How does the introduction of invasive species, such as the brown tree snake, upset the stability of an ecosystem?

Invasive species like the brown tree snake is responsible for the extinction of native birds and lizards and decrease of endemic wildlife biodiversity. They also have an impact on seed propagation and pollination in the forest and nearby agricultural lands. This is because brown tree snakes food source are native forest animals, such bats, and flying foxes which are natural pollinators and seed propagators decreased as the brown tree snakes increase in number rapidly.