Invasive species

Some plants and animals move to new homes.

These are called invasive species. They can hurt the land and the things living there.

They often grow or have babies very fast. This helps them take food from other living things.

When they take the food, the old friends have none left.

Sometimes people move them to new places. This can happen by accident. It can also happen on purpose.

Some plants grow over trees.

Other animals can hunt the birds in a new land. It is important to learn how to help our world stay safe.

Some living things move to new homes. These are called invasive species. An invasive species is a plant or animal that harms its new home. They can hurt the land, the water, or the money people make.

Many invasive species arrive because of people. Humans move them on purpose or by accident. They might travel on ships or in cars. This happens a lot with global trade.

Invasive species often have special traits. They might grow very fast. They might also have many babies quickly. This helps them win against native species. Native species are the ones that belong in that area.

Invasive plants can take over a space. The kudzu vine is one example. It can grow over trees.

Some animals can also cause trouble. The brown tree snake has hurt bird populations on the island of Guam.

Islands can be easy to invade. This is because the animals there may have few predators to stop the newcomers.

An invasive species is a living thing that moves to a new home and causes harm. These species can be plants, animals, fungi, or even tiny microbes. They can damage the environment or cause economic problems for people. Some invasive species might even hurt human health. While moving to new places is a natural thing, humans have changed how it happens. People often move species on purpose or by accident. This has caused many more species to spread much faster than before.

How does a species become invasive in a new place? First, a small number of individuals must arrive and survive. They often need to reproduce many times to build a strong group. Sometimes, things like ships or cars moving along highways help them arrive often. This constant arrival is called high propagule pressure. Once they are there, they look for a way to live. They might find an empty niche, which is a special role in nature. If they can grow faster than the native species, they might take all the food.

Scientists have studied these changes for a long time. In 1958, a man named Charles Elton wrote a book about this. His book was called "The Ecology of Invasion by Animals and Plants." He thought that places with many different types of life were harder to invade. Other scientists later had different ideas about this. Most research on these species did not grow much until the 1990s. Today, people study this using a field called invasion biology. This field helps us understand how to protect our natural worlds.

There are many famous examples of invasive species around the world. The kudzu vine is a plant that grows over trees in the United States. In the water, the water hyacinth can form thick mats that block light. Some animals can be very tough on new homes too. The brown tree snake has hurt many birds on the island of Guam. In New Zealand, rats and dogs arrived with settlers around the year 1300. Even domestic cats can become invasive when they live in the wild.

Many invasive species share similar traits that help them win. They often grow very fast or have many babies quickly. Some plants can even make copies of themselves without seeds. These traits help them outcompete the native species that already live there. Islands are often very easy for these species to take over. This is because island animals might not have many predators to stop them. However, the big ocean can also act as a wall to keep invaders out.

An invasive species is a non-native organism that causes harm to its new environment. These organisms can be plants, animals, fungi, or microbes. They cause damage to habitats, bioregions, and the economy. They may also threaten human health. While species moving to new areas is a natural phenomenon, humans have changed the process. Since the 20th century, human activity has increased the rate and scale of these invasions. People act as dispersal agents through both accidental and deliberate movements. This acceleration has become a serious global threat to biodiversity and social stability.

For a species to become invasive, it must first successfully establish itself. Usually, an introduced species must persist at low population densities first. They often face challenges when trying to reproduce or sustain a viable population. Sometimes, multiple introductions are required before they can truly establish. A key factor is high propagule pressure. This occurs when there are repeated opportunities for species to arrive. Examples include ship traffic between ports or vehicles traveling on major highways.

Once established, invasive species often change the balance of an ecosystem. Stable ecosystems maintain a resource equilibrium. Invasive species can disrupt this balance by outcompeting native species for food. This is especially true when resources like nitrogen and phosphorus are limited. Every species occupies an ecological niche, which is a specific role in its environment. Invaders may occupy unused niches or create entirely new ones. For example, edge effects occur when land is cleared for agriculture. This creates a boundary habitat that can host species that would not thrive elsewhere.

Scientists study these events through invasion biology or invasion ecology. Much of this research was influenced by Charles Elton. In 1958, he published "The Ecology of Invasion by Animals and Plants." Elton suggested that high species diversity makes an ecosystem harder to invade. He believed that more diverse areas had fewer unoccupied niches. However, later studies showed that large-scale ecosystems might actually be more susceptible. This debate often depends on the spatial scale of the study. Research in this field grew significantly during the 1990s. It remains an interdisciplinary field involving zoology, agriculture, and pathology.

Different systems respond to invasions in unique ways. Island ecosystems are often very prone to invasion. This is because island species frequently face few competitors or predators. This leaves many "open" niches for newcomers to fill. For instance, the brown tree snake has decimated native bird populations on Guam.

In contrast, the ocean can act as a barrier. Island nations like Australia and the Galapagos have many endemic species. These are species found nowhere else, protected by geographical isolation.

Invasive species also display specific biological traits. Many invaders are extremely resilient and grow or reproduce very quickly. Some plants use vegetative reproduction to spread without seeds. One study found that 86% of invasive species could be identified by these traits. Other invaders change the physical landscape through processes like bioturbation or bioconstruction. The Chinese mitten crab, for example, increases bioturbation and bioerosion rates.

Even native species can become invasive if humans alter the food web. The purple sea urchin harmed California kelp forests after humans overharvested sea otters.

There are many notable examples of these biological shifts. The kudzu vine is a famous example in the southeastern United States. It was originally introduced to control soil erosion, but it grew uncontrollably.

In aquatic environments, the water hyacinth forms dense mats. These mats limit light penetration and harm other organisms.

Animals like the domestic cat can also become invasive predators. In places like the Florida Keys, feral cats negatively impact local wildlife.

These examples show how deeply invasive species can reshape the natural world.