Content reproduced with permission from Indiana University Press. The following essay was published in The Natural Heritage of Indiana, copyright 1997, Indiana University Press.

“Each species inhabits only a part of the earth's surface, occurs only in some habitats, and varies in abundance over, its geographic range, These ranges change dynamically, usually starting small, experiencing increases and decreases in size, and finally decreasing to extinction, Contemporary forms will eventually become extinct as well, leaving future species in their places” -James H Brown and Arthur C Gibson, Biogeography (1983)

BIOGEOGRAPHIC CONTROLS

The flora and fauna of an area are almost never static, but are constantly changing as climate, vegetation, land use, and other factors exert their influences on the distribution patterns of populations of plants and animals, and on habitat use by individual organisms, The documentation of these changes, historical and earlier, [or many species is incomplete, but there are fairly good data for some, Most of the historical writings and observations by naturalists, hunters, travelers, and others who might have made comments on the natural history of our state, date from after 1800, Information from earlier periods is dependent on the sketchy fossil record or other paleoecological evidence.

The flora and fauna of Indiana are composed mostly of species widely distributed throughout the eastern United States, Since our state was originally primarily heavily wooded with deciduous forests, as was much of the country eastward to the Atlantic Ocean, it is not surprising that these eastern affinities are evident in species found here today A few species with more western associations, formerly present on the prairie areas, have extended their ranges eastward or have invaded from the west as tlie forests were cut away and the state became largely farmland and open country A small group of plants and animals is restricted to the southern part of Indiana, where they are near, or at, one of the northern limits of their geographic distribution. In addition, a few species of more northern origin and affinities remain, some perhaps as relicts from the glacial age.

In general, most plants, invertebrates, amphibians and reptiles, and mammals (with the possible exception of bats) tend to be more sedentary and to have less extensive ranges than do winged insects, stream fishes, and birds. Flight enables winged insects and birds to more easily find and exploit new habitats and to move into them, and allows species to surmount barriers that make it impossible for small terrestrial, non-flying forms to expand their ranges. Streams, being largely continuous, open-ended habitats, allow fishes to move rather freely over long distances, hence to disperse widely Such mobility allows individuals to live in one area in summer and another in winter; thus the birds that migrate annually Many species of birds leave Indiana in the fall to winter in South America. A few bats may also carry out rather extensive seasonal migrations, as do some insects.

But a small shrew or meadow vole may spend its entire life in an area of less than one acre. Even animals as large as cottontail rabbits are quite sedentary if all their habitat needs are met locally. A given species can be confined to a certain small geographic area by necessity; its demands for life may be met there, but not in adjacent areas. It must have space, food, water, shelter, a place to reproduce, and perhaps other needs; the absence of ay of these required resources will render that habitat untenable. Under those conditions, the animal must find an alternate, suitable habitat or perish.

Just what makes a habitat livable for a particular species is not always apparent to the human eye. We may look at two areas which appear about the same to us. Yet, If we sample the plant or animal life in these locations, we may find certain present in one, but not the other.

Our inability to recognize and quantify habitat characteristics necessary to sustain some species frequently makes our job of protecting and managing wild species quite difficult. No doubt research will continue in this area for a long time. We do know that many of the differences may be subtle and complex. The interdependence of organisms may be so intricate and so delicately balanced that some slight, apparently insignificant, change in conditions may destroy the entire system. Unfortunately, humans are changing local environments almost daily and at such a rapid rate that we can rarely obtain vitally needed research data at the same pace.

One of the major features of habitats is the amount and type of vegetation. It is quite obvious that certain birds and mammals live in grassy and weedy fields, and different species live in forests. Indiana originally offered animals roughly three major habitats-deciduous forests, prairie grasslands, and aquatic areas (lakes, marshes, rivers, etc.).

These prevailing habitats were the results of the glacial, climatic, geologic, and other historic events that operated [or thousands of years to exert their effects on plant and animal life. The last glacial ice sheet retreated from the state some 10,000 years ago, so what we see today is the result of changes since that time. The south-central hill region that was not under the influence of glaciation exhibits a much different topography from that of the remainder of lndiana. And even though there are no mountain ranges in Indiana and elevations statewide do not differ greatly, numerous plant and animal species do not occur throughout the state, Indeed, some are quite restricted in their geographic ranges.

FAUNAL DISTRIBUTIONS

The amount of moisture available is obviously important to most plants and may be important to some shrews. Woodrats are usually associated with limestone escarpments or caves; caves also provide ideal wintering habitat for several species of bats. Nesting shorteared owls prefer rather extensive grasslands (which resemble the prairies these owls find to their liking). The greater sandhill crane prefers to avoid humans as much as possible during the nesting season and frequents somewhat isolated marshy sites. Only small numbers of both of these birds now nest in Indiana, mainly because of the lack of suitable habitat and (perhaps) because of human disturbance.

I am earth's native; No rearranging it!
-- Robert Browning

There is tremendous variation in the ability of species to adapt to environmental changes. Some simply seem incapable of such adaptations, and thus have been extirpated from the state. A good example is the greater prairie-chicken; through the destruction of the prairie areas needed by the birds, human land use eliminated the species. In the 1930s, scarcely anyone thought the pileated woodpecker would survive for long The sighting of one of these great birds in the wooded counties of southern Indiana at that time was a real treat. But it made a remarkable comeback and is still moving back into areas where it had been absent for more than 75 years.

We do not know by what mechanism some species are able to adapt to change; for those that cannot, extinction may be their final fate. The coyote was a resident of Indiana (though probably mostly restricted to the original prairie region) for hundreds of years. When the forests were removed, the coyote was able to take advantage of this large amount of open habitat formerly not suitable for it. The extermination of the wolf throughout most of the eastern U.S. may also have allowed the coyote to partially exploit the niche formerly occupied by timber wolves. Also, wolves possibly took coyotes as prey during times of food shortages. Coyotes are now found throughout the state and to the eastern coast of the United States. They adapted not only to major habitat changes, but to living successfully with humans. In this way, the coyote is similar the red fox and gray fox. All three canid species have been persecuted by man for decades, yet each has survived and is doing well.

Coexisting with humans has become a prerequisite for the survival of several species. Most nesting chimney swifts in Indiana now construct their nests in chimneys. Before European settlement, the birds probably nested in hollow trees (a few still do), which are less common in to day's forests. The mourning dove has readily accepted people and their surroundings, frequently nesting around human habitations. Crows have also adapted well to human presence, now common residents and nesters in cities, suburbs, and urban parks. Road-killed animals provide a ready protein source [or crows and opossums. We hardly need to mention the house sparrow, European starling, and domestic pigeon, all imported aliens that not only find human haunts to be congenial places to live, but also have become serious pests.

Native species of birds that live in urban-residential areas include the American robin, northern cardinal, chipping sparrow, song sparrow, Baltimore oriole, chickadees, tufted titmouse, woodpeckers, blue jay, common grackle, and many others. In recent years, a newcomer, the house finch, has appeared on the scene. It is a western species that was originally absent east of the Mississippi River. It became established on long Island (and probably other places), from which it moved westward to invade Indiana and other states.

In some areas, there may be about as many raccoons and cottontails living in cities as there are in the surrounding intensively cultivated farmlands. White-tailed deer, squirrels, cottontails, raccoons, opossums, mice, rats, shrews, bats, and sometimes even foxes or mink all associate with humans in urban situations.

"The prime enemy working against wildlife in urban environments is not so much the crowded human community itself as it is the monoculture created by humans."
-William L Robinson and Eric G. Bolen, Wildlife Ecology and Management (1991)

Our largest woodpecker, the pileated, is much more common now than it was several decades ago. Apparently regrowth of second-growth forests has favored its increase.

As the human population continues to increase and habitats are altered, we will find other species adapting, and some failing to do so. Fragmentation of habitats, more roads, and increased vehicular traffic all combine to pose a serious threat to many animal species, owing to road kills and lack of habitat units of suitable size. Box turtles and snakes which bask on warm macadam roads at night are especially vulnerable to road kill. Mammals seem most prone to road kill during the fall and spring "shuffles." During the former, young of the year move about searching for home ranges in which to spend the winter; in spring, males and females range more widely seeking mates, hence they likely are less cautious.

Among the mammals found in Indiana that typically have a more northern distribution are the red squirrel, masked shrew, star-nosed mole, and least weasel. Some of the nesting birds in this category are the very, long-eared owl, short-eared owl, least flycatcher, chestnutsided warbler, Canada warbler, rose-breasted grosbeak, and swamp sparrow. Of the northern mammals, the star-nosed mole is most restricted in range in Indiana. Most of the known populations are in the northeastern corner, where the mucky soils and swampy/marshy habitats suitable to the moles are found.

The only Canada warbler nest found in Indiana was also in this region, but the bird has been noted in other northern sites during the breeding season. Similarly, the only verified record of magnolia warblers breeding here occurred in 1995 in northern relict habitat at Shades State Park. The short-eared owl presents an interesting case. The few nesting records for the state II ere in northern Indiana prior to 1940. When coal companies created prairie-like habitats by reclaiming large acreages of surface-mined lands in southwestern Indiana, this owl began nesting there. To our knowledge, the species had never before nested in this region.

Southern birds that more or less reach one of the northern limits of their total nesting range in Indiana include the black vulture, worm-eating warbler, summer tanager, and Bachman’s sparrow. Similar mammals are the eastern woodrat, swamp rabbit, southeastern shrew, gray myotis, southeastern myotis, and eastern big-eared bat. Amphibians and reptiles with southern affinities include the green salamander (recently found as a new state record in Crawford County), alligator snapping turtle, crowned snake, scarlet snake, cottonmouth moccasin) known here for only about a decade), and ravine salamander (which occurs primarily in southeastern Indiana).

Although there are no recent records for the big-eared bat, its habitat (caves) appears unchanged from earlier years. Its exact status at this time is conjectural. The swamp rabbit presently seems to be the most threatened species owning to habitat(caves) appears unchanged from earlier years. Its exact status at this time is conjectural. The swamp rabbit presently seems to be the most threatened species owing to habitat destruction; its range has decreased considerable within the past 30 years. We could witness its extirpation in the next decade, although its small population of about 53 individuals appears to be holding steady during last two years. Bachman's sparrow has virtually disappeared since around 1950, when it was widely scattered and nesting throughout much of southern Indiana. We have no idea what caused its decline, but habitat changes were possibly the reason.

Some birds have invaded from the west and now nest in Indiana, but did not at the turn of the last century. Again, this expansion eastward was in response to the opening up of land originally forested, and altering habitats to more prairie-like or open field conditions. Relatively new arrivals include the western meadowlark, Brewer's blackbird, and Bell's vireo. Although only one nest of the western meadowlark has been found in Indiana, the species has been present at least since the late 1930s. The first reported nesting of Bell's vireo was in 1945, but there are sight records for the species as early as 1922. Brewer's blackbird was reported from lake County in 1949, and the first nest was found there in 1952.

With the exception of the western harvest mouse, there have been no new mammal immigrants from the west. But the 13-lined ground squirrel, badger, and coyote (all characteristic of prairie-like habitats) have enjoyed eastward range expansions in Indiana following wide-scale land clearing. It is quite likely that the prairie vole and eastern cottontail also followed this pattern of distribution change in times past. The spadefoot toad, western ophisaur or glass lizard, and crayfish frog are primarily western species, but apparently not recent to Indiana. The appearance of the house finch represents the only significant invasion of a bird or mammal into Indiana from the east in recent times.

SOME FLORISTIC CHANGES

The vegetation and individual plant species of pre-settlement Indiana were still adjusting to climatic changes and soil development following the glacial retreat when clearing and other land-use changes began. Plant species, as well as animals, are continually on the move, adjusting their distribution ranges as landscapes and their associated environments change. If conditions become suitable and propagates are available for dispersal, they will arrive.

Sometimes in a fragmented landscape such as Indiana now is, it may be necessary that a habitat island be relatively large in order for an invading plant species to "find" it--much as a larger target is easier to hit. For example, some species that are rare or unique in the state apparently haw arrived at the 65 ,OOO-acre Jefferson Proving Ground (JPG) in southeastern Indiana since it 1\,,5 acquired by the federal government in 1939. Just recently, the rare climbing fern (Lygodium palmatum) was discovered in JPG as a new floral addition to the state. Other species that have extended their ranges into Indiana at other locations by dispersal of airborne seeds or spores include spring ladies;-tresses orchid, the netted chain-fern, and three new species of Eupatorium, a genus which also includes the more common Joe-Pye weed, white snakeroot, and boneset. All of these floral additions were unknown in Indiana prior to 1975.

Additional new species such as primrose willow and Virginia buttonweed apparently arrived from the south by entering Indiana along the Ohio River. Some species of primarily western distribution have used highways, roads, and railroads as artificial migration corridors to extend their ranges eastward into Indiana. Foxtailbarley, which thrives on saline soils, now waves its glistening, longawned, grassy flower heads along many highway and road margins of the state in midsummer and autumn. Similarly, sea blite, stinking marigold, and freewaysedge are western species now occurring here. During and following the Great Depression, the abandonment of once-cultivated fields created habitats that permitted the increase and spread of such old-held and prairie species as prairie three-awn and little bluestem grasses, hairy-sheathed sedge and two lovely wildflower species, little ladies'-tresses orchid and plains blazing star. Similarly, native species in Indiana that were once rare but are now relatively common and expanding their ranges (perhaps because of genetic adaptations to disturbance) include oval ladies'-tresses orchid and southern ground-cedar.

But some of our best-loved plant species (including favorite trees) have declined drastically in recent times. American chestnut was lost as a forest species in Indiana (as elsewhere in the eastern US) as the result of an introduced fungal pathogen whose cankers girdle and kill adult trees. Occasional root sprouts from chestnut stumps are still found in southern Indiana, but fruiting trees are exceedingly rare. Our most prized shade and street tree, the American elm, has been essentially eliminated from both urban sites and natural forests as mature trees. The introduced Dutch elm fungus in tandem with phloem necrosis, a stem disease, has devastated both American and slippery elm populations, but the former has been hardest hit. More recently, all ten species of dogwoods native to Indiana, including the beautiful flowering dogwood, have become infested internally by a fungal blight (Discula clestructiva) that appears to be increasing mortality rates among dogwoods in Indiana and elsewhere in the eastern U.S. Hopefully, these and other declining species can hold on as native populations until we can find ways to help restore them to their former importance.

Frequently it is quite difficult to determine if a species is expanding irs geographic area, or if its range is contracting. One clue to changing distributions is the residence of outlier populations disjunct from the geographic range the species occupies generally A common geographic principle, though by no means universally true, is that population advances across a landscape are characterized by a more uniform range margin, whereas retreats typically have outlier populations along the trailing edge. For example, northern relict species such as eastern hemlock, Canada yew, and eastern white pine lag behind as scattered stands in the cool microclimates of refugia along the Sugar Creek Valley on the deglaciated landscape of Montgomery and Parke counties, and most likely represent holdovers of retreating species.

Species ranges and the distribution patterns of individual animals are continually varying as the populations fine-tune their adjustments to the constantly changing environment. When tolerance limits are exceeded for any length of time, populations dwindle to zero, at least locally. Our hope is that continued human manipulation of remaining habitats will not create conditions whereby additional species are extirpated from Indiana, Perhaps long-existing trends in habitat destruction and environmental change can be reversed, thereby allowing threatened species to recover through the efforts of restoration ecology Perhaps surveillance by our capable staff of the Indiana Natural Heritage Program will permit us to respond favorably to any future threats to our plant and animal neighbors.

"To do science is to search for repeated patterns, not simply to accumulate facts, and to do the science of geographical ecology is to search for patterns of plant and animal life that can be put on a map. The person best equipped to do this is the naturalist who loves to note changes. " -Robert H MacArthur, Geographical Ecology Patterns in the Distribution of Species (1972)