Biodiversity at Risk

Humans endanger biodiversity when they introduce invasive species, or non-natives that have the ability to out-compete native species. In 1890, the American Acclimatization Society released 16 European starlings in New York City’s Central Park. The organization’s poetic goal was to establish populations of every bird mentioned in Shakespeare’s works in North America. In their new home, the starling population grew exponentially—today, an estimated 150 to 200 million inhabit North America and compete with eastern bluebirds, tree swallows, northern flickers, and other birds for nesting sites. Starlings also cause an estimated $800 million in damage to U.S. agriculture each year.

The Norway maple is another example of an invasive species. It was introduced by British horticulturalists to North America in the mid-1700s, and grew in popularity in the 1870s and 1880s in American cities as an “ornamental variety” that adapted well to urban streets and parks. Soon, Norway maples “escaped” the city and began to dominate native forests. These trees produce large quantities of seeds that can quickly germinate. When full-grown, Norway maples create dense shade and displace native trees and other plants.

Humans also endanger biodiversity through their impacts on climate change. Climate change will result in changes to temperature and precipitation patterns, which will modify the distribution of plants and animals and disrupt food webs. Climate change is very complex, making it impossible to know exactly how each species will respond to it--not all species will be adversely affected. We can, however, use our existing knowledge of historic species ranges and habits to predict how climate change will affect them. These mussels, for example, may soon find their midwestern habitats unsuitable to continue living in.

Many of the passenger pigeons in the Chicago Academy of Sciences were "collected" from meat markets during the late 1800s and early 1900s. These birds were a common food source.

Restoration often works best when it focuses on providing quality habitat. Beavers are the largest rodents native to North America and are known for their ability to construct lodges and dams that help to create wetland habitats. During the 1700s and 1800s, beaver fur was in great demand for hats and coats. Millions of beaver were killed, almost to the point of extinction. Today, however, their populations have recovered and can be found in the Chicago region.

Zoos, like the one where this elephant lived, can play an important role in conservation.

Pika are adorable relatives of rabbits that live on the talus slopes of mountains worldwide. During the summer, they make hay from the flowers and grasses of surrounding fields, which they later eat during the winter. Pika live on talus slopes because they offer shelter from predators, but also because they exist on higher parts of mountains where it is relatively cool year-round. Brief heat waves of more than 77° F (25°C) can kill pikas. Pikas also need the weather to cooperate in order for them to make hay—too wet and the hay will mold, too dry and the plants they harvest won’t be able to grow.

Redwoods are the world’s tallest trees, bristle cones are the oldest, and aspen cover the most ground. To attain such extremes, these species require a stable climate for thousands of years. If the climate becomes unsuitable for reproduction, adult trees—which tolerate extremes that would kill seedlings—may still live for decades or centuries, but the forest will eventually disappear.

One of the world’s 23 species of crocodilians, the American alligator lives throughout most of the southeastern United States. Like all crocodilians, it eats almost any kind of meat, but only hunts from water. The water also offers shelter from predators and extreme temperatures. Crocodilians, like many other reptiles, have “temperature-dependent sex determination.” A 1.8 °F (1°C) change in temperature could produce all males or all females, and a gender imbalance could cause species to go extinct.

Rats are another diverse group of rodents that can be found all around the world. Two species, the black rat and the brown rat, are perhaps best known as pests that spread disease and destroy food supplies. Brown rats prefer cool weather. Because they live underground, they can avoid a few hot days just by staying home. If it stays hot for too long, though, the tree-climbing black rat will soon take over the territory.

Franklin's ground squirrel, a state threatened species in Illinois, could face possibly-insurmountable challenges adapting to climate change. Franklin's ground squirrel is a grassland mammal that inhabits areas with tall, dense herbaceous cover. Such areas are fragmented even in its current Midwestern range. If climate change forced this species to migrate north, the availability of suitable habitat would severely limit the establishment of new populations.

Unionids are a group of freshwater mussels that reach their greatest diversity in the United States, and that also supply freshwater pearls. Unionids, including the scale shell pictured here, are the world’s most endangered group of animals, in part because they require such high quality water conditions. Dams and diversion of streams can destroy local populations. When runoff deposits excess sediment or nutrients into the water, or when it changes the water temperature or stream flow, mussels may also be negatively impacted. Although unionids can live in warmer water, they require seasonality to stimulate reproduction. Even if they could reproduce, it’s likely that the fish populations they need as larval hosts would also be negatively affected.

Orchids are usually considered tropical flowers, but did you know that there are many native to the United States, including nearly 50 species found in Illinois? Unfortunately, half of these are gone or nearly so. Like tropical orchids, our native species are a very diverse group that require specific conditions to grow successfully. Our native orchids become inactive during the winter, but an unseasonal cold snap can easily kill new flowers in spring, preventing reproduction. Similarly, our orchids can grow well in hot weather, but if it warms up too soon orchids may flower before their pollinators are active, preventing seed creation. Finally, orchids do not disperse very well, meaning that when environmental conditions do change, they have a difficult time adjusting.

Black bears are omnivores that eat a variety of plants and animals. These large mammals need a lot of space—the typical territory for a male black bear is between 15 and 80 square miles. As trappers and hunters killed bears for their valuable fur and meat, and as farmers destroyed large tracts of natural habitat to make room for agriculture, bears were eliminated from their historic range in the Midwest. Bears still live in much of the rest of the country, but their existence may be threatened as climate change affects access to resources, and as humans continue to encroach on suitable habitat.

The beautiful adult stage of the Karner blue butterfly that you see here is the last of a series of miraculous transformations that began with an egg laid on a specialized host plant. For their host plant, Karner blue butterflies only use lupine that naturally grows in open clearings along the dunes and forests of the Great Lakes. Hot weather causes butterfly larvae to develop more rapidly, causing subsequent generations to be small and weak. Hotter and/or drier weather can also change the time of lupines’ germination and blooming, potentially leaving young Karner blues with no food. Karner blue caterpillars are vulnerable to bacterial and fungal infection if weather gets too wet, though.

The earliest dragonflies lived in ancient swamps that formed today’s coal deposits. Although we see dragonflies flitting about streams, ponds, fields, and maybe our own backyards, they spend most of their lives underwater as voracious predators. Many dragonfly species do very well in hot climates, but as temperature increases, nymphs (dragonfly youngsters) may transform into adults more quickly. Conversely, weather that is too cold will kill adult dragonflies.

Lynx look a lot like bobcats—in fact, they are closely related. The biggest difference between the two species is the luxurious fur and huge padded feet of the lynx that allow it to survive in areas with cold deep snow. Hot spells can cause snow to melt early, making it hard for lynx to travel and hunt. Lynx might starve to death or have their territory invaded by bobcats, coyotes, and other competitors. Wet weather can be dangerous for lynx as well because it can saturate their coats and expose them to hypothermia (dangerously low body temperature).

Kirtland's warblers are highly specialized birds that pass through our backyards every spring and autumn, during migration. These birds winter in the Bahamas, but, in the summer, migrate to find young jack pine stands in northern Michigan. Too-old or too-young trees are unsuitable for breeding, and forests that are too sparse are accessible to brown cowbirds, a nest parasite. Kirtland’s warblers can only nest in jack pine stands that are 6 to 15 years old—warmer and/or wetter climates promote the growth of other tree species that can outcompete jack pines. Increased droughts, on the other hand, might allow more fires to keep forests small and young, allowing jack pines to compete successfully against other trees and making more nesting habitat for Kirtland’s warblers. However, drought could also negatively affect the birds’ wintering grounds in the Bahamas.