Biodiversity and invasive species
A fall in the number of species of living things in a unit area of the biosphere is called loss of biodiversity. A fast-changing environment drives it.
For example, parts of some plants grown to decorate the environment are thrown away when they are pruned, and they spread fast in other environments. Likewise, when ornamental fish such as catfish grow large they are released into streams and canals. These species take over the other species of the environment and have become a threat.
Invasive species
Because the environment has been changed, invasive plant and animal species suited to the changed environment arise in place of the species that lived there for a long time. Examples: the giant sensitive plant (yodha nidikumba), rainbow trout, andara plants, water hyacinth (gadapana).
Assignment 15.8
Find out about the invasive plant and animal species spread in Sri Lanka and prepare a report.
Economic loss
Once polluted, extra effort and expense must be spent to keep the environment in proper condition.
Why invaders win
A species brought from another country arrives without the predators, diseases and competitors that kept it in check at home. With nothing to hold it back, it can breed faster than the local species and crowd them out of the food web. Water hyacinth covers a whole tank and blocks the light; catfish eat the eggs and young of native fish. Each local species lost removes links from the food web, so biodiversity falls and the ecosystem becomes easier to upset — and removing the invader costs a great deal of money, part of the economic loss of pollution.
Fewer species, more invaders
Rapid change reduces biodiversity and lets invasive species such as water hyacinth and catfish take over; restoring the environment costs money.