Invasive biology 2: Interesting dynamics

Question 1

Interesting dyamics when species invade: Chain reaction

Answer 1

• The effects of introduced species/organisms on native ecosystems often involve complex chains of interconnected interactions.

Example: Invasion of cats effecting seed dispersal
- The invasion of cats to many islands reduces the populations of lizards as the are preyed upon
- lizards are key for the dispersal of seeds
- The disitrbution of plant species is altered.

East Africa: bug head ants
- Big headed ants kill Acacia ants which sting elephants and stop them from destroying whistling thorn trees and in return they get nectar and shelter
- so with more trees destroyed (7x rate) there is greater visibility and lions kill less zebras

Question 2

Interesting dyamics when species invade: Invasive meltdown

Answer 2

The presence and activities of one invasive species can facilitate the success and proliferation of other invasive species, creating a feedback loop that intensifies impacts and promotes secondary invasions.

Example: Morella faya in Hawaii
- This tree puts down dense stands and is nitrogen fixing, impacting the survival of native species
- The tree promotes fire which promotes proliferation of introduced earth worm population. This further promotes burial of nitrogen from fire tree litter
- Introduced pigs and songbirds (Japanese white eye) disperse the seeds of this tree
- Complex interplay of interactions which collectively contribute to displacement of native species.

Example: invasion of Great Lakes by zebra mussels improved water quality as they ate phytoplankton and sunlight penetrated deeper. Allowed for invasion of watermifoil

example: provide refugee for prey threatens by Australia fox invasion

Question 3

Interesting dyamics when species invade: multiple effects

Answer 3

invasive species can have multiple, varying effects on different species

Example: Red swamp crayfish
- negative impacts on amphibians but benefits predators like storks and otters.

Question 4

Interesting dyamics when species invade: Lag times

Answer 4

Species may be introduced and have no negative impact until there is a change in the system whichc causes the species to become dangerous

Example: Cordgrass hybridisation
- S.alterniflora is an invasive cordgrass species that was present in England for years having no impact.
- S.a hybridised with a native cordgrass species and this hybrid was highly invasive, outcompeting native species.

Example: allee effect
- substantial population required before can be invasive - ‘positive correlation between fitness and density’
- Can lead to underestimation of species threat

Dn/dt = n x f(n)

F(n) is per capita growth which is a function of population size

Example: Allee effect in house finch lead to slower dispersal around North America
- disproportionate lowering of reproduction below a threshold density due to reduced probability of finding a mate

Question 5

What impacts Invasion dynamics and how?

Answer 5

There can be synergism between alien invasive species and other drivers of biodiversity change and these drivers can facilitate the establishment and spread of the invasive species.

• Climate change
• Habitat modification

How do these other factors impact the effect on invasive species?

1) Interaction chain effect
- Total invasive impact on native species is effected by the indirect effect of haitat modification/ climate change on invader abundance (does not effect per capita invader impact)

Example: Habitat degredation in Mediterranean caused an increase in abundance of invasive mussel species, displacing the native speccies to near-shore habitats. Shift in importance of competitive ability versus stochastic colonisation success.

2) Interaction modification effect
- Total invasive impact on the native species if effected by invader abundance and the way that the habitat modification alters the ecological interaction between invasive and native species.

Example: Grassland conservation to agriculture in california has driven up invasive earth worm abundance and lead to a competitive reversal over native earthworms (makes it more competitive)
- native better at acquiring resources in low productivity conditions

3) Climate change changing territories

• Climate change may not change the abundance of the species or the nature of the interaction but it may effect the range of the invasive species therefore altering the native species it can impact.

Example: Honey creepers in Hawaii
- Honey creepers found strong holds in high altitude regions where the mosquito vector carrying malaria could not reach them
- Climate change means that the moquitos are able to move to higher altitudes.

The synergism between habitat modification/ climate change mean it is hard to predict the future effect of invasive species.
- Only 1.2% of studies released between 2002-7 investigate land use change and species invasion simultaneously
- models tend to focus on main effects and not interactions

Example: manage feral cats in new Zealand which threaten skinks
- feral cats eat prey from heavily grazed grasslands
- solution is to restore degraded habitats to reduce prey abundances

Question 6

Invasive species solutions

Answer 6

1) Prevention and preparedness (most cost effective)
- strictly enforced import controls,
- pre-border, border and post-border biosecurity,
- measures to address escape from confinement.

Particuarly important on islands and marine/ connected systems where eradication and containment will be challenging.

2) Early detection

3) Containment
- Effective when aeradication is not possible

4) Eradication
- Successful for small and slow spreading populations in isolcated ecosystems

Example: Failed eradication of mice from Gough
- During 2021 Winter 3 stints of baited (toxic) traps were put down but the mice were no eradicated

Managemet should be very case specific and take into account the unique interaction of factors for each invasive species.
- May be indirect management strategies.

Question 7

Overview

Answer 7

There are many interesting dynamics that occur during the spread of invasive species which makes every case unique and dependent on a range of factors.
- Chain effect
- invasion meltdown
- lag times
- multiple effects

Key factors that impact the dynamic of invasions (synergism)
- Climate change
- habitat modifications

Solutions to invasions
- prevention
- early detection
- eradication
- containment

Solutions are case dependent.

Humans are the heart of the problem as we facilitate the transport, introduction, establishment and spread of invasive alien species.