In this model, invasion success is quantified in terms of the biomass of the invader.
It is a common observation that simple, disturbed, human habitats are more readily invaded by insects and other invaders than complex, undisturbed, natural habitats.
However, these extraterrestrial invaders of suburbia have breached humanity's ultimate boundary, that between itself and the universe.
For example, resources are shared with competitors, so competitors indirectly decrease invader growth.
When invaders penetrated the area, both as raiders and traders, there was a dual process.
When the territory boundary is breached, males confront the invader with species-typical aggressive displays and threats.
Yet not all sections of the population were united in opposition to the invaders.
Some parasites can also directly reduce the abundance of an invader's competitors.
