Organisms may appear to be alike and be different species. For example, Western meadowlarks Sturnella neglecta and Eastern meadowlarks Sturnella magna look almost identical to one another, yet do not interbreed with each other — thus, they are separate species according to this definition. Organisms may look different and yet be the same species. For example, look at these ants. You might think that they are distantly related species.
In fact, they are sisters—two ants of the species Pheidole barbata , fulfilling different roles in the same colony. Many characteristics can vary within a single species. We already pointed out two of the difficulties with the biological species concept: what do you do with asexual organisms, and what do you do with organisms that occasionally form hybrids with one another? Other difficulties include:. The Rights Holder for media is the person or group credited.
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Reproduction is the production of offspring. There are two main forms: sexual and asexual reproduction. In sexual reproduction, an organism combines the genetic information from each of its parents and is genetically unique.
In asexual reproduction, one parent copies itself to form a genetically identical offspring. Sea turtles are an example of an animal that reproduces sexually, a volvox green algae is an example of an organism that reproduces asexually, and a brittle star can reproduce in either way.
Help your students understand the sexual and asexual reproduction with these classroom resources. The theory of natural selection was explored by 19th-century naturalist Charles Darwin. Natural selection explains how genetic traits of a species may change over time.
This may lead to speciation, the formation of a distinct new species. Select from these resources to teach your classroom about this subfield of evolutionary biology. But the first formal genetic study was undertaken by a monk named Gregor Mendel in the middle of the 19th Century. Mendel bred peas and noticed he could cross-pollinate them in certain ways to get green or yellow seeds. Today, the field of genetics is breaking new ground searching for new ways to treat disease or develop crops more resistant to insects or drought.
Empower your students to learn about genetics with this collection of resources. A keystone species helps define an entire ecosystem. Without its keystone species, the ecosystem would be dramatically different or cease to exist altogether. A species is often defined as a group of organisms that can reproduce naturally with one another and create fertile offspring. However, the classification of a species can be difficult—even riddled with controversy. Join our community of educators and receive the latest information on National Geographic's resources for you and your students.
Skip to content. Twitter Facebook Pinterest Google Classroom. Encyclopedic Entry Vocabulary. One difference between the two subspecies is their migration behavior. Both groups of birds breed in North America, then fly south in winter. But russet-backed thrushes migrate down the west coast to land in Mexico and Central America.
Olive-backed thrushes fly over the central and eastern United States to settle in South America. Which directions do hybrids get? To investigate, Delmore trapped hybrid birds in western Canada. She placed tiny backpacks on them. A light sensor in each backpack helped record where the birds went. The birds flew south to their wintering grounds, carrying the backpacks on their journey. The next summer, Delmore re-captured some of those birds back in Canada. The length of the day and timing of midday differs depending on location.
They flew somewhere down the middle. These treks, though, took the birds over rougher terrain, such as deserts and mountains. That could be a problem because those environments might offer less food to survive the long journey. But that strategy might also cause problems.
Normally, birds learn cues on their way south to help them navigate back home. They might notice landmarks such as mountains. But if they return by a different path, those landmarks will be absent.
One result: The birds migration might take longer to complete. These new data might explain why the subspecies have remained separate, Delmore says.
Following a different path may mean that hybrid birds tend to be weaker when they reach the mating grounds — or have a lower chance of surviving their yearly journeys.
If hybrids survived as well as their parents, DNA from the two subspecies would mix more often. Eventually these subspecies would fuse into one group. Sometimes, hybrids are shaped differently than their parents. And that can affect how well they avoid predators. Anders Nilsson recently stumbled onto this finding. He is a biologist at Lund University in Sweden. In , his team was studying two fish species named common bream and roach not to be confused with the insect. Both fish live in a lake in Denmark and migrate into streams during winter.
To study their behavior, Nilsson and his colleagues implanted tiny electronic tags in the fish. The team used a device that broadcast a radio signal. Tags that received the signal sent back one of their own that the team could detect. But the researchers noticed other fish that looked like something in between. The main difference was their body shape. Viewed from the side, the bream appears diamond-shaped with a taller middle than its ends.
The roach is more streamlined. Roach and bream must have mated to produce those in-between fish, the scientists thought. That would make those fish hybrids. And so the team began tagging those fish, too.
Fish-eating birds called great cormorants live in the same area as the fish. Cormorants gobble fish whole. Afterward, they spit out unwanted parts — including electronic tags. And the hybrids appeared to fare the worst. For their efforts, the team found 9 percent of the bream tags and 14 percent of the roach tags.
But perhaps their shape makes them easier targets. Its diamond-like shape makes bream hard to swallow.
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