Invasive species can compete and prevail with native species for resource use or habitat, thus changing the structure of the community and leading it towards extinction.

For example, a fish species known as grass carp can pose a danger to fish and fisheries in a habitat.

Invasive species are capable of causing extinctions of native plants and animals, reducing biodiversity, competing with native organisms for limited resources, and altering habitats. This can result in huge economic impacts and fundamental disruptions of coastal and Great Lakes ecosystems.

New species that are not included in the natural fauna of a particular ecosystem and that come to a region from outside in different ways are called invasive species. The establishment of new corridors between various geographic regions with the developing transportation technology has significantly increased the rate at which many living things pass from one ecosystem to another. As exotic species occupied the habitats of natural communities (bioistyla), local species that could not cope with this spread began to disappear.Invasive species that settle in new areas, begin to be observed naturally in these areas, then multiply and cause a decrease in biodiversity, also negatively affect human life. Invasive species; It can consist of microorganisms, plants, animals, pathogens, detritivores, parasites, herbivores and omnivores. These species cause damages in new ecosystems that they reach in different ways.

The direct threats of invasive species include preying on native species, outcompeting native species for food or other resources, causing or carrying disease, and preventing native species from reproducing or killing a native species' young.

There are indirect threats of invasive species as well. Invasive species can change the food web in an ecosystem by destroying or replacing native food sources. The invasive species may provide little to no food value for wildlife. Invasive species can also alter the abundance or diversity of species that are important habitat for native wildlife. Aggressive plant species like kudzu can quickly replace a diverse ecosystem with a monoculture of just kudzu. Additionally, some invasive species are capable of changing the conditions in an ecosystem, such as changing soil chemistry or the intensity of wildfires.

Which can lead to environmental havoc. 

Without anything to keep their population in check, some invasive species—especially the prolific breeders—often flourish. They can destroy native plants, gobble up native animal populations and introduce disease, upending the delicate balance of organisms that provide food or support for each other, or provide a check on each other’s growth. Extinctions have proliferated.

Globalization has fueled the problem of invasive species. When European colonizers sailed to the Americas, they disrupted existing animal populations while also introducing new ones. Invading creatures have long affected the United States, as people imported new animals for study, sport, fur or even the love of Shakespeare. (Yes, really.) Here are seven invasive species that still pose a threat to the U.S. today.

Portugal has a platform of information and citizen-science about invasive plants, which aims to raise awareness about biological invasions, make known the different invasive plants in Portugal and stimulate public participation in mapping of species, the control of plant populations and education. (https://invasoras.pt/en)

According to this platform, in mainland Portugal, over the last two centuries, and especially in more recent decades, the number of exotic species (including casual, naturalized and invasive) has increased significantly, currently amounting to about 670 species, which corresponds to approximately 18% of the total native flora (Almeida and Freitas 2012).

The photograph below shows an invasive species that we can see in my school yard. It is called Erva das Pampas or Plumas but its scientific name is Cortaderia Selloana.