Invasive species Flashcards
how have the rate of invasive species increased over time
Dispersal is a natural process so invasive species have always occurred, however, anthropogenic change has drastically modified natural dispersal patterns and increased its speed e.g. the routes of human transportation are dispersing species faster and further in greater numbers
what is a native species
a species which occurs within its natural range (past and present) and dispersal potential (ie within the range it could occupy without introduction by humans
what is an alien species
a species which occurs outside of its natural range or dispersal potential
what is an invasive alien species aka invasive species
an alien species which becomes established in natural or seminatural ecosystems or habitats, is an agent of change, and threatens native biological diversity e.g. grey squirrel, Japanese knotweed
how have global trends changed in the discovery rate of alien species
rapidly increasing with high rates in countries such as Australia and New Zealand due to deliberate introductions by European settlers
why are islands at particular risk of invasive species
lack of prior adaptation to species associating with humans such as rats, cats and pigs
how does invasion of invasive species occur
1517 recorded invasive species
- 39% introduced intentionally
e.g. European starlings introduced in Newyork in 18090s by a group who wanted all birds ever mentioned in shakesperes work or cane toads to control insect pops in Australia
- 26% introduced unintentionally
e.g. - 22% spread by both intentional and unintentional introductions
- 13% no information available
what are the three stages of invasion
1) species must be able to survive dispersal to a new area and undergo dispersal
2) abiotic environment act as a filter, are the environmental conditions suitable for the species
3) biotic environment, can it compete with local species and defend from predators, parasites and pathogens
if a species can pass through these filters they become invasive
explain how invasive species disperse
some species are more able to survive human-mediated dispersal than others
1) maritime transportation- attach to boat hulls (ie molluscs), survive in ballast waters (e.g. seeds and larvae), live in close association with humans (e.g. rats, cats and livestock)
2) over-land transportation- species involved in the pet or horticultural trade, stowaways in cargo e.g. food shipments can occur via any transport route including avaiation
how to invasive species establish abiotic factors
in most cases species die before they establish a new area as climate and resources must be suitable
establishment increases with
1) number of introductions
2) number of individuals introduced
what are the four hypothesis thought to be able to explain how invasive species establish biotic factors
1) empty niche= alien species exploit niches not filled by native species = Levine et al
2)novel weapons = alien species gain advantages over native plants by expression allelopathic chemicals which kill resident plants= Ni et al
3) Enemies release hypothesis= alien species are released from top-down control when natural enemies are not transported with them= Torchin et al
4)novel environment= humans create novel habitats that are well suited for alien species, suggest successful invasions have little to do with resident community of native species and more to do with a species history of association with humans and human modified ecosystems
what did Murphey and Romanuk find about the impacts invasive species had on biodiversity
- they decrease native species richness by an average of 24%
- they ranked biodiversity impacts of invasiveness as second to land use changes with predators causing extinction of 87 birds, 45 mammals and 10 reptile species
what did dornelas et al find out about the impact of invasive species on biodiversity
the introduction of alien species might not cause an over all decline in biodiversity in an areas but they do cause homogenisation (making environments more similar) as endemic species are lost and replaces with globally common ones
what are some ecosystem level impacts of invasive species
invasive plants speed up rates of nutrient recycling (nitrogen accumulation and decomposition) and increase primary production, nutrient rich ecosystems tend to have low biodiversity as some species dominate
how can invasive species have economic impacts
e.g. The emerald ash borer has been one of the most economically damaging invasive alien species in US forestry, acccidently introduced in 1990s they killed 53 million as trees causing $11 billion of damage as females lay eggs in bark fo ash trees killing them if infections become havy enough
how can economic impacts of invasive species differ between more well develops vs less developed countries
high income such as america and europe have the highest costs however lower income countries have fewer resources to combat invasive species so suffer high costs as a proportion of GDP
how can the presence of alien species be goof
many non-native flowering plants introduced are good for pollination
some species are used for food e.g. potatoes and tomatoes
some species used for recreation
biological pest control e.g. cassaca mealy bug controlled by specialist parasitic wasp
give an example of a species which caused confusion about if it was native or not
pool frog- originally thought to be introduced to the UK from europe and so was not conserved eventually presumed exinct in UK
after this conservationist realised that they were native so reintroductions underway
what are the stages of managemnet and control
horizon scanning
risk assessment and management
prioritization
management plan
what is a risk assessment
a formal process for determining the probaility that an event will occur and the consequence or impacts if it does
- identify risk
- decide who might be infected and how
- analyze risks and decide precautions
- record findings and generate risk summary
how do we know what the consequences of will be before an invasion happens
look at traits of the species which could be introduced and the ecosystem
- this can be difficult if the species hasnt been studied
- risk assessments can differ depending on whether they prioritise effects on biodiversity, ecosystems, human health or ecology
what is the easiest and cheapest way to eradicate invasive species through risk management
best way to get rid of them is in the early stages of colonisation achieved though
1) public engagement and education
2) trade and transport policies
3) biosecurity screening
when is eradication more likely to be more successful
1) if land area is small
2) sufficient resources are allocated
3) Biology or target organisms have been considered e.g. larger mammals easier to eradicate than plants
give an example of an invasive species which underwent management and control
The removal of Pacific rats from Henderson Island
- 2011 RSPB attempted to eliminate rates by dropping 75 tonnes of poisoned bait on the island at a cost of £1.5 million
- seemed successful but in March 2012 a rat was seen and pops have rise back to around 100,000
what went wrong
- a genetci study of the surviving rates revealed that the population was reduced to less than 80 individuals but this was enough to recolonise
what control measures can be done if eradication is not possible
1) using chemical control ( can often have harmful effects)
2) biological control
3) humans used e.g. bounty on invasive species or encouraging use for human food sources
4) keep them out of reserves such as with fencing or local eradication programmes
