Nature Notes: Welcome, Stranger
Perhaps during no other time in the history of modern man have so many people from so many countries and territories been on the move to seek new lands in which to live. This is the age of emigration and immigration, born of choice, vocational opportunity, the need to survive, mostly the latter. But it’s not just humans that are on the move. With global warming becoming more and more of a reality, plants and animals of all kinds are extending the ranges, moving from one place to another.
When, a plant or animal spreads into a new area we call it range extension. Perhaps the best example of it in the United States in the 20th and 21st centuries has been the eastward movement of coyotes from west of the Rocky Mountains. Whether they are pure in genetic composition or coywolves, as some back here have turned out to be, it’s been an amazing run. Several thousand years earlier the red fox did the same. They apparently came from Siberia during the Ice Age across Beringia when sea level was very low and North America was still in the grips of a massive glacier, the same one that created the better part of Long Island.
We won’t count the Norway rat, which started out in Eurasia and is now found on every continent and almost every ocean island throughout the world. It didn’t get around entirely on its own doing; it traveled mostly in the hulls of sailing ships. Our own osprey is one of those species that became ubiquitous worldwide using its wings.
Birds, fishes, and marine mammals and reptiles are better at getting around than land mammals, snakes, most reptiles and amphibians. The latter have to navigate rivers, climb mountains, cross deserts, and overcome several other difficult hurdles in order to conquer new territories.
Flying insects can be blown from one continent to another in order to start a new life. Some that are parasitic ride on birds or mammals to establish new territories. The lone star tick is one of those that got here from more southern climes by hitchhiking on another organism, most likely a migratory bird species. It’s been around for less than a half a century, yet in that short time it’s become the most prevalent and widespread of the three major local tick species.
In order for one of these newcomers to establish itself in a new land, a niche has to be available. No problem for southern ticks, almost any mammal or bird will do. For the deer, or black-legged, tick, their favorite niche is the white-footed mouse genus, species of which are found throughout the United States and Canada. The Norway rat, once it got here from across the ocean, didn’t have much of a problem either. It was used to living near humans, whether in the country or in cities. Interestingly, Long Island doesn’t have a native rat of its own, so there was never a problem for the garbage rat in settling down.
On the hand the local white-footed mouse does just as well in houses as the Eurasian house mouse. The latter is now much less common here than it was 50 years ago. When two species compete for the same niche in the same area, invariably one wins out in the long run.
Birds have the easiest time of spreading from one life zone to another. In the last 70 years we’ve seen Long Island populated by southern bird after southern bird. Cardinals, mockingbirds, tufted titmice, Carolina wrens, red-breasted woodpeckers, blue-gray gnatcatchers, boat-tailed grackles, and even some parrots that have taken to cities are all fairly recent residents. Niches with wild and domestic fruit have been available for cardinals and mockingbirds, and there is almost never a shortage of insects around for the others, except in the winter, when feeders with seeds and other edibles help them through.
Among the higher plants, the family with the most species is one that includes dandelions, asters, goldenrods, and hundreds of other genera, almost all of which produce seeds with feathery appendages that allow them to waft through the air mile after mile in a brisk wind. Several grasses, say, the bluestems and broomsedges, also have seeds with feathery appendages that scatter in the wind.
Plants that produce edible berries are transported by the birds that eat them and then defecate the hard indigestible seeds here and there. That is precisely why the black cherry is so prevalent throughout the Northeast. There is hardly a wood or old field on Long Island that doesn’t have several of them.
One of the most cunning propagators of all belongs to a diverse group collectively know as tumbleweeds. One of these is our own purple lovegrass, Eragrostis spectabilis. It fruits in the late summer and early fall when southwesterly and westerly winds are still prevalent. The entire plant breaks off at the root and rolls down a road or through open fields, pushed by the slightest of breezes. It’s become more and more common locally and has become one of the prevalent grasses on the Sunrise Highway median in the new millennium.
With the inroads made by new species from the south and west, and those brought by humans, either accidentally or on purpose, over the past two centuries, local habitat types or “plant associations” are in trouble. Every year a newcomer such as mile-a-minute vine or giant hogweed arrives and begins to establish itself as the new kid on the block, some more readily than others. It seems that the dandelion has been here forever, but mugwort, garlic mustard, common St. John’s wort, and a host of others are more recent. They normally begin to our west, then spread eastward, especially accelerated by mowers operated by the state’s Highway Department along major state roads.
The inroads made by such “weeds,” say at the United States Fish and Wildlife Service’s Morton Wildlife Refuge in Noyac, compromise an entire ecotype, producing what modern plant ecologists have termed “novel ecotypes” because they have as many invasive species as native ones. But some local plant associations have been able to hold their own, especially those dominated by beech trees, pitch pines, and white pines. They are a kind of keystone species. As long as they form healthy long-lived stands and have the appropriate undergrowth species, say as the huckleberries and blueberries found in pitch pine and oak stands, they provide a shield against invasives. But, should one of these keystone-safeguarded associations be attacked by a novel species that is immune to the keystone species protection, anything goes.
That is precisely what is happening across Long Island’s pine barrens at this time. A novel species, the southern pine borer, has arrived from the south and is desecrating mature pitch pines. A ride along the Sunrise Highway through Southampton and Brookhaven Towns is an ample demonstration of such carnage.
More than 100 years ago, oaks and hickories were the keystone species for most of Long Island’s deciduous forests. That was before gypsy moths were loosed in Massachusetts, where they had been imported and cultivated to produce silk. Every 10 to 20 years since the end of World War II our oaks-and-hickory forests have suffered mightily at the hands of these moths’ larvae. Depending upon the extent of the damage with each new incursion, the forests come back, but less stately in appearance, with fewer white oaks and very few centenarian trees.
As our climate continues to heat up, look for more southern trees — to wit the southern red oaks establishing in Montauk — to set in and more southern birds nesting in them. Change is inevitable!
Larry Penny can be reached via email at [email protected].