Invasive Species Flashcards
What is an invasive species?
- dispersal = natural process
- anthropogenic change = modified natural dispersal patterns and increased its speed
- lead to huge conservation problems
What is a native species?
occurs within its natural range (past or present) and dispersal potential (i.e. within the range it could occupy w/o introduction by humans)
What is an alien species?
occurs outside of its natural range or dispersal potential
what is an invasive alien species (aka invasive species)?
alien species that becomes established in natural or seminatural ecosystems or habitat, is an agent of change, and threatens native biological diversity
what is the trend of invasive species?
- increasing problem
- global time trends in the discovery rate (e.g. of first recorded instance) of alien species - increase as year increase
Why might the trend of invasive species be increasing?
better at monitoring it now than 200 years ago
Where is invasive species higher and why?
high rates in some countries (e.g. Australia, New Zealand and the USA) due to deliberate introductions by European settlers
Where is at high risk and why?
Islands = at risk due to lack of prior adaptation to species associating with humans such as rats, cats, pigs etc
How many invasive species were introduced intentionally, unintentionally, both and no information?
1517 invasive species reviewed by Turbelin and colleagues (2017)
- 39% introduced intentionally
- 26% introduced unintentionally
- 22% spread by both intentional and unintentional introductions
- 13% no information available
Intentional introductions - European Starlings
- NY Central Park - 1890s
- by people who want America to have all bird species that Shakespeare mentioned
- one of most abundant birds in North America w/ over 200 M European Starlings from Alaska to Mexico
Intentional Introductions - Cane toads
- Australia from Hawaii
- to control insect pests of economically valuable sugarcane crop
- reproduced rapidly, increasing population over 200 million individuals
- numerous ecological effects, loss of native species that toads eat and loss of native predators that dies from eating can toads, poison-secreting glands (release bufotoxin when threatened)
- no evidence introduction of toads had any impact on pests they were introduced to control
Intentional introductions - Giant African Snail
- through pet trade and as food resource
- considered one of top 100 problematic IAS in world - damage to agricultural crops and native plants - also serves as intermediate host of Angiostrongylus cantonensis, a nematode worm that can cause deadly meningoencephalitis in people
Unintentional introductions - black or ship rat (Rattus rattus), brown or Norway rat (R. norvegicus), and Pacific rat (R. exulans)
- spread to much of world as hitchhikers on ships
- remote islands too
- due to human exploration of world’s oceans
- invasive alien rats = dramatic effects on unique flora and fauna of islands, preying on eggs of variety of seabird species that use island as nesting habitat
Unintentional introductions - Eurasian zebra mussel
- to numerous countries in Europe, USA, and Canada
- after planktonic larvae of species traversed the Atlantic Ocean in ballast water of ocean-going ships
- damage manmade structures and blocking pipework etc.
Unintentional Introductions - Giant salvinia (kariba weed)
- free-floating fern
- exported as part of pet industry to be used in aquaria and garden ponds
- escaped or deliberately released to wild - spread rapidly
- blocks sunlight, killing water plants, prevents normal gas exchange and decomposition reduces O2 levels
What makes an invasive species?
3 stages:
1. species must be able to survive dispersal to new area + undergo dispersal
Once species arrive, 2 ‘filters’ that determine whether it will establish
2. Abiotic environment - are environmental conditions suitable for the species?
3. Biotic environmental - can it compete with local species, and defend from predators, parasites and pathogens?
If species passes filters, they can become invasive
Stage 1: How do they disperse? (Becoming an invasive species)
- maritime transportation: attach to boat hulls, survive in ballast water, live in close association with humans
- Shipping canals allow dispersal between previously disconnected places e.g. Suez Canal
- Over-land transportation: species involved in pet or horticultural trade
- stowaways in cargo (e.g. food shipments) can occur via any transport route, including via aviation
Stage 2: How do they establish? - Abiotic factors (Becoming an invasive species)
chances of establishment increases with:
- number of introductions
- number of individuals of introduced
as increase, chances that some well adapted individuals arrive and survive increase
large stochastic element involved e.g. the first 31 purposeful attempts to introduce red deer (Cervus elaphus) to New Zealand failed
- on 32nd attempt, population exploded and it is now a major pest
Stage 3: How do they establish? - Biotic factors (Becoming an invasive species)
What are the hypothesis’? (4)
- Empty Niche Hypothesis
- Novel Weapons Hypothesis
- Enemies release hypothesis
- Novel environment hypothesis
Stage 3: How do they establish? - Biotic factors (Becoming an invasive species)
- Empty Niche Hypothesis
- primary alien species become established in local community by exploiting vacant niche
- either use biological resources in new way that allows avoidance of competition with native species, or by performing a completely new “job” that was previously unfilled by native species
- Levine et al. (2004) - meta-analysis of 65 experiments - quantified strength of competition between native and alien plant species - showed that competition w/ native plants significantly reduced establishment and performance (biomass, growth, or fecundity) of alien species
Stage 3: How do they establish? - Biotic factors (Becoming an invasive species)
- Novel weapons hypothesis
- alien species gain advantage over antive plants - by expressing allelopathic chemicals that kill resident plants
- Ni et al. (2012) - found allelopathic chemicals contributed to successful establishment of 25/33 (76%) of most noxious invasive plants in China
Stage 3: How do they establish? - Biotic factors (Becoming an invasive species)
- Enemies release hypothesis
- alien species controlled by natural enemies (e.g. pathogens, predators, and parasitoids) in native ranges, when small number of individuals of alien species = introduced to new location, their natural enemies may not be transported with them - when released from top-down control of natural enemies, the alien species can establish in the new location
- Torchin et al. (2003) compared parasite loads of 26 species of mollusks, crustaceans, fishes, birds, and mammals between native and invasive ranges
- species averaged 16 types of parasites in native ranges, only 3 were transported with alien species to introduced ranges (average 4 new parasite species)
- alien populations less heavily parasitized, with frequency of infections and infection loads per individual reduced - found that species had half number of parasite species infecting them in invasive ranges compares to their native ranges
Stage 3: How do they establish? - Biotic factors (Becoming an invasive species)
- Novel environmental hypothesis
- suggest successful invasions related to species association with humans than with resident community
- plant invasive alien species in many geographic regions are composed primarily of “weeds” that occur in agricultural fields, along roadsides, and around human settlements - many of most successful animal invasive species have commensal relationships with humans; the housefly (Musca domestica), common cockroach (Periplaneta americana), house sparrow (Passer domesticus), and house mouse (Mus musculus) = all tracked human settlers throughout world
- differs from others - suggest successful invasions little to do with resident community of native species, and more to do with species history of association with humans and human-modified ecosystems
What did Murphy and Romanuk (2014) find? (Impacts on biodiversity)
- invasive alien species decrease native species richness by average of 24%
- ranked biodiversity impacts of invasives as second only to land-use change
How many extinctions do invasive mammalian predators cause? (Doherty et al., 2016)
extinction of:
- 87 birds
- 45 mammal
- 10 reptile species
- 50% of these groups’ contemporary extinctions worldwide
Effects of introduction of alien species
- might not cause an over-all decline in biodiversity in an area
- introductions happen faster than extinctions
- cause homogenisation
- endemic species are lost and replaced with globally common ones
What did Dornelas et al. (2014) find?
- analysed 100 time-series data sets
- where researchers monitored 35,613 species of mammals, birds, fishes, invertebrates, and plants measured at 430,324 locations around the planet (mostly in oceans) - found that in 79 out of 100 time-series data sets, ecological communities were being homogenized at a rate of 10% of their species per decade
What can invasive species cause?
ecosystem-level changes
economic impacts
Example of invasive species effect on nutrient cycling
speed up rates of nutrient cycling (nitrogen accumulation and decomposition) and increase primary production
What is the biodiversity of nutrient rich ecosystems?
low biodiversity as some species can dominate
When, where and effect of The emerald ash border (Agrilus planipennis) being accidentally introduced? (economic impact)
- in USA and Canada in 1990s
- killed 53 million ash trees (Fraxinus spp) causing $11 billion of damage
- huge economic impact
Where are highest absolute costs experienced?
high income region such as North America and Europe experience highest absolute costs
Who suffer from high costs as a proportion of GDP?
lower income countries have fewer resources to combat invasive species so suffer high costs as a proportion of GDP
Example of non-negative impacts of alien species
Aesculapian snake (Zamenis longissimus)
native to mainland Europe and accidently released in UK (next to London Zoo and Welsh Mountain Zoo, and in Bridgend)
Example of alien species with positive impacts
e.g. many non-native flowering plants introduced to gardens = good for pollinators
Example of alien species used for food
potatoes and tomatoes
Example of alien species used for recreation (which has economic benefits)
many introduced freshwater fish
Example of non-native species that are particularly positive
- biological pest control - 16% of introductions of non-native enemies result in complete control of target pest
- Cassava mealy bug, accidentally introduced to Africa in 1970s
- insecticide control = costly and environmentally damaging
- now controlled by a specialist parasitic wasp, originally discovered in mealybug’s native range
- introductions for biological control have to be very carefully considered
Example of benefits of alien species
arguments over which species are native
e.g. Pool frog (Pelophylax lessonae) originally thought to be introduced to UK from Europe - not conserved in UK
- presumed extinct in UK in 1995
- after, conservationists realised they were probably native
- reintroduction programmes are now underway
Management and control: risk assessment
What is a risk assessment?
- formal process for determining probability that an event will occur and consequences or impact of it does occur
- identify threats
- decide who might be affected and how
- analyse risks and decide precautions
- record findings and generate risk summary
- review and monitor
Management and control: risk assessment
How do we know consequences before invasion happens?
- look at traits of species that could be introduced
- and ecosystem it could be introduced in
difficult if species hasn’t been studied - databases of traits being created
Why may risk assessments differ?
depends on whether they prioritise effects on biodiversity, ecosystems, human health or economy
How are risk assessments used by governments?
to restrict import of certain species
Prevention and eradication of invasive species
easier and cheaper to eradicate in early stages of colonisation - detection for eradication = difficult when species is rare
prevention is easiest and cheapest option
How can prevention be achieved?
- public engagement and education
- trade and transportation policies
- biosecurity screening
What does eradication require?
network of volunteers, or hi-tech surveillance such as eDNA (Environmental DNA)
When is eradication more likely to be successful?
- land area = small
- sufficient resources are allocated
- biology of target organism has been considered (e.g. larger mammals easier to eradicate than plants)
Case Study: Removing Pacific rats form Henderson Island
- 43 square km, largest island attempt rate eradication
- 2011, RSPB attempted by dropping 75 tonned of poisoned bait on island - cost of £1.5 million
- seemed successful
- March 2012 - Rat seen and rat population increased to around 100,000
what went wrong?
- recolonisation from another island?
- resistance to poison?
- not enough rats killed?
- genetic study of surviving rats revealed the population reduced to <80 individuals
What to do if eradication is not possible?
control numbers
How to control numbers instead of eradication?
e.g. using chemical control (but often harmful effects)
OR biological control (e.g. cassava mealy bug & parasitic wasp)
Humans can be used (putting bounty on invasive species, encouraging using them as human food source)
can try to keep them out of reserves e.g. with fencing or local eradication programs
