Invasions Flashcards
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
Altered soil ecological processes
- Soil nutrient and carbon cycling are affected by the composition of plants growing in a community
- Soils invaded by alien plants can have altered nutrient availability microbial activity
Can alter nutrients of soil. Nitrogen fixers make it available to other plants in the soil around their roots.
Could be direct (eg mycorrhiza, root feeding fauna, pathogens) or indirect (detritus food web)
Brown tree snake
Accidentally introduced by US military to Guam. This snake was devastating for bird community on the island. Endemic Guam flycatcher now thought to be extinct. Birds are behaviourally niave to this predator.
Study showed if you compare Guam to nearby island that still have their bid communities can see significant increase in number of spider webs. Increase in abundance of spiders bc realised by predator from birds. Top down cascading effect
Birds can be pollinators (?). if we compared Guam to Saipan, see Saipan has way more sampling and sedlings. So recruitment is better without the invader. Birds visiting flowers at potential pollinators, can see lots in Saipan. Got a few insects in Guam. May lose tree species because of these snakes.
Cane Toad, Australia
Originally realised (1935, 3000 indivs) as biological control agent for sugar cane grub was a pest. Started to spread, started to eat native species. become a problem because it releases toxins from glands on its neck that is poisonous. Native predators have no experience of this toxin so kills them quickly. Main predators are the quoll, snakes, and monitor lizards. Side effect of monitor lizards is it can lead to increase in abundance of native birds that monitor lizards feed on. Crimson finch fledging success increases.
Species of toxin toad from asia has been introduced to Madagascar. M has lots of endemic spp
Water hyacinth
Formed mats on the top of water bodies. Nile perch also introduced species. Mats block aspects for spawning areas for fish. Reached high areas of spread till mid 1990s then control agent introduced that was successful. After 1999 the area coverage reduces lots and stayed at low levels. BC can work sometimes. Mats blocked access to perch/tilapia spawning areas
Decreased dissolved O2
Increased macro invertebrates (snails)
Shift in prey for the nile perch (also intro) to macro inverts
Hybridisation
Hybridization
Rudy duck ornamental species introduced from UK. Spread to continental Europe where the white-headed ducks occurred. Because ruddy duck aggressive courtship behaviour it is a threat to the existence. So shot ruddy ducks in 2000.
2000- about 5000 indivs
2014- about 20-100 indivs
May end up losing native variety.
Spanish bluebell widely planted in UK gardens and hybridises with native british. 1 in 6 woodlands contain spanish or hybrid plats. May end up loosing native
- a new study has found that it has hardier pollen and actually out-competes non-native flowers.
- The greater fertility of the native British bluebell coupled with the huge numbers of individuals that exist in the wild means that it’s got considerable resilience against any threat from these introduced plants
- To evaluate any potential genetic threat, scientists planted the Spanish variety next to the British in large numbers and allowed them to breed naturally.
- Scientists also analysed pollen samples from the two different bluebell varities.
Even though the Spanish bluebell can escape, spread and be hard to remove from gardens and public areas, it is thought to already be a hybrid and have reduced fertility. Scientists discovered that it has misshapen pollen, making it harder for it to breed.
What determines the impacts of invasive species
Novelty
- new predators eg brown tree snake
- novel defences (weapons) eg toxins of cane toads
- evolutionary naive natives
Similarity
- greater fitness than natives but overlapping niches leads to competitive exclusion eg cane toad thought to outcompete native toad for food resources
- hybridisation, eg ruddy duck similarity to white head duck
Social impacts of invaders
Ambrosia artemisiifolia incr pollen count period in the region (Switzerland). Extends hayfever season
Water hyacinth blocks access to fishing areas so reduce matchability for local fishers (reduction up to 45%)
Reduced water flow caused by wood invasive plants. Can exacerbate drought. People have been employed to remove invasive plants from a number of catchment areas –> jobs and preserving important ecosystem functions
Why should we try to predict invasions?
Prevention is better than a cure. Cheaper to prevent it in the first place. Better to identify high risk species in first instance. Risk assessment used to distinguish intro app that have a high risk of becoming invasive. FOrcasting under future conditions, predicted where and how many intro spp will be successful. More time a spp is in an area for costly and difficult it is to remove.
POP
Communities: disturbance and resources
Theory of fluctuating resource availability: a plant community becomes more susceptible to invasion whenever there is an increase in the amount of unused resources.
There could be a decline in resource uptake eg due to disturbance, removal of plants from a community makes more physical space and resources available
Could be an increase in the amount of resources going into a community- eg an incr in nutrients or water or a combination of both (flood events may incr with cc)
Experiment about involves and disturbing a community
4 Community 2 that was weeded and the 2 other undisturbed
2 were wet and 2 were dry (fewer resources)
Invaders did better when higher resource availablility. Community resists invasion when undisturbed and water limiting.
Success in terms of potentially invasive spp at community scale is a function of competition and resources
Disturbance and resource availability: knotweed
Some spp are better at taking up resources than others and some can handle disturbance better. When you have common aliens and natives they tend to increase biomass when you add nutrients - rare aliens and natives don’t/less so
If you give knotweed constant low nutrients = < 5% of the community
Constant higher nutrients does a bit better
But fluctuating high nutrients does the best- pulses. Very good at taking up nutrients compare to native competitors when available. Eg if river floods banks sudden influx of nutrients would suit this plant.
Common natives respond well the high nutrients, but not so well to fluctuations
Invasions can happen when resources are limited
N fixing spp (especially in volcanic soils). Invaders in Hawai’i. Across phylogenetically related pairs of invasive and native spp, invasives show a greater resource us efficiency when light and nutrients are limited.
Measured how well spp phot and how much c is fixed per photon. Invaders tend to perform better in limiting conditions. In experiments invaders do better in all conditions (light, water, and N-limited). More efficient use of resources
Fitness and niche differences
All hypotheses about invasions boil down to fitness or niche differences. Need niche differences that allow a spp to invade. If no niche difference available could only invade if it has a higher fitness in a niche than a native eg fitness advantage from enemy release
If big fitness difference and no niche difference then it can invade and exclude native. If co-existence
If co-existence= less of a difference in fitness and niche
Species by region, why spp are risky?
Weed-risk assessment estimate the likelihood and magnitude of threats posed by introducing a non-indigenous plant spp using ecological, biological, geographical, and life history info.
Can be qualitative- panel based (Europe and Mediterranean Plant Protection Organisation)
Can be quantitative and survey based (Aus and New Zea).
Ultimately the result is to create a white and black list
What is WRA
Weed Risk Assessment
49 ques: intro history, climate suitability life history spp traits (growth and reproduction) management
Summed score puts spp into one of three categories
- low <0 (let in)
- intermediate 0-6 (evaluate)
- high (ban) 6+
Thresholds vary depending on regions
What is risk
Likelihood x impact
WRA adapted and applied elsewhere
Amani Botanical Garden
Established 1900 by Germans then continued by brits
500 spp intro, planting locations mapped
Wayne recorded scales of invasions in 2005
- Exotic, surviving, regenerating, naturalised, and spreading
WRA doesn’t predict all invaders well
- spp in plantatiosn score low bc dont move
- open areas score low
- forest edge and interior invaders score higher
BUT found 7 forest edge invaders let in.
For forest interior invaders letting 2 in and evaluating 4.
Tells us WRA can predict open area invaders? but not so good for forest invaders. May be bc different set of traits and life history. SO we need to be careful
Model of spp introduction and establishment
POP
Trade and invasive spp
Trade up to 1990 best predicts number of established spp
They managed to predict pretty well the invasions observed. Over predicted argentina, japan. Under predicted australia canada and NZ and US.
More recent trade so ability to predict being diminished
For 2008 predicted number overestimated.
A 20 year lag between trade to intro and detection. So can start to make predictions about what’ll happen in the near future
In future think more spp coming in from asia to eu. Interesting to see how patterns change as global economy develops. Other factors like CC come into play too
Interactions between invasions and other global change drivers
Global drivers include habitat change, climate change, invasive spp, over-exploitation, pollution (NP). But they dont operate in isolation. More info is needed concerning the nature of drivers. In particular the regions and across scales.
Millenium Ecosystem Assessment 2005
How will trades effects be moderated by warming? eg brazil and indonesia (similar now) may become mismatched
Currently, increasing invaded regions dominated by developing economies. With CC this incr dampened for warmer regions, but incr for temperate. CC does interact with trade and invasions.
Habitat destruction and disturbance often means invasive can take hold. Simplification of habitats through destruction make them more easily invisible (secondary forests). Primary are resistant to invasion bc complex structure and multiple layers of shading –> difficult for incoming spp to infiltrate and establish. more light in secondary with uniform canopy. With secondary lose key players
Fragmentation- less easy to move between patches- may limit invasion
- Edging effect- open up new niche space. Different light regime (far red to red ratio changes). More light available for phot of pioneer spp. High light adapted.
- local extinctions bc of changes to env, may open up niches.
- May open up channels for invasion. If organisms can move along edges may incr dispersal
- trees on edge get more wind, erodes edge further. exotic lianas do well on edges can lead to more disturbance- trees more likely to fall
Urbanisation
- remove space for invasions- more hostile environment
- more pople to transport in urban areas
- take away natural spp, novel ecosystem so potential for invaders to come in to a novel ecosystem
- cities tend to be warmer (urban heat island) and
- human provided food suits generalist alien and native spp
CC and ornamental alien plants in Eu
Horticulture trade is a major pathways for introductions >23,000 introduce plant spp and varieties in Eu (garden flora).
Most spp not established in wild, some are invasive elsewhere. Might be invasive where climate is a bit warmer and more suitable - climate in Eu in future.
Spp often sold and cultivated norther of their current range in Ey (have head start). May find similar thing with ornamental aline.s As climate changes may not need human support to grow. may be in suitable areas so p of establishing higher
WhoIsNext project
Main aims:
- predict how ornamental plant spp will respond to cc in eu
- which spp most likely to become invasive
- which regions will be most vulnerable to invasion
Warmign experiment with ornamental aliens
Konstanz (READ)
37 ornamental alien
13 established alien
14 native spp
Sown into native grassland community
Treatments:
- 2 degree warming (infrared heaters)
- disturbance (tilling or no)
Natives suffered more from heating than aliens, disturbance incr establishment
Ornamental might outcompete natives
Ornamental more tolerant to warming and community scale invasions
Which part of eu most vulnerable to invasions
Use data on: native ranges GloNAF GBIF Climate
Focus on spp present but not yet established in Eu but established elsewhere
738 eu garden flora established elsewhere
Spp distribution models identify hotspots of invasions under IPCC climate predictions
Accounting or landuse (available for cultivation)
Stacked climate suitability model and identified areas where large number of spp can establish in the future. Hotpspots can change once landuse taken into account
Invasions now
POP
Decr frost days incr exotic spp in switzerland
Novel evergreen forests forming
No of frost days declined dramatically since 1940, S Switzerland. Also see uptick in exotic spp in forests
Palms trees in the alps
Native to E asia, planted in parks in Eu. Number of days without frost is increasing. As it gets warming spp can pass barriers to invasion success
SO:
planted in parks –> reproduce –> small palms in herb layer –> palms in shrub layer –> reproducing palm pop
Days with frost decr so they can reach reproduction age and spread
