Biological invasion
Problem statement, framework and definitions
Synonyms
- Exotic species, nonnative species, non-indigenous species, foreign species, introduced species
and neobiota (including neozoa)
Neobiota (incl. neozoa) are organisms that occur in an area that is not their native distribution region
➔ These are all species that occur outside their original biogeographical range; however, they
don’t have to be introduced by humans, they can also have spread themselves.
Introduced species
➔ This is a foreign species that has been introduced by humans but it’s unsure that they will
establish and reproduce ; settle or disperse ; become a plague.
Terms
- Casual / introduced: alien species that may flourish and even reproduce but do not form self-
replicating populations (rely on repeated introductions)
- Naturalized / established: alien species that reproduce and sustain populations over many life
cycles without human intervention (temporal dimension > introduced long ago > regarded as
native)
- Alien: (un)intentionally introduced outside their natural biogeographical range by human
activities
- Invasive: native or alien species that produce reproductive offspring in large numbers and cause
significant environmental impact
Invasiveness
- Or the propensity of invasive alien species (hereafter IAS) to invade, can be identified from
comparative metrics between invasive and non-invasive alien species, such as those related to
translocation bias, propagule pressure, and foraging/reproduction/dispersal traits (Pyšek and
Richardson 2007).
- Invasiveness is further related to the potential impacts of IAS on the function and service of
recipient ecosystems and thus dictates the prioritisation, prevention and control strategies in
response to biological invasions → alien species aspect
Invasibility
- A property of recipient ecosystems and involves the elucidation of features that determine its
vulnerability to invasion such as community diversity, composition and assembly.
- Invasibility is thus a measure of network instability → ecosystem aspect
Biological invasions of river basins
Connectivity and species area relations
- larger area = more connected – more alien species
e.g., Asian clam Corbicula fluminea
, 1. Multiple hotspots for primary introductions:
• Intentional introduction sites?
• Estuaries (harbours)
2. Rapid secondary spread in European network of waterways: via all corridors
3. Gradual upstream dispersal and hopping pattern
4. Pathways: shipping, fish, waterfowl, Asian food markets
5. Dispersal rates: 27 – 276 km.y-1
Approach for assessing impact of environmental change
Ecological concepts for biological invasions
1. Tens rule (Mark Williamson)
- 1/10 alien species that arrive escape from captivity or gardens
- 1/10 become established
- 1/10 of the established go on to be regarded as invasive
- 1/1000 arrivals poses high risk
- Ratio varies from place to place
, 2. Propagule pressure and establishment hypothesis
- The number of established species can be related to the propagule pressure (= number of
introduction events and number of individuals introduced per event).
- Establishment of alien species increases by repetitive and extensive introduction.
Weed scientist Robert Pemberton examined old catalogues from nurseries
- Plants sold for just one year: 2 % established in the wild
- Popular species sold for over 30 years: 69 % established.
3. Biotic resistance / invasional meltdown models
4. Empty niches concept
- Species addition (seeds) in 147 prairie grassland plots
- The success of invaders decreases as diversity of resident species in plots increases
- Resident species inhibit the establishment and growth of introduced species with similar
resource use patterns
- Introduced species attained lower abundances when functionally similar species were
abundant and when resident species left lower levels of resources unconsumed, which
occurred at lower species richness
5. Enemy release hypothesis
1. The specialist enemies of the alien species will be absent from the new region
2. Host switching by specialist enemies of native congeners and other species will be rare
, 3. Generalists will have a greater impact on the native competitors
Based on a three-point logical argument
- Natural enemies are important regulators of plant populations
- Enemies have a greater impact on native than on alien species
- Alien species are able to capitalize on a reduction in enemy regulation, resulting in
increased population growth
-> originally proposed for introduction of alien plant species
A = native range
B = introduced area of invasive species
e.g.
- Diversity of parasites associated with alien freshwater invertebrates (n = 22)
- Comparison of native range with entire invaded range
- Lower diversity of parasites in invaded range
- Lower epizootic impact in invaded range
- Mainly due to loss of low impact parasites
- Average number of high impact parasites did not differ
- Mainly acquisition of new high impact parasites
- Susceptibility of novel host: ‘naïve host syndrome’
6. Species pool environmental filtering concept
Problem statement, framework and definitions
Synonyms
- Exotic species, nonnative species, non-indigenous species, foreign species, introduced species
and neobiota (including neozoa)
Neobiota (incl. neozoa) are organisms that occur in an area that is not their native distribution region
➔ These are all species that occur outside their original biogeographical range; however, they
don’t have to be introduced by humans, they can also have spread themselves.
Introduced species
➔ This is a foreign species that has been introduced by humans but it’s unsure that they will
establish and reproduce ; settle or disperse ; become a plague.
Terms
- Casual / introduced: alien species that may flourish and even reproduce but do not form self-
replicating populations (rely on repeated introductions)
- Naturalized / established: alien species that reproduce and sustain populations over many life
cycles without human intervention (temporal dimension > introduced long ago > regarded as
native)
- Alien: (un)intentionally introduced outside their natural biogeographical range by human
activities
- Invasive: native or alien species that produce reproductive offspring in large numbers and cause
significant environmental impact
Invasiveness
- Or the propensity of invasive alien species (hereafter IAS) to invade, can be identified from
comparative metrics between invasive and non-invasive alien species, such as those related to
translocation bias, propagule pressure, and foraging/reproduction/dispersal traits (Pyšek and
Richardson 2007).
- Invasiveness is further related to the potential impacts of IAS on the function and service of
recipient ecosystems and thus dictates the prioritisation, prevention and control strategies in
response to biological invasions → alien species aspect
Invasibility
- A property of recipient ecosystems and involves the elucidation of features that determine its
vulnerability to invasion such as community diversity, composition and assembly.
- Invasibility is thus a measure of network instability → ecosystem aspect
Biological invasions of river basins
Connectivity and species area relations
- larger area = more connected – more alien species
e.g., Asian clam Corbicula fluminea
, 1. Multiple hotspots for primary introductions:
• Intentional introduction sites?
• Estuaries (harbours)
2. Rapid secondary spread in European network of waterways: via all corridors
3. Gradual upstream dispersal and hopping pattern
4. Pathways: shipping, fish, waterfowl, Asian food markets
5. Dispersal rates: 27 – 276 km.y-1
Approach for assessing impact of environmental change
Ecological concepts for biological invasions
1. Tens rule (Mark Williamson)
- 1/10 alien species that arrive escape from captivity or gardens
- 1/10 become established
- 1/10 of the established go on to be regarded as invasive
- 1/1000 arrivals poses high risk
- Ratio varies from place to place
, 2. Propagule pressure and establishment hypothesis
- The number of established species can be related to the propagule pressure (= number of
introduction events and number of individuals introduced per event).
- Establishment of alien species increases by repetitive and extensive introduction.
Weed scientist Robert Pemberton examined old catalogues from nurseries
- Plants sold for just one year: 2 % established in the wild
- Popular species sold for over 30 years: 69 % established.
3. Biotic resistance / invasional meltdown models
4. Empty niches concept
- Species addition (seeds) in 147 prairie grassland plots
- The success of invaders decreases as diversity of resident species in plots increases
- Resident species inhibit the establishment and growth of introduced species with similar
resource use patterns
- Introduced species attained lower abundances when functionally similar species were
abundant and when resident species left lower levels of resources unconsumed, which
occurred at lower species richness
5. Enemy release hypothesis
1. The specialist enemies of the alien species will be absent from the new region
2. Host switching by specialist enemies of native congeners and other species will be rare
, 3. Generalists will have a greater impact on the native competitors
Based on a three-point logical argument
- Natural enemies are important regulators of plant populations
- Enemies have a greater impact on native than on alien species
- Alien species are able to capitalize on a reduction in enemy regulation, resulting in
increased population growth
-> originally proposed for introduction of alien plant species
A = native range
B = introduced area of invasive species
e.g.
- Diversity of parasites associated with alien freshwater invertebrates (n = 22)
- Comparison of native range with entire invaded range
- Lower diversity of parasites in invaded range
- Lower epizootic impact in invaded range
- Mainly due to loss of low impact parasites
- Average number of high impact parasites did not differ
- Mainly acquisition of new high impact parasites
- Susceptibility of novel host: ‘naïve host syndrome’
6. Species pool environmental filtering concept
