A tale of two islands: Ant diversity on Tuckernuck and Muskeget Islands

Submitted in fulfillment of a 2013 Nantucket Biodiversity Initiative grant.

Ellison (2012) found unexpectedly high ant diversity on Nantucket Island - about 50% of the species and 70% of the genera found in all of New England. The closely affiliated islands of Tuckernuck and Muskeget, while much smaller in size, might also be expected to have relatively high species diversity for their areas. Using the equilibrium island biogeography area equation, S=cAz, we predicted 16 to 33 species for Tuckernuck Island and 11 to 29 species for Muskeget Island.

We tested these predictions by sampling ants with pitfall traps, baits, hand collections and litter samples along ten transects on Tuckernuck and five transects on Muskeget. A total of 42 people-days of fieldwork were spread across four field trips in June, July, August and September of 2013. Among 3,935 specimens collected on Tuckernuck, we found 38 species. The most common species were Myrmica americana, Aphaenogaster rudis, Crematogaster lineolata, Lasius cf. niger, and Solenopsis cf. texana. Five species, including Lasius cf. niger, Camponotus pennsylvanicus, Camponotus neartica, Formica argentea, and Myrmica rubra, were not reported in Ellison’s synthesis of Nantucket’s ants. Among 16,621 specimens collected on Muskeget, we identified seven species all of which were also found on Tuckernuck. Muskeget’s ant fauna is dominated by Crematogaster lineolata, which comprised 98% of the specimens, followed by Lasius cf. niger with 1.7% of the specimens.

Our predictions of species diversity were underestimates for Tuckernuck (38 observed and 33 maximum predicted) and overestimates for Muskeget (11 minimum predicted and 7 observed). Using published equations of ant island biodiversity to predict diversity on Nantucket, Tuckernuck and Muskeget yielded results that were not consistent among the islands. Together our findings suggest area alone is not a good predictor of ant diversity on Tuckernuck and Muskeget. The higher than predicted diversity of ants for Tuckernuck may be the result of high habitat diversity for its area and lower human disturbance rates when compared to Nantucket and Muskeget. The lower than predicted diversity of Muskeget may be the result of reduced number of habitats and its higher disturbance rates when compared to Nantucket and Tuckernuck.

An unexpected finding was the high densities of the invasive ant Lasius cf. niger on both islands. Only one individual of this species, captured in 2011 in southeastern Massachusetts, had been documented previously on the East Coast. Another invasive species, Myrmica rubra, was documented for the first time on Tuckernuck, but has not yet been seen on Nantucket.