Invasive species, whether plant or animal, are often singled out as being harmful to native species, which are unable to combat the onslaught of these nasty invaders... Various initiatives, including the "Stop the knotweed" campaign organised by the ASL, aim to eradicate these species in order to relieve the pressure on native species and preserve local diversity. As you can see, invasive species are harmful to our ecosystems, but why?
A species is said to be invasive when its proliferation in a natural environment that is not its own causes drastic changes in the composition, structure and functioning of the colonised ecosystem. In order to achieve this, it needs to combine a number of specific properties, such as a high rate of multiplication, to stay one step ahead of local species, the ability to adapt to all environments and a high level of resistance to disturbance. In short, an invasive species makes a colossal mess of its surroundings, causing a considerable reduction in diversity.
But how can ONE species upset an entire balance? It's quite simple: it took millions of years for evolution to gradually select the species best suited to living together in a given environment. This balance is maintained by the presence of each element, like the mesh of a net. The invasive species will interfere with this net and disrupt it by influencing the various links until they are gradually destroyed.
Lake Geneva has also fallen victim to a number of invaders, including American crayfish, which carry a fungus that is harmless to them but fatal to our native crayfish. There is also the famous Japanese knotweed, which is pretty and decorative but a real scourge for less competitive plants, and quagga and zebra mussels, whose populations have exploded in the lake.
Native to Asia, Japanese knotweed is in balance with the species that surround it in its natural environment. They are even beneficial; for example, knotweed does not need a rich environment to develop, and colonises lava shortly after eruption, fertilising the soil and allowing other plants to recolonise these areas. Here, on the other hand, they have no place and take the place of other native plants.
In addition to their capacity to invade, the origin of their colonisation is the same: humans. Indeed, the increase in human activity through general growth, mobility and globalisation are the main vectors of these unwanted migrations.
Invasive and deadly to natural environments, invasive species are considered to be guilty. But the objective remains the same: to safeguard our ecosystems and their biodiversity!
For more information, take a look at our quarterly "Lémaniques", available free of charge on our website asleman.org :
n°60 " American invasion of Lake Geneva "
n°113 " Peloton of mussels at the Tour du Léman "
as well as 60 secondes info from ASL " The sad story of the white-clawed crayfish "to be found on our website asleman.org.
Photo credit: David Aeschiman
