The changes in our climate make it hard to predict whether it will be plants or animals who will win the war. A change in conditions could favour either the plants or the herbivores, breaking the balance. If one side of the war gets an advantage, their population could grow unchecked leading to an 'outbreak'.
Sue Hartley's fifth and final lecture of the series looks at what effects climate change is having on plants and asks whether it might compromise their ability to defend themselves.
Just like humans and other animals, plants need to communicate, particularly when they are under threat. But although these chemical defence mechanisms might save them from being eaten, it uses up vital energy that could otherwise be used for growth.