Northeastern Naturalist Vol. 21, No. 1 V.S. Banschbach and E. Ogilvy 2014 NENHC-1 2014 NORTHEASTERN NATURALIST 21(1):NENHC-1–NENHC-12 Long-term Impacts of Controlled Burns on the Ant Community (Hymenoptera: Formicidae) of a Sandplain Forest in Vermont Valerie S. Banschbach1,* and Emily Ogilvy1 Abstract - Sandplain Pine-Oak-Heath forest is one of Vermont’s most threatened natural communities due to fire suppression and land development. We studied the ant community in the largest remaining tract of sandplain forest in the state of Vermont, at the Camp Johnson Army National Guard Base, in Colchester. We investigated the long-term impacts of controlled burns conducted in 1995 and 1998 by examining ant specimens collected in burned and control (unburned) areas during September and early October of 2006, 2007, and 2008. The 1750 ant specimens from 911 pitfall traps yielded 29 ant species. Although sample effort was un-even, there was a greater than two-fold difference in species richness between the sites: 28 species in the burned site and 13 species in the control site. Ant abundance was significantly greater at the burned site compared to the control, and the Shannon index of species diversity differed as well. Canopy cover was significantly different in the burned site compared to the control site. Increased habitat diversity and increased forestfloor temperature following from the more open canopy in the burned area could potentially account for the greater abundance, species richness, and diversity of ants in the burned area. The striking differences in the ant communities of the burned versus the control areas 8–10 years post-burn demonstrate the potential usefulness of monitoring ants as indicators of the long-term ecological change induced by burning of the sandplain forest. Introduction One of Vermont’s most threatened plant communities is sandplain or Pine-Oak- Heath Forest (Nongame and Natural Heritage Program Newsletter 2006). Sandplain forest is a fire-adapted community belonging to the more general category of pine barrens found across the Northeastern US, but lacking the completely open areas or stunted trees characterizing true pine barrens (Engstrom 1991). Historically, Chittenden County, in northwestern Vermont, contained nearly 6100 ha of sandplain forest. Today, only 265 ha remain. Engstrom (1991) concluded that although the sandplain forest in Vermont contains a low plant species diversity, it features a disproportionate number of rare plants at the upper limit of their geographic range. Some 27 rare plant species are found in sandplain forest. Most of these are shadeintolerant species, and their presence is facilitated by the open nature of the sandplain forest canopy (Engstrom 1991). Therefore, sandplain forest is an important habitat to conserve. Fire suppression presents a key threat to sandplain forest viability. Fire suppression in pine barrens communities of the Northeast has been shown to lead 1Saint Michael’s College, Colchester, VT 05439. *Corresponding author - vbanschbach@ smcvt.edu. Manuscript Editor: Christopher M. Heckscher Northeastern Naturalist NENHC-2 V.S. Banschbach and E. Ogilvy 2014 Vol. 21, No. 1 to decreased barrens size and decreased plant species diversity as the community shifts toward hardwood forest (Milne 1985). In the sandplain forests of Vermont, Acer rubrum L. (Red Maple) in particular becomes increasingly abundant over time as a result of fire suppression. The forest canopy also becomes more closed, shading out heath shrubs and Pinus rigida Mill. (Pitch Pine) seedlings that are characteristic of the sandplain forest. To understand the impacts of fire, vegetation can be monitored directly to assess its return to the native forest type, but it would be useful to identify other indicators of the ecological change occurring during post-burn forest succession. Our study focused on how the ant community in the sandplain forest was affected by a controlled burn, 8–10 years post-burn. Few studies have assessed the impact of vegetation change on ant communities (Ellison et al. 2007) and, more specifically, little is known about the impacts of controlled burns on ant communities (Hoffman 2008). Studies of the impacts of fire on arthropods have focused more often upon tropical savannas or temperate grasslands (e.g., Anderson et al. 1989, Parr et al. 2004, reviewed in Swengel 2001) rather than temperate forests. We engaged undergraduate students in the laboratory portion of our Introduction to Ecology and Evolution course at Saint Michael’s College, Colchester, VT, in censusing the invertebrates and plants on the largest remaining parcel of sandplain forest in the state, 162 ha, at the Vermont Army National Guard Base, Camp Johnson, in Colchester, VT (Nongame and Natural Heritage Newsletter 2006). Although the students collected a wealth of data, we chose to focus solely on the ants, given the key roles they play in ecosystems—as nutrient-cyclers, bioturbators, prey, mutualists, etc.—that make them a strong potential bioindicator group (Majer et al. 2007). Ants may be a logical choice as a biological indicator group, but more data are needed to support this hypothesis for cold temperate biomes (Ellison 2012). Here, we focused on ants as indicators of ecological change brought about by the controlled sandplain burns. Our objectives were two-fold: (1) to determine if some characteristics of the ant community differ between burned areas and unburned areas, 8 to 10 years post-burn, and (2) to relate features of the ant community to characteristics of the tree and shrub communities, burned and unburned. We predicted that a more open canopy, resulting from the post-burn succession, and consequent increased vegetation diversity, would lead to more niches for ants and increased ant species diversity. Methods Study site Our field site was the 162 ha of sandplain forest at the Camp Johnson Vermont Army National Guard Base in Colchester, Chittenden County, VT (hereafter, Camp Johnson; elevation: 91–97.5 m.a.s.l.; 44.51°N, 73.16°W). Sandplain forest occurs on soils that are sandy, well drained, acidic, and nutrient poor. Camp Johnson’s sandy soils are the result of its location on the Winooski River Delta and from recent glaciation of Vermont. The characteristic tree species of sandplain forest are Northeastern Naturalist Vol. 21, No. 1 V.S. Banschbach and E. Ogilvy 2014 NENHC-3 Pitch Pine, Pinus strobus L. (White Pine), Quercus velutina Lam. (Black Oak), and Quercus rubra L. (Red Oak). Red Maple is quite common and becoming increasingly dominant in areas of Camp Johnson that have not been burned in a long time. Heath shrubs thriving in the acidic soil are Vaccinium angustifolium Ait. (Lowbush Blueberry), Vaccinium pallidum Ait. (Blue Ridge Blueberry), Gaylussacia baccata (Wangenh.) K. Koch (Black Huckleberry), and Kalmia angustifolia L. (Sheep Laurel) (Engstrom 1991). In some areas of the forest, the larger shrubs Corylus cornuta Marshall (Beaked Hazelnut) and Hamamelis virginiana L. (Witch Hazel) are common, forming a high shrub layer (Engstrom 1991). In order to manage this threatened ecosystem, two controlled burns affecting 6 ha were carried out in the 1990s by the Vermont Army National Guard and collaborating community partners (Fig. 1; Vermont Fish and Wildlife Department and The Nature Conservancy; Nongame and Natural Heritage Newsletter 2006). After the first burn of 3.25 ha (“hot burn” area in Fig. 1) in 1995, Pitch Pine seeds from the Camp Johnson Pitch Pine population were germinated. Those seedlings were Figure 1. Location of Camp Johnson (Vermont Army National Guard Base, Colchester, VT) study areas (2004 image). The “hot burn” area was burned for the first time in 1995 and burned again in 1998. The “cool burn” area was burned once in 1998. Fine lines depict trails utilized by the National Guard for training exercises. Orthophoto courtesy of Brett Engstrom. Northeastern Naturalist NENHC-4 V.S. Banschbach and E. Ogilvy 2014 Vol. 21, No. 1 then planted and protected from the second burn, which was conducted in 1998. In 1998, 3.25 ha that were burned previously and 2.6 additional ha (“cool burn” area in Fig. 1) were burned. In total, 400 Pitch Pine seedlings were planted between 1995 and 1999 in the burned area. To foster the growth of the Pitch Pine seedlings, competing vegetation was cut between 1995 and the 1998 burn and again in 1999 (Nongame and Natural Heritage Newsletter 2006). Data collection We worked with vegetation data and ant specimens collected by undergraduate students supervised by Saint Michael’s College faculty at the study site in 2006, 2007, and 2008. Vegetation data were collected along sixty-three 20-m transects. Along each transect, the students identified trees and shrubs to species, measured shrub and canopy coverage (densiometer readings), and recorded diameter at breast height of trees in order to calculate importance values for trees. To sample ants, students placed pitfall traps in the control forest (habitat unburned in recent times) and both burned areas (Fig. 1). The pitfall traps were 50-ml centrifuge tubes, half-filled with Sierra brand antifreeze (propylene glycol) diluted to 50% by adding an equal volume of tap water. Students were given freedom as to where to place traps and how many traps to utilize, resulting in an uneven sampling effort across the control and burned areas. We were careful to account for this uneven sampling effort in our statistical treatment of data by adjusting ant abundance at each site for trapping effort and by using rarefaction analysis with curves generated only up to the number of individuals in the smaller sample. Students placed traps with the openings flush with the surface of the soil by digging in with a soil corer and collected them after two weeks. All trapping occurred between mid-September and the first week of October of each year. Students sorted ants from other collected macroinvertebrates and preserved them in 95% ethanol. We curated the ants and conducted statistical analyses to examine trends in abundance and diversity. We made a point-mounted voucher collection from the pitfall trap ants and identified ant specimens using keys (Coovert, 2005, Ellison et al. 2012, and Fisher and Cover 2007), photographs on Antweb.org, and to a reference collection made by V.S. Banschbach for an oak-hardwood forest in Jericho, VT (Banschbach et al. 2012). Identities of vouchers in the oak-hardwood reference collection were confirmed by Stefan Cover, Museum of Comparative Zoology, Harvard University. Voucher specimens are housed in the insect collection of the Biology Department at Saint Michael’s College, Colchester, VT. Frequency (number of ants of a given species per total number of traps), and relative abundance (number of ants of a given species per total ants) were tabulated for ants from the control area and the burned areas pooled (“hot burn” and “cool burn” areas). We performed rarefaction analysis to estimate species richness using the EstimateS software version 9.0, Colwell (2013). We used the Chao 1 metric to estimate species richness for the control versus burned areas (Gotelli et al. 2011). Rarefaction curves were generated using EstimateS software (Colwell 2013). For the species richness rarefaction and estimation, we used individual-based procedures because the data were not cataloged by each pitfall trap. Northeastern Naturalist Vol. 21, No. 1 V.S. Banschbach and E. Ogilvy 2014 NENHC-5 Our dataset included all ant specimens collected by the classes in 2006, 2007, and 2008, and a record of collection location, date, and number of traps used, but we did not have a record of ant occurrences in each individual trap utilized. The Wilcoxon Rank Sums and chi quare goodness-of-fit tests were used to compare measures across control and burned areas. Results The ant community samples from 911 pitfall traps yielded 1750 ants from 29 species, 14 genera, and 5 subfamilies. The collections made at the two sites differed significantly in ant abundance, diversity, and species richness (Table 1). Across all species, significantly more ants were captured per trap at the burned site than at the control site (Table 1). More than twice as many ant species were collected in the burned site compared to the control site (Table 1). The Shannon index for the burned site was also higher than for the control site (Table 1). Of the 29 species collected in total, 16 were only collected in the burned area, and just one species was unique to the control area. The Morisita-Horn index of overlap for the two sites’ ant species composition was 0.898; overlap was high—the burned site contained all but one of the species found in the control site. In contrast with the ant-community data, plant-community measures showed less differentiation between the burned and control sites. Eighteen tree species and nine shrub species were found on transects covering 3800 m (trees) and 2500 m (shrubs) in the burned and control areas. Of the 18 tree species sampled, four were found only in the burned site and two solely in the control site. For the nine shrub species, three were found only in the burned site and none solely in the control site. Shrub coverage did not differ between the burned and control areas (Table 1), but canopy coverage differed significantly, with a 20% more open canopy in the burned Table 1. Summary of sampling effort, ants collected, and vegetation characteristics of the burned and unburned sandplain forest sites at the Camp Johnson (Vermont Army National Guard Base, Colchester, VT). Transects used for vegetation sampling were 100 m in length. An asterisk represents statistically significant differences between sites at P < 0.05. Burned site Control site Statistic (P-value) Ants Number of pitfall traps 628 283 Number collected 1585 165 Number per trap 2.52 0.583 W = 628 (0.0004)* Number of species 28 13 χ2 = 5.49, df =1 (0.019)* Shannon diversity index 1.98 1.51 Trees Number of transects 26 12 Number of species 16 14 χ2 = 0.133, df =1 (0.715) Percent canopy cover 57.60 77.60 W = 336 (0.0013)* Shrubs Number of transects 16 9 Number of species 9 6 χ2 = 0.600, df =1 (0.439) Percent coverage 21.14 21.88 W = 115 (0.9323) Northeastern Naturalist NENHC-6 V.S. Banschbach and E. Ogilvy 2014 Vol. 21, No. 1 area versus the control area (Table 1). Across the data for all transects, five tree species in the burned area had importance values (IV) greater than 30 on a 300-point scale: Black Oak, Red Maple, White Pine, White Oak, Fagus grandifolia Ehrh. (American Beech), and Pitch Pine. For the control site, four tree species registered IV greater than 30: Red Maple, White Pine, White Oak, and Black Oak. The ant communities at the burned and control sites differed in terms of species composition and abundance. Of the 29 ant species collected, Aphaenogaster rudis (likely a species complex; Umphrey 1996) and Myrmica punctiventris were common at both sites (relative abundance; Table 2). At the burned site, however, Camponotus pennsylvanicus and M. detritinodis were also common species, each representing at least 10% of the ants collected (Table 2). In contrast, at the control site, Aphaenogaster rudis and M. punctiventris represented 52% and 24%, respectively, of the ants collected (Table 2), with no other species commonly occurring in our samples. Table 2. Ant species frequency (ants per trap) and relative abundance (ants per total ants) in the burned and unburned sandplain forested sites at the Camp Johnson (Vermont Army National Guard Base, Colchester, VT). Burned site Control site Ant species Ants/trap Ants/total ants Ants/trap Ants/total ants Aphaenogaster rudis Enzmann 0.873 0.346 0.304 0.521 Camponotus herculeanus L. 0.003 0.001 0.000 0.000 Camponotus pennsylvanicus De Geer 0.244 0.097 0.000 0.000 Formica exsectoides Forel 0.005 0.002 0.000 0.000 Formica lasioides Emery 0.006 0.003 0.000 0.000 Formica neogagates Viereck 0.008 0.003 0.000 0.000 Formica neorufibarbis Emery 0.013 0.005 0.000 0.000 Formica subintegra Wheeler 0.005 0.002 0.000 0.000 Formica subsericea Say 0.002 0.001 0.000 0.000 Formica sp. 0.000 0.000 0.004 0.006 Lasius sp. 0.018 0.007 0.007 0.012 Lasius alienus Forster 0.005 0.002 0.000 0.000 Lasius flavus Fabricius 0.003 0.001 0.004 0.006 Lasius nearcticus Wheeler 0.006 0.003 0.000 0.000 Lasius neoniger Emery 0.013 0.005 0.000 0.000 Lasius umbratus Nylander 0.006 0.003 0.004 0.006 Myrmecina americana Emery 0.024 0.009 0.028 0.048 Myrmica detritinodis Emery 0.365 0.144 0.028 0.048 Myrmica fracticornis Forel 0.186 0.074 0.021 0.036 Myrmica punctiventris Roger 0.540 0.214 0.141 0.242 Ponera pennsylvanica Buckley 0.008 0.003 0.004 0.006 Prenolepis imparis Say 0.078 0.031 0.007 0.012 Protomognathus americanus Emery 0.002 0.001 0.000 0.000 Solenopsis molesta Say 0.002 0.001 0.000 0.000 Stenamma diecki Emery 0.005 0.002 0.000 0.000 Stenamma schmitti Wheeler 0.035 0.014 0.028 0.048 Stigmatomma pallipes Haldeman 0.008 0.003 0.000 0.000 Tapinoma sessile Say 0.032 0.013 0.004 0.006 Temnothorax longispinosus Roger 0.030 0.012 0.000 0.000 Northeastern Naturalist Vol. 21, No. 1 V.S. Banschbach and E. Ogilvy 2014 NENHC-7 Both observed and estimated species richness were higher in the burned area than the control site (Fig. 2). Estimated total species richness based on pooled pitfall data for each site (considering the total collection of ants from each site as a single sample) was calculated using the Chao 1 estimator for the aggregate samples. For the control site, the estimated total species richness was 16.33 spp. with 95% C.I. = 13.5–35.07 (n = 165). For the burned site, the estimated total species richness was 31 spp. with 95% C.I. = 29.25–45.01 (n = 1585). Figure 2. Results from pitfall trapping for ants at two sandplain forest sites at Camp Johnson (Vermont Army National Guard Base, Colchester, VT): (A) Number of species observed, with standard deviation for the burned site; and (B) estimation of species richness-based incidence records using the Chao 1 estimator, with standard deviationfor the burned site (see text). Northeastern Naturalist NENHC-8 V.S. Banschbach and E. Ogilvy 2014 Vol. 21, No. 1 Discussion We predicted that the burned sandplain forest would support a more diverse ant community than the unburned sandplain forest because of increased habitat diversity due to post-burn succession. Our results show a clear difference between the ant communities in the burned and unburned areas, 8 to10 years post-burn; the burned area contains a significantly greater abundance, greater species richness, and greater species diversity of ants. While we did not have pre-burn ant community data from the burned forest, the very close proximity of the burned and unburned areas, and their similarity in other ecological respects, makes it likely that our results reflect effects of the burn on the ant community. Previous studies have documented a short-term impact (less than a few months post-burn) of fire on ant communities (Bess et al. 2002) and a medium-term effect (a few months to one year post-burn) of fire on abundance of certain ant species (Underwood and Christian 2009, Underwood and Quinn 2010), or found no impacts of fire on abundance and richness of ants (Houdeshell et al. 2011, Parr et al. 2004, Vasconcelos et al. 2008). Therefore, our results are novel in that they are consistent with a long-term effect of fire on the ant community. We expected that the effect of fire on the ant community would occur due to increased habitat diversity created by differences in tree and shrub species composition, vegetation profile, and microclimate. In support, we found a strong difference in canopy cover between the two sites, with the burned area featuring a more open canopy by twenty percent. The key difference in tree species IV between the sites was the increased prevalence of Pitch Pine (reintroduced) and American Beech at the burned site. The shrub coverage was similar at the two sites, with species at the control site consisting of a smaller subset of the species at the burned site. Consistent with the ant-community species-composition patterns, some additional shrub species (3 spp.) were found in the burned area that were absent from the control area, likely due to the more open canopy resulting from the burn. An open canopy featuring Pitch Pine as a common tree species is characteristic of sandplain forest, speaking to the efficacy of the burns and Pitch Pine seedling reintroduction as components of the management plan for sandplain forest restoration (Engstrom 1991). At our sandplain forest study site, one impact of the more open canopy is a warmer forest floor (V.S. Banschbach, unpubl. data; Banschbach et al. 2012), perhaps benefitting growth and survival of ant colonies and leading to increased abundance of ants in the burned area samples. A slight difference in microclimate can lead to ant-nest temperature differences that may have a dramatic influence on colony demography, reproduction, behavior, and survival of workers (e.g., Banschbach et al. 1997, Oldroyd 2009, Porter 1988). This effect would be especially noticeable in September and early October when northern temperate-forest ant species are preparing for and entering into winter dormancy either by moving underground or entering dormancy inside of pre-formed cavities of sticks and acorns in the leaf litter. Impacts from increased wind penetration due to decreased tree canopy coverage would likely be negated by the lack of shrub cover difference between the two sites. The timing of the sampling in the late Northeastern Naturalist Vol. 21, No. 1 V.S. Banschbach and E. Ogilvy 2014 NENHC-9 summer and early fall allowed us to capture a marked difference in ant abundance between these sites that suggests the burned habitat allows ant colonies to achieve a longer growing season. The species composition of the ant communities in the burned and control areas overlapped substantially, supporting the idea that the burned area contains not only the same ants found in the unburned forest in greater abundance, but an additional set of species that were able to thrive in the burned area into the late summer and early fall. The most common ant species at both sites was Aphaenogaster rudis, comprising 35% of the catch in the burned site and 52% in the control site. Aphaenogaster rudis ants are behaviorally subordinate to Camponotus spp. and Formica spp. (Stuble et al. 2012), but A. rudis is quick to discover baits and employs tool use at liquid or semi-solid food resources in order to avoid physical confrontation with other ant species (Banschbach et al. 2006). Some of A. rudis’s dominating competitors were found in the burned area (e.g., Camponotus spp. and Formica spp.) but were not taken in traps in the control site, perhaps due to decreased temperature of the forest floor at the control site, similar to the findings of Lessard et al. (2009). In contrast to A. rudis, M. punctiventris had a similar relative abundance in both our control and burned areas. In the month of September when the pitfall trapping was conducted, the minimum average air temperature was 10.5 °C, and the maximum average air temperature was 20.8 °C (mean from 1981–2010; National Weather Service 2013). Lessard et al. (2009) found that M. punctiventris had the greatest foraging temperature range and commonly foraged at a much lower temperature (15 ºC) than the six common ant species in a southern Appalachian high-elevation ant community. Myrmica punctiventris may thrive in both burned and control areas because it is tolerant of a wider range of temperatures than other species. The burned area is in a post-fire successional stage featuring a more open canopy and increased richness of shrub species as well as, putatively, an increased number of niches for ants. Del Toro et al. (2013) found that early successional, open habitats in Massachusetts were critical to increasing ant biodiversity in White Pine forests, due to the impacts of the cool temperatures of the forest floor in mature forests reducing abundance of some species. Furthermore, pine barrens, with their open canopies, had a greater species richness than White Pine forests (Del Toro et al. 2013). Our results provide additional evidence that a more open canopy leads to increased ant species richness. In rarefaction analysis, species richness was higher for the burned site than for the control area even when examining values up to just 160 individuals sampled. The estimated species richness of 31 ant species (Chao 1 estimator based upon data for all 1585 ants sampled) in the burned area is comparable to other findings for similar habitat types in New England (e.g., Chao 2 richness estimate of approximately 30 ant spp. in pine barrens of Massachusetts [Del Toro et al. 2013]; 15 to 35 spp. collected for sandplain heathland and Pitch Pine heathland habitats on the island of Nantucket, MA [Ellison 2011]). If the controlled burn is the cause for the increased species richness of the ant community by enhancing the capacity for ants Northeastern Naturalist NENHC-10 V.S. Banschbach and E. Ogilvy 2014 Vol. 21, No. 1 to fill the many niches they occupy in forest ecosystems, this result speaks to the efficacy of sandplain forest restoration via controlled burning and planting of Pitch Pine seedlings. Our ongoing work at the Camp Johnson field site includes late spring/early summer and late summer/early fall study of a more recent controlled burn conducted in May 2013 in a previously unburned area of the forest. The addition of late spring/ early summer data collection utilizing a range of standard techniques (pitfall trapping, baits, and Winkler samping) will allow us to determine how much of the increased species richness may be accounted for by season. Phenology of the ant community in relation to burned and unburned areas needs to be better understood. If the differences in the ant community are not as strong in the Summer, this result would suggest that our current findings relate to the fact that in September, in the cooler control area, many species have begun to enter dormancy. By tracking the results of the 2013 burn, compared to control (unburned) areas at the Camp Johnson site, we will be able to detect the temporal changes for the ants and the plants. Furthermore, we will be able to compare replicate samples , rather than individuals, in our summer datasets, avoiding a statistical limitation of our current dataset (Gotelli et al. 2011). Taken on their own, the data reported here support the idea that high ant species richness serves as an indicator of ecological change in the case of sandplain forest restoration via controlled burning. Acknowledgments The authors thank the Vermont Army National Guard officers and civilian staff at Camp Johnson for allowing the Saint Michael’s College Biology Department faculty and students to study the sandplain forest management area. In particular, Mike O’Hara, Vermont Military Lands Administrator, and Major Jacob Roy, Environmental Protection Supervisor, have provided invaluable support. Brett Engstrom, Nature Conservancy of Vermont, has also provided useful data and expertise based on his long-term study of the natural communities of Vermont. Emily Ogilvy was funded by a Vice President for Academic Affairs (Saint Michael’s College) Summer Student Research Grant and a VPAA travel grant. We are also grateful to the Biology Department faculty who teach the Introduction to Ecology and Evolution course for their expert guidance of the students who have collected data on the sandplain forest for the past 7 years at Saint Michael’s College. Literature Cited Anderson, R.C., T. Leahy, and S.S. Dhillion. 1989. Numbers and biomass of selected insect groups on burned and unburned sand prairie. American Midland Naturalist 122:151–162. Banschbach, V.S., N. Levit, and J.M. Herbers. 1997. Nest temperatures and thermal preferences of a forest ant species: Is polydomy a thermoregulatory mechanism? Insectes Sociaux 44:109–122. Banschbach, V.S., A. Brunelle, K.M. Bartlett, J.Y. Grivetti, and R.L. Yeamans. 2006. Tool use by the forest ant Aphaenogaster rudis: Ecology and task allocation. Insectes Sociaux 53:463–471. Banschbach, V.S., R.L. 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