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Ch. 10 Invasive Exotics Species & geography • May be iconic • Ranges shift, but limited by barriers • major or seemingly minor ~ mountains or soil pH • short or enduring • For a population to become distinct enough from others to be considered a new species, there must be some type of isolation. Isolation • Filters migrants out • Keeps new alleles in • Different environments, different selective pressures • evolution of distinct populations or new species • Diminishing worldwide • humans inadvertently move other species Terms to know • Exotic ~ a species living outside of its native range • Invasive ~ species that once in an ecosystem cause problems, either ecological, economic, or in human-health • native species can be invasive too • Invasive exotics People Move Species Accidently People Move Species Purposefully • Subsistence ~ familiar foods, timber • feral ~ escaped domestics established in wild • Commerce ~ boost fisheries, fur trapping People Move Species Purposefully • Recreation ~ fishing, hunting • Whimsy • acclimatization societies formed by colonists in the late 19th century. • Aesthetics People Move Species Purposefully • Science ~ breeding colonies and experimental populations • Biological control ~ use of a species natural competitors to control its population • when a species is introduced to a new area its predators, pathogens, or whatever interactions regulated its population are often left behind -> big populations • if an exotic is out of control, introduce it’s competitor to control it • works occasionally, but not always Anthropogenic Changes Facilitate Species Movement • Species can take advantage of changes people make to the environment to move themselves • canals • deforestation Impacts of Invasive Exotics • May be relatively minor if ecosystem already dominated by humans • Affect 1/3 of listed species in the US • Cost billions of dollars Predators and Grazers • Stephen Island wren, extinct because of a single cat • Introduced brown snakes kill island birds and lizards • 200 fish spp. extirpated after Nile perch introduced to lake Victoria • Agricultural pests • Generalist herbivores ~ island plant species have no defenses against grazers; population declines of primary producers affect the rest of the food web Competitors • Invasive exotics often outcompete native species • • • • space food nesting sites nectar and pollen Hybridization • Breeding between subspecies, or occasion different species • causes decline in native species or populations • Gene flow between domestics and their wild relatives • Genetic swamping ~ genes of one species or subspecies dominate the gene pool, reduces diversity Ecosystem Effects • New predator/competitor/pathogen • Changes in productivity, nutrient cycling, disturbance regimes, habitat composition and structure What makes a successful invader? • Number of individuals introduced • Being introduced to an island • more available niches • resident species not used to competitors/predators • Being introduced to a disturbed ecosystem • Having evolved with humans ~ more adopted to human disturbances Discussion Qs • Some exotics encouraged, others condemned. Why? • What about exotics that support native species? • What about exotics that fill the niche of extirpated/extinct local species? • What about species, like horses, that were extirpated from an area by humans, and then reintroduced? • What about hidden exotics, species we assume are native, but were introduced a very long time ago?