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LECTURE 18 INVASION ECOLOGY Relevant pages in text: 17-18; 195; 287-8; 340; 342; 346-7; 364-5; 402-3; 559-60; 561; 575-7 MAJOR CONCEPTS 1) Invasion occurs in three stages: arrival, establishment, spread 2) Arrival happens by deliberate and accidental introductions by humans 3) Establishment depends on a predictable suite of traits. 4) Spread occurs because of escape from natural enemies, being strong competitor, or being preadapted to disturbed habitats. 5) Vulnerability of an ecosystem to invasion depends open niches, disturbed habitat, low species diversity, or little history of predators and competitors (as on islands). 6) Control is sought by use of biological control species, minimizing disturbance, or use of pesticides/herbicides. 7) Invasive species imperil endangered species and result in biotic homogenization. I. Definitions Introduced species: non-native or exotic species moved accidentally or deliberately to new ecosystem Invasive species: introduced species that spread after establishment II. Invasive species threaten native, Rank #2 in threatening endangered species (# 1 = habitat degradation/loss) III. ARRIVAL General mechanisms deliberately introduced immigrants bring from native country; bring game animals for hunting, domestication General mechanisms accidentally introduced ship ballasts; unprocessed wood; fruit shipments; bypass natural barriers IV. ESTABLISHMENT A. Traits of introduced species that increase probability of successful establishment non-specific diet and habitat needs, including microbes self-fertilization small body size high reproductive potential good competitor social/gregarious B. Looking for generalities to make the science predictive V. SPREAD A. Hypotheses that explain why an introduced species successfully spreads escape from natural enemies (predators, parasites, pathogens) increased competitive ability outcompete native species pre-adaptation to disturbed habitats B. General mechanisms by which introduced species displace (eliminate) native species act as predator, competitor, parasite, pathogen modify habitat promote spread of other invaders C.Displace native species vs. replace native with invasive species argument Biotic Homogenization - increasing similarity in species among areas Habitat loss and modification couple with widespread introduction of a few species leads to homogenization VI. Vulnerability of ecosystems to invasion: hypotheses – Biotic resistance to invasion via high species diversity Disturbance with fewer species and more open niches allows invasion. Human areas have many species that have been associated with humans for a long time Species on islands have little evolutionary history with competitors/natural enemies. VII. Ecological Costs of Invasion Displace native species Alter native species’ interactions Modify habitat Change ecosystem processes (e.g. nutrient cycles) VII Ways to control invasive species use pesticides/herbicides biological control – introduce natural enemy from native range but, if not species-specific to invasive species, may affect other species minimize disturbance to landscape VIII. Problem associated with pesticide use kill more species than targeted invasive species acts as selective agent for resistance to pesticide pose health risk to humans IX Prevention of problems arising from invasive species Education Research for generalities Monitor for early detection Use quarantine once found so does not spread Increase regulations/inspections