From Fish Farms to Invasive Species
People brought the Pacific oyster to Europes North Sea in the 1960s as a commercial shellfish. This oyster requires a very specific, warm-water temperature to reproduce. The cold North Sea was not the right temperature, so people believed the species was safely confined to aquaculture farms. Unfortunately, water temperatures have changed due to global warming. In the 1990s, the Pacific oyster started reproducing successfully in the North Sea, and it has begun displacing some of the native oyster species.
A species range is the area where a particular species can be found during its lifetime. Species range includes areas where individuals or communities may migrate or hibernate.
Every living species on the planet has its own unique geographic range. Rattlesnakes, for example, live only in the Western Hemisphere, in North and South America. The U.S. state of Arizona is part of the range of 13 species of rattlers, making it the state with the greatest variety of these reptiles. Only four species of rattlers have a range east of the Mississippi River.
Some species have a wide range, while others live in a very limited area. For example, the range of the leopard (Panthera pardus) encompasses more than 20 million square kilometers (7.7 million square miles) across Africa, the Middle East, and Asia. Another type of wild cat, the rare Iriomote cat (Prionailurus iriomotensis), lives only on Japan’s Iriomote Island. Its range is only about 292 square kilometers (113 square miles).
Species with ranges that cover most of the Earth are said to have a cosmopolitan distribution. Blue whales (Balaenoptera musculus) have a very cosmopolitan distribution—they are found in every ocean on the planet. Human beings (Homo sapiens) also have cosmopolitan distribution, inhabiting every continent except Antarctica.
The Antarctic midge (Belgica antarctica), on the other hand, is found only in Antarctica—it is endemic, or native, to that continent. Species with a limited range, like the Antarctic midge or Iriomote cat, have an endemic distribution.
Species with two or more ranges that do not connect with each other have a disjunct distribution. Mountain ranges, deserts, or oceans sometimes separate the ranges of these species. The kudzu plant (Pueraria lobata) has a disjunct distribution in the southern islands of Japan and the southeast Asian mainland, as well as the United States. The Eurasian pygmy shrew (Sorex minutus) has a disjunct distribution in Europe and the island of Ireland.
Factors Contributing to Species Range
Several factors determine species range. Climate is one important factor. For example, polar bears (Ursus maritimus) travel on sea ice, so the limit of their range is determined by the amount of sea ice that forms in the winter. Many species of cacti and other succulent plants are adapted to live in very hot, dry climates. They cannot survive in areas with lots of rainfall or long periods of cold.
Food sources also affect species range. Living things can only survive in regions where they can find food. The giant panda (Ailuropoda melanoleuca) obtains almost all of its nutrients from various species of bamboo, especially dragon’s head bamboo (Fargesia dracocephala). The natural range of the giant panda is limited to the natural range of the dragon’s head bamboo, mostly the Qinling and Minshan mountains in western China.
When a food source disappears or alters its range, species that rely on it must find another food source, extend their range, or risk extinction. The range of the Arctic fox (Alopex lagopus) is the cold, northern latitudes. It feeds mostly on small rodents such as lemmings. The Arctic fox is uniquely adapted to the Arctic and cannot change its range if lemmings become more difficult to hunt. (Lemmings are not rare or endangered. They only become more difficult to hunt when the Arctic fox must compete for the prey with other animals, such as the red fox.) However, Arctic foxes have other food sources in their range: seals, fish, and even carrion, or dead animals.
Like food, water is a critical component in a species range. Some creatures live in riparian habitats—areas on the banks of rivers or streams. Animals such as river otters depend on the river’s ecosystem for survival. When people dam rivers to make reservoirs or produce electricity, the wildlife downstream often cannot survive. Their range has been cut off. In fact, loss of habitat is the leading threat to endangered species today.
Access to water can also determine a species range for animals that do not have a freshwater habitat. Many species of African elephants migrate more than 60 kilometers (100 miles) to find watering holes and streams in the dry season. The search for fresh water determines the limits of their range.
Landscape features can also determine species range. The mountain goat (Oreamnos americanus) got its name because it lives in mountainous areas. Its large range extends throughout western North America: the Rocky Mountains, the Cascade Mountains, and the Chugach Mountains.
Changes in Ranges
Species range can change over time. Many species have different summer and winter ranges. Canada geese (Branta canadensis) spend summers in Canada and the northern United States, but migrate to the southern U.S. and northern Mexico during winter.
Some species also have different ranges for breeding. Many species of Pacific salmon have a freshwater range and a saltwater range. They hatch and spend their early lives in freshwater rivers and streams. On reaching adulthood, they migrate to the ocean. Some salmon stay within a few hundred kilometers of their home stream, while others, like the Chinook salmon (Oncorhynchus tshawytscha), can travel as far as 4,023 kilometers (2,500 miles). When it is time to reproduce, salmon return to their freshwater range. The eggs hatch in the fresh water, and the cycle begins again.
Humans have changed the range of many species by transporting them. These are “introduced species.” Introduction can happen accidentally, when a living thing “hitches a ride” with unsuspecting human travelers. This has been happening for thousands of years. The disjunct distribution of the Eurasian pygmy shrew, for instance, is probably a result of introduction. Scientific research shows that the Irish population of Eurasian pygmy shrews appeared about the same time that Europeans sailed to Ireland and established settlements there.
People continue to accidentally introduce species to new ranges today. The natural range of the zebra mussel (Dreissena polymorpha) is central Asia, in lakes and the Black and Caspian seas. In the 20th century, these animals were accidentally transported beyond Asia when they attached themselves to large cargo ships. They eventually reached the Great Lakes of North America, where they established a new range.
Zebra mussels, like many introduced species, are a major threat to native species of the area. For example, the brown tree snake (Boiga irregularis), native to Australia and nearby islands, was accidentally transported to Guam through air or ship cargo. Few local animals could defend themselves against this new predator, and the brown tree snake caused the extinction of many native birds and lizards on the island. Because some of the animals it killed were pollinators, many native plant species also declined.
People also introduce species to new ranges on purpose. People transport plants and animals to use for food, decoration, pest control, or pets. One of the most famous examples of an introduced species is the Burmese python (Python molurus bivittatus) in the Florida Everglades. People kept the snakes, whose native range is the jungles of southeast Asia, as pets. The care and feeding of Burmese pythons is intense, and some pet owners who could not support the reptiles simply released the snakes into the wetlands of the Everglades. The pythons thrive in the Everglades, which has a hot, humid climate similar to southeast Asian jungles. Pythons compete with native species like the American alligator for food and resources.
Plants can also be introduced to new ranges, and threaten endemic species. The purple loosestrife (Lythrum salicaria), with its pretty lavender-colored flowers, hardly seems threatening. But this plant has done extensive damage to North American wetlands. People brought the flower from Europe in the 1800s for decoration and medicinal purposes. The plant grows rapidly along river banks and other freshwater wetlands. It produces many seeds, and is pollinated by many insect species. As a result, it can spread quickly, reduce water flow, and crowd out native plants such as cattails.
In some of the wetlands of the Chesapeake Bay, in the U.S. state of Maryland, purple loosestrife has displaced more than half of the native plant species. It provides poor food, shelter, and nesting sites for local wildlife. Its dense, snarled root system can clog drainage and irrigation ditches.
Effects of Climate
The Earth’s changing climate affects species range. Ranges can move, shrink, or grow as a result of climate changes. Sometimes, changes in climate can even cause species to go extinct. For instance, many animals that were adapted to Ice Age conditions—such as mastodons, mammoths, and saber-toothed cats—no longer exist in today’s warmer climate.
Earth’s climate has changed many times over the course of our planet’s lifespan. These changes happen as a result of natural events and cycles. Today, human activities are contributing to climate change. This global warming has an effect on the ranges of many organisms.
European bee-eaters (Merops apiaster), for instance, are brightly colored birds native to the Mediterranean coast of Europe and northern Africa. In the 20th century, bee-eaters began to be spotted in central Europe. Today, their range includes nesting sites in Germany and the Czech Republic—countries that once would have been too cold for these warm-weather birds.
In aquatic environments, climate change favors warm-water species. On the Atlantic coast of the U.S., brown shrimp, grouper, and southern flounder are expanding their range from the Carolinas to the Chesapeake Bay. Unfortunately, creatures that have traditionally lived in the bay, including rockfish, sturgeon, and clams, are threatened by warming temperatures and increased competition for resources.
Species that are considered pests or that spread diseases can wreak havoc on local populations when their ranges expand. For example, many species of the spruce budworm are destructive to evergreen trees in western North America. The insect’s traditional range includes the forests of the U.S. state of Washington and the Canadian province of British Columbia. Warming temperatures are allowing this caterpillar to eat its way northward, all the way to the U.S. state of Alaska, for the first time in history. The expanded range of the spruce budworm threatens the American and Canadian timber industries.
Many species of mosquito are expanding their range as the climate grows warmer. Mosquitoes carry a variety of diseases that can be deadly to people: malaria, encephalitis, West Nile virus, and yellow fever. Many communities and health-care organizations are unprepared for the increased number of cases brought by mosquitoes’ expanded range.
Term Part of Speech Definition Encyclopedic Entry antler Noun
horn-like bony outgrowth on deer and related animals.
having to do with water.
to produce offspring.
goods carried by a ship, plane, or other vehicle.
the U.S. states of North Carolina and South Carolina.
flesh of a dead animal.
larva of a butterfly or moth.
Chesapeake Bay Noun
large, shallow estuary of the Susquehanna and other rivers that flow through the U.S. states of Maryland, Virginia, West Virginia, Delaware, Pennsylvania, and New York and the capital of Washington, D.C., before emptying in the Atlantic Ocean.
all weather conditions for a given location over a period of time.
Encyclopedic Entry: climate climate change Noun
gradual changes in all the interconnected weather elements on our planet.
Encyclopedic Entry: climate change continent Noun
one of the seven main land masses on Earth.
Encyclopedic Entry: continent cosmopolitan distribution Noun
range of a species found across most parts of the Earth.
structure built across a river or other waterway to control the flow of water.
having parts or molecules that are packed closely together.
a harmful condition of a body part or organ.
disjunct distribution Noun
range of a species found in two or more geographic areas that are not connected to each other.
in the direction of a flow, toward its end.
dry season Noun
time of year with little precipitation.
community and interactions of living and nonliving things in an area.
Encyclopedic Entry: ecosystem electricity Noun
set of physical phenomena associated with the presence and flow of electric charge.
sometimes fatal disease, often transmitted by mosquitoes, affecting the brain.
endangered species Noun
organism threatened with extinction.
Encyclopedic Entry: endangered species endemic Adjective
native to a specific geographic space.
endemic distribution Noun
range of a species found in a very limited geographic area.
to form or officially organize.
vast swampy region flowing south of Lake Okeechobee in Florida.
tree that does not lose its leaves.
to enlarge or continue.
no longer existing.
process of complete disappearance of a species from Earth.
popular food fish with a flat body.
ecosystem filled with trees and underbrush.
water that is not salty.
global warming Noun
increase in the average temperature of the Earth's air and oceans.
Encyclopedic Entry: global warming Great Lakes Noun
largest freshwater bodies in the world, located in the United States and Canada. Lake Huron, Lake Ontario, Lake Michigan, Lake Erie, and Lake Superior make up the Great Lakes.
bottom-dwelling marine fish native to non-polar waters.
environment where an organism lives throughout the year or for shorter periods of time.
Encyclopedic Entry: habitat havoc Noun
to reduce activity almost to sleeping in order to conserve food and energy, usually in winter.
Ice Age Noun
last glacial period, which peaked about 20,000 years ago.
to live in a specific place.
type of animal that breathes air and has a body divided into three segments, with six legs and usually wings.
two or more individuals or communities that rely on each other for survival.
introduced species Noun
a species that does not naturally occur in an area. Also called alien, exotic, or non-native species.
Iriomote cat Noun
small wild cat native to Iriomote Island, Japan.
irrigation ditch Noun
channel dug between a source of water and crops. Also called an irrigation canal.
tropical ecosystem filled with trees and underbrush.
the geographic features of a region.
Encyclopedic Entry: landscape latitude Noun
distance north or south of the Equator, measured in degrees.
Encyclopedic Entry: latitude malaria Noun
infectious disease caused by a parasite carried by mosquitoes.
one of many extinct species of large animals related to elephants, with long, curved tusks. The last mammoths became extinct about 5,000 years ago.
one of many extinct species of large animals related to elephants. The last mastodons became extinct about 11,000 years ago.
tiny insect related to the fly.
to move from one place or activity to another.
insect capable of piercing the skin and sucking the blood of animals.
aquatic animal with two shells that can open and close for food or defense.
nesting site Noun
place where birds build nests and raise their young.
substance an organism needs for energy, growth, and life.
Encyclopedic Entry: nutrient ocean Noun
large body of salt water that covers most of the Earth.
Encyclopedic Entry: ocean pest Noun
harmful or annoying person or thing.
pest control Noun
process of removing unwanted species (pests) from a specific geographic area.
animal, object, or force such as wind that transfers pollen from one plant to another, allowing seeds to develop.
animal that hunts other animals for food.
animal that is hunted and eaten by other animals.
non-venomous snake native to tropical climates.
venomous reptile, native to North America, with hollow joints at the end of its tail that can be rattled to warn predators.
animal that breathes air and usually has scales.
natural or man-made lake.
Encyclopedic Entry: reservoir resource Noun
available supply of materials, goods, or services. Resources can be natural or human.
having to do with a river or stream.
large stream of flowing fresh water.
Encyclopedic Entry: river river otter Noun
mammal, related to the weasel, that lives near streams and rivers.
marine fish that lives near rocky shores.
order of mammals often characterized by long teeth for gnawing and nibbling.
saber-toothed cat Noun
one of many extinct species of large, wild cats with long, sharp teeth.
sea ice Noun
frozen ocean water.
community or village.
structure that protects people or other organisms from weather and other dangers.
type of small mammal resembling a mouse with a long nose.
group of similar organisms that can reproduce with each other.
species range Noun
native, geographic area in which an organism can be found. Range also refers to the geographic distribution of a particular species.
Encyclopedic Entry: species range spruce budworm Noun
moth larva that is a destructive pest to evergreen trees.
type of marine or freshwater large, long, bony fish.
type of plant that has thick leaves and stems for storing water.
to develop and be successful.
wood in an unfinished form, either trees or logs.
one of a kind.
watering hole Noun
small pond or spring where animals travel to drink.
Western Hemisphere Noun
area of the Earth west of the prime meridian and east of the International Date Line.
West Nile virus Noun
infectious disease spread by mosquitoes, with symptoms ranging from mild flu to possible death.
area of land covered by shallow water or saturated by water.
Encyclopedic Entry: wetland wildlife Noun
organisms living in a natural environment.
to inflict or bring about something painful.
yellow fever Noun
infectious disease spread by mosquitoes, primarily affecting the liver.