In a remote corner of the Caribbean,
researchers have turned sixteen tiny islands
into miniature ecological experiments.
What they've found could change the
way that we think about invasive species,
and it's all because of one little lizard.
This is a brown anole.
It spends its time sat on tree trunks, waiting
for food to wander along the ground.
Hunting down here keeps brown anoles out of the
way of the green anoles, who hunt up in the trees.
But when a new top predator is introduced
into the ecosystem, this all changes.
This is a curly-tailed lizard.
Curly tails eat brown anoles, as well
as competing for the same food.
In response, the brown anoles spend 
more of their time up in the branches,
away from the curly tails.
But now, they're competing
with the green anoles for food.
Prevailing ecological theory suggests
that having predators around
should increase the diversity of an ecosystem
by keeping prey populations in check.
So, do the curly tails benefit the other island species?
A team of ecologists decided to investigate.
They introduced curly-tailed lizards to
several small islands in the Bahamas.
These islands are self-contained
ecosystems with similar habitats.
By tracking the lizard populations
and their behaviour, the researchers
were able to examine exactly what
happens when a new top predator arrives.
What they found was that when the
brown anoles took refuge in the canopy,
they drove the green anoles to extinction
in two out of the four populations studied.
In this case, it seems that introducing predators has actually decreased the diversity of the ecosystem.
If this kind of interaction is common, it could
have important implications for conservation.
Human activity has introduced invasive predators
into ecosystems across the world.
If predators are damaging diversity in this way,
conservationists may need to work
even harder to control their spread.
Back in the Bahamas, the ecosystems on 
these islands have been changed for good,
but it's allowed this team of researchers 
to challenge a core principle of ecology,
and it's deepened our understanding of the role
that predators play in structuring ecosystems.
