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Quiz 7
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Native species
A species that occurs where it evolved in situ
Still a native species even if it once required colonizing a distant location—as long as they did it without the help of people
Exotic species
A species that has been moved by people—intentionally or unintentionally—to a region where it did not evolve
Invasive species
A subset of exotic species that have large ecological or economic impacts
Example: Mongoose from India introduced to Hawaii to kill a bird species
Invasions
The human-mediated redistribution of species to areas where they do not naturally occur/did not evolve/they did not colonize without human assistance
Exotic species vs. invasive species
Exotic species: have little/no ecological impact
Invasive species are a subset of exotic species that:
Spread on their own into wildlands
Establish large, self-sustaining populations
Directly displace native species (competition or predation) or indirectly by altering ecological interactions (disrupt mutualisms)
And/or alter ecosystem processes
Invaders can be any taxa
Plants
Diseases
Invertebrates
Vertebrates
Mammals, fish, reptiles
Biological invasions
Intense competition with native places
Alteration of the aquatic environment so that it is unsuitable for native species
Impacts pollinators—parasitoids and herbivores
Disrupts a highly coevolved mutualism between a plant and its pollinator/seed disperser
The biggest way for invaders to cause ecological impacts
Invaders can alter disturbance regimes
Disturbance regime
Any natural, external event that removes established plants very quickly
Examples: fire and floods
Why are invasions different than naturally-occurring colonization events?
Rate of colonization, abundance upon arrival
Identity/trophic role of the colonist
Consequences of invasions
Homogenizing flora and fauna globally
Loss of endemic species
Creates exotic communities
Disruption of native ecosystem processes
Lowering diversity—less diverse communities are less stable
Three requirements for every invasions
Propagule supply
Has to be a sort of invasive species introduced
Propagule: anything that is capable of reproducing
Characteristics of the invader
Needs to be well suited to the local conditions
Community invasibility
Invasibility: susceptibility to invasion
Diversity-invasibility relationship
More diverse communities should be less susceptible to invasion compared to less diverse communities
More intense competition for resources that the invader has to battle for
Resilience
How quickly did the species recover
Resistance to disturbance
Plant community is altered very little by levels of disturbance
Resilience following disturbance
The community returns to its pre-disturbance composition quickly following disturbance
Biotic resistance
The ability of communities to resist exotic invasions
Stability =
resistance + resilience