Myrmica Rubra Microhabitat Selection and Putative Ecological Impact

Ecological Entomology (2019), 44, 239–248 DOI: 10.1111/een.12700

Myrmica rubra microhabitat selection and putative ecological impact

ROBERT J. WARREN II1 ABBY MATHEW1 KATELYN REED1 SONYA BAYBA1 KEVIN KRUPP1 and DAVID J. SPIERING2 1Department of Biology, SUNY Buffalo State, Buffalo, New York, U.S.A. and 2Tifft Nature Preserve, Buffalo Museum of Science, Buffalo, New York, U.S.A.

Abstract. 1. Myrmica rubra (European fire ant) has invaded northern latitude coastal areas in North America. This macroscale distribution suggests that M. rubra is moisture- and temperature-limited, but the distribution of the invaded range may reflect the legacy of original introduction locations preserved by limited dispersal. 2. This study examined a two-decade population change in M. rubra (1994–2015) and the microscale abiotic (moisture and temperature), biotic (plants), anthropogenic (pesticide) and physiological (thermal tolerance) limits on the invasion at the Tifft Nature Preserve in Buffalo, NY (U.S.A.). Changes in the abundance of native ants and other invertebrates were also examined. 3. Despite localised declines with pesticide treatments, overall M. rubra forager abundance increased 27% between 1994 and 2015. Abundance increased the most in the warmest areas (native ants were unaffected by temperature), but M. rubra colony locations were strongly linked to higher soil moisture and lower soil temperature. Myrmica rubra ants also exhibited relatively low thermal tolerances consistent with high-latitude and high-elevation ants. 4. Where local M. rubra populations increased the most, native ant species decreased, and where local M. rubra populations declined, native ant species increased. Some arthropod species had lower abundance with M. rubra presence, but the impacts were less striking. 5. Myrmica rubra population growth was promoted at the microhabitat scale where relatively higher temperatures prompted foraging, and relatively lower temperatures and high moisture supported nesting. These results suggest that macroscale M. rubra invaded-range distributions in northern climates near coastal areas are replicated at the microscale where the ant prefers cooler, moister microsites.

Key words. European fire ant, habitat management, invasive species, urban ecology.

Introduction 2011). Whereas M. rubra is widespread throughout Eurasia, ranging from the Arctic Circle to the Black sea, the invaded The European fire ant, Myrmica rubra (Linnaeus, 1758), proba- range is much narrower, currently limited to northeastern North bly arrived in northeastern North America sometime in the late America, with some M. rubra populations also in northwestern 19th/early 20th century (Wheeler, 1908; Wetterer & Radchenko, North America. Both the native and invaded-range populations 2011), possibly in the soils of trade-ship ballast and/or ornamen- only occur north of the 40th parallel, suggesting they may be tal plant pots (Groden et al., 2005; Hicks et al., 2014). Despite limited by the environmental tolerances of a single or few source its long residence time, most reports of M. rubra beganinthe populations or a legacy of limited original introduction points early 21st century (Groden et al., 2005; Wetterer & Radchenko, (Groden et al., 2005; Wetterer & Radchenko, 2011; Hicks et al., Correspondence: Robert J. Warren II, SUNY Buffalo State, 1300 2014). Elmwood Avenue, Buffalo NY 14222, U.S.A. E-mail: hexastylis@ Myrmica rubra is a generalist omnivore, eating everything gmail.com from prey to pollen (proteins), as well as honeydew and nectar

(carbohydrates) by tending Homoptera (aphids) and extracting limits (minimum and maximum thermal tolerances). In order to nectar from plants with extrafloral nectaries (EFNs; Reznikova assess M. rubra impacts, we also investigated how native ant & Panteleeva, 2001; Le Roux et al., 2002; Ness et al., 2013). species abundance changed with M. rubra population growth Experimental field trials indicated high predation of Collem- between 1994 and 2015, and whether arthropod abundance bola (springtails) (Reznikova & Panteleeva, 2001) as well as correlated with M. rubra abundance. active protection of homopterans for honeydew (McPhee et al., 2012). Myrmica rubra also is a scavenger of dead insects and elaiosome-bearing seeds (Groden et al., 2005; Prior et al., 2014; Materials and methods Bologna & Detrain, 2015). In the invaded range (North America), colonies are both Study site polygynous (multiple queens) and polydomous (workers move The Tifft Nature Preserve (Tifft) is a 107-ha urban nature pre- between colonies), and M. rubra forms ‘supercolonies’ con- serve of woodlands, freshwater wetland and grassland adminis- taining tens of thousands of workers and hundreds of queens tered by the Buffalo Museum of Science near the western shore (Groden et al., 2005). These massive M. rubra colonies can sat- of Lake Erie (Figure S1; 42.844 075, −78.854 797). The pre- urate local ecosystems, coinciding with marked decreases (up serve is a former trans-shipment centre once used for industrial to 99%) in native ants and sometimes decreases in other inver- activities as well as refuse dumping until the early 1970s. Past tebrates (Groden et al., 2005; Ouellette et al., 2010; Naumann industrial dredging and dumping created a soil base composed of & Higgins, 2015). Myrmica rubra delivers a painful sting (Gro- natural and artificial materials, and the forest soils contain athin den et al., 2005; Wheeler, 1908), making the formation of dense layer of humus above mineral soil mixed with industrial dredge, supercolonies problematic for human populations as well (D. building debris, and residential and industrial refuse (Spiering, Brasure, unpublished; Groden et al., 2005; Spiering, 2009). 2009). Historic aerial photos indicate that trees began estab- Myrmica rubra generally occurs in woodlands, nesting in logs, lishing in Tifft in the 1950s. The dominant canopy species in under stones and sometimes in leaf litter, but it also occurs in the woodland areas is Populus deltoides (eastern cottonwood). lawns, gardens and other anthropogenically altered landscapes Myrmica rubra was first reported at Tifft in the mid-1980s (D. (Groden et al., 2005; Michlewicz & Tryjanowski, 2017). In its Brasure, unpublished). native range, M. rubra generally occupies mesic/humid habitats, but appears limited in its invaded range to coastal/wetland habitats, such as the shores of the North Atlantic and Pacific Bait station surveys Oceans and the Great Lakes (Groden et al., 2005; Wetterer & Radchenko, 2011; Ness et al., 2013). Unlike several other In 1994, as part of a Tifft management plan aimed at control- non-native invasive ants in North America (Warren II et al., ling M. rubra, an intensive bait station survey was conducted in 2017), M. rubra does not appear to be limited by cold temper- invaded woodland areas by D. Brasure (unpublished). ‘Tic-Tac’ atures. Indeed, M. rubra appears best suited to relatively cold candy boxes containing a strip of cotton and 20 drops of 50% temperatures (Brian, 1973), although direct microhabitat and sugar water were placed at 127 sites at 50-m intervals along physiological data for M. rubra are limited. In North Amer- woodland trails at Tifft (M. rubra does not occur in the grass- ica, M. rubra’s association with coastal areas at northern lati- land habitat). At the time of the 1994 survey, M. rubra occurred tudes suggests that the invaded-range populations are moisture- in the southern half of the wooded habitat at Tifft; Since then, and temperature-limited. However, given that invaded-range M. it has invaded the northern portion (R.J. Warren II, pers. obs.), rubra queens do not engage in nuptial flights, limiting M. rubra but those areas were not used for the 2015 replication of the bait dispersal to ‘budding’ dispersal (Groden et al., 2005; Hicks, station surveys; however, the northern woodlands were included 2012), the current North American distributions could simply in the transect and log surveys. The bait boxes were placed at reflect the original introduction points preserved by the limited c. 12.00 hours and left out for 1.5 h. The boxes were then closed, dispersal. and the ants freeze-killed. Bait station surveys were done seven Our objective was to examine a two-decade population change times between June and October 1994. In 2015, we repeated the in an M. rubra invasion (1994–2015) and the microscale 1994 study using 50-ml centrifuge tubes instead of ‘Tic-Tac’ abiotic limits on the ant invasion. Given that the initial M. boxes at the same locations and intervals. We chose the cen- rubra population survey was taken approximately a decade trifuge tubes because they contain the same internal volume after M. rubra was discovered at the Tifft Nature Preserve as the ‘Tic-Tac’ boxes. We also recorded dominant vegetation (Buffalo, NY, U.S.A.), our first question was whether the (> 75% of the plants within 1 m2 of the bait station), soil mois- population was still growing two decades later. Given that M. ture and temperature at each bait station location in 2015. Soil rubra populations generally occur in coastal areas at northern moisture was measured using a Hydrosense soil moisture sensor latitudes in North America, we investigated the impact of with 20-cm stainless steel rods (Campbell Scientific, Logan, UT, microhabitat conditions (moisture and temperature), as well U.S.A.) at three points near each station and values were aver- as pesticide applications, on M. rubra foraging and nesting. aged; soil temperature was measured using a wide-range ther- We investigated whether M. rubra was associated with local mometer (Taylor Precision Products, Las Cruces, NM, U.S.A.) dominant plants, including a non-native plant with EFNs, and we at5cmdepth. collected M. rubra foraging items to assess diet and behaviour. Tifft managers began applying amidinohydrazone-based pes- Finally, we examined M. rubra’s physiological temperature ticides annually (except 2002) in 1994 to reduce or remove M.

© 2018 The Royal Entomological Society, Ecological Entomology, 44, 239–248 Myrmica rubra microhabitat selection 241 rubra foragers from some of the recreation trails, many of which colony, and the ants were immediately placed individually into were proximate to the bait stations. We included these treatments 16-mm glass test tubes filled with some nest soil and plugged in the assessment of M. rubra and the native ant population. In with moistened cotton to maintain humidity and reduce stress. 1994, the pesticides were applied to most (105) of the bait station The cotton plugs also reduced movement during subsequent locations; however, by 2015, given that the pesticides failed to thermal testing. The field-collected test tubes were placed in effectively eliminate the ants, site managers limited treatments racks and in a cooler with ice to prevent overheating during to locations (67) where the ants were most likely to come in con- transport to the laboratory (with an insulator between the test tact with (and sting) visitors. In all years, the pesticide treatments tube racks and ice). Thermal testing was done on the same were limited to recreational trails and their immediate vicinity, day as the collection. From each 15-ant sample, ants were leaving most of the Tifft Preserve untreated. randomly assigned, five each to CTmax,CTmin and a control. A mean temperature for the loss of righting response (the ability to regain upright status after being knocked down) served as Transect surveys the index for thermal tolerance for each sample at each site. A control sample of five ants from each colony was keptin Given that the bait station surveys captured microhabitat con- the same test tube conditions as the thermal tolerance samples, trols on ant foraging patterns but not necessarily colony loca- except that they were not put in the water bath. None of tions, we established 32 non-overlapping haphazard GPS tran- the control specimens lost their righting response during the sects of varying lengths (80–400 m depending on woodland testing. After thermal tolerance testing was completed, all ants edges) to survey the Tifft woodlands. Transects were surveyed were catalogued and stored in the Warren laboratory at SUNY between June and August 2015. All rocks and logs found Buffalo State. within 2 m of the GPS transects were investigated (n = 273 For CTmax (heat tolerance), we pre-warmed an Ac-150-A40 sampling points). Myrmica rubra and native ant colony pres- refrigerated water bath (NesLab; ThermoScientific, Portsmouth, ence was recorded, as well as soil moisture and temperature. In NY,U.S.A.) to 30 ∘C. We placed five test tubes with ants into the May–June 2016, we conducted a second haphazard nest sur- bath and allowed them to equilibrate for 10 min, at which point vey throughout Tifft to investigate whether M. rubra colonies the temperature was increased by1.0 ∘Cmin−1.Theantswere were correlated with arthropod communities in downed wood checked 60 s after the unit reached the next temperature interval. (i.e. arthropods). We surveyed 50 pieces of downed wood At every interval, the ant righting responses were observed by for the abundance of M. rubra, native ant colonies and other lifting each test tube out of the bath very briefly. If the individual invertebrates. was immobile, the test tube was turned and tapped to verify the ability to stay upright. Once an individual lost its ability to right itself, it was removed and the corresponding interval Thermal tolerance temperature recorded. Testing concluded after all individuals in a sample lost the ability to right themselves. For CT (cold The physiological thermal limits of ectothermic organisms min tolerance), the water bath was pre-cooled to 20 ∘C, and the ants reflect their sensitivity to temperature extremes which, in turn, were allowed to equilibrate for 10 min. After the adjustment provides an insight into their putative fitness and geographic period, the temperature was decreased 1.0 ∘Cmin−1, and the distributions in response to climate (Huey & Kingsolver, 1989; same procedure was followed as CT . Terblanche et al., 2011; Sunday et al., 2012). Insects exhibit max a wide array of physiological and behavioural adaptations to regulate their temperature (Heinrich, 1996). Given that the Simulated herbivory microhabitat distribution of ants may reflect larger-scale climate conditions (Menke et al., 2014) or dispersal limitation (Groden In the bait station surveys, we found the highest abundances et al., 2005; Hicks, 2012), the underlying physiological climate of M. rubra foragers in plots containing Urtica dioica (stinging tolerance of ants can provide mechanistic insights into their nettle) and Fallopia japonica (Japanese knotweed). Myrmica distributions. Thermal tolerance is a commonly used trait that rubra attends plants with EFNs, which secrete nectar to attract essentially delineates the lower (critical thermal minimum, ant protectors when damaged by herbivores (Kawano et al., ‘CTmin’) and/or upper (critical thermal maximum, ‘CTmax’) 1999; Ness et al., 2013). Given that F. japonica has EFNs, physiological temperature limits for an organism – often mea- but U. dioica does not, we investigated potential M. rubra sured as the sublethal thermal limit at which motor function facilitation with a field experiment in which we manually fails (Huey & Stevenson, 1979). simulated herbivory. We randomly created 10 100 m2 plots that In May–July 2016, we sampled live M. rubra ants from eight contained individuals of a plant with EFN (F. japonica)anda colonies at six study sites in the western New York region: plant without EFN (U. dioica). We selected two individuals of Times Beach Nature Preserve, George J. Hartman Play Fields, each species in each plot (n = 20 of each species) that were Fort Niagara State Park, Golden Hill State Park, Lewiston within 10 m of one another. We randomly selected one of Town Park and Woodlawn Beach State Park (two colonies each species per plot (n = 10 each) and simulated herbivory were collected each at Fort Niagara and Golden Hill state by manually cutting one-third of the leaf area of all leaves, parks) (Fig. S1). We minimised spatiotemporal confounding by a treatment level that induces EFN nectar production and ant sampling haphazardly (no particular order or pattern) throughout response in F. japonica (Ness et al., 2013). We surveyed ants at the summer. We collected 15 workers from each M. rubra 4 and 30 days after the treatments.

Log survey Table 1. Generalised linear models with quasi-Poisson error distribution for: (a) ant abundance as a function of species (Myrmica rubra, During May–June 2016, we conducted a second nest sur- native ants), year (1994, 2015), treatment (pesticide/no pesticide), soil vey throughout the Tifft woodlands to estimate the impact moisture (%) and soil temperature (∘C); and (b) population change of M. rubra on invertebrate communities in downed wood (i.e. (Δabundance 1994–2015) as a function of the same variables except arthropods, gastropods and annelids). We haphazardly surveyed year. 50 pieces of downed wood for the abundance of M. rubra, Coeff. SE t-value P-value native ants (Hymenoptera), Isopoda, Diplopoda, Chilopoda, Oligochaeta, Coleoptera, Arachnida and Gastropoda. (a) Ant abundance Species 3.910 0.335 11.652 < 0.001 Year 0.222 0.093 2.377 0.017 Forager loads Treatment −0.480 0.106 −4.492 < 0.001 Moisture −0.001 0.002 −0.231 0.817 To get an estimate of M. rubra scavenge items, we set up Temperature 0.024 0.045 0.532 0.595 (0.25 m2) plots with a white piece of cloth on the ground in (b) Population change heavily trafficked M. rubra areas for 15 min. We monitored these Species −2994.534 1002.175 −2.988 0.003 Treatment 12.559 75.880 0.166 0.868 ‘forager load’ plots 25 times during June–July 2016. All M. Moisture −0.012 1.599 −0.008 0.993 rubra workers that walked on the cloth were observed with a Temperature −6.398 36.574 −0.175 0.861 hand lens and collected if they were carrying anything in their Species × treatment −290.394 106.599 −2.724 0.006 mandibles. The items were immediately placed in alcohol and Species × temperature 170.212 51.291 3.000 0.001 identified in the laboratory with a stereoscope.

Data analysis analysis using the factominer and factoextra packages (Le et al., 2008). We used the first two principal components, All statistical analyses were conducted using the r statistical which explained 40% of the variance in loadings. We used package (version 3.5.0; R Core Team, 2016). Potential collinear- the minimum contribution if all variable loadings contributed ity between predictor variables was evaluated using variance equally (33% here) to determine the most important loadings inflation factors generated in thecar ‘ ’ package (Fox & Weis- for each principal component, and we plotted all variables in a berg, 2011). The variance inflation factors for the predictor vari- biplot. ables were all < 1.5, indicating they independently predicted variance. For logistic regression, we used ‘quasi’ error distri- > butions if overdispersion was 2.0. Results We analysed ant forager abundance at bait stations as a function of species (M. rubra or any native species), year (1994 Bait station surveys or 2015), pesticide treatment (treated, untreated), 2015 soil moisture (%) and 2015 soil temperature (∘C) using a generalised A total of 62 906 M. rubra workers were collected in 1994 linear model (GLM) with quasi-Poisson error distribution. We (82.6 ± 7 ants per sample, mean ± SE) and 80 445 in 2015 analysed ant population change (2015 baitsi – 1994 baitsi)as (106.5 ± 7 ants per sample) at the same bait stations using the a function of the same independent variables as the abundance same methodology in each year. Totals of 1733 other ants of model (except year) using a linear regression model. eight genera were collected in 1994 and 1120 of eight genera We analysed M. rubra colony presence along transects as a (not all the same as 1994) in 2015. Overall ant population function of soil moisture and temperature using a GLM with a change did not appear to be affected by moisture or temperature, binomial error distribution. and non-significant species × treatment, species × moisture and For the simulated herbivory experiment, we analysed ant species × temperature interaction terms were removed from the forager abundance (M. rubra and native ants) as a function of model. Whereas M. rubra populations increased, and native plant species (F. japonica or U. dioica) and simulated herbivory ant populations decreased, between 1994 and 2015, M. rubra (damaged or undamaged) at days 4 and 30 using GLM models populations declined where pesticides were applied, whereas with quasi-Poisson error distributions. The coefficients for the native ant populations were essentially unaffected by pesticide fitted GLM models were estimated using analysis of deviance treatments (Table 1; Fig. 1a). Myrmica rubra foragers averaged (anodev) with 𝜒 2 tests. anodev is a maximum likelihood 258 ± 20 ants per bait where pesticides were applied, and approach used with GLMs fit using an anova model with a 𝜒 2 420 ± 58 ants per bait where they were not (means across both test. Comparisons between the reduced model and full model, years). Myrmica rubra populations increased the most between which includes all predictors, are made using scaled deviance. 1994 and 2015 where 2015 soil temperatures were higher, The model output produces a table with rows corresponding to whereas native ant populations were unaffected by temperature each of the parameters with an additional top row for the null (Table 1; Fig. 1b). Myrmica rubra population change did not model. appear to be affected by soil moisture, and a non-significant We analysed variation among M. rubra and co-occurring species × moisture interaction term was removed from the native ants and arthropods under logs with principal component model.

Fig. 1. (a) Native ants (which had 1% of the abundance of Myrmica rubra) were unaffected by localised pesticide treatments at Tifft Nature Preserve (Buffalo, NY, U.S.A.), whereas M. rubra populations were considerably lower with pesticide treatment. (b) Overall, M. rubra numbers increased 27% between 1994 and 2015, and M. rubra forager abundance increased the most at relatively warmer locations, whereas native ants were unaffected.

Table 2. Generalised linear model with binomial error distribution for Simulated herbivory Myrmica rubra colony presence as a function of moisture (%) and temperature (∘C). Myrmica rubra foragers increased on F.japonica plants 4 days after experimental herbivory but remained the same on U. dioica Coeff. SE z-value P-value plants (Table 3, Fig. 3). Native ant foragers were higher on F. −1 Myrmica rubra colony presence japonica (1.2 ± 0.1 native ants plant [mean ± SE]) than U. −1 Moisture 0.024 0.007 3.367 < 0.001 dioica (0.1 ± 0.1 native ants plant ), but were unaffected by the Temperature −0.120 0.570 −2.094 0.036 experimental herbivory. At 30 days, M. rubra foragers were the same on F. japonica (3.0 ± 1.0 M. rubra plant−1)andU. dioica (2.1 ± 0.5 M. rubra plant−1) plants whereas native ant foragers In the 2015 survey, we found most M. rubra foragers at bait remained higher on F. japonica (1.2 ± 0.9 native ants plant−1) stations with vegetation dominated by U. dioica (1068 ± 60 than U. dioica (0.1 ± 0.1 native ants plant−1). ants) and F. japonica (968 ± 57 ants). Other common plants in the plots were Rhamnus cathartica (European buckthorn), Cirsium spp. (thistle), Phragmites australis (common reed) and Log survey Ageratina altissima (white snakeroot). Principal component analysis of invertebrate communities in downed wood indicated that most variance occurred along Transect surveys the PC1 axis (23%) where the most important variables were Isopoda, Coleoptera, Diplopoda, Arachnida and Gastropoda, all Myrmica rubra colonies were found under 60% of the downed of which negatively covaried with M. rubra (Fig. 4). On the wood (native ants under 21%). Myrmica rubra colonies were PC2 axis (17% of the variance), all of the variables were impor- more common in and under downed wood at temperatures tant, and native ants (Hymenoptera), Oligochaeta, Chilopoda, c.1∘C cooler (19.2 ± 0.2 ∘C, mean ± SE) than when they Isopoda and Diplopoda negatively covaried with M. rubra, were absent (20.2 ± 0.2 ∘C), and more common in much wet- Arachnida and Coleoptera. ter microhabitats (30.2 ± 1.9%) than when they were absent (18.5 ± 1.5%) (Table 2; Fig. 2). A non-significant temperature × moisture interaction term was removed from the model. Forager loads At Tifft, 39.6 ± 3 ants per plot (mean ± SE) were observed Thermal tolerance carrying approximately 17.6 ± 5 items per plot, and hence approximately 43% of the foragers that entered a plot were ∘ Mymica rubra CTmax was 41.8 ± 0.1 C(mean± SE) and carrying something. The most common items being carried ∘ CTmin was 4.3 ± 0.2 C. by M. rubra foragers at Tifft were parts of other M. rubra

Fig. 2. (a, b) Myrmica rubra nests were found at lower frequencies in downed wood in warmer locations (a), and at much greater frequencies in comparatively wetter locations (b).

Table 3. Myrmica rubra (a, c) and native ant (b, d) abundance on plants with extrafloral nectaries [Fallopia japonia (Japanese knotweed)] and those without [Urtica dioica (stinging nettle)] at day 4 (a, b) and day 30 (c, d) after simulated herbivory treatments.

d.f. Dev. Res. d.f. Res. dev. P-value

(a) Myrmica rubra abundance (day 4) Null 36 156.990 Plant species 1 2.948 35 154.040 0.357 Treatment 1 23.373 34 130.670 0.013 Plant species × treatment 1 17.201 33 113.460 0.031

(b) Native ant abundance (day 4) Null 39 128.573 Plant species 1 24.957 38 103.616 0.044 Treatment 1 11.644 37 91.972 0.164

(c) Myrmica rubra abundance (day 30) Null 36 233.790 Plant species 1 0.706 35 233.090 0.754 Treatment 1 1.635 34 231.450 0.634

(d) Native ant abundance (day 30) Null 39 33.856 Plant species 1 8.317 38 25.538 0.007 Treatment 1 2.911 37 22.627 0.101

Res, residual, Dev, deviance. ants (20% of all items), parts of arthropods (15%) and seeds Discussion (17%; most were P. deltoides) (Table 4). Also common was the carrying of live M. rubra queens (5%), workers (3%) Despite localised declines due to pesticide treatments, M. rubra and larvae (11%). Coleoptera was the most common single forager abundance increased 27% between 1994 and 2015 at non-ant taxon carried by the foragers (11%), and workers were Tifft Nature Preserve, more than 30 years after the non-native ant found carrying intact corpses of other ants (2%), including was first noticed at the site. Myrmica rubra forager abundance Camponotus, Crematogaster and Temnothorax spp. increased the most in the warmest areas (whereas native ants

Fig. 3. Myrmica rubra abundance (4 days after treatment) was unaffected by simulated herbivory on stinging nettle (Urtica dioica), but increased significantly after simulated herbivory on Japanese knotweed (Fallopia japonica), which provides extrafloral nectaries.

Table 4. Items carried by Myrmica rubra foragers at the Tifft Nature rubra. Overall, these results suggest strong population growth of Preserve (Buffalo, NY, U.S.A.) in June and July 2016 as a percentage of M. rubra decades after invasion, with colony locations limited all items carried. by relatively low moisture and high temperature and, at least temporarily, local pesticide application. Local increases in M. Forager loads % rubra forager populations coincided with declines in native ants Diptera 6.5 and some local arthropods. Coleoptera 10.6 Tifft was created as a nature preserve in the 1970s in an indus- Other arthropods 4.4 trial area once used as a coal and grain shipyard (Lehigh Val- Arthropod parts 15.4 ley Railroad), and later for dumping iron slag and municipal Native ants 2.4 waste. Myrmica rubra was first noticed at the preserve in the Ant larvae 10.9 mid-1980s (D. Brasure, unpublished), and the 1994 survey indi- M. rubra workers 2.7 cated that it already was widespread and numerous. Between M. rubra queens 4.8 1994 and 2015, when the P. deltoides canopy increased, native M. rubra parts 19.8 Seed 16.7 ants declined overall, but moist woodland and cool-weather ants Soil and detritus 5.8 such as Aphaenogaster spp. and Prenolepis imparis (Say, 1836) increased in parts of the preserve where M. rubra numbers were low; concomitantly, more urban, disturbed habitat ants, such as Formica neogagates (Viereck, 1903) and Tetramorium cae- were unaffected), but nest location appeared more strongly spitum (Linnaeus, 1758), decreased. Interestingly, P. imparis linked with high soil moisture, and the ants avoided nesting in appears to resist displacement by another non-native invasive the warmest soils. Simulated herbivory on a plant with EFNs ant, Linepithema humile (Mayr, 1868), through its unique for- increased M. rubra abundance compared with a non-EFN plant, aging window (∼winter) and strident chemical defence (Sor- but there was no link otherwise between M. rubra abundance rells et al., 2011). Prenolepis imparis also tends homopterans and any particular plant species. At locations where local and EFNs. Native ants were 1% the abundance of M. rubra in M. rubra populations increased the most between 1994 and the 1994 and 2015 bait station surveys, strikingly similar to the 2015, native ant species decreased, and where local M. rubra proportion reported by Naumann and Higgins (2015) in British populations declined, native ant species increased. Earthworms, Columbia (Canada). Whereas the inverse relationship between centipedes and millipede abundances were also lower under M. rubra and the native ants at Tifft is remarkable, both spatially logs inhabited by M. rubra than under unoccupied logs. Finally, and temporally, a manipulative experiment is required to conclu- dead arthropods and seeds appeared to be the main forage sively establish that the non-native ant displaces the native ant carried by M. rubra workers, along with live and dead M. community (King & Tschinkel, 2008).

Fig. 4. Principal component analysis of Myrmica rubra abundance under downed wood with co-occurring abundance of arthropods, annelids and arachnids for principal component axes PC1 × PC2 (which explained 40% of the variation in the data). Arrows pointing in the same direction indicate positive covariation, and those pointing in opposite directions indicate negative covariation. Shading indicates percentage contribution, with darker shades indicating variables that contribute relatively more to the principal component axes.

Whereas M. rubra foraging (measured at the 1994 and 2015 loads were seeds, and most of the seeds being carried were P. bait stations) increased with warmer temperatures and was deltoides (which are very abundant at Tifft due to the extensive relatively indifferent to soil moisture, nest placement (transect cottonwood canopy). Myrmica rubra generally retrieves seeds surveys) was correlated to cooler (∼19 ∘C) and wetter (∼30% with elaiosomes (Prior et al., 2014; Bologna & Detrain, 2015), soil moisture) microhabitats. Similarly, Brian (1973) reported but P. deltoides seeds do not have elaiosomes, and the retrieval that M. rubra increased activity in temperatures > 23 ∘C in its of non-myrmecochorous plant seeds by M. rubra has not been native range, but colony performance was best in temperatures of reported. We also found several workers carrying pieces of soil 19–21 ∘C. Elmes and Petal (1990) reported that optimal colony and other ground debris. Some species of ants use debris and soil growth for M. rubra in Dorset, England, occurred at 16 ∘C. grains to transport liquid food (Banschbach et al., 2006; Maak Brian (1973) noted that M. rubra is widespread throughout et al., 2016), although this behaviour has not been reported for Europe, but is restricted to mountains and woodlands in southern M. rubra, and we did not deserve the origin of the debris and soil. Europe. We found that WNY M. rubra exhibited minimum and Almost 40% of M. rubra forager loads were other M. rubra: maximum temperature tolerances that were lower than those of corpses, workers, queens and larvae. It is unlikely that any of urban Temnothorax curvispinosus (Mayr, 1866) ants in nearby these items were food. Myrmica rubra, like many other social Cleveland, OH (also on the shore of Lake Erie), and more in insects, remove their dead (necrophoresis) (Diez et al., 2012), line with high-elevation Aphaenogaster spp. ants in the Southern which is a hygienic behavioural characteristic for large colonies Appalachian mountains (Warren II & Chick, 2013; Diamond (Choe et al., 2009), and we have observed several M. rubra et al., 2017). ‘graveyards’ at Tifft where the dead ants were piled up. The At Tifft, M. rubra have been observed eating bird and mammal carrying of live ants, including M. rubra (Abraham & Pasteels, carrion, as well as killing and eating earthworms (D. Brasure, 1980), particularly other workers, can be a foraging strategy unpublished; R.J. Warren II, pers. obs.). We found that arthropod in which ‘scouts’ bring other foragers to food sources as a parts, beetles and seeds were the most common potential food recruitment behaviour (Guenard & Silverman, 2011), whereas items carried by M. rubra foragers. However, our methods did queen and larvae carrying is probably a behaviour associated not let us distinguish between the items as prey or scavenge. with colony emigration (Franks & Sendova-Franks, 2000). We did find decreased abundances of earthworms, centipedes Given that M. rubra forms supercolonies in the invaded range and millipedes under logs occupied by M. rubra compared with with highly polygynous and polydomous colonies, high levels logs without colonies. A considerable portion of the forager of emigration and intercolony exchanges might be common.

Myrmica rubra dominates the local ecosystem at the Tifft Choe, D.-H., Millar, J.G. & Rust, M.K. (2009) Chemical signals associ- Nature Preserve, appearing to decimate the local native ant com- ated with life inhibit necrophoresis in Argentine ants. Proceedings of munities and possibly taking over the understorey food web. The the National Academy of Sciences, 106, 8251–8255. results of this investigation show that the overwhelmingly dom- Diamond, S.E., Chick, L., Perez, A., Strickler, S.A. & Martin, R.A. inant, and continuously growing, M. rubra population at Tifft (2017) Rapid evolution of ant thermal tolerance across an urban-rural temperature cline. Biological Journal of the Linnean Society, 121, coincides with a dramatic decrease in the native ant popula- 248–257. tions at the nature preserve. However, an additional experiment Diez, L., Deneubourg, J.L. & Detrain, C. (2012) Social prophylaxis is required to assess whether the invasive ant is, in fact, displac- through distant corpse removal in ants. Naturwissenschaften, 99, ing the native ants, or whether they are just better suited to the 833–842. altered Tifft habitat. Myrmica rubra is associated with northern Elmes, G.W. & Petal, J. (1990) Queen number as an adaptable trait: climates and coastal areas at the macroscale, and this patterning evidence from wild populations of two red ant species (genus was replicated at the microscale, with the ant nesting in rela- Myrmica). Journal of Animal Ecology, 59, 675–690. tively high soil moisture and moderate temperatures – although Fox, J. & Weisberg, S. (2011) An R Companion to Applied Regression. warmer temperatures prompt greater foraging. Annual pesticide Sage, Thousand Oaks, California. treatments conducted since 1994 effectively knocked back local Franks, N.R. & Sendova-Franks, A.B. 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