AN INTRODUCTION TO DUNE ECOLOGY
Living things cover the face of the earth from the torrid sands of the
desert to the cold wastes of the Arctic, and every variation in
environment develops a closely knit community of plants and animals.
They are the ones best adapted to living where they do, or they may have
been the first to arrive there, filling all available homesites and
monopolizing the food and water supply to create a “closed” community.
In each environment, a delicate balance is established between its
various residents and between them and their surroundings. The study of
all these interrelationships is called “ecology.”
Beginning with the environment, we have seen in our brief look at the
origins of Castle Neck how drastically an area can be altered as
conditions change on the earth’s surface. Environment is affected in
other ways, too. Man’s activity can change it almost overnight as a
bulldozer clears land for a housing development, a dam alters the flow
or course of a river, or careless disposal of a cigarette or campfire
lays waste to acres of woodland. Or, as in the slow development of a
forest, the growth of the trees themselves can change the environment,
the maturity of one species whose seedlings require sunlight
contributing to the growth of those better adapted to shade. If you
should watch an old abandoned pasture over a period of many years, you
could see environment gradually altered. First there are the mosses and
grasses that create a fertile soil. Then come the Poplars and shrubs. As
these grow they offer shade where Pines and, finally, the broad-leaved
trees can flourish. This change in vegetation will also bring about a
change in the resident animal communities.
When parts of Castle Neck were rich farmland, specialized forms of life
which thrive in that type of environment were abundant there. We have
only to look at Castle Hill, just a few hundred yards from the dunes, or
at some of the swamps that dot the Neck to see how different are the
inhabitants from those of the dunes. On the Hill live the Oaks, Maples,
Jumping Mice, Raccoons, and Toads, plants and animals that would be
misfits indeed—if they could live at all—in the world of moving sand.
Maples and Oaks, relics of the time when the dune area was fertile, may
still be found dying and being buried over by drifting sand. Now it is a
different community of plants and animals living here. The continually
shifting sand and the scarcity of water limit the variety of life found,
but each dune dweller is specially adapted to this homesite, and no
matter how lush, green, and more attractive a neighboring meadow may
look to us, many of these specialized organisms could not survive there
at all.
It has taken millions of years for the long, slow process of evolution
to develop specific adaptations that suit dune dwellers to their
environment. There are variations between individuals in every form of
life. Mostly these are normal inherited variations, such as height or
color. But sometimes sudden variations, called “mutations,” occur
through accidental changes in the genes controlling inheritance. These
are new characteristics not found in other members of the same species.
If the mutation is advantageous it may be passed on, and it is in this
way that new life forms slowly develop. If the mutation allows a species
to live more easily in its environment, it may displace some older form,
which may then be unable to compete successfully for food, water, or
shelter.
Indeed, all life is engaged in a constant struggle for survival; it is
those individuals and species best able to adapt to the changing
conditions of their environment that endure. Think of the whole series
of crises faced by any living thing in its lifetime, then of these
crises being met and overcome in the seemingly inhospitable environment
of the dunes. In the beginning, our dune dweller must be born, a
difficult enough task without interference from unkind surroundings; it
must feed itself, here in an area where meals would certainly seem at a
premium; it must grow, oftentimes shedding its skin in the process; it
must live not only in the summer’s heat but, if its life span is that
long, in the winter’s cold; it must endure long periods of drought,
flood, wind, and storm; and most important of all, it must survive long
enough to reproduce its kind, or else it has missed its goal. But such
is the wonder of nature’s specializations that our dune dwellers can
usually meet these normal crises. Their adaptability and rate of
reproduction safely insure the future of their kind, and their
overpopulation, if left to nature, is delicately controlled by available
food and shelter and their predators.
Exploring the dunes and making the acquaintance of the inhabitants, you
can see this environmental community meshing its lives together, and you
can observe the fine degree of adaptation developed by each life form.
You may find an occasional Apple tree growing out of the sand, rooted in
a more fertile soil below, a reminder of the time when that bit of the
Neck was a rich farmland. The roots of the Beach Plum also reach down to
the water table, and it is thus able to grow out of the sand, although
its seedlings cannot take root in the sand. Most of all, you will have
an opportunity to note many special animal and plant peculiarities the
dune dwellers have developed to suit their particular environment.
SOME ANIMAL ADAPTATIONS
_A Nest Deep Down in the Sand_
Walking through the dunes, you will frequently notice a small hole in
the sand. Poke a blade of grass into it and you will find the hole quite
deep. As a matter of fact, it may extend down two feet. This hole is
made by the Sand Dune Wolf Spider (_Lycosa pikei_) to provide a home
where the female may raise her young. Wolf Spiders are a species that
elsewhere carry their young on the back and hunt down their food wolf
fashion, not even taking time to construct a web. On the exposed dunes,
the Sand Dune Wolf Spider protects its young in this hole far beneath
the ground.
_No Nest at All_
Dozens of Common Terns are to be found nesting at the southern tip of
the Neck. Long ago, the Common Tern began laying its eggs on the bare
sand, and made no nest at all. Each egg is sand-colored, with speckles
resembling pebbles. Only a patient search will locate a Tern nest on the
Beach, and then, unless you are cautious, the discovery may come after
you have accidentally stepped on the eggs.
_Eating What Comes to Hand_
Bayberries have a hard wax covering that makes them seem quite
unpalatable to us, compared to the more succulent berries found away
from the dunes. Yet here the Crows, Tree Swallows, and Myrtle Warblers
are Bayberry-eaters. The Myrtle Warbler in particular derives most of
its winter diet from Bayberries. In fact, its name comes from the
scientific classification of the Bayberry, which is in the Wax Myrtle
Family.
_The Art of Being Inconspicuous_
The sand offers few places of retreat and few for hiding. It is not
surprising, then, that many of the living things here have a
sand-colored protective coloration. There is a large Grasshopper, or
Locust, commonly found on the Beach. Its dull, gray, speckled
wing-covers make it practically invisible when at rest. But the
underwings, used for flight, are a striking orange with black bands.
When discovered, the Locust flies up, confusing its attacker with this
bright flash of color and a loud whirring noise. Unlike most insects,
this Locust eats the thick-skinned, dry Beach Grass.
PLANT ADAPTATIONS
Any plant that is adjusted to living in a region where there is a
decided lack of water is called a “xerophyte.” There are many different
ways in which plants have adapted their structure and way of life to the
dune environment. For instance, to reduce water evaporation they may
have a very small leaf, to offer less surface area to the sun; or
smaller and more numerous stomata than other plants (“Stomata” are tiny
openings through which plants exchange gasses. A pair of guard cells
surround them and control the size of their opening); or a very thick
cuticle (waxy protective covering found on many plants); or their sap
may be changed chemically. Xerophytes may also be very fleshy, like the
cactus, to give more storage space for water. Their roots may drive very
deep into the ground to reach the water table, or they may be shallow
and spread out over a wide area to cover more surface. Their leaves may
grow in closely packed bundles to reduce further the surface area, or
they may be very thorny and prickly as a protection in exposed
surroundings.
Here are just a few common examples of xerophytes and other plant
adaptations to be found at Crane’s Beach.
_Anchor for the Dunes_
Beach Grass (_Ammophila breviligulata_) is a true xerophyte and has many
sand-dwelling characteristics. Its grasslike blade is rolled in at the
sides, oftentimes becoming a tube, in order to reduce the surface area.
As you will probably discover, it has a pointed tip that can prick a
finger and, as you may well imagine, acts as a deterrent to those who
would eat or walk through it. Its underground stems, in true xerophyte
fashion, extend over a large area in an attempt to gather all possible
water, and these dense root-mats serve to anchor the dunes and prevent
their migration.
_A Tough Sand Dweller_
The Woolly Hudsonia (_Hudsonia tomentosa_) carpets the dunes, preferring
its place in full sun to more shaded spots. The tiny leaves are
awl-shaped and press very tightly against the stem, as though trying to
hold in as much water as possible. Hudsonia is covered with a
velvet-like down, which is less susceptible to evaporation than a
smooth, large surface would be.
_An Adaptable Mushroom_
Since mushrooms generally require plenty of water, you would not expect
to find them at the beach. Several species, however, may be discovered
here. The most readily identifiable is the Earth Star (_Geaster
hygrometricus_), which resembles a Puff Ball but differs in having the
outer layer of the skin divided into tough, star-shaped segments. During
the dry seasons, this star is drawn up around the ball by its
contraction, thus protecting it against further desiccation. In wet
weather, the ball swells and holds the star against the ground to allow
for water absorption. The “roots” of the Earth Star are shallow, so the
plant may readily be dislodged. The wind easily blows it across the
dunes, spreading the spores over a wide area.
NOW IT’S UP TO YOU
There is something new to be known about every animal and plant. Now
it’s up to you! Careful observation will allow you to discover many
other examples of special adaptation to life in the shifting dunes, and
the next chapters will introduce you to some of the more common of the
living things inhabiting this strange sand-world. And if you wish to
read more about ecology, try these books:
Ernest Neal, _Woodland Ecology_. Cambridge, Mass.: Harvard University
Press, 1958. $1.75
John H. Storer, _The Web of Life: A First Book of Ecology_. New York:
New American Library, 1956. $.35