canopied habitat in High Falls State Park, while only 20.0 ± 4.4% were preyed upon in the open habitat at that location. Similarly, 44.7 ± 5.5% of the alates were preyed upon in the canopied habitat at Indian Springs State Park, while only 14.1 ± 4.8% were preyed upon in the open habitat at that location. During the warmer months, coinciding with greater ant activity, mortality by predation was 84.4 ± 5.4% in the canopied habitat in High Falls State Park and 74.4 ± 6.7% in the canopied habitat in Indian Springs State Park. During this same time period, predation in the open habitats was significantly less (33.3 ± 7.6% at High Falls State Park and 46.5 ± 7.6% at Indian Springs State Park). During the late spring and the summer months, 100% alates were preyed upon within 24 h in the canopied habitats at both locations. This was not observed in the open habitats.

Ant predators preying on alates were observed, recorded, and collected when possible (Table 4). However, alates were usually dismembered and removed, rendering collection and recording of ant predator species at times impossible. Of those species found to be predators of alates, four had not been previously reported as predators of S. invicta. These are Aphaenogaster picea (Wheeler), Pr. imparis, and two Dacetine ants, Strumigenys ornata (Mayr) and Pyramica rostrata (Emery). Among these, A. picea was most frequently observed in canopied habitats at both locations.

Table 4

Ground-dwelling ant species observed preying upon Solenopsis invicta alates in open and canopied habitats at High Falls State Park and Indian Springs State Park from September 2001 through August 2002 in central Georgia.

Ground-dwelling ant species observed preying upon Solenopsis invicta alates in open and canopied habitats at High Falls State Park and Indian Springs State Park from September 2001 through August 2002 in central Georgia.
Ground-dwelling ant species observed preying upon Solenopsis invicta alates in open and canopied habitats at High Falls State Park and Indian Springs State Park from September 2001 through August 2002 in central Georgia.

Foraging activity. Foraging for termite prey was more intense in canopied than in open habitats, with 100% predation of the prey occurring at Indian Springs State Park within 60 min in September 2001, June 2002, and August 2002, and 100% predation occurring at High Falls State Park within 60 min in July 2002 (Fig. 5B). Foraging activity decreased in all habitats in the winter months. From September 2001 through August 2002, the mean (±SEM) time for the onset of predation of termites in canopied habitats was 39.1 ± 1.9 min at High Falls State Park and 31.7 ± 2.1 min at Indian Springs State Park. The mean time for the onset of predation of termites in the open habitats was greater at High Falls State Park (47.6 ± 1.8 min) and at Indian Springs State Park (47.8 ± 1.9 min). Predation time decreased in all habitats due to higher ant activity as mean daily temperatures increased. Within the warmer months, coinciding with increased ant activity, mean time for the onset of predation in the canopied habitat at High Falls State Park was 34.2 ± 2.7 min and 20.8 ± 2.5 min at Indian Springs State Park. Mean time in the open habitats was 45.4 ± 2.5 min at High Falls State Park and 41.2 ± 2.8 min at Indian Springs State Park. Lowest mean time for the onset of predation of termites was during September 2001, October 2001, June 2002, July 2002, and August 2002.

More species of ant predators were observed foraging on termites during the warmer months than colder months in canopied habitats at both locations (Table 5). Among these, A. picea, Camponotus americanus Mayr, Camponotus nearcticus Emery, Formica pallidefulva Latreille, and P. imparis were the dominant taxa that preyed upon the termites in the canopied habitats.

Table 5

Ground-dwelling ant species observed removing termites in open and canopied habitats at High Falls State Park and Indian Springs State Park in central Georgia from September 2001 through August 2002.

Ground-dwelling ant species observed removing termites in open and canopied habitats at High Falls State Park and Indian Springs State Park in central Georgia from September 2001 through August 2002.
Ground-dwelling ant species observed removing termites in open and canopied habitats at High Falls State Park and Indian Springs State Park in central Georgia from September 2001 through August 2002.

Camponotus americanus was collected only from Indian Springs State Park. During the colder months, P. imparis was the only predator observed in canopied habitats. Solenopsis invicta remained the dominant forager in the open habitats at both locations throughout the study. In these studies, collections of individual ants were conducted when feasible. However, because foraging usually occurs within seconds, collections of individuals were limited.

During this study, a total of 140 termites (58% out of 240) were preyed upon in the canopied habitats as compared to a total of 68 (28% out of 240) in the open habitats. At High Falls State Park, 55% of the termites were preyed upon in the canopied habitat, while only 30% were preyed upon in the open habitat. Similarly, 62% of the termites were preyed upon in the canopied habitat at Indian Springs State Park, while only 27% were preyed upon in the open habitat at that location. Foraging activity and predation of termites decreased during the months with cooler temperatures, thus coinciding with the observations of predatory rates.

In central Georgia, canopied habitats as compared to open habitats support a greater diversity of native ant species that compete with S. invicta. Furthermore, native ant species diversity and S. invicta population levels appear to be inversely related regardless of habitat type. These results suggest that S. invicta population levels are at least partially regulated by varying degrees of competitive interactions that are also associated and positively correlated with native ant species diversity. These interactions are predation of S. invicta alates by native ant species and competition for food resources by foragers of native ant species. These competitive interactions occur more frequently and at a greater intensity in canopied habitats than in open habitats in central Georgia.

Solenopsis invicta activity was greater in open habitats than in canopied habitats in this study, thus further supporting that S. invicta activity appears to be inversely related to native ant species diversity. Few native ants were observed to inhabit areas dominated by S. invicta. We found Monomorium viride Brown, Paratrechina vividula (Nylander), Ph. dentata, Ph. tysoni Forel, Forelius analis (Andre), and S. molesta (Say) in sufficient numbers in open habitats to indicate coexistence with S. invicta in those habitats. However, most other native ant species collected in open habitats were sporadically collected and were represented by only a few workers, and they apparently do not successfully coexist with S. invicta in these central Georgia habitats.

Predation of alates at each location was directly related to species diversity in the habitats. Hence, more predation of S. invicta alates occurred in the canopied habitats where species diversity was greater in comparison to the open habitats. While there were insufficient numbers of queens for this predation study, it was assumed that predation of the alates corresponded to that for founding queens. Indeed, predation of newly mated S. invicta queens was found to be a significant factor impacting S. invicta founding success in northern Florida (Nickerson et al. 1975; Whitcomb et al. 1973). Bhatkar et al. (1972) and Whitcomb et al. (1973) discovered that Lasius neoniger Emery destroyed S. invicta alates in their claustral cells. Certain native ant species have reportedly preyed on S. invicta alates before they enter the soil. These include species Ap. floridana Smith, So. geminata (F.), Ph. dentata, Ph. morrisii Forel, Fo. schaufussi Mayr, Ca. floridanus Buckley, and Paratrechina spp. In addition, several species of the genus Dorymyrmex (=Conomyrma) have been documented to coordinate attacks with conspecific members, bringing S. invicta queens into their nest (Whitcomb et al. 1973).

Solenopsis invicta is also subjected to subterranean predation by ants of the subgenus Diplorhoptrum (Buren 1983; Whitcomb et al. 1973). Buren (1983) further indicated that in this way Diplorhoptrum species could potentially suppress S. invicta populations in the United States. He noted that these ants have the greatest potential effect on regulating S. invicta populations because of their subterranean habits. In this study, the subterranean Diplorhoptrum ant species, So. molesta (Say), was observed preying on S. invicta alates. Furthermore, five additional ant species other than those reported by Whitcomb et al. (1973), Nickerson et al. (1975), and Nichols and Sites (1991), which are not subterranean predators, were observed preying of S. invicta alates. Strumigenys ornata (Mayr) and Py. rostrata (Emery) were observed preying on alates in canopied habitats. This is the first report of the genus Strumigenys, considered to be specialist predators of Collembola (Holldobler and Wilson 1990), preying on another ant species.

Foraging activity at each location also was directly related to species diversity. Not only were more termites foraged upon in canopied habitats, but the time to discover the prey item was lower in canopied than in the open habitats. Torres (1984) reported that arrival at a bait resource first was significantly correlated with bait dominance. This allows poor or equally dominant competitors to coexist in an area because first arriving species can recruit more workers than can later arriving species (Torres 1984). This may be occurring in open habitats. Monomorium viride was observed on numerous occasions foraging on termites in the absence of S. invicta.

In the canopied habitats, species such as Ap. picea, Ap. fulva Roger, Ca. pennsylvanicus (De Geer), and Fo. pallidefulva were represented equally at the foraging stations. These fast-recruiting species discovered prey items quicker than did others. In addition, canopied habitats contained additional species of Camponotus and Formica whose workers also forage individually, thus also allowing for a quicker response time to individual prey items.

Canopied habitats in central Georgia support a high diversity of native ant species. These native ant species occurring in canopied habitats appear to be able to compete successfully against S. invicta for food resources and to significantly (P = 0.05) reduce S. invicta population levels. In open habitats, S. invicta is extremely competitive and becomes the dominant ant species. Ecological disturbance of habitats may reduce the number of possible niches for use by native ants via a simplification of the environment that disrupts native ant assemblages and allows the successful invasion and establishment of S. invicta. There is evidence of similar ecological perturbations in California with the Argentine ant, Linepithema humile (Mayr), and in southwest Columbia with the little fire ant, Wasmannia auropunctata (Roger), whereby simplification of the environment produced more nesting sites for these invasive pest species (Armbrecht and Ulloa-Chacon 2003, Human et al. 1998, Suarez et al. 1998). Based upon the results of the study reported herein, conservation of habitats that support and sustain competitive native ant species assemblages will maintain high biodiversity of native ant populations and help reduce invasion of S. invicta into canopied habitat in central Georgia.

We thank Hal Peeler and Mark Brinkman for their assistance in completing sampling components of this study.

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