Invasive species

Question 1

how have the rate of invasive species increased over time

Answer 1

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

Question 2

what is a native species

Answer 2

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

Question 3

what is an alien species

Answer 3

a species which occurs outside of its natural range or dispersal potential

Question 4

what is an invasive alien species aka invasive species

Answer 4

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

Question 5

how have global trends changed in the discovery rate of alien species

Answer 5

rapidly increasing with high rates in countries such as Australia and New Zealand due to deliberate introductions by European settlers

Question 6

why are islands at particular risk of invasive species

Answer 6

lack of prior adaptation to species associating with humans such as rats, cats and pigs

Question 7

how does invasion of invasive species occur

Answer 7

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

Question 8

what are the three stages of invasion

Answer 8

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

Question 9

explain how invasive species disperse

Answer 9

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

Question 10

how to invasive species establish abiotic factors

Answer 10

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

Question 11

what are the four hypothesis thought to be able to explain how invasive species establish biotic factors

Answer 11

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

Question 12

what did Murphey and Romanuk find about the impacts invasive species had on biodiversity

Answer 12

• 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

Question 13

what did dornelas et al find out about the impact of invasive species on biodiversity

Answer 13

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

Question 14

what are some ecosystem level impacts of invasive species

Answer 14

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

Question 15

how can invasive species have economic impacts

Answer 15

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

Question 16

how can economic impacts of invasive species differ between more well develops vs less developed countries

Answer 16

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

Question 17

how can the presence of alien species be goof

Answer 17

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

Question 18

give an example of a species which caused confusion about if it was native or not

Answer 18

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

Question 19

what are the stages of managemnet and control

Answer 19

horizon scanning
risk assessment and management
prioritization
management plan

Question 20

what is a risk assessment

Answer 20

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

Question 21

how do we know what the consequences of will be before an invasion happens

Answer 21

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

Question 22

what is the easiest and cheapest way to eradicate invasive species through risk management

Answer 22

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

Question 23

when is eradication more likely to be more successful

Answer 23

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

Question 24

give an example of an invasive species which underwent management and control

Answer 24

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

Question 25

what control measures can be done if eradication is not possible

Answer 25

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