Ant diversity on islands in Nantucket sound: Rising sea level, super saturation and island migration

Background/Question/Methods

Ellison (2012) found unexpectedly high ant diversity on Nantucket Island (area 125 km²)– 59 species comprising about 50% of the species and 70% of the genera known in all of New England. The closely affiliated islands of Tuckernuck (3.6 km²) and Muskeget (1.2 km²), 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=cA^z, we predicted 16 to 33 species for Tuckernuck Island and 11 to 29 species for Muskget 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. 

Results/Conclusions

Among 3,935 specimens collected on Tuckernuck, we found 38 species, five species more than our predicted range. The most common species were Myrmica americana, Aphaenogaster rudis, and Crematogaster lineolata. Five species found were not reported in Ellison’s synthesis of Nantucket’s ants. Among 16,621 specimens collected on Muskeget, we identified sever species, four species fewer than our predicted range. 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. 

We concluded that area alone is insufficient to predict ant diversity on Nantucket, Tuckernuck and Muskeget. The higher than predicted diversity of ants for Tuckernuck may be due to a super saturation of species. It became it own island within the last 2500 years due to raising sea level. Tuckernuck also has relatively high habitat diversity for its area and lower human disturbance rates when compared to Nantucket and Muskeget.  The lower than predicted diversity of ants for Muskeget is likely because it is over-washed by the ocean and is moving at the rate of ½ mile a century creating a reduced number of habitats and higher disturbance rates when compared to Nantucket and Tuckernuck.