Definition of introduction
The plant or propagule has been transported by humans across a major geographical barrier
Naturalisation - Richardson et al 2000
Starts when abiotic and biotic barriers to survival are surmounted and when various barriers to regular reproduction are overcome
So overcome 1. Geographical 2. Abiotic and biotic 3. Reproductive barriers
Invasion
Further requires that introduced plants produce reproductive offspring in areas distant from sites of introduction spreading seeds and other propagules
Spread into areas away from sites of introduction requires plant to overcome barriers of dispersal within the new region and can cope with the abiotic environment and biota in the general area
• Invasions are a process:
- Introduction->survival->establishment->spread
Charles elton invasion ecology
1st catalogued invasions. 3 main components
- Over millions of years continents have become distinct
- Human trade and travel reducing these distinctions
- Major implications for cons and diversity
He also suggested mechanisms explaining invasions
Invasion example
Malaria in brazil
Anopheles gambiae s.l. (A. arabiensis)
- Native to Tropical Africa and Madagascar
- Accidental introduction by ships
- Malaria cases: 100,000s
- Malaria deaths: 10,000s
- Brazilian Government/Rockefeller Foundation eradication programme (larvicide and adult insecticide): > US $ 3,000,000,000
Zika in south america, mosquitos breed in tyre water
Cryphonectria (Endothia) parasitica
- Fungal pathogen from Eastern Asia/Japan
- Infected American Chestnut (Castanea dentata)- 1 in 4 trees in Eastern forests were this species. Important forestry tree
- Imported to N America on nursery plants early 20th C
- 1911: had spread to > 10 US states, losses US $ 25,000,000
- 1950: Most trees dead
- Efforts to breed resistant strains
- European Starling
• Sturnus vulgaris
- From Eurasia
- 3rd attempt to establish in NY Central Park successful (~80 birds)
- American Acclimatization Society (Eugen Schieffelin)
- Tried to introduce all bird spp. from Shakespeare!
- Now ~150 million birds, from S Canada to Mexico - Japanese Knotweed
• Fallopia japonica
- Collected from Japan, brought to Holland by Philipp Franz von Siebold
- Awarded Gold medal by Society of Agriculture and Horticulture of Utrecht
- 1850: Specimen added at RBG Kew
- Widely sold and planted
- Vigorous vegetative growth: one female clone in Europe
- Damage to infrastructure eg $130 million to remove it from the london olympic site - Sea Lamprey
• Petromyzon marinus
- N Atlantic species, spawns in streams
- Improvements to Welland Ship Canal in 1919
- Spread to Lake Huron (1937) and Michigan; Lake Superior (1946)
- Hunting predator and ectoparasite
- Decimated commercially important lake trout populations
- In 10 yrs, catch fell from 3900 Tonnes to <12 Tonnes
- Control costs $14 million/yr, losses if control stopped = $500 million/yr
Invasions as a process
POP
GloNAF
Global Naturalised Alien Flora
This is a database that comprehensively displays all the naturalized plant species. The warm colours show the more numbers of invasive plants. Mostly islands and coastal regions.
There are more than 13,000 plants on the database which means that 4% of flora has been invasive at some point.
Which continents are the biggest exporters and importers
Number of native plants highest in south america so expect this to be the biggest donor. But temperature Asia and Eu exported the most. Asia is a large continent, so lots fo spp with wide ranges so more likely to invade. Europe is a big donor bc colonisation.
NB corn/crop spp dont often invade bc cant establish wild pops without human intervention
Islands and invasions
Elton recognised islands as being particularly vulnerable
Mostly the Island are the hotspots. Hawaii has the highest alien species richness, others that are very high include Singapore, New Zealand, Seychelles and Mauritius.
Why are islands so heavily invaded? The native species have experienced less competition/predation and so are less fit and have less evolutionary experience so are easily outcompeted. They may also be naive to predators so predated easily, also lack of predators means that invasive predators fill empty niche space. Along the same lines there are lots of gaps in the communities for invasive species to exploit. There also might be less natural enemies such as herbivores.
Latitudinal patterns
Tropics have fewer invaders more species so fewer niches to be filled by invaders. Competitors are already there so there is more biotic resistance to diseases as well as herbivores. There may also be less initial introductions due to trade patterns. Finally, there may be stability in terms of climate/environmental conditions so an equilibrium/saturation of communities has already been reached due to more time to evolve.
What gives Alien plants invasion success?
No one size fits all, traits that give species fitness advantage or niche difference over natives.
What barriers must invasive spp overcome to become invasive
- Biogeographic
- Environmental
- Reproductive
Then its naturalised
In many cases, ‘invasive’ species are a subset of naturalized species that are known to have negative ecological impacts. Most alien plants useful eg wheat, horticulture, drugs, forestry. Only small % become invasive. Need to try and predict which will become dangerous
How do we measure invasiveness
Can measure its invasiveness with different dimensions, eg how many habitats it can invade, the size of the range, how abundant it can get.
Determinants of invasion success
Environment human factors Traits
Invasion is a function of species traits, given human factors, given environmental conditions. Factors can interact to determine invasion success. Can fit SDM to see if climate is appropriate for spp to establish. Project into introduced range and evaluate.
Env
- climate, resources, native community, enemies
Hum
- disturbance, propagule pressure, time since intro
Tra
- growth, reproduction, resource acquisition, dispersal
Range comparisons image
POP
Expansion into 1 may be post intro evolution (new range)
Predicted to be an increasing impact on boreal and coastal
Human factors of invasion
Propagule pressure
Number of introductions/locations higher the increased likelihood of pop overcoming stochasticity (demographic or environmental). Actual number of individuals introduced rarely available
Time since intro
Spp introduced/planted earlier are more likely to escape cultivation and naturalise. Spp present for longer have more time to reproduce and release propagules to the environment. More environment conditions and more likely to find suitable range.
• Species present for longer have had more time to reproduce and release propagules into the environment
- Greater sampling of envt by species
- Greater likelihood of detection
- May be correlated with propagule pressure
Traits and invasion
Pine spp are more likely to be invasive if they:
- Start reproduction early
- Have short interval between mast years (seeds)
- Smaller seed mass
- Also true for other non-minus conifers. Suggest invasive woody plant spp are at r-end of rk spectrum.
- If smaller seeds can make more and light so can disperse further
- r= live fast, die young
- K= slower growing, live longer, higher likelihood of survival
Dispersal
Amani Botanical Garden in Tanzania. >500 spp introduced. Many now established and spreading. intro about 100 ya. Spp dispersed by birds and primates.
Arboreal and wind spp tend to spread more
Phenotypic plasticity
Invasive spp may be able to alter their traits (phenotype) within a genotype according to the environment.
- If this maintains fitness: ‘Jack-of-all-trades’ can invade wide range of envts
- If fitness is optimised in one environments ‘Master-of-some’ invades particular environments
- Combination: ‘Jack-and-Master’
POP
Invasive Knapweed (Centaurea spp.) are ‘Jack-of-all-trades’
- Invasive Hawksbeard (Crepis spp.) are ‘Masters-of-some’
However, Studies often limited by restricted range of environments covered by reaction norms
Might falsely get patterns because we just focus on one environmental gradients. POP
Bakers ideal weed
POP
What is the enemy release hypothesis
Native soil had a more negative effect of invader plant growth than new soil. In new range rebased from enemies
- Specialist enemies important
- Soil pathogens
Whats EICA
Evolution of Increased Competitive Ability
• Evolution of increased competitive ability at a cost of resistance against herbivores and pathogens.
POP
Evolves with less investments in antiherbivore defences and allocates more resources to vegetative and reproductive growth. Differs to the enemy release hypothesis because believes invasives have lower fitness at time of intro and evolve to be more fit by the time its considered invasive
Allelopathy
• Invasive species can release phytotoxic chemicals that are novel to resident native species
- Can suppress growth and germination (an example of ‘interference’ competition)
> 100 000 different low-molecular-mass natural compounds have been identified of which many are species specific
Eg spotted knapweed invaded montana grassland
One study measured it and said they only found one example of these compounds at cons comparable with original paper. They did find the compound was photo toxic-
SO it might be more realistic that most of the time is occurs in low populations, so bit of doubt whether it will have a major effect on competitive plants in the area
Mutualists- co-invasions
- Mycorrhizas important for establishment success
- Pinaceae conifers and ectomycorrhizal fungi (ECM) in S Hemisphere
- Conifers in Argentina grow better on soils near to existing plantations
- Inoculation with ECM on far soils improves growth
Because it is missing its ectomicrohizal partner that it has at plantations, if you inoculate the soil with the fungus then it gets better
Have to have coinvasion of ectomicrrhizal partner and pine species
Ecological impacts of invasive spp
Ecological impacts can involve:
- Reduced abundance of native species
- Diversity and species loss (extinction- particularly on islands)
- Altered ecological and ecosystem processes
- Alternative stable states (particularly issue in freshwater systems invaded by plants can lead to nutrient changes)
- Positive impacts on some species can also be ecological, economic and social
Many studies have measured impact of invasive plants by comparing invaded and neighbouring non-invaded patches
Using meta-analysis: invasive plants largely have negative impacts on native diversity, abundance and fitness across studies
Issue with these approaches, invasion could have been triggered by a factor eg change in nutrient. This disturbance may have impacted the plants that were native. So are the natives drivers of passengers of sudden change. Need experiments to tease this apart.
Extinctions caused by invasives
Most of south America at least of quater of species on the red list are threatened by invasive species. as colours get warmer number of threatened by invasive is higher. Africa could be less is known about the invasive species, or that the threats to species here are different eg habitat destruction
• Major vertebrate taxa have many species that are endangered (IUCN red list), due to IAS
Batrachochytrium dendrobatidis vector- fungus spread around the world. Claw frog was the vector for the fungus. The fungus now threatens lots of amphibian species. one example of a species gone extinct is the golden toad.
Rats and cats also wreak havoc of feeding on eggs on nesting birds but also they eat chicks. Rats predating on nesting seabirds eg south Georgia
Cats big problem on islands like new Zealand
