Invasion biology I: Definitions, routes, impacts Flashcards
Primary research areas in invasive biology
- Establishing which genetic, physiological, or behavioural traits characterize invaders;
- Analysing the invasion process, primarily using models;
- Estimating the impacts of invasive species on native species and ecosystem processes;
- Identifying management strategies to reduce the impacts of invasive species.
Definitions: Alien species, Alien inavsive species, native species, biological invasions
Alien species (or non-native species) - animals, plants, and other organisms that have been introduced by humans to new regions.
Invasive alien species (or invasive non-native species) - a subset of alien species, known to have established and spread with negative impacts on nature. Many invasive alien species also have impacts on people.
Native species – species inhabiting its natural range including shifting its range, without human involvement.
It is not always clear whether a species is invasive or native.
Did it disperse naturally?
Example: mtDNA show that mud turtle’s on African islands have independent colonisation from different mainland regions.
It invaded a long time ago?
Example: Dingo invaded Australia 4000 years ago
- Cook says that invasive species are adapting so quickly that they may be considered a new native species -> neo- natives
Huge amounts of uncertainty over definition in the field ->
- uncertainty raised doubts in public and exploited by denialists -> hinder management
- search web including term uncertainty and invasive or alien brought back 658 articles
Biological invasions: the intentional or unintentional transport or movement of a species outside its natural range by human activities and its introduction to new regions, where it may become established and spread
Are all alien species invasive?
Low proportion of alien species are invasive as they must survive and establish.
Depends on:
The propagule pressure= number of individuals per invasion (and health) x number of invasions
Features:
- Capable of asexual as well as sexual reproduction
- Rapid body growth
- Early sexual maturity
- High reproductive rate
- High dispersal ability
- Generalist diet
- Phenotypic plasticity
- Tolerant to broad range of environmental conditions
- Synanthropy (beneficial association with humans)
Invasive species as a threat
Invasive species are one of the 5 major driver’s of biodiversity loss
- 16% of global exintctions are caused solely due to invasive species
- 60% due to invasive species plus other
Invasive species and islands
Islands are very sensitive to invasive species (20% of all impacts on islands)
Features due to island syndrom
- Lack of predators
- Few species and many open niches
- ecologically niave species
- Slow growing, large bodied species with low reproductive output
Example: flightless, groundnesting, ecolgically niave island birds
Islands are also sensitive to cliamte change which amplifies the risk of invasive species.
Example: Brown tree snake invasion of Guam
- Snake introduce in WWII and by 1970 they covered the whole island due to lack of predation
- They exploited the naive vertebrate and decimated the avifauna (12 bird species eradicated)
- Major impacts on the food web (became more simple and dominated by snake)
Pathways of alien introduction
- Release in nature
- The intentinal release of live alien organisms for the purpose of human use in the natural environments
- e.g. biological control, fishing (Rainbow trout)
- E.g. In America 82% of woody plant species identified as colonising outside of cultivation have been used in landscaping
- e.g. pheasants - Escape from confinement
- The movement of alien specie from confinement (e.g. zoo/ botanical garden) into the natural environment
- The species were intentionally brought into the country but unintentionally escaped
- Example: Burmese python released from breeding facilities in Florida following huricane
- Pygmy hippo released from private collection in Aus in 2003 and then shot in 2006 as thought to be a ‘pig’-> other examples where must fatally control - Transport-contaminant
- The unintentional movement of live organisms as contaminants of a commodity that is intentionally transferred through international trade, development assistance, or emergency relief.
- Example: pests and disease of food - Transport-Stowaway
- The moving of live organisms attached to transporting vessels.
- Example: transport on boats
- Example: zebra mussels invade American Great Lakes due to transport in ballast water of boats -> efficient water cleaners - Corridor
- The movement of alien organisms into a new region following the construction of transport infrastructure without which spread would not have occurred.
- second phase of invasion coincides with Industrial Revolution
- Example: The suez canal allowed lionfish to invade the medditeranian and change the food web structure. Sharks were initially apex predators until dominated by Lionsish.
- example: Panama Canal, 4 years after constructions there were 11 new marine species in lake Gatun - unaided
- Secondary natural dispersal after invasive species have already been introduced.
Mechanisms of impact: Ecosystem modification
Invasive species can change habitat structure
Example: Beavers in Argentina
- Beavers were introduced in Argentina in order to promote the fur trade
- They transformed beach forests into meadows dominated by grass due to their dam building
Example: watermilfoil
- submerged aquatic plant that outcompetes native plants forming dense bags of vegetation, degrade water quality and ruin habitats
- invaded North America
Mechanisms of impact: aggression/ interference
Invasove species can interfer with the lifecycle of native species
Example: Crystalline ice plant change the salt concentration of the soil affecting native taxa
Mechanisms of impact: Resource competition
Invasive species can lead to local reasource competition with native species.
Example: parakites and bats in Spain/ medirra
- Parakite introduction lead to decline in bat populaton
- However, parakite introduction in medirra did not effect the bats as the parakites were unable to establish.
Example: shrew in Ireland
- invasive shrew in Italy ears large invertebrate and is large body sized
- switches to smaller invertebrate that native shrew relies on in order to outcompete and become established
- dietry overlap increases from 11% to 39%
Mechanisms of impact: Predation
Invasive species can effect predation in two ways:
- They can be key predators and reduce prey populations
- They can predate on key predators changing the food chain dynamic and potentially increasing population of the predators prey
Example: Mice in Gough
- Mice were introduced to the gough island in the 19th century by sailors
- They eat around 1,500,000 sea bird chicks each year
- They impact different sea birds differently
- > Winter breeders: higher impact as the mice have less food
- >Below ground nesters: higher impact as chicks are smaller
Example: feral cats and red foxes have reduced 2/3 of Aus digging mammals
Overview
There are certain features that make alien species more likely to be invasive.
Invasive species have a enhanced impact on islands.
Different mechanisms of invasion
- Transport contamination
- Transport stoaway
- unaided
- containment escape
- release in nature
- Corridor
Alien species have a major impact on biodiversity
- Predation
- resource competition
- interferance
- herbivory
- parasites/ pathogens
Mechanisms of impact: Herbivory
Invasive species can be maojr herbivores changing the composition of the landscape.
Examples: Hippo introduction into South America
- Pablo Escobar imported 4 hippoes to his estate in south America where they proliferated and now there is a population of 100. (growing by 9.6% a year)
- They are a danger.
- They graze very close to the ground creating grazing lawns which effect the species composition
Example: invasive aphid herbivore be aphid
- study looked at effect of invasive aphid herbivore on native aphid and two milkweed plants
- 10 fold decrease in native aphid population and 30% increase in plant mortality
- increased inter specific competition between plants -> competing plant species that share herbivores -> move between them and differentially effect their performance and alter competition dynamics
Mechanisms of impact: Parasites and pathogens
Parasites and pathogens can also invade.
Example: White nose syndrom (fungal syndrome)
- White nose syndrone invaded North America in cave equiptment
- Reduced populations declines of up to 90% in some species of bats
- Bats are pest control for crops so in their basense pesticides were used (pollution)
Mechanisms of impact: Hybridisation
Invasive species can hybridise with native species effecting their genetic integrity.
Example: Domesticated and wild cats in Scotland
- Many domesticated cats are invasive and have been shipped from abroad.
- For 2000 years wild and domesticated cats have not interbred in scotland.
- In the last 20 years due to anthropenic effects there has been interbreeding with wild cats haing a genetic integirty of 46%
- Potential benefits: wild cats have gained resistance to certain diseases.
Example: hybridisation between red dear and introduced sika deer in the far east
- consequences: reduction of adaptation due to maladaptive genes and reduction in fitness, increase extinction risk due to outbreeding depression, repeated back crossing leading to species resembling invader
