A Little Island Biogeography


ISLANDS have fascinated people for a very long time. Think of creation myths like Turtle Island or the numerous accounts of catastrophic floods. Think of Odysseus’s misadventures among the Aegean Islands. Think of the vikings who discovered and settled Iceland and wrote the sagas. Think of William Shakespeare and the magical island of The Tempest. Think of Herman Melville and the grim, volcanic islands recounted in The Encantadas or Robert Louis Stevenson and the buccaneers and buried gold stashed inside the covers of Treasure Island. Here’s a list that could go on and on, yet, even curtailed, it’s an island list redolent of mystery and adventure.

Many early scientists, explorers, and naturalists expressed a penchant for islands, some as ardently as the storytellers. Most preeminent being Alfred Russel Wallace and Charles Darwin. Wallace collected insects and birds among the islands of the Malay Archipelago, wondering what might explain their distributions and variations. Darwin puzzled through similar oddities encountered on the many islands he visited during the five-year voyage of the Beagle, resulting…eventually…in his theory of natural selection. During the century and a half since Wallace and Darwin, numerous scientists have focused their research upon the natural laboratories that are islands—Ernst Mayr, E. O. Wilson, and Peter and Rosemary Grant to name but a few. The big story of island biogeography, its rich history and relevance to modern times, has been masterfully told by David Quammen in his magisterial book, The Song of the Dodo.

Biogeographers study the distribution of plants and animals—which species live where, and why—bringing to prominence the role geography plays in the process of evolution. Island biogeographers study the same thing, only with a focus on the more restrictive and clarifying setting of islands, delineating the special role isolation plays in the formation of new species.

Two main factors influence the formation of new species on islands: location and size. If an island is small or close to the mainland nothing too extraordinary happens. On the other hand, if an island is large or distant enough from other land masses so that vagrant species arrive only with great irregularity over great spans of time speciation is more likely to occur among the plants and animals that happen to make it to the island and that survive to establish populations. Extinction plays a role as well. As evolution’s unavoidable shadow, extinction reduces and subtracts and trims island diversity, this permanent negation creates an absence that new species might fill.

Pale Lichen Moth
Pale Lichen Moth
In August, I had the privilege to visit Mallard Island, an island of some renown on Rainy Lake in Minnesota, a mile or so from the Canadian border. The island is a lance-shaped skelf of bedrock, one and a half acres in size (an area roughly equal to that of a football field), covered in pine and lichen and moss. The island’s notability can be credited to Ernest Oberholtzer (1884 – 1977), who occupied the island for some forty years beginning in the 1920s. During those four decades, Oberholtzer constructed a number eccentric dwellings and outbuildings upon the island, built various stone walls, bridges, and gardens, amassed a library of more than 10,000 books, and helped protect a vast amount of wilderness, work that led directly to the establishment of Voyageurs National Park and the Boundary Waters Canoe Area Wilderness. And, near the end of his life, he created the Oberholtzer Foundation in order to preserve the rugged and secluded charm of his beloved island—and bring forward his conservationist legacy.

As member of a small group of people invited to stay on the island for one of the Oberholtzer Foundation program weeks, I arrived Sunday afternoon ready for six days of intense reading, new conversations, and an abundance of time out-of-doors. The focus of this week’s program, as laid out by the organizers, was on art and science. The purpose, and our purpose in participating, was to expand our views, to strengthen our resolve, to collaborate across the distances and differences, all with an eye to the economic and environmental struggles that we all are facing and which will only intensify in the years to come as human populations increase and resources dwindle.

Now, according to some people, powerful spirits inhabit Mallard Island. Inanimate objects like books are said to leap into your hands as if in magical apprehension of your wants or shortcomings. And while I do my best to respect the angels and demons encountered by others, I have to say right off that I’m a skeptic in my own sphere, content enough with the wonder-filled world as it is, finding any superadded spirit world unnecessary. Nonetheless, I’ll admit it can seem uncanny, in such a sweeping assemblage, to immediately find a book that is extraordinarily apt and directive. For instance, as soon as I had the opportunity to look at books I happened upon a copy of Shan Walshe’s Plants of Quetico and the Ontario Shield. “There are occasions when luck goes farther than wisdom” I’d read recently, and this is true. Thus I allowed my luck to direct my activities for the week. For the next few days I would unburden myself of the role of writer, turn truant from the island’s other books (as best I could), try my hand at some botany, conduct a little island biogeography.

Realizing full well that most island biogeography happens on oceanic islands not islands on freshwater lakes, I didn’t expect to discover any endemic species or any vast differences among these small islands. Rather I expected them to be similar and express only subtle differences. Separated by less than a mile of water from the mainland, having strong “land communication” to use Wallace’s term, the flora and fauna should be nearly identical across the islands and representative of the fire-dependent, northern forest ecosystems that covers much of the Canadian Shield. However, some small variations could be expected, reflecting the happenstance of slight differences in physical shape, human habitation and use, and microclimates.

I took photographs. I made lists. I mapped the flowers as if I were a bee. My entomological surveys consisted of two nights of mothing and various incidental encounters with other insects. My botanical surveys consisted of daily excursions and rambles: a hike on Crow Island, from tail-feathers to beak; fishing the circumference of Gull Island, noting the trees and shoreline vegetation; an east-to-west ramble the length of Mallard Island, pen in hand; an afternoon exploring Hawk Island; a paddle into the long, marshy bay of Grassy Island; a boat ride to Blind Bay in Canadian waters (thanks to the generosity of fellow naturalist Mary Lysne); ending the week with a second trip to Crow Island.

Scarlet-winged Lichen Moth
Scarlet-winged Lichen Moth
Midway through the week, on Wednesday afternoon, I visited Hawk Island. To get there I waded the narrow channel separating it from Mallard Island, shoes in hand, camera slung over my shoulder. Barefooted, I could feel the ridges and recesses in the bedrock. The stone underlying the islands had formed many millions of years ago. Those original rock strata had been broken, turned on edge, and scoured by glaciers. Only the stars overhead at night were older.

Once across the channel, the only way onto the island was up a steep rock face, so I climbed and entered the woods. My transect of exploration sliced across the middle of the island. Reaching the abrupt cliffs that define the south edge of this island (a pattern interestingly repeated on the other islands), I veered and puzzled my way to the eastern tip, where the bare rock thins and dips beneath deep lake water the color of iced-tea. From there I worked back. A few flowers on the wave-beaten rocks, Hedge Nettle and Grass-leaved Goldenrod, before the Jack Pine and Reindeer Lichen and mosses thickened as I climbed inland. In a small, mossy clearing, I came upon a beaver skull missing the bottom jaw, turned to reveal the upper teeth. The clean, white bone of the skull brightened the forest floor. Here was a reminder that there existed a time element to this timelessness; islands come and go; species evolve and go extinct.

On hands and knees I inched as close as I could to a shiny, brassy-green soldier fly that had perched on a blueberry leaf. After it flew, I sat back. A few deep breaths. A few hearty exhalations, sighs of satisfaction and gratitude for this time, for this place. Then I moved on, continuing this fine-scale perusal of the surroundings. I smiled at pixie-cup lichens so small that a single drop of rain would overfill one. I shook my head in wonder at the clubmosses so perfectly replicating the form of trees on a miniature scale. I made my way across a seemingly stochastic quilt of vegetation, and yet I knew that it wasn’t purely random, but patterned in subtle ways. Eventually I reached the edge of the forest where the bedrock drops away. Time to return to the other island. Though before I left, taking a final glance back, the forest produced a parting surprise, a ghost plant, a small clump of Indian Pipe.

Even as I began to learn the names and recognize certain patterns of occurrence, I was humbled by the sheer abundance and complexity of these small islands. Goethe once wrote of Rome that “the immensity of the place has a quieting effect. In other places one has to search for the important points of interest; here they crowd in on one in profusion… One would need a thousand styluses to write with. What can one do here with a single pen?” Wild, unbounded nature, not urban complexity, confronts one here and leaves one the task of organizing its subtle immensity into the simplicity of a few paragraphs. How does one write a long, slender island into an essay? A splinter of schist, a sliver of seed must be forced into a simple sentence that proceeds: noun, verb, stop. Or elaborated, the serendipitous occurrences of flower and insect and observer intersecting at a moment in time on an island gets written into a sinuous sentence, full of detours and wrong turnings, break downs and bad luck, or simple exuberance, the description going all out, on and on, forming a widening interior, fattening the page, where eventually the reader walks out of the forest and finds the shore at land’s end.

Painted Lichen Moth
Painted Lichen Moth
On Thursday, after some morning reading—sonnets by Conrad Aiken, a natural history of worm-lions by Morton Wheeler—I took oars from the rack on the side of the library and headed off on a return visit to Crow Island. I rowed past Japanese House on the westernmost tip of Mallard Island, then past Fawn Island, rounding the westernmost tip of Crow, doubling back into a small bay, beaching the boat at the landing, snug in a thicket of sweet gale. Once on land, I worked my way up to the sunlit outcroppings, hoping to find and photograph a Dragonhunter, a large dragonfly I’d seen flying and landing on the waterside ledges just the day before. When no dragonfly materialized, I fell into surveying the plants.

All week I’d stepped carefully around bumble bees nectaring on oregano that grew in thick patches in and out of the rock gardens on Mallard Island. Several times I stopped for a closer look at the handsome workers. Tri-colored Bumble Bees (Bombus ternarius), attractive yellow, orange and black bumble bees, are small, not much different in size than a honey bee, though fuzzier. Their abundance indicated a thriving population, with perhaps a number of hives located nearby. Now, as I prepared to leave, a very large bumble bee, much larger than the workers observed on the other island though patterned the same, buzzed by me and landed on the ground. It, also, had arrived on the island looking for something. I watched the bee as it searched about the pine needles and duff. It started to dig, disappearing into the dirt. How curious. My first thought was that it had entered a hive…but when no other bumble bees came or went, I realized that wasn’t correct. Then I remembered the abundance of bumble bees from the other island—the hidden hives—the workers working the oregano flowers, had succeeded in producing queens, the goal of their summer labors. Though it seemed early in the year, with next year’s summer certainly a long way off, this queen was likely searching out a hibernaculum, a safe place to wait out the winter and dream bumble bee dreams.

Here was a being adept at finding its way about the world. Another kind of island biogeographer in fact, locating suitable sites for hives, mapping the flowers. The shooting stars, which the other residents and I had witnessed in the night sky this week, were not more wondrous than this, nor more rare. To see this, to think about this had something to do with presence and absence…of leaving and longing to come back.

Black-and-yellow Lichen Moth
Black-and-yellow Lichen Moth
In the end, I realized that I would be returning home to my own small island of house & family. The small city lot on which our house sits surrounded by so many groomed and lawn-care-tended plots is certainly a kind of island refuge for insects and weeds. And the city parks and college natural lands that I often visit, while not islands surrounded by water, are engulfed by vast acreages of agricultural and urban/industrial development (for many plants and animals a far more treacherous crossing than water) making them islands as well. In fact, our increasingly fragmented landscapes make islands everywhere. Which is the very reason the science of island biogeography plays an increasingly important role in wildlife conservation and preservation.

A quick note about the following list: The first and most obvious caveat is that the list is not complete; I missed and overlooked many species, nor did I survey each island equally, nor did I include animals and insects. Secondly, links are provided for photo observations that have been submitted to iNaturalist.org, a crowd-sourced species identification system and database. If you notice something that’s been misidentified please let me know.


Review Islands Flora

Jack Pine (Pinus banksiana) *
Eastern White Pine (Pinus strobus) *
Black Spruce (Picea mariana)
Paper Birch (Betula papyrifera)
White Cedar (Thuja occidentalis) *
Common Juniper (Juniperus communis) *
Chokecherry (Prunus virginiana)
Alder (Alnus sp.)
Serviceberry (Amelanchier sp.)
Velvetleaf Blueberry (Vaccinium myrtilloides) *
Creeping Juniper (Juniperus horizontalis)
Beaked Hazel (Corylus cornuta)
Smooth Sumac (Rhus glabra) *
Balsam Fir (Abies balsamea)
Meadowsweet (Spiraea alba) ‡
Sweet Gale (Myrica gale) ‡
Bebb’s Willow (Salix bebbiana)

FLOWERS & Other Plants
Grass-leaved Goldenrod (Euthamia graminifolia) ‡
Field Goldenrod (Solidago nemoralis)
Northern Bugleweed (Lycopus uniflorus)
Wild Sarsaparilla (Aralia nudicaulis)
Dotted Knotweed (Persicaria punctata)
Water Smartweed (Persicaria amphibia)
Crested Arrowhead (Sagittaria cristata)
Marsh Skullcap (Scutellaria galericulata)
Fringed Loosestrife (Lysimachia ciliata)
Swamp Candles (Lysimachia terrestris) ‡
Floating Bur-reed (Sparganium fluctuans)
Indian Pipe (Monotropa uniflora)
Pussytoes (Antennaria neglecta)
Common Snowberry (Symphoricarpos albus)
Pearly Everlasting (Anaphalis margaritacea)
Bearberry (Arctostaphylos uva-ursi)
Silverleaf Cinquefoil (Potentilla argentea)
Marsh Woundwort (Stachys palustris)
Bull Thistle (Cirsium vulgare)
Harebell (Campanula rotundifolia) ‡
Pale Corydalis (Capnoides sempervirens)
Canada Hawkweed (Hieracium umbellatum)
Wild Columbine (Aquilegia canadensis)
Checkered Rattlesnake Plantain (Goodyera tesselata)

Slender Rush (Juncus tenuis)
Woolgrass (Scirpus cyperinus)
Bur-reeds (Sparganium)

Spinulose Wood Fern (Dryopteris carthusiana)
Rusty Woodsia (Woodsia ilvensis)
Wood Horsetail (Equisetum sylvaticum) *
Rock Spikemoss (Selaginella rupestris) *
True Mosses (Bryopsida)
Ostrich-plume Moss (Ptilium crista-castrensis)
Prickly Tree Clubmoss (Dendrolycopodium dendroideum) *

British Soldier Lichen (Cladonia cristatella)
Common Powderhorn (Cladonia coniocraea)
Gray Reindeer Lichen (Cladonia rangiferina)
Mealy Pixie Cup (Cladonia chlorophaea)
Red-fruited Pixie Cup (Cladonia pleurota)
Speckled Shield Lichens (Punctelia sp.)
Rock Tripes (Umbilicaria sp.)

* Fire-dependent indicator species
‡ Inland Lake with Boulder Shore indicator species

    Books referenced:

MacArthur, R. H. and E. O. Wilson. The Theory of Island Biogeography. Princeton Landmarks in Biology Edition. 2001
Minnesota Department of Natural Resources. Field Guide to the Native Plant Communities of Minnesota: the Laurentian Mixed Forest Province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. MNDNR Saint Paul, MN. 2003.
Quammen, David. The Song of the Dodo: Island Biogeography in an Age of Extinctions. Scribner. 1996.
Walshe, Shan. Plants of Quetico and the Ontario Shield. University of Toronto Press. 1980.