Many ecosystems have been so overrun by invasive species that
efforts may seem impossible. What causes some ecosystems to become
apparently "stuck" in an invaded state?
This website will allow you to learn about several ecological
mechanisms that can lead to stuck invasions. We have created a model
tool that will allow you to explore the consequences of these
mechanisms as well as different management practices that might be
effective at controlling invasions and restoring native systems.
FeedbackOne ecological mechanism that can lead to a persistent invasion is feedback. Feedback can be either negative or positive. Negative feedback occurs when the system returns to its original state if it is disturbed. The heating system in your home is like this: if it gets too cold the thermostat turns the heat on and your home gets hotter; if it gets too hot the thermostat turns off and your home gradually cools; this negative feedback keeps the temperature of your house more or less as warm as you want. With positive feedback, on the other hand, small changes to the system will keep getting reinforced and lead to ever larger changes. This is what happens when a microphone or an electric guitar is held too close to its amplifier: a small noise gets amplified and picked up by the microphone as a louder noise, which in turn gets amplified, and so on.
The same thing can happen in ecological systems. An invasive
species, once established, can change the ecosystem in ways that
favors itself and hurts its competitors. One example is when an
invasive species that produces flammable litter invades and makes the
ecosystem more flammable than it was before. If the exotic also
better to fire than its competitors, this sets up the conditions for a
positive feedback: increased fire leads to increased invasion, which
leads to even greater fires, and so on. It is often assumed that really
persistent invasive species maintain their dominance through positive
feedbacks, but native species may also.
Plants, as individual organisms, are sedentary, but they do move around
the landscape by producing and sending out seeds. Some species can
produce thousands of seed per individual and can send them long
distances (like a dandelion). Other species produce few seeds each year
and drop them close to the parent. It is often observed that many
successful invasive species produce many more seeds than native species
and their seeds are often wind dispersed, but this is not always the
case. How invasive and native species disperse across the landscape,
combined with their abilities to produce positive feedbacks can lead to
very different invasion dynamics.
To learn more detailed information about the ecology, click here.