Lecture 20: Predicting Invasions

Question 1

Is there evidence yet for saturation of invading species?

Answer 1

• no

Question 2

What is risk?

Answer 2

the probability of an undesired event
e.g. likelihood that an introduced sp will become established
OR the probability that a particular event will occur and will have an undesired impact
e.g. likelihood of a native sp being extricated by an invading species

Risk = (events/time) x (impact/event)= Impact/Time

Question 3

How can risk be estimated?

Answer 3

as the probability of a series of intermedia events
e.g. events1/time x events2/time etc
ex invasion via Ballast water
Risk = P uptake x P delivery |uptake x P establishment|delivery

Question 4

What are the stages of Risk assessment applied to ballast water

Answer 4

1. Uptake at donor region
2. Delivery to receiving port
3. Establishment at the receiving port

Question 5

Risk Assessment of Ballast Water:

Stage 1. Uptake of organisms at donor port

Answer 5

• risk of taking an invader depends on timing
• seasoning and shipping differences
• ex toxic dinoflagellate blooms are super seasonal

Question 6

Risk Assessment of Ballast Water:

Stage 2. Delivery to receiving port

Answer 6

• dinoflagellates don’t live long in tank bc of absence of light
• can form cysts
• fall out of water column into sediment
• when taking on water you are stirring up the sediment into the column which can be dropped off in the next bay
• *longer the voyage = more likely cysts will be buried
• major risk = transport of dormant cysts

Question 7

Risk Assessment of Ballast Water:

Stage 3. Establishment at receiving port

Answer 7

• discharge volume is not necessarily a good risk indicator BC a single cell could establish a population of dinoflagellates
• frequency of ship visits is a better risk predictor during different seasons
• environment similarity btwn donor and receiving port is important for establishment (temp for dinos)
• we can predict how things will continue to happen based on how they previously happened

Question 8

Give the variables a simple model would need to predict the number of potential invaders delivered by ships.

Answer 8

1. no of ships moving from A to B
   2, Number of Species at one port
2. Number of propagules per volume loaded
3. Survial rate of propagules in tank
4. Volume of water released
5. Survival rate of propagules at receiving bay

Question 9

What are useful predictors of invasion ?

Answer 9

1. Invasion Corridors
L> vectors and pathways
2. Propagule Pressure
L> rate at which organisms are delivered 
3. Habitat suitability 
L> water quality, ph, temp, salinity etc
4. Invasion history of a species
L> previous invasion success of a species 
L> precious susceptibility of a region

Question 10

List guidelines for simple risk assessment.

Answer 10

1. Identify invasion corridors and potential donor regions based on:
   - trade patterns and regions with similar climates
2. Identify potential invaders based on:
   - biological traits
   - habitat tolerance
   - previous invasion success
3. Rank relative risk of invasion based on:
   - strength of invasion corridor (vector traffic) and habitat suitability

Question 11

Invasion risk model?

Answer 11

• Probability of introduction (propagule pressure like vector traffic) x probability of survival (habitat)

Question 12

Whats the problem with detecting rare high risk invaders?

Answer 12

• if there is a big pool, diluting the rare one will be causing a lot of false positives