Invasive species

Biological invasion

Establishment of a species outside of its native range

Establishment

A self-sustaining population of a non-indigenous species moves into an area beyond its original range and persists

propagule pressure

Propagule size x propagule number

What do natural invasions involve

Removal of either a geographic, physiological or biotic barrier

Propagule size

Number released (eg seeds)

Propagule number

Number of release events

5 major impacts of invasive soecies

Predation, competition, ecosystem function change, disease, hybridisation

Biotic resistance hypothesis

Ecosystems with high biodiversity are more resistant to invaders than those with low biodiversity

Acceptance hypothesis

Positive relationship between native and alien species

Result of the biotic resistance hypothesis

Negative relationship between native and alien species richness

Island susceptibility hypothesis

Invasive species are more likely to become established and have major impacts on islands than continents

Invasional meltdown hypothesis

Presence of invasive species in an ecosystem facilitates invasion by additional species, increasing their likelihood of survival or ecological impact

Novel weapons hypothesis

In exotic habitats, invasive have a competitive advantage becuase they possess novel weaponry

Enemy release hypothesis

Absence of enemies in the exotic range is a cause of invasion success

Tens rule

10% of species successfully take consecutive steps of the invasion process

Controlling invasive species (2 methods)

Continuous predator control, or introduction of a disease