AP Syllabus focus:
‘Invasive species may exploit new niches or outcompete native species, altering ecosystem dynamics.’
Invasive species can rapidly reshape communities by changing who survives, who reproduces, and how energy and nutrients move through food webs. Understanding invasion pathways and impacts helps predict ecosystem change and guide management.
What makes a species “invasive”?
Invasions occur when organisms are transported beyond their native range, establish self-sustaining populations, and spread.
Invasive species: A non-native organism that establishes, spreads, and causes ecological, economic, or health harm in a new environment.
Practice Questions
FAQ
Lag phases can occur when populations are initially small and vulnerable to chance events.
Other causes include:
Time needed for suitable disturbances or climate conditions
Gradual build-up of propagules from repeated introductions
Genetic changes (adaptation, increased variation through multiple sources)
Propagule pressure is the number and frequency of introduced individuals.
Higher propagule pressure:
Reduces extinction risk at low density
Increases genetic diversity, aiding adaptation
Raises the chance of landing in a suitable microhabitatv
Although founders may start with low diversity, rapid evolution can occur via:
Multiple introductions from different source populations
Strong selection in the new habitat
High reproduction rates generating more mutations per unit time
Biocontrol agents can:
Attack non-target native species
Become invasive themselves
Shift interactions (e.g., freeing another pest from competition)
Strong host-specificity testing reduces, but does not eliminate, these risks.
Risk assessment often combines:
Climate/habitat matching models
Species trait data (diet breadth, fecundity, dispersal)
History of invasiveness elsewhere
Small-scale trials with strict containment and monitoring
