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.