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Science
Volume 40 Issue 11 • July 15-21, 2010
now in our 40th season

Uniquely Nantucket 


Many of the things that makes Nantucket habitat and creatures unique center around what is here and what is not here. We do not have many of the mammals found on the mainland. Common North American mammals found in America but not here include skunks, possums, raccoons, foxes, coyotes, otters (although some river otter track sightings have been reported), and beavers. The lack of predators for ground-nesting birds means we are blessed with least terns, piping plovers, and northern harriers that have fewer worries of creatures eating their eggs.  Islands such as Nantucket provide an interesting and truly unique experimental plot to study evolution trends and the impact of things like habitat fragmentation. Very much like the island’s Homo sapiens residents, some of the island’s creatures must learn to live in close proximity and adapt to smaller habitat ranges. Across the world, island faunal and floral communities are being studied to see how quickly they may be responding to changes in the extent of seasons and in temperature relative to climate change observations.

The denudation of the island by the sheep here in the 18th and 19th century enabled large swatches of sandplain grasslands to develop and make space for endangered plants and animals endemic to that habitat. Sandplain grasslands are a globally rare habitat that is found abundantly on Nantucket. They are disturbance dependent, which means they thrive and can be best maintained using management techniques such as prescribed burning and mowing to impede shrub encroachment.  We can learn about how Nantucket has evolved to become such a good host for this habitat from the Nantucket Conservation Foundation’s web site (www.nantucketconservation.org): “While natural and human-induced fire is believed to have been a common historical occurrence, the direct impact of Europeans and their grazing animals was the most important force that shaped the island’s unique grassland and heathland habitats. Nantucket was one of the largest whaling capitals in the world during the 1700’s and early 1800’s, and a large number of settlers that came to the island during this period brought sheep and other grazing animals with them. By 1845, it was estimated that there were over 15,000 sheep grazing on the island. The sheep overgrazed trees and shrubs, allowing low-growing heathland and grassland plants to develop without competition for sunlight and nutrients. The sandy, nutrient-poor quality of the soils and constant maritime salt spray influence were environmental factors that also contributed to the development of these rare and unique vegetation communities.”

Much of our flora and fauna has adapted quite quickly to this abundance of open meadow-like vegetation populated by a large variety of wildflowers and other plants ideally suited to a disturbed environment. Groups like the Nantucket Conservation Foundation, Mass Audubon, and the Land Bank use a variety of land management tools from mowing to sheep grazing to prescribed fire techniques to protect this cultural landscape. Scientists who come to the island are able to observe nature on our fifty square mile terrarium out in the sea and can ideally set up biological monitoring that picks up on changes that occur when land is separated from the natural and physical phenomena of the mainland (over terrain migration; changes in hydrology, etc.)

As far as color and species changes, we already are observing a phenotype change in garter snakes which are differently colored than those on the mainland. And as researchers Andrew McKenna Foster and Cheryl Comeau Beaton at the Maria Mitchell Association have found, black widow spiders on Nantucket not only exhibit different body coloring (red bars instead of the hourglass shape) but they also have evolved to be “friendly” and occupy much less space and different habitats than their mainland and Nantucket cousins. Currently, they are calling the Tuckernuck northern black widow a latrodectus sp. while they do genetic testing and additional behavioral tests to see if this is truly a new species. They are also investigating a purseweb spider species called Sphodro rufipes that they found in relatively high densities on Tuckernuck that builds its web in grass and dead sticks instead of on trees or rocks, adapting to the environment common to Tuckernuck.

Even the invasive plants on island have ideas about their own identity. University of Massachusetts Boston recent doctoral graduate, Mimi Gammon found that a hybridized invasive plant created from a combination of genes from Fallopia japonica (Japanese Knotweed) and Fallopia sachalinensis (Giant Knotweed) may exist here on island. This hybrid apparently occurs when you leave two similar plant species alone together on an island in an effective but slow moving romantic comedy (rom com for those in the biz). An additionally interesting and worrisome fact that was revealed as part of their research and is reported by others is that Japanese knotweed in North America is capable of sexual reproduction whereas in Europe it reproduces clonally (essentially asexually). So someone needs to stop playing that Barry White album over by Coffin Park.

Back to our landscape and habitats and how it may be reflected in some of the animals here. The effect of having more exposure for some animals and a distinct landscape has changed the coloring of some animals. For instance, as was mentioned in the first installment of this article last week, the Muskeget vole is also known as the beach vole because of its lighter coloration. It has to hide and blend into a sandy background with beach grass as its primary vegetation—there is no need to blend into a woodland background.

There are six species of snake found on the islands: garter snake, ring-neck snake, eastern milk snake, northern water snake, ribbon snake, and smooth green snake. More than you might ever want to know about snakes found on Nantucket and where they can be found and what they look can be found in my 2008 article about them at www.yesterdaysisland.com/2008/features/snakes.php

Here on Nantucket, many recent biology-related scientific discoveries are a result of the creation of the Nantucket Biodiversity Initiative which provides small grant funds, logistical support and additional personnel to assist scientists on island in biodiversity related research.  The Nantucket Biodiversity Initiative is a partnership between Nantucket conservation organizations, universities, non-governmental organizations, and individuals interested in documenting the biodiversity of the islands and adjacent waters and monitoring and conserving that biodiversity over time. One of the scientists awarded a research grant over the past few years from the NBI is Scott Smyers  with Oxbow Associates, Inc. who is doing a comparative study of the garter snakes (Thamnophis s. sirtalis) on Nantucket versus those he finds near the Wachusett Mountain (www.friendsofwachusett.org/snakes.php). 

Many of the projects start out as simple biological monitoring expeditions that then expand to answer more specific questions. Garter snakes on Nantucket exhibit a different color pattern than mainland garter snakes which can be theorized to be as a result of their very specific habitat which includes areas like sandplain grasslands where they are more exposed.  The picture accompanying this article showing a large strip of darker red down the center is of a garter snake scale pattern for a Wachusett Mountain specimen; the picture showing much smaller spots is from a garter snake captured during a Nantucket survey (both photos courtesy of Scott Smyers)

What makes them different? Are some populations really different compared to others? Scott and his colleagues are working on these questions and others by collecting data and images from two populations in very different parts of Massachusetts: Wachusett Mountain and Nantucket Island. This is a collaborative effort between the Friends of Wachusett Mountain and the Nantucket Biodiversity Initiative with support from the NBI and from the Maria Mitchell Association and Tuckernuck Land Trust employees and volunteers. For the surveys, they place cover boards around the island (and on the Mainland near Wachusett Mountain to check out the snakes who prefer skiing to the beach) and then inspect the area underneath the boards where snakes like to hang out and cool off to find out who may be hiding there. The snakes are identified, sexed, counted, measured, and tagged for mark-recapture experiments.  Snippets of their tails are taken for DNA analysis to find out if these color variations are genetically important and identifiable. In Scott’s NBI report, he tells us “there is no mitochondrial DNA differentiation between these snakes and mainland snakes, only this color pattern variation. Color variation between individual garter snakes and actual frequencies of certain color patterns within populations has been the subject of discussion and research among herpetologists for more than 30 years.”

Check out the NBI website to learn more about his research and to become involved n this year’s NBI week; a week long set of surveys and science forays out into the various biodiversity plots on island. More info can be found at www.nantucketbiodiversityinitiative.org. This year’s guest speaker (kick off event for the NBI week on September 15th at the Unitarian Universalist Church at 7:00 pm) is Dr. Doug Tallamy, author of “Bringing Nature Home; How you can Sustain Wildlife with Native Plants.” We’ll discuss his book and biodiversity on Nantucket in more detail in a future column,
During my forays on the internet to find additional information for this article, I came across a much more thorough blog than my blog online. If you go to http://matthewwills.com/tag/nantucket/ you’ll find a nice cross-section of nature entries regarding Nantucket. It’s full of some very nice pictures and an easy to digest tutorial on some of the critters from bunnies to osprey that you’ll see on island.

 

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