What is an ecosystem?

All the living things around us play a vital role in nature but some species can disrupt that balance - we call them invasive species. So before understanding what threat they pose, we’ve got to know what was there in the first place - and how that system is connected and set up. Izzie Clarke met up with Andrew Tanentzap at the Cambridge University Botanic Garden...

Andrew - So we’re right in the heart of Cambridge, at the Cambridge University Botanic Garden, surrounded by many beautiful native plants but also some really great examples of introduced species that are really important.

Izzie - Now you look into exploring ecosystems, so what exactly is an ecosystem?

Andrew - Ecosystems are all of the living things in a place, so this will include plants and insects, and larger animals, and small microscopic bacteria and fungi that we can’t see, and how they all interact with one another and their surrounding physical or non-living environment.

Izzie – So it’s almost like a giant web, I'm picturing lots of interactions from plants to animals?

Andrew - Exactly. So it might be just like that nursery rhyme a lot of people might remember from their childhood, with the cat eating the mouse, that ate the spider, that ate the fly. So it involves all of these interactions among organisms that live in a place and that’s what really defines ecosystems.

Izzie – And what happens if you introduce something new into that system because it sounds like there’s quite a lot to balance?

Andrew – Right, exactly. Many ecosystems have evolved these interactions that I talked about over millions of years so there’s a very sort of delicate balance amongst the species that make up these ecosystems. So the real risk with introducing novel species is that they can disrupt effectively, that balance amongst all the organisms that have been in this place for a really long time.

Izzie - Now we are standing in front of what I can only describe as a history, almost a timeline, of plants. So what’s actually going on here?

Andrew - We are at the chronological bed in the Botanic Garden and this charts a timeline of plant introductions to Britain, all the way going back to the Romans, up to the present day. Now a lot of these species, they’ll be introduced for our gardens, so we can see snowdrops that will be out flowering this time of year. But there are also other species that are really useful in our everyday lives for food, so things like the cherry tomato all the potato that were introduced from South America.

But at the same time there are also some of these species that can be real nuisances in the natural environment. Some of the ones that we’ve seen, not here in the bed but walking around the garden, has been the rhododendron for example, that has escaped from many gardens and poses a real problem to many British woodlands.

Izzie - How is that a problem? You see them everywhere!

Andrew - They’re problematic because they displace the native species and, in many cases, they might be more competitive than the native species that live here already. For example, because they have different predators that don’t exist in their new range, or they produce chemicals to deter other species from interacting with them. And the species that live here aren’t adapted to those forms of warfare and that allows these species to really take hold and displace many of the native species that live in these ecosystems.

Izzie – Gosh. So they're brought in but because there aren't things like predators or their usual threats they can almost, quite literally get their roots in, and take over a place?

Andrew – Exactly, that's the real risk. And when they displace many of those native species, along with that loss of those species so too do we lose many of the benefits that many of those species provide.

Izzie - And can it just be plants that are an invasive species?

Andrew - Certainly not. A really good example in the East of England is the Chinese water deer that’s been introduced from Asia. It’s absolutely thriving in the Fens, this watery, marsh-like habitat all around Cambridge. We’ve done some research on the impacts of deer around Cambridge and so what happens is they have a tremendous appetite for tiny little tree seedlings. And so what happens is that as the big trees get old and die, there aren’t these little trees to replace them.

Izzie - So what actually turns something from being an alien, a non-native species into an invasive species?

Andrew - There are a few defining characteristics. Some of them are going to be really short generation time and the ability to produce a lot of offspring, so it doesn’t take very long to reach sexual maturity. And then when the organism does, it’s just swamping the environment with offspring. And another, third, important factor is going to be the ability to disperse, to move out into the landscape. That’s really going to heighten the likelihood that an alien species becomes invasive and a real nuisance.

Here in the systematic bed that we are looking at is the artichoke that is introduced from the Mediterranean and so we can cultivate it here with relatively little concerned that it’s going to get out of hand because the climate is so different. And that’s really different from other species like Japanese knotweed that some of your listeners might be familiar with, where there is a real risk.

Izzie - Because that’s a real problem, I mean he is now impacting people’s homes. So it’s not just, I've got this pesky weed in my garden, it's having a real knock-on effect. And if an invasive species got a bit out of hand, what have we got to lose?

Andrew - Everything. So it’s not just the tremendous cost to infrastructure, but also there’s this tremendous risk to natural ecosystems and all of the benefits that they provide to people in terms of purifying our drinking water, giving us clean air, giving us lots of biodiversity that has this sort of intrinsic value to us in terms of recreation and cultural value. So basically, we’ve got everything to lose, more than money can buy.