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 non-native 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.