Conservation Bio Exam 3: Effects of Exotic Species

Mechanisms by which exotic species can affect native species

increased pressure from natural enemies, increased competition, interbreeding, alter ecosystem processes

what is a major cause of endangerment / extinction for species native to oceanic islands

exotic natural enemies (predators, pathogens)

why are island species so vulnerable to population decline as a result of exotic natural enemies

island species largely have evolved in the absence of terrestrial predators and in the absence of many pathogens AND islands are difficult to get to so mammals and pathogens don’t arrive

disharmony

the absence of groups of organisms that are common in continental habitats from islands

what do exotic pathogens induce

trophic cascades

example of pathogens and trophic cascades

before rinderpest: abundant impala and few acacia trees; during rinderpest: abundant rinderpest, few impala, abundant acacia trees

first problem with interbreeding between exotic species and native species

outbreeding depression; off-spring of matings between distantly related individuals (different species or sub-species) have low fitness

second problem with interbreeding between exotic species and native species

introgression of genes ofthe exotic species into the native species gene pool, homogenizing the native and exotic species’ gene pools

introgression

gene flow between populations of species that hybridize

first mechanism by which exotic species can alter ecosystem processes

change the types, frequencies or intensistites of disturbances in an ecosystem

second mechanism by which exotic species can alter ecosystem processes

alter quantity or timing of resource availability in an ecosystem

first example of exotic species altering ecosystem processes

invasion of sagebrush steppe by B. tectorum; increased fire frequencies

second example of exotic species altering ecosystem processes

invasion of western riparian zones by tamarix sp. has altered the hydrological cycle, including transpiration rates and depth of available soil water.

invasional meltdown

synergistic interactions among exotic species may promote the spread of exotic species

first factor affecting the invasibility of ecosystems

species richness; low species richness may leave more unused resources creating greater opportunity for exotic species

second factor affecting the invasibility of ecosystems

altered disturbance regime; if native pops are kept small by intense, frequent disturbances then more resources may remain unused vreating opportunities for exotics

third factor affecting the invasibility of ecosystems

propagule pressure; number of individuals of exotic species introduced

first trait affecting invasiveness of an exotic species

high reproductive potential

second trait affecting invasiveness of an exotic species

tolerant of a wide range of ecological conditions

third trait affecting invasiveness of an exotic species

evolutionary history with predators, pathogens, and competitors

what is the best predictor of invasiveness

has the species been invasive elsewhere previously