Northeastern Naturalist 1 J.J. Rykken and B.D. Farrell 2018 Vol. 25, Special Issue 9 Six-Legged Colonists: The Establishment and Distribution of Non-Native Beetles in Boston Harbor Islands NRA Jessica J. Rykken1,* and Brian D. Farrell2 Abstract - Boston Harbor Islands National Recreation Area lies in a busy, urban harbor that has been receiving immigrants, both vertebrate and invertebrate, since the 17th century. As part of an All Taxa Biodiversity Inventory conducted in the park from 2005 to 2011, we documented the abundance and distribution of native and non-native beetles across 15 islands and peninsulas in Boston Harbor. We hypothesized that proportions of non-native species on the islands would be high relative to the nearby mainland (Rhode Island) and other more isolated coastal islands in Massachusetts. We also compared distribution patterns between native and non-native species and tested the predictive value of island size and isolation for determining species richness on individual islands. Focusing on 6 beetle families, we documented 105 non-native beetles out of a total of 442 species. The proportion of nonnative species was 2–3 times higher in Boston Harbor Islands than in Rhode Island for all 6 beetle families, as well as for beetles on several Massachusetts islands. We discuss likely routes of immigration for beetles over the past several centuries and why islands in Boston Harbor may be attractive to non-native species. Within the park, non-native species in most focal families were, on average, more abundant and widespread across islands than native beetles, but the number or proportion of non-native species was not strongly related to island size or isolation. The high proportions of non-native species in the park, including some known pests and several new state, US, and North American records, emphasize the need for continued inventory and surveillance. Introduction The 34 islands and peninsulas that make up Boston Harbor Islands National Recreation Area (NRA) lie in an urban harbor that has been a center of international trade for more than 4 centuries. From the time that European human immigrants began settling in Massachusetts in the early 17th century, plant and animal immigrants have also hitchhiked or been intentionally introduced to Boston Harbor and its islands. Some of the first invertebrate immigrants to Boston Harbor were likely beetles, as evidenced by the remains of a rich fauna of European beetles found in an excavated privy in the North End of Boston, dating back to 1650 (Bain 1998). Many of these early arrivals were pests of grains and other stored products, and many came in ballast, dunnage, and in the feed and dung associated with domestic animals arriving on cargo ships from Europe (Buckland et al. 1995, Lindroth 1957). Over subsequent centuries, modes of cargo transport have changed, as have the types of cargo and trade routes. Not surprisingly, invertebrate hitchhikers have kept up with the times, arriving with plants, soil, lumber, and other products in cargo 1Museum of Comparative Zoology, Harvard University, 26 Oxford Street, Cambridge, MA 02138. *Corresponding author - jrykken@oeb.harvard.edu. Manuscript Editor: Joshua Ness Boston Harbor Islands National Recreation Area: Overview of Recent Research 2018 Northeastern Naturalist 25(Special Issue 9):1–22 Northeastern Naturalist J.J. Rykken and B.D. Farrell 2018 2 Vol. 25, Special Issue 9 ships and airplanes from all over the world to ports across North America (Mc- Cullough et al. 2006). Purposeful arthropod introductions for biocontrol (e.g., lady beetles to prey on aphids; leaf beetles to feed on invasive plants) have been another mode of entry. Boston Harbor has continued to receive new six-legged colonists through direct immigration, domestic translocation, and unassisted dispersal from this ever-growing pool of non-native insects. Today, both the flora and fauna of the Boston Harbor Islands reflect several centuries of immigration. Most of the islands are dominated by non-native plants, which make up 44% of all vascular plant species found on the islands (Elliman 2005). Among the more than 1700 species of terrestrial invertebrates documented as part of an All Taxa Biodiversity Inventory (ATBI) in the park, 13% were known or suspected to be non-native to North America (Rykken and Farrell 2013). Given the location of the islands in one of the oldest continuously active ports in North America, their long history of human activity, and their isolated nature, we hypothesized that over the centuries the islands have accumulated a higher proportion of non-native insect species than is typical for mainland coastal New England or other less-trafficked coastal islands. We also hypothesized that because most non-native species are, by definition, adept colonists, the distribution patterns of non-native insect species may differ from those of native species across islands and be affected by island biogeographic factors such as island size and isolation. For example, Long et al. (2009) found that among plants on the Boston Harbor Islands, the isolation effect on species richness was much stronger for native species than non-native species, and the proportion of non-native species increased with isolation. However, more evidence is needed to generalize such patterns to other taxa (Guo 2014). Coleoptera (beetles) are an ideal group to consider when assessing the relative dominance and distribution patterns of non-native species in Boston Harbor because they have a long history of introductions in North America (Bain and King 2011, Buckland et al. 1995, Lindroth 1957) and they are an extremely diverse order of insects in terms of species richness, mobility, and feeding habits. Beetles are also a relatively well-studied group, both historically and more recently, especially in northeastern North America (Klimaszewski et al. 2010, Majka et al. 2011, Sikes 2004). In the Boston Harbor Islands ATBI, beetles were by far the most diverse order (693 species identified) and had the highest proportion of non-native species among the holometabolous orders (18%; Rykken and Farrell 2013). We therefore decided to use 6 diverse families of beetles (Carabidae, Chrysomelidae, Curculionidae, Elateridae, Scarabaeidae, and Staphylinidae) as representative taxa to ask the following questions in Boston Harbor Islands NRA: (1) Are proportions of nonnative beetle species on islands/peninsulas in Boston Harbor high relative to nearby mainland areas or other, more isolated, coastal islands? (2) Do non-native beetles differ significantly in their distribution and abundance across islands compared to native species? (3) Is the strength of the relationship between island size or isolation and species richness similar for non-native versus native beetles or for non-native beetles vs. non-native plants? Northeastern Naturalist 3 J.J. Rykken and B.D. Farrell 2018 Vol. 25, Special Issue 9 Field-site Description The 15 islands and peninsulas in Boston Harbor sampled for beetles varied in size from 1.1 to 104.5 ha, and in isolation between 0 km and 3.4 km from the mainland (Table 1). The primary vegetation communities in the park include forest, woodland, maritime shrub, old field, and beach strand, although many of the islands, especially those in the outer harbor, have little tree-cover; non-native woody and herbaceous plant species dominate many of these communities (Elliman 2005). The mainland surrounding the harbor comprises several towns, varying from somewhat less-developed landscapes in Hingham and Weymouth in the south to heavily urbanized landscapes in Boston and Winthrop, including international port facilities for marine and air transport. Over the past several centuries, all of the more accessible and sizeable islands have hosted human structures and activities (Kales 2007). In the present day, almost all of the islands in the park are open to human visitors, but the islands vary greatly in the intensity of human traffic and impacts. Several islands (including Bumpkin, Grape, Lovells, Spectacle, Thompson) are serviced by public ferries between May and October. Islands with ferry service and the peninsula World’s End receive thousands to tens of thousands of visitors per year. Many of the remaining islands, which do not have public ferry service or rangers stationed on them, probably receive on the order of hundreds to low thousands of visitors per year, but visitation is not monitored. Table 1. Area and isolation (distance from the mainland) for each island or peninsula sampled for beetles in Boston Harbor Island NRA. An asterisk (*) indicates islands we surveyed intensively for all arthropods utilizing a structured sampling design in 2005–2008; all other islands were sampled sporadically between 2005 and 2010. Island or peninsula Code Terrestrial area (ha)3 Isolation (km)4 Bumpkin1,* BM 12.2 0.6 Calf* CF 7.5 3.3 Georges GE 15.8 1.5 Grape* GP 21.9 0.5 Great Brewster* GB 7.5 2.3 Langlee* LN 1.8 0.5 Lovells LV 19.6 2.2 Middle Brewster MB 5.0 3.1 Outer Brewster OB 7.7 3.4 Rainsford RF 6.6 2.4 Ragged* RG 1.1 0.3 Snake* SN 2.9 0.3 Spectacle* SP 34.6 1.9 Thompson1,* TH 54.2 0.5 Worlds End2, * WE 104.5 0.0 1Island connected by sand spit to mainland at very low tides. 2Peninsula, connected to mainland at all times. 3Terrestrial area above high tide line from Bell et al. (2002). 4Shortest distance between island and mainland; measured using GoogleEarth (earth.google.com). Northeastern Naturalist J.J. Rykken and B.D. Farrell 2018 4 Vol. 25, Special Issue 9 Methods As part of a larger terrestrial invertebrate ATBI, we sampled beetles on 15 islands and peninsulas between 2005 and 2010 (Table 1). We implemented an intensive, structured sampling regime targeting all arthropods and gastropods on 10 of the islands/peninsulas. We conducted sampling for at least one full growing season (May to October ) on 9 Islands; Ragged Island was sampled only August to October 2005, during the pilot season. We sporadically visited 5 additional islands to undertake opportunistic collecting, bioblitzes, and/or student projects. We used a variety of traps and methods to sample different habitats. On islands with structured sampling, we stratified the sampling by dominant habitat types: woodland, shrubland, meadow, beach, marsh, or pond edge. Passive-sampling methods included pitfall traps, malaise traps, and light traps. We also sampled actively by hand-searching and using aerial and sweep nets, beating sheets, and aspirators. A detailed description of our sampling design, collecting and sampleprocessing methods, insect-curating procedures, and taxonomy protocols can be found in Rykken and Farrell (2013). All beetle specimens were deposited in the entomology collections of the Museum of Comparative Zoology (MCZ), Harvard University, Cambridge, MA. Analyses To compare proportions of non-native species in Boston Harbor Islands NRA relative to the mainland and other coastal islands, we focused on 6 beetle families (Table 2). These taxa met the following criteria: (1) collectively, they represented a diversity of feeding groups and dispersal abilities; (2) each family was relatively well-sampled in our study, with comparable sampling efforts across islands; and (3) within each family, most or all of the specimens had been identified by an expert taxonomist. For the very diverse family Staphylinidae (rove beetles), we did not include the subfamily Aleocharinae, as the taxonomy for this hyper-diverse Table 2. Six focal Coleoptera (beetle) families used for analyses comparing mainland and island faunas and distribution patterns across islands. Family Common name Feeding mode Dispersal mode Carabidae Ground beetles Mostly predators Good runners, many can fly (some seed-eaters) Chrysomelidae Leaf beetles Herbivore Most can fly, but stay close to host plants Curculionidae Weevils Herbivore Some species can fly (various plant parts) Elateridae Click beetles Various (herbivores, Most species can fly predators) Scarabaeidae Scarab beetles Various (dung, carrion, Some species can fly plants) Staphylinidae Rove beetles Mostly predators Most species can fly (excluding Aleocharinae) (some fungivores, scavengers) Northeastern Naturalist 5 J.J. Rykken and B.D. Farrell 2018 Vol. 25, Special Issue 9 sub-group is notoriously difficult. We used beetles collected on all 15 islands listed in Table 1 for our comparisons. For our comparison data set for the mainland, we used a published checklist of Coleoptera from the neighboring state of Rhode Island (Sikes 2004, Sikes and Webster 2005), which we surmised would be similar to the fauna occurring in mainland eastern Massachusetts. Although the Rhode Island checklist includes 32 species within our focal families collected only on Block Island (D. Sikes, University of Alaska Fairbanks, AK; unpubl. data), all but 2 of these species (both non-native scarabaeids) are also known from mainland Connecticut and/or Massachusetts (Bousquet 2012; Downie and Arnett 1996a,b; Majka et al. 2011), suggesting they likely occur in mainland Rhode Island. There is currently no comparable comprehensive Coleoptera checklist for mainland Massachusetts. For a comparison with non-native beetle faunas on nearby but more isolated coastal islands, we used a list of species in the beetle family Carabidae from Nantucket (Purrington 1996) and a list of Scarabaeidae from 9 coastal Massachusetts islands (Nantucket, Martha’s Vineyard, and 7 much smaller islands; Goldstein and Simmons 2002). We employed simple linear regression to examine the relationships between the (a) species richness versus island size for native and non-native beetles, and (b) proportion of non-native species on an island versus island isolation for both beetles and plants, using plant species-richness data from Elliman (2005). For these analyses, we used only the 9 islands and 1 peninsula that were intensively sampled with a structured-sampling design (indicated by * in Table 1). We considered R2 values for the regressions to be statistically significant at a level of α = 0.05. Results We identified a total of 442 beetle species among the 6 focal families; of these, 105 were non-native to North America (Appendix A; see Rykken and Farrell [2013] for a complete list of species and their distribution across islands). Several of these species were suspected or known to be new introductions to the US or North America (Appendix A). We characterized as native in our analyses 2 species that have been introduced to northeastern North America but are native to the continent—Leptinotarsa decemlineata (Say) (Colorado Potato Beetle) and the antloving beetle Eupsenius glaber LeConte). Not surprisingly, total species richness for the 6 focal Coleoptera families in Boston Harbor Islands was much lower than that documented for all of Rhode Island, varying from 26% (Scarabaeidae) to 52% (Elateridae) of the Rhode Island fauna (Fig. 1). While the order of lowest to highest proportion of non-native species among families was almost the same between the 2 areas, the proportion of nonnative species was much higher in Boston Harbor Islands than in Rhode Island for all families, varying from 2 times (Curculionidae) to 3 times (Elateridae, Staphylinidae) higher (Fig. 1). Across the 6 beetle families, non-native beetles made up 10% of the total in Rhode Island, compared to 24% in Boston Harbor. The proportion of non-native carabid beetles documented on Nantucket was exactly the same as in Rhode Island (0.06), and the proportion of non-native scarabaeid beetles on 9 Northeastern Naturalist J.J. Rykken and B.D. Farrell 2018 6 Vol. 25, Special Issue 9 Massachusetts coastal islands (0.15) was also similar to Rhode Island; both of these proportions were half or less of the proportion of non-native species documented for these 2 families in Boston Harbor Islands NRA. The mean number of islands on which non-native species occurred was higher than for native species, across all beetle families except Elateridae (Fig. 2). Figure 1. Comparison of native and non-native species richness for 6 Coleoptera families in Boston Harbor Islands (BOHA) and Rhode Island (RI); additional comparisons for Carabidae on Nantucket, and Scarabaeidae on 9 Massachusetts islands. The proportion of non-native species for each family is labeled above bars. (Rhode Island data compiled from Sikes 2004, Sikes and Webster 2005; Nantucket data from Purrington 1996; MA islands data from Goldstein and Simmons 2002). Figure 2. Mean number (± 95% confidence interval) of islands (out of 15, including 1 peninsula) on which native versus non-native species occurred for 6 beetle families in Boston Harbor Islands NRA. n = number of species in each group used to calculate the mean. Northeastern Naturalist 7 J.J. Rykken and B.D. Farrell 2018 Vol. 25, Special Issue 9 Variability was higher for non-native species in each family comparison. Non-native scarabaeid beetles were the most widespread group, with each species occurring on an average of 5.9 islands. Variability was especially high among non-native scarabaeid species because of 2 very widespread Asian June beetles: Maladera castanea (Asiatic Garden Beetle) and Nipponoserica peregrina (Orange Scarab Beetle), which were found on 12 and 11 islands, respectively. Similarly, the mean abundance for non-native species across islands was higher than for native species in all families except Elateridae (Fig. 3). Again, large confidence intervals indicated higher variability in non-native species abundances, especially for Carabidae and Scarabaeidae. There was a significant positive correlation between species richness and logtransformed island area for native beetles, and a very weak positive relationship for non-native beetles (Fig. 4). World’s End peninsula and its neighboring small island, Ragged Island, had far more native species than their respective sizes would predict, while Spectacle Island had fewer species overall than predicted by its size. Figure 3. Mean abundance (± 95% confidence interval) of native versus non-native species in 6 beetle families across 14 islands and 1 peninsula in Boston Harbor Islands NRA. n = number of species in each group used to calculate the mean. An asterisk (*) indicates that the confidence interval for Scarabaeidae (± 214.9) was cut off at the top in order to view data for other families more clearly. Northeastern Naturalist J.J. Rykken and B.D. Farrell 2018 8 Vol. 25, Special Issue 9 Although the proportion of non-native plants was strongly positively correlated with island isolation (the distance to the nearest point on the mainland), non-native beetles showed little response to isolation (Fig. 5). Snake Island was a strong outlier with a very high proportion of non-native species, but a location relatively close to the mainland. Discussion Non-native beetles are diverse, abundant, and widespread throughout Boston Harbor Islands NRA. Among the 6 beetle families we considered, which included predators, herbivores, dung feeders, and scavengers, the percentage of non-native species (24% across all taxa) in Boston Harbor was consistently 2–3 times higher than for the same families on the mainland or on Massachusetts coastal islands. These comparisons suggest that Boston Harbor Islands NRA is a hotspot of nonnative biodiversity in coastal New England. The arrival and establishment of non-native beetles in Boston Harbor Introductions of invertebrates into Boston Harbor span at least 4 centuries. Several European beetle species documented in the ATBI (including the staphylinid Creophilus maxillosus and the chrysomelid Phyllotreta striolata) are known from archeological excavations to have been present in Boston as early as 1650 (Bain 1998). Lindroth (1957) introduced the term “cultural steppe” to describe the open landscapes cultivated in northeastern North America by European colonists. Figure 4. The relationship between species richness and log-transformed island area for non-native and native beetle species on 9 islands and 1 peninsula (WE) in Boston Harbor Islands NRA. Fitted simple-regression lines are shown; black line for native beetles and gray line for non-native beetles. Island codes are defined in Table 1. Northeastern Naturalist 9 J.J. Rykken and B.D. Farrell 2018 Vol. 25, Special Issue 9 Pastures, crop fields, gardens, buildings, and waste places all provided new but familiar habitats to immigrant insects, in a region where the native fauna had previously been primarily associated with forests (Buckland et al. 1995, Spence and Spence 1988). It is worth noting that human disturbance in these areas was not new; Native Americans had cleared much of the forest with fire in the vicinity of Boston and on some of the islands prior to European settlement (Richburg and Patterson 2005). It is no surprise then, that European invertebrate colonists exploited opportunities in the New World. Ballast, dunnage, feed, and dung associated with domestic animals arriving on cargo ships from Europe harbored the early arrivals of non-native beetles (Klimaszewski et al. 2010). Lindroth (1957) surveyed the ground-dwelling invertebrate fauna of 8 ballast sites on the southwest coast of England, from where building rubble, rock, soil, and sand were known to have originated for ships bound to Newfoundland and other ports. Among the 242 native beetle species he documented there, 28% had been carried to North America. At least 26 of these species also found their way to the Boston Harbor Islands, including 20 species in our 6 focal beetle families (Appendix A). More than half of these species were in 2 predominantly ground-dwelling families, Carabidae and Staphylinidae. Another 3 species were curculionids in the genus Otiorhynchus, which according to Lindroth, make the ultimate colonists because they possess the following characteristics: ground-dwelling; adapted to dry, disturbed habitats (i.e., the cultural steppe); polyphagous; parthenogenic; and brachypterous (having no functional wings, Figure 5. The relationship between the proportion of non-native species (vascular plants or beetles) on an island or peninsula (WE) and that island’s distance from the mainland (isolation) in Boston Harbor Islands NRA. Fitted simple linear-regression lines are shown; black line for plants and gray line for beetles. Data for vascular plants taken from Elliman (2005). Island codes are defined in Table 1. Northeastern Naturalist J.J. Rykken and B.D. Farrell 2018 10 Vol. 25, Special Issue 9 they cannot jump ship!). Interestingly, Lindroth’s 1957 list does not include the tiny ground beetle Bembidion nigropiceum, a European coastal species that was rediscovered in the Boston Harbor Islands ATBI more than 100 years after it was first documented in Massachusetts (in 1897), at which time it was mistakenly described as a new species for North America (Davidson and Rykken 2011, Erwin and Kavanaugh 1980). However, Lindroth documented this species on the south coast of England in a later publication (Lindroth 1974). The littoral habitat of B. nigropiceum would certainly have made it a good candidate for transport in ballast. We also found 6 species of non-native staphylinid beetles (one in common with Lindroth) that are seashore dwellers (Majka et al. 2008). Many of the ballast-carrying ships coming from England and Europe were headed to ports in Newfoundland and the Maritime Provinces of Canada, and it is worth noting that proportions of non-native ground-dwelling beetles found on some of the islands in Atlantic Canada are as high as those in Boston Harbor. For example, proportions of non-native carabids on Prince Edward Island (PEI), insular Newfoundland, and Cape Breton were all similar to Boston Harbor Islands, varying from 0.12 to 0.16 (Larson and Langor 1988, Majka et al. 2007b). On PEI, the proportion of non-native staphylinids (0.33) was slightly higher than on the Boston Harbor Islands (Majka and Klimaszewski 2008). Among curculionids (many of which are ground-dwelling), proportions of non-natives on PEI and Cape Breton were almost identical to the islands in Boston Harbor (0.39–0.40; Majka et al. 2007a). After 1880, there was little ballast crossing the Atlantic, but other events in the US were influencing the types of cargo with which non-native insects could travel. With the founding of the US Department of Agriculture in 1862, and accumulating wealth in post-civil war industrial regions, a demand for foreign crops and ornamental plants brought in large numbers of herbivorous insects, including beetles (Sailer 1978). The Plant Quarantine Act of 1912 slowed the exponential growth of insect immigration by about 1920 (Sailer 1978). More recently, intentional introductions of beetles and other insects for biocontrol have added to the North American fauna. In Boston Harbor Islands, biocontrol agents include 3 chyrysomleid beetles: Cassida rubiginosa (Thistle Tortoise Beetle), Chrysolina quadrigemina (Klamath Weed Beetle), and Neogalerucella calmariensis (Purple Loosestrife Beetle). It is doubtful any of these species were intentionally brought to Boston Harbor, but rather dispersed from other points of introduction. Global changes in modes of cargo transportation (including air), as well as in the types of cargo and trade routes have influenced more-recent faunal introductions to North America (McCullough et al. 2006, Work et al. 2005). For example, the islands now have many adventive species from Asia, including 4 established species of scarab beetles (the plant pests Maladera castanea, Anomala orientalis, Nipponeserica peregrina, and Popillia japonica); Cyrtepistomus castanaeus (Asiatic Oak Weevil); the broadnosed weevil Myosides seriehispidus; and the ambrosia beetles Ambrosiophilus atratus and Euwallacea validus. Interestingly, almost half of non-native focal beetle species we found on the islands were first detected in North America between 1891 and 1980 (Fig. 6), well Northeastern Naturalist 11 J.J. Rykken and B.D. Farrell 2018 Vol. 25, Special Issue 9 after the heyday of trans-oceanic ballast transport (Sailer 1978). These species included many ground-dwelling carabid and staphylinid beetles, but also increasing numbers of herbivorous beetles, especially scarabaeid beetles (Fig. 6). It is likely many of these taxa came with the soil or plants from nursery stock. They also included 7 species that were first detected in or introduced to western North America, and 9 species that originated from Asia (Appendix A). There are many reasons why islands in Boston Harbor might have a high occurrence of non-native species relative to mainland sites or even other coastal islands. Certainly, with hundreds of years of human activity such as burning, building, agriculture, and waste disposal, the islands present an ideal “cultural steppe” landscape in which species adapted to open, disturbed habitats could thrive, and also offer beaches for littoral species. It is probable that ballast was dumped directly onto at least some of the islands as ships came into port in Boston, as was the case in Newfoundland, where discharging ballast directly into the harbor was illegal (Lindroth 1957). Boston has remained an active port and now receives air and domestic rail traffic as well. Runways at the international airport lie less than 1 km from Snake Island. Forty-four percent of plant species documented for the islands are non-native, and while some of these have arrived as opportunistically as the invertebrates, many have also been imported intentionally for cultivation, including for ornamental plantings, pasture feed, and soil stabilization (Elliman 2005, Richburg and Patterson 2005). It is not unlikely that herbivorous and/or soil-dwelling invertebrates would accompany these introductions. Soil and fill have also been transported to the islands in more recent times, including 2.8 million m3 of excavated soil, gravel, and clay from the Central Artery/Third Harbor Tunnel Project (“Big Dig”) in Boston that was transported to Spectacle Island to cap an existing landfill in the 1990s (Kales 2007). Boston is the largest metropolitan area in New England, and the tens of thousands of human visitors travelling to and between the islands each year are also very likely responsible for bringing in a variety of species. Figure 6. First reported dates of detection in North America for 101 non-native beetle species in 6 families collected in Boston Harbor Islands NRA between 2005 and 2010. Northeastern Naturalist J.J. Rykken and B.D. Farrell 2018 12 Vol. 25, Special Issue 9 Present-day patterns of distribution across the Boston Harbor Islands Variation among taxa. For almost all the focal beetle taxa (except Elateridae), non-native species were, on average, more widespread across islands in the park than native species and were also more abundant. These results suggest more frequent and/or successful dispersal activity among non-native species, such as drifting, flying, or human-assisted transport. Many of the non-native species are synanthropic and so are also well-adapted to open, disturbed areas, which comprise much of the habitat on the islands. Many of the non-native herbivorous species feed on a variety of native and non-native plants; for example, Popillia japonica (Japanese Beetle) is associated with over 300 plant hosts (Potter and Held 2002). Elateridae did not fit this general pattern of distribution and abundance but the number of non-native species for this family was very low. The 3 elaterid species were suspected to represent new records for the state, country, and continent (Appendix A); thus, they were presumably relatively recent introductions. Therefore, it is not surprising that their occurrence across islands and abundance was low. Variability in abundance and species occurrence across islands was very high for some families. This result was, in part, due to the super-abundance of a few non-native species, such as the 2 very widespread Asian scarabaeid beetles, Nipponoserica peregrina and Maladera castanea. These 2 species are nocturnal feeders, and readily come to lights, often in large numbers, which is primarily how they were trapped. Thus, trapping biases may also have had some influence on our results. Other non-native species which were collected in very high abundance were the carabid beetles Amara bifrons and Harpalus rufipes. Both of these species are associated with dry, open places, and are strong fliers (Bousquet 2010). The 2 species were most abundant on Spectacle Island, which was essentially a newly-created island on which an old landfill was capped and covered with fill and soil from the mainland and then landscaped with imported plants. Not only did this activity create a “cultural steppe” landscape that promoted invasion, but it also provided many empty niches for active colonization. Although most of the abundant non-native species were also widespread across islands, this was not the case for A. bifrons which occurred almost exclusively on Spectacle Island. It is worth noting that passive trapping methods for insects (i.e., traps) or active searching by amateurs may be favorably biased to collecting widespread, abundant, and generalist species. The ATBI relied mainly on a structured sampling design involving various kinds of traps, as well as active collecting by citizen scientists; thus, our sampling may have been biased toward non-native species. Many native species can also be collected with traps, but more-cryptic or specialist species often require focused hand-searching by experts. To illustrate how under-sampling may also bias native vs. non-native ratios, results from a 5-y beetle inventory on Block Island (in RI) by Sikes and colleagues (Sikes 2002) produced 219 species across 41 families, which Sikes estimated represented approximately 30–45% of the true total on the island. Collecting was conducted primarily by hand in more-open areas on the island. Proportions of non-native species were even higher on Block Island than on the Boston Harbor Islands for several families, but the total number Northeastern Naturalist 13 J.J. Rykken and B.D. Farrell 2018 Vol. 25, Special Issue 9 of species collected in each family was much lower, for example, Chrysomelidae: 0.31 non-native species on Block Island (16 species total); Curculionidae: 0.43 (21 species total); Scarabaeidae: 0.35 (26 species total); and Staphylinidae: 0.60 (5 species total). Thus, we can suppose that sampling bias and/or under-sampling in the Boston Harbor Islands ATBI may have inflated non-native species proportions to some (unknowable) degree. Variation among islands. As predicted by the theory of island biogeography (MacArthur and Wilson 1967), there was a strong positive relationship between island size and species richness for the native focal beetles on 9 islands and 1 peninsula. However, the relationship was weak for non-native beetle species. These results differ markedly from patterns of plant richness across the islands: both native and non-native plant species showed almost identical strong positive relationships with island size (Long et al. 2009). The largest island-like site we sampled, World’s End, is in fact a peninsula connected to the mainland and a managed nature reserve; this parcel had far more native beetle species than its size would predict, and far fewer non-native species. World’s End also has more native plant species than the other islands, and relatively high habitat diversity. All of these factors likely contribute to its high native beetle diversity. At the other end of the size spectrum, the tiniest islands, Ragged and Langlee, also had more native species and fewer non-natives than predicted by their size. Both islands lie very close to World’s End and likely receive species from the peninsula. Other notable outliers were Spectacle and Snake Islands, which had far fewer species overall than expected. As mentioned in the previous section, Spectacle was recently rebuilt from the soil up and thus has had less time to be colonized compared to the other islands. Long et al. (2009) found that among vascular plants on 25 Boston Harbor Islands (they did not include World’s End in their analysis), the proportion of non-native species increased significantly with island isolation. The same pattern held true for plants on the 10 islands/peninsulas we sampled in our study (using data from Elliman 2005), but not for beetles. The strongest outlier in this case was Snake Island, which had a much higher proportion of non-native beetles (50%) than its proximity to the mainland would predict and far more than any other island. Snake Island is one of the smaller islands in the harbor, but it lies to the north and is almost completely surrounded by urbanized or industrialized landscapes, including the runways of Logan International Airport less than 1 km away. When compared to a similarly sized island such as Ragged Island, which lies at the south end of the harbor and has 22% non-native species, it seems plausible that differences in the mainland-source pools of potential new colonizers in these 2 areas (i.e., urban/industrial versus more natural landscapes) may influence the species composition of these small islands. All of the islands farther from the mainland (Spectacle, Great Brewster, Calf) had high proportions of non-native beetles, and several of the hypotheses proposed by Long et al. (2009) to explain why non-native plants may have an advantage in colonizing more-distant islands could also apply to beetles, with the most likely being greater dispersal abilities, better adaptations to early-successional habitats, and higher tolerance of harsher Northeastern Naturalist J.J. Rykken and B.D. Farrell 2018 14 Vol. 25, Special Issue 9 environments (especially on the more exposed, outer islands, Calf and Great Brewster). In trying to discern patterns of non-native species richness across islands, one thing is clear: making generalizations from what we know about native species or other taxa is not necessarily helpful for predicting what we will find on any given island in Boston Harbor. As Guo (2014) has discussed, varying intensities of human- aided dispersal and disturbance strongly influence where and how non-native species colonize islands, making patterns highly variable and difficult to predict using the classic variables of island biogeography. Potential impacts of non-native species in the park and region From a management perspective, it is interesting to consider what the impact of so many non-native species might be on the native flora and fauna of the Boston Harbor Islands. Many of the non-native species we collected are well-established and widespread weedy species in the region and have likely been on the islands for a long time, such as the carabid beetles Carabus nemoralis and Harpalus rufipes. There is little evidence to suggest that these kinds of species will have significant negative impacts on the native fauna (Majka et al. 2006, Wheeler and Hoebeke 2009). In fact, some have argued that non-native species may enhance the existing fauna of a given area, especially synanthropic species in open, disturbed habitats that are unlikely to invade native, natural habitats (e.g., native forest; Spence and Spence 1988). Other species, such as the Purple Loosestrife Beetle, which was introduced to North America for biocontrol of Lythrum salicaria L. (Purple Loosestrife), may even be beneficial in helping to control small infestations of this noxious weed in wet areas of the islands. A component of the suite of non-native beetles we collected are known pests in agricultural, horticultural, and forested landscapes in North America (e.g., Crioceris asparagi [Asparagus Beetle], Japanese Beetle, or Xylosandrus germanus [Black Stem Borer]). Other non-native species collected in Boston Harbor Islands are known to be pests in their region of origin but are recent arrivals to North America and have not yet become invasive; thus they are important species to monitor. For example, the bark beetle Ambrosiophilus atratus, a pest of conifers and hardwoods in Asia, was first detected in Tennessee in 1988 and its spread is currently being monitored by the US Department of Agriculture (Haack 2006). The elaterid beetle Athous haemorrhoidalis is a below-ground crop pest in Europe and was first detected in North America in Ontario in 2003 (Douglas 2011). Our specimens from Boston Harbor represent the first published records for A. haemorrhoidalis in the US; thus, monitoring the spread of this species will also be important. Several of the non-native beetles we collected that represent new published records for Massachusetts are known or suspected pests (Appendix A), reinforcing the importance of regional biodiversity inventories in keeping track of non-native and native species. Northeastern Naturalist 15 J.J. Rykken and B.D. Farrell 2018 Vol. 25, Special Issue 9 Acknowledgments Funding was generously provided by the Stone Foundation, the Green Fund, and the National Park Service. Many, many scientists, park staff, students, interns, citizen scientists, and volunteers were involved with the project and we are indebted to them all. We are especially grateful to the community of coleopterists who generously shared their expertise to identify beetles from the Boston Harbor Islands: Robert Anderson, Ross Bell, Adam Brunke, Don Chandler, Bob Davidson, Matt Gimmel, Pat Gorring, Richard Hoebeke, Paul Lago, Serge Laplante, Stephanie Madden, Ed Riley, and Wolfgang Rücker. Literature Cited Bain, A. 1998. A seventeenth-century beetle fauna from colonial Boston. Historical Archaeology 32:38–48. Bain, A., and G. King. 2011. Asylum for wayward immigrants: Historic ports and colonial settlements in northeast North America. Journal of the North Atlantic Special Volume 1:109–124. Bain, A., and L. LeSage. 1998. A late-seventeenth–century occurrence of Phyllotreta striolata (Coleoptera: Chrysomelidae) in North America. The Canadian Entomologist 130:715–719. Bell, R., M. Chandler, R. Buchsbaum, and C. Roman. 2002. Inventory of intertidal habitats: Boston Harbor Island, a national park area. 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Field guide for the biological control of weeds in the Northwest. Technical Report FHTET-2014-08. USDA Forest Health Technology Enterprise Team, Morgantown, WV. 333 pp. Work, T.T., D.G. McCullough, J.F. Cavey, and R. Komsa. 2005. Arrival rate of nonindigenous insect species into the United States through foreign trade. Biological Invasions 7:323–332. Northeastern Naturalist 19 J.J. Rykken and B.D. Farrell 2018 Vol. 25, Special Issue 9 Appendix A. List of non-native beetles collected in Boston Harbor Islands NRA in 2005–2010 in 6 focal families. Total abundance and distribution across 15 islands are shown. Notes = whether species was on Lindroth’s 1957 list of arthropods found on “ballast beaches” in southwestern England (L), or is a new record or first published record for North America (NA), the United States (US), or Massachusetts (MA; record confirmed by expert or not recorded for MA in Downie and Arnett [1996a, 1996b] or Majka et al. [2011]). See Rykken and Farrell (2018, [this issue]) for additional notes on first published records. Date = date of first detection in North America. State or province = where first detected. Origin abbreviations = Palearctic (Pal); Europe (Euro); Eurasia (Eura); Cosmopolitan (Cosm); regional designations come from various sources thus there is some overlap in terms. Known impact = whether a species is a known pest (p), biocontrol introduction (bc), or h as no known significant impact (-). State Number of Total or Known Species islands beetles Notes Date province Origin impact Reference Carabidae Agonum muelleri (Herbst) 5 23 L 1840 NF Pal - Bousquet 2012 Amara aenea (DeGeer) 3 4 L 1904 NY Euro - Bousquet 2012 Amara apricaria (Paykull) 3 4 less than 1865 PQ Pal - Bousquet 2012 Amara aulica (Panzer) 7 101 MA 1929 NS Euro - Bousquet 2012 Amara bifrons (Gyllenhal) 4 825 MA 1929 NS Euro - Bousquet 2012 Amara familiaris (Duftschmid) 2 2 L 1901 RI Euro - Bousquet 2012 Amara ovata (Fabricius) 3 6 L 1925 MA Euro - Bousquet 2012 Asaphidion curtum (Heyden) 2 3 1930 NY Pal - Bousquet 2012 Bembidion nigropiceum (Marsham) 4 85 less than 1897 MA Euro - Davidson and Rykken 2011 Carabus nemoralis Müller 8 507 1890 NB Euro - Bousquet 2012 Clivina fossor (L.) 2 6 1915 PQ Pal - Bousquet 2012 Harpalus affinis (Schrank) 6 38 L less than 1798 PA Pal - Bousquet 2012 Harpalus rubripes (Duftschmid) 7 16 MA,L 1981 NH Pal - Bousquet 2012 Harpalus rufipes (DeGeer) 9 1020 L 1937 PEI Euro - Bousquet 2012 Laemostenus terricola terricola (Herbst) 2 4 US less than 1894 NS Euro - Bousquet 2012 Ophonus puncticeps Stephens 7 64 L 1954 NY Pal - Bousquet 2012 Perigona nigriceps (Dejean) 2 3 1853 GA Asia - Klimaszewski et al. 2012 Pterostichus melanarius Illiger 8 194 1926 NS Euro - Bousquet 2012 Chrysomelidae Cassida rubiginosa Müller 2 2 1902 PQ Eura bc Majka and LeSage 2008 Chrysolina quadrigemina Suffrian 3 12 1946 CA Pal bc Hoebeke 1993 Crioceris asparagi (L.) 2 3 1859 NY Euro p LeSage et al. 2008 Northeastern Naturalist J.J. Rykken and B.D. Farrell 2018 20 Vol. 25, Special Issue 9 State Number of Total or Known Species islands beetles Notes Date province Origin impact Reference Epitrix pubescens (Koch) 4 10 NA 1975 PQ Euro p Deczynski 2016 Longitarsus pratensis (Panzer) 4 63 1929 NY Pal - LeSage 1988 Longitarsus rubiginosus (Foudras) 4 7 US 1957 ON Pal - LeSage 1988 Mantura chrysanthemi (Koch) 3 13 less than 1950 ? Pal - Klimaszewski et al. 2010 Neogalerucella calmariensis (L.) 5 15 1992 US Pal bc Klimaszewski et al. 2010 Phyllotreta cruciferae (Goeze) 6 23 MA 1921 BC Pal p Brown 1967 Phyllotreta striolata (Fabricius) 4 10 1675–1700 MA Pal p Bain and LeSage 1998 Plagiodera versicolora (Laicharting) 4 7 1915 NY Euro p Mattson et al. 1994 Psylliodes affinis (Paykull) 7 52 1968 NY Eura p Hoebeke and Wheeler 1983 Psylliodes napi (Fabricius) 2 7 1966 NY Euro - Tahvanainen and Root 1970 Curculionidae Ambrosiophilus atratus (Eichhoff) 2 2 1988 TN Asia - Haack and Rabaglia 2013 Barypeithes pellucidus (Boheman) 10 223 less than 1916 USA Pal - Majka et al. 2007a Cathormiocerus aristatus (Gyllenhal) 4 22 1964 ON Pal - Majka et al. 2007a Cathormiocerus asperatus Boheman 3 8 1843 MA Pal - Majka et al. 2007a Cyrtepistomus castaneus (Roelofs) 6 192 1933 NJ Asia - Mattson et al. 1994 Euwallacea validus (Eichhoff) 2 8 1976 NY Asia - Haack and Rabaglia 2013 Gymnetron netum (Germar) 2 2 1937 NA Euro bc Winston et al. 2014 Gymnetron pascuorum (Gyllenhal) 3 12 1956 MD Pal - Majka et al. 2007a Gymnetron tetrum (Fabricius) 2 4 less than 1916 USA Pal - Majka et al. 2007a Hypera nigrirostris (Fabricius) 2 2 1873 MA Pal p Majka et al. 2007a Hypera punctata (Fabricius) 3 5 1853 QC Pal - Majka et al. 2007a Isochnus populicola Silfverberg 2 19 1922 NJ Pal - Majka et al. 2007a Larinus planus (Fabricius) 2 5 1929 US Pal bc Klimaszewski et al. 2010 Mecinus pyraster (Herbst) 2 4 MA 1954 NA Euro - Mattson et al. 1994 Myosides seriehispidus Roelofs 10 210 1973 CT Asia - O’Brien 2000 Otiorhynchus ovatus (L.) 6 25 L 1839 NF Euro - Majka et al. 2007a Otiorhynchus rugosostriatus (Goeze) 6 38 MA,L 1876 NA Euro p Mattson et al. 1994 Otiorhynchus singularis (L.) 6 25 1872 MA Euro p Majka et al. 2007a Otiorhynchus sulcatus (Fabricius) 6 38 L 1831 MA Euro p Majka et al. 2007a Pachytychius haematocephalus (Gyllenhal) 2 3 MA 1964 NY Euro - USDA 1964 Northeastern Naturalist 21 J.J. Rykken and B.D. Farrell 2018 Vol. 25, Special Issue 9 State Number of Total or Known Species islands beetles Notes Date province Origin impact Reference Polydrusus sericeus (Schaller) 2 5 1934 CT Euro - Majka et al. 2007a Rhinoncus castor (Fabricius) 3 7 1895 NJ Pal - Majka et al. 2007a Rhinoncus pericarpius (L.) 5 30 1928 MA Pal - Majka et al. 2007a Sciaphilus asperatus (Bonsdorff) 4 11 1884 NS Euro - Mattson et al. 1994 Scolytus mali (Bechstein) 2 4 MA 1868 NY Euro p Haack and Rabaglia 2013 Sitona cylindricollis (Fahraeus) 4 8 1924 QC Pal p Majka et al. 2007a Sitona hispidulus (Fabricius) 3 7 L 1875 NJ Eura p Majka et al. 2007a Sitona lepidus Gyllenhal 2 2 L 1839–1842 NF Pal p Majka et al. 2007a Strophosoma melanogrammum (Forster) 8 30 1885 NJ Euro - Majka et al. 2007a Trachyphloeus angustisetulus Hansen 5 10 ? ? - Trachyphloeus bifoveolatus (Beck) 2 2 MA 1917 NY Pal - Majka et al. 2007a Tychius meliloti Stephens 2 3 1975 QC Pal p Majka et al. 2007a Tychius picirostris (Fabricius) 4 10 L 1908 NY Pal p Majka et al. 2007a Tychius stephensi Schönherr 2 3 1913 CT Pal p Majka et al. 2007a Xyleborinus saxeseni (Ratzeburg) 4 203 1911 CA Eura p Haack and Rabaglia 2013 Xyleborus californicus Wood 3 4 1944 CA Asia - Haack and Rabaglia 2013 Xylosandrus germanus (Blandford) 7 109 1931 NY Asia p Haack and Rabaglia 2013 Elateridae Agriotes lineatus (L.) 6 19 MA,L 1840 NF Eura p Majka and Johnson 2008 Athous ?bicolor (Goeze) 2 3 NA? 2007 MA Eura - Rykken and Farrell 2013 Athous haemorrhoidalis (Fabricius) 3 6 US 2003 ON Eura - Douglas 2011 Scarabaeidae Amphimallon majale (Razoumowski) 3 4 1940 NY Euro p Mattson et al. 1994 Anomala orientalis (Waterhouse) 10 51 1920 CT Asia p Mattson et al. 1994 Aphodius pseudolividus Balthasar 2 2 ? ? Cosm - Gordon 1983 Maladera castanea (Arrow) 13 254 1921 NJ Asia p Mattson et al. 1994 Nipponoserica peregrina (Chapin) 12 977 1937 NY Asia p Arnett et al. 2002 Onthophagus nuchicornis (L.) 3 5 1844 PA Eura - Hoebeke and Beucke 1997 Onthophagus taurus Schreber 3 4 1971 FL Pal - Hoebeke and Beucke 1997 Popillia japonica Newman 9 34 1916 NJ Asia p Mattson et al. 1994 Northeastern Naturalist J.J. Rykken and B.D. Farrell 2018 22 Vol. 25, Special Issue 9 State Number of Total or Known Species islands beetles Notes Date province Origin impact Reference Staphylinidae Anotylus insecatus (Gravenhorst) 4 27 MA 1914 ON Pal - Klimaszewski et al. 2013 Anotylus tetracarinatus (Block) 2 2 MA 1877 IN Pal - Majka and Klimaszewski 2008 Creophilus maxillosus (Gravenhorst) 2 2 1673 NL Euro - Bain and King 2011 Gyrohypnus angustatus (Stephens) 2 5 MA 1860 QC Pal - Majka and Klimaszewski 2008 Habrocerus capillaricornis (Gravenhorst) 6 19 1931 MA Pal - Majka and Klimaszewski 2008 Lithocharis tricolor (Fabricius) 2 4 less than 1886 CA Pal - Klimaszewski et al. 2013 Medon fusculus (Mannerheim) 2 2 1959 ON Pal - Klimaszewski et al. 2013 Ochthephilum fracticorne (Paykull) 7 15 1968 QC Pal - Klimaszewski et al. 2013 Ocypus brunnipes (Fabiricius) 2 2 1966 NH Eura - Brunke et al. 2011 Ocypus nitens (Schrank) 10 62 1944 MA Eura - Brunke et al. 2011 Philonthus carbonarius (Gravenhorst) 6 17 1905 NL Pal - Majka et al. 2008 Philonthus cognatus Stephens 2 2 1884 NC Pal - Majka and Klimaszewski 2008 Quedius curtipennis Bernhauer 7 34 MA,L 1934 WA Pal - Klimaszewski et al. 2013 Rugilus orbiculatus (Paykull) 2 4 L less than 1885 NY Pal - Klimaszewski et al. 2013 Rugilus rufipes Germar 3 5 1971 QC Eura - Klimaszewski et al. 2010 Sepedophilus immaculatus (Stephens) 3 5 NA 2006 MA Pal - Webster et al. 2016 Sepedophilus testaceus Fabricius 4 9 1884 NY Pal - Majka and Klimaszewski 2008 Stenus clavicornis (Scopoli) 6 25 L 1968 QC Pal - Majka and Klimaszewski 2008 Tachinus corticinus Gravenhorst 4 36 1967 QC Pal - Majka and Klimaszewski 2008 Tachyporus dispar (Paykull) 4 14 1927 BC Pal - Klimaszewski et al. 2013 Tachyporus nitidulus (Fabricius) 7 51 L 1834 IN Pal - Majka and Klimaszewski 2008 Tachyporus transversalis Gravenhorst 2 3 1963 ON Pal? - Klimaszewski et al. 2013 Tasgius ater (Gravenhorst) 8 49 L 1802 NA Pal - Majka and Klimaszewski 2008 Tasgius melanarius (Heer) 10 130 1935 QC Pal - Majka and Klimaszewski 2008 Tasgius winkleri (Bernhauer) 11 36 1931 NY Pal - Brunke et al. 2011 Xantholinus linearis (Olivier) 6 23 1930 BC Pal - Majka and Klimaszewski 2008