Part 4 You will hear part of an ecology lecture about invasive species of plants and animals.

First, you have some time to look at questions 31 to 40.

Now listen carefully and answer questions 31 to 40.

Today, I'm going to talk about invasive species.

Let me start by saying what an invasive species is, and what it's not.

Invasive species are any animal or plant that is introduced into an environment by humans, and which is then harmful to that environment.

It's important to be clear that not all introduced species are invasive.

Many introduced or non-native species thrive in new areas without posing any threat.

In some cases, invasive species have changed the natural world beyond recognition.

So let's look at the different ways they can be problematic.