Biological Invasions Flashcards
Define the following:
- Non-indigenous species
- Invasive species
- Alien species
- Invasive alien species
Non-indigenous = species introduced beyond its native range by human activity.
Invasive species = non-indigenous that has become hyperabundant.
Alien species = occurring outside of its native range and dispersal potential due to human activity.
Invasive Alien Species = alien species that threatens native biological diversity.
Define the following:
- Alien plants
- Casual alien plants
- Naturalised plants
- Invasive plants
- Weeds
- Transformers
Alien plants = plant taxa in a given area due to intentional or accidental introduction.
Casual alien plants = cannot form self replacing populations and rely on repeated introductions.
Naturalised plants = Can sustain populations without human intervention.
Invasive plants = Naturalised plants that can spread over large areas.
Weeds = Plants that grow where they are not wanted.
Transformers = Invasive plants that change the condition of the ecosystem.
What are the 3 stages invasive species follow?
Introduction, colonisation and naturalisation.
What is the ‘Tens rule’?
Out of 1000 species,
1/10 of imported species escape = 100
1/10 of these introduced species becomes established = 10
1/10 of established species becomes a pest = 1
What are some life history traits of invasive species?
High reproductive output
Pioneer species/generalist
Small body size
High dispersal rates
Very competitive
Human commensalism
Broad native range
What is the establishment of exotic species correlated with?
Human population density, anthropogenic habitats/disturbance and low diversity systems.
How can disturbance increase susceptibility to invasion?
Changes in fire regime may promote invasion, which can further change the fire regime and facilitate invasion by other species by increasing soil nitrogen.
Human activities such as urbanisation and agriculture facilitate invasions of exotic plants e.g. California examined distribution of 834 invasive plant species and found human activity facilitated invasion and these species had spread in front of human development into areas with threatened species.
Why are islands more susceptible to invasion?
More vacant niches and fewer species
Smaller geographic area
Fewer predator and competitors
Rate of introduction is often higher
Ecological release
What are some generalisations of invaded habitats?
Climatically matched with native range
Hyper disturbed
Low species richness
Absence of predators
Vacant niches
Low connectance of food webs
Nutrient rich
What are the four theories why species become invasive?
Predator escape - exotics are released from natural enemies that control their population.
Evolution of invasiveness - exotics go through rapid genetic change due to new environments.
Vacant niche - exotics use resources left by absent natives.
Novel weapons - Exotics bring novel ways of biochemical interactions to recipient communities.
What is the enemy release hypothesis and what is the evidence for it?
Introduced species become invasive pests because they benefit from escaping their coevolved enemies.
Species are supressed in their native range, immigrate to a new area without grazers and disease and are no longer affected by biotic constraints - depends on enemies in new range.
Evidence: Chrysanthemodies native to SA but invasive in Australia, acacia longifolia native to Australia but invasive to SA. There are few pests in invaded area and they do much better as an invader.
What is the biodiversity hypothesis?
High biodiversity = high community stability
Stable communities are not invaded and are more resistant
What are the seven empirical rules for invaders?
1) Most invaders fails
2) Most successful invasions do not extirpate native species
3) All systems are invaded to varying degrees
4) Increasing impacts when native species are low
5) Human disturbance makes systems more vulnerable
6) Native species are likely to replaced in stressed systems
7) Long term invaders will succeed in systems that match their native range.
