Naturally neighbors

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ruby throated hummingbird

The ruby throated hummingbird, one of the most common hummers in the East, favors flowers with warm colors and tube-shaped corollas such as this Trumpet Creeper.

What makes a neighborhood? Many old-timers envision a place with friends just down the road ready to lend a cup of sugar or watch the kids for a few hours. But the concept of a true neighborhood is much more complex than outdated imagery of groomed lawns and white picket fences. Upon closer inspection, “neighborhoods” actually exist all around us, in big cities, little towns and even in places one would never think to look—like nature. 

One enlightening way to think about neighbors and neighborhoods is to use the natural world as a guide. Neighborhoods correlate to ecosystems that are populated by neighbors functioning in one way or another to facilitate nature’s life cycles. In fact, the term neighborhood can be stretched to fit any natural aspect of Earth, big or small. Within Earth’s giant ecosystem exist a multitude of smaller ecosystems, and inhabitants are neighbors of one kind or another.

Broadly speaking, symbiosis describes any interaction between species. Commensalism is a relationship in which one organism benefits and the other organism is basically unaffected. Mutualism is a relationship in which both organisms benefit, and parasitism is a relationship that benefits one organism while adversely affecting the other.

But unlike traditional human neighborhoods in which the whole block knows who the good and bad neighbors are, biologists eschew such anthropogenic terms when describing neighbors in their ecosystems. It’s not for humans to say whether it was a “good” hawk or a “bad” hawk that caught the squirrel and ate it. Though predator-prey relationships, or even parasitic ones, are an integral part of nature, there are many natural interactions that we might consider to be more “neighborly.”

Birds provide an easy to observe example of mutually beneficial relationships in nature. Pileated woodpeckers are the largest woodpeckers in the United States and favor heavily wooded forests with large, mature trees into which they drill looking for insects, especially carpenter ants and wood-boring beetle larvae. Male woodpeckers carve out their nests in dead trees, then seek to attract a female to raise a brood. Once the nest is abandoned, smaller birds like chickadees, nuthatches, and bluebirds in turn nest in these holes their metabiotic hosts made. Even owls or raccoons may make use of the abandoned tree cavities. Though pileateds are territorial birds and do not migrate, they are more tolerant of their neighbors in winter.

Seeds generally are dispersed by wind and water, but there is a host of plants that depend on animal pollinators and seed dispersers. Dr. Fred Alsop, an ornithologist and professor of biology at East Tennessee State University, is the author of numerous field guides, a series of Smithsonian handbooks on birds and the Smithsonian Birds of North America. Most people readily accept hummingbirds as pollinators but may not be aware of how important they really are in this role, and how neighborly that role really is, Alsop said. 

“Hummingbirds as pollinators are always easy to explain,” Alsop said. “The hummingbird is obtaining a source of food, and the plant is contracting a dependable pollinator who will be there no matter what the weather.”

Some hummingbirds are so specialized to a particular flower species or flower group their beaks have coevolved to match the length and shape of the flower, Alsop said. One of the most striking examples of this is the Andean swordbill and the ornithophilous passionflower. The swordbill has a beak more than five inches long, corresponding with the long corolla of the passionflower. The resident hummer in the East, the ruby-throated, is more of a generalist, Alsop says, but it still favors flowers with warm colors and tube-shaped corollas.

“Jays are great dispersers of acorns and promote the distribution of oak trees with their caching of nuts in the fall for their future use.  Some are not found and germinate into oak seedlings,” Alsop said. “Some mammals that eat big fruits with hard seeds such as opossums, raccoons and bears pass the seeds through their guts and disperse them in their droppings.”

Dr. James Costa, director of the Highlands Biological Station and a professor and researcher at Western Carolina University, points to the phenomenon of obligate mutualism, which indicates that neither species can survive without the other. Case in point, the yucca plant and the yucca moth survive through this manner of co-existence in this. In other words, this is a neighborhood that wouldn’t exist without close neighbors, except the neighbors in this neighborhood have lived side by side for more than 40 million years.

Each spring yucca moths emerge from underground cocoons to rendezvous on yucca plants. The females collect pollen from the yucca flower, using their specialized tentacles, and make a moth line to another yucca flower where they deposit their eggs, visit the stigma of the flower to deposit a small amount of pollen, and emit a pheromone to let other moths with eggs know that eggs have already been deposited. This is critical because if too many eggs are laid in any one flower the yucca plant will abort that bloom. Female yucca moths adjust the amount of eggs they lay based on the pheromones present.

Some ants even go so far as to care for other animals, cultivating special relationships with aphids, tree hoppers, and certain caterpillars—these insects all produce nutritional secretions that are valuable to the ants. Aphids and treehoppers produce honeydew, a sugary secretion produced from the sap they feed on, and the caterpillars have specialized nectary organs that produce amino acids. Meanwhile, the ants provide protection services—tending and fiercely defending the aphids, hoppers and caterpillars from predators in exchange for the secretions. 

Visitors who descend upon the Great Smoky Mountains National Park every spring for the Annual Spring Wildflower Pilgrimage owe a debt of gratitude to ants, Costa said. Many spring wildflowers have a mutualism with ants, he said. The plants produce special nutritious bodies attached to their seeds that the ants harvest, and in so doing, the ants carry off the seeds, spreading the plant. The phenomenon is called myrmecochory. 

Similarly, birds are notorious seed spreaders. 

“Perhaps this relationship is one of our major problems with invasive shrub spread,” said Dr. Dan Pittillo, professor emeritus in botany at Western Carolina University, author, environmentalist and advisor to several organizations including the National Park Service and the North Carolina Nature Conservancy. “They spread the seeds of plants like multiflora rose, privet, Japanese honeysuckle, certain viburnums and winged euonymus that are notorious invasives across the landscape of Western North Carolina,” Pittillo said. 

One of the most common mutualistic plant relationships is between fungi and vascular plants. “Most species of woody plants will have mutualistic connections with the fungus that support the fungus with nutrients and aids the plant with absorption of the minerals needed for growth,” Pittillo said. “In certain herbaceous plants, especially orchids, there would be no establishment without this fungus connection.”

One such example is the golden mane moss that lives on branches of old red cedars. The golden mane, also known as Sullivant’s or shaggy maned-moss, is listed as a rare species in North Carolina. He has found it on Cedar Cliff in Jackson County and said that it has been reported from seven other mountain counties in the state. It seems that sometimes, even in the wild, neighbors just need somebody to lean on.

So while it may not be correct to say that there are “good” neighbors and “bad” neighbors in the natural world—it’s easy to see that there are certainly neighbors that are good for one another.

Make some pileated friends

Pileated woodpeckers are striking birds with bright red feathers atop their head. Though some homeowners may consider the birds a nuisance due to their noise and tendency to seek out insect-infested wood—which might include a house’s eaves or deck posts—the birds are very beneficial to the environment, controlling insect populations and creating nesting sites for other birds and small mammals. 

Attracting woodpeckers is a matter of allowing dead trees to hang and rot, typically called a snag, which creates a buffet of bugs and easy nesting. Suet also is a powerful woodpecker pull, particularly suet that includes black oil sunflower seeds. Also consider landscaping with trees and shrubs that provide cover, perches, and berries such as oaks, pines, holly, and dogwood.