BIOLOGICAL INVASIONS
A FEW IMPORTANT DEFINITIONS
Immigrant – an individual that arrives in a new range. No prediction on its fate.
Transient species – immigrant populations that may survive for a few generations but
eventually go extinct.
Naturalized species – a species that now occurs in persistent population(s) in a new range.
No statement on abundance or extent of new range.
Invasive species – the non-native species is abundant (reproducing prolifically) and has
extensive new range. Although not strictly in the definition, the species is causing harm in
the new range.
POTENTIAL CAUSES OF NATURALIZATIONS
Immigration to a new range without accompanying parasites, predators, etc and no/few
few biotic barriers [“enemy release”]
Disturbance in new range that favors immigrants more than native spp.
Immigration of a species playing a role unrepresented in the native biota [“empty niche
hypothesis”].
Environmental stochasticity – random occurrence of events among environmental factors
that enhance or decrease population size, e.g. yr-to-yr variation in rainfall, predator
numbers.
BIOTIC RESISTANCE: ACTIONS BY PREDATORS, COMPETITORS, GRAZERS, PARASITES,
MUTUALIST
To be an effective component of biotic resistance a predator should be:
Omnivorous, opportunistic (including ready acceptance of novel food) [abundant in the
new range, present year round], e.g. opossum, peccary, capuchin monkey, raccoon
Parasite – obtains resources from a host with which it lives in intimate association; may
cause death eventually; may be highly specific to hosts
Competition – seeking together resources in short supply; perhaps least likely to act as an
agent of eradication.
Merremia spp. in Oceania (Solomon Is.)
Rhododendron ponticum (Ireland and the U.K.)
Lantana camara (India): shelter for Glossinia spp., carrier of trypanosoma spp.
(trypanosomiasis)
Mimosa pigra (Australia)
Cenchrus (Pennisetum) ciliare (Australia)
New Zealand grasslands: few native annual plants; many invasive annual spp., e.g. Bromus
tectorum
Opuntia vulgaris (Yunnan, China)
Ageratina adenophora (S. China)
Miconia calvescens (French Polynesia)
Eichhornia crassipes (Uganda): harbor dipteran vectors of Plasmodium spp. (malaria)
Lionfish – in the Caribbean
Effects of Invading Species
Ecosystem alteration: fire cycle, nutrient regimen, hydrology, soil properties
Competition/predation/parasitism on economically important spp (crops, livestock,
poultry, forage spp.).
Extinction of native species.
Human health hazards
CONCLUSIONS
No region is immune to biological invasions
As connectivity of global commerce continues to grow, more invasions will emerge.
Biological invasions are a truly international problem, requiring international cooperation
to combat and prevent them.