Bio-invasions & management samenvatting
H1: Introduction to invasion science
Alien / Exotic / Non-indigenous / Non-native / Introduced / Noxious Species = species living outside its native
distributional range, & has arrived there due to human activity (intentionally or accidentally).
• Natural range of species is determined by their inherent dispersal mechanisms & biogeographical barriers
Invasive Species = species able to establish in new environment & to spreads & reproduces. Causing ecological,
economic, or health impacts
=> All invasive species are alien, but not all alien species are invasive.
Invasion science = focus lies on social-ecological systems (= socio-economic & biophysical
context) with research on
• Ecology, evolution, & biogeography of non-native species (animals, plants, fungi, &
microorganisms)
• Mechanisms driving introduction, establishment, & spread
• Economic, & other consequences of invasions
• Management of biological invasions
• Ethical, social, legal, & policy dimensions related to invasive species
It integrates multiple disciplines => ecology, evolutionary biology, geography, climatology, socio-political sciences &
conservation biology
Invasion biology/ecology = focuses on biological & physiological aspects of non-native species
Both invasion science & biology employs diverse range of approaches & methodologies => observational &
experimental studies, citizen-science initiatives, surveys & questionnaires, satellite data, modeling, & meta-analyses.
Charles Elton is considered founding figure of invasion biology. Elton’s work was pioneering because he:
• Examined biological invasions as global phenomenon across both terrestrial & marine ecosystems
• Identified invasions as serious threat to natural world
• Explored factors that promote or inhibit invasions
• Highlighted human activities as major drivers reshaping species distributions
• Proposed hypotheses that continue to guide modern research (many of which are still being tested today)
• Emphasized importance of understanding what drives biological invasions & developing general theoretical
framework to explain them.
Citation data over time shows that it took ca 35 years for this field to establish itself as recognized scientific discipline,
but since 2015 scientific journals have increasingly publishing studies on invasive species (was rare before). Making
invasion biology young but rapidly expanding branch of biology, with growing scientific & societal interest in impacts
& management of biological invasions. Field now has:
• Its own handbook (1st edition published in 2007)
• Dedicated peer-reviewed journals => Biological Invasions, Aquatic Invasions, NeoBiota, …
• Coverage in major high-impact scientific journals
Publication of unsuccessful management attempts are often excluded in other disciplines, but in this field these are
considered essential to prevent repetition of ineffective strategies.
1.1: Global Threat of Invasive Alien Species
Example: Northern Snakehead Fish (Channa argus) has
• Native range = China, possibly Korea & Russia
• Invasive range = Across US => part of 1st well-documented fish invasion in US. It started when local fishermen
caught unfamiliar fish & took photographs to show scientists. By time it was identified, it had already spread
, extensively. Northern snakehead introduced in US via private individual who bred this fish & released it into
local waterways (intentionally to establish local food source for fishermen or accidentally). This fish introduction
has ecological impact, as it’s top predator that exerts strong top-down effect on aquatic ecosystems & thus
disrupts natural food webs, alters community structure, & competes with native species for resources.
=> This illustrates how new invasive species are often discovered today, by people encountering unfamiliar
organisms, take photographs, & send them to scientists for identification.
Invasive alien species are severe global threat that has long been underappreciated, underestimated, &
unacknowledged. It was only in 2019 that global scientific community formally recognized invasive species as major
global issue. This is late & other ecological problems had received more attention. Some countries have implemented
strong anti-invasive species policies, others show minimal concern.
Despite importance of Intergovernmental Science-Policy Platform on Biodiversity & Ecosystem Services (IPBES) report
(resembles IPCC reports in scale & scope) it received very little media coverage. 2019 IPBES Global Assessment
Report identified invasive alien species as 1 of 5 primary direct drivers of biodiversity loss, along with:
• Changes in land & sea use
• Direct exploitation of species
• Climate change
• Pollution
Governments requested IPBES to provide best scientific evidence & policy options to address biological invasions.
Resulting report involved 86 experts from 49 countries working over 4,5 years, drawing on more than 13,000
references, & with contributions from indigenous peoples & local communities. Making it most comprehensive
assessment conducted on invasive alien species worldwide.
Invasion Process is not 1 single event but multi-stage process, where each stage corresponds to crossing specific
barrier & is linked to different management strategies. => Unified Framework & Categorization of Alien Populations
created risk assessment classifying populations according to their invasion stage (from A to E), which gives
categorization scheme for populations in unified framework.
Invasion process:
A. Transport stage = not transported beyond limits of
native range.
=> barrier = geography ➔ species must be moved
across natural geographic boundaries (usually by
humans) to get into next stage.
B. Introduction stage = individuals transported beyond
native range limits & are
o B1 = in captivity or quarantine (such as individuals
provided with conditions suitable for them, but
explicit measures of containment are in place).
o B2 = in cultivation (such as individuals provided with conditions suitable for them but explicit measures to
prevent dispersal are limited at best).
o B3 = directly released into novel environment
=> barrier = captivity/containment barrier ➔ Individuals must escape from confinement (such as aquariums,
zoos, gardens) to get into next stage.
C. Establishment = individuals released into wild in location where introduced &
o C0 = introduction is for significant period
o C1 = no reproduction (cross ½ barriers)
o C2 = reproduction occurring, but population not self-sustaining (failed to cross 2nd barrier)
o C3 = population self-sustaining (crossed 2/2 barriers)
=> 2 barriers = Survival & reproduction barrier ➔ individuals must survive & reproduce successfully under new
environmental conditions to get into next stage.
D. Spread stage = self-sustaining population in wild, with individuals
o D1 = surviving significant distance from original point of introduction
, o D2 = surviving & reproducing significant distance from original point of introduction
=> barrier = dispersal ➔ individuals must spread beyond initial introduction site.
E. Final stage = fully invasive species with individuals dispersing, surviving & reproducing at multiple sires across
spectrum of habitats & extent of occurrence
Terminology at different stages
• B1–E stages = Alien species => has crossed geographic barrier through human activity
• C0–C2 = Casual/Introduced alien species => may survive or reproduce but cannot sustain populations
• C3–E = Naturalized/Established species => self-sustaining & reproducing over several generations
• D1–E = Invasive species => capable of long-distance spread & significant impacts
=> Human-mediated dispersal created new categories (B1, B2) & extended persistence of populations in C0–C2
stages.
According to 10% hypothesis (still being tested), ca 10% of species advance from 1 stage to next stage.
In European Union, ca 4000 species enter at 1st barrier => Effective border control is therefore crucial, but open-
border system in EU makes prevention difficult. (example: New Zealand has strict biosecurity measures & intensive
border inspections).
Examples: Species Categorization
• Sibinia fastigiata => Introduced in Australia for biological control of Mimosa pigra. Despite successful
host-range testing, it failed to establish (possibly due to differences in flower timing between native &
invasive ranges). → C0 (= released into wild but did not establish).
• Acacia species introduced to South Africa
o Acacia rostriformis was introduced & cultivated, but no naturalization → B2 (= cultivated, but
no spread).
o Acacia mearnsii (black wattle) spread widely across South Africa → E (= fully invasive).
• Budgerigar (Melopsittacus undulatus) => Native to Australia & often kept as pet.
o Escaped individuals in UK & did not survive long → C0.
o Small population on Tresco Island (1972–1975) survived due to supplemental feeding → C2
(= temporary, non-self-sustaining).
o In Florida populations expanded but later declined (“boom & bust”) → C3 to C0 transition
over time. (These show that invasion stage can vary across regions & time).
New species are often poorly understood, & thus comprehensive studies are required before management or
eradication can begin.
Each stage is linked to different management strategies, & prevention (= intervening at earliest stages) is most
effective & cost-efficient approach (AKA early detection & prevention are key). But different species vary in their
manageability & impact. Some invasions are easily contained, while others are persistent & complex. Diversity of
invasive species (in form, ecology, & behavior) makes management multidisciplinary challenge.
Invasion is gradual, multi-barrier process, not 1 single event. Human actions (both intentional & accidental) remain
main driver of biological invasions.
1.2 Transport and Introduction of Alien Species
Great Acceleration (in 1950) = time marked by explosive increase in human population &
spread of invasive species. This acceleration was driven by post–World War II economic
recovery, use of synthetic fertilizers, large-scale dam construction, & industrial expansion.
Anthropocene = era where human activities became dominant driver of planetary change,
including global redistribution of species => Scientists propose that Anthropocene started in
, 1950 & is current geological epoch defined by human dominance of Earth’s systems. This aligns with:
• Global dispersal of radioactive elements from nuclear bomb testing, leaving detectable geological signal.
• Major socio-economic changes, including industrialization of agriculture, notably industrial-scale breeding of
chickens.
Alien species is nothing new & introduction has long history. Many crops &
domestic species in Europe originated elsewhere. Example: Tomato, potato,
maize, vanilla were all introduced after Columbus’ voyages (= Columbian
Exchange) between Europe, Africa, & Americas. Potato originated in Peru &
reached Belgium in the 1500s.
Introductions after 1500 CE are considered biological invasions, but:
• Introductions before 1500 CE are not considered biological invasions.
• If species is reintroduced to region where it was native but locally extinct, it is not considered invasive.
Species are introduced into new regions through variety of intentional or unintentional pathways:
• Horticulture & Ornamental Plants => Use of alien plants in horticulture is major introduction route. Nurseries
continuously seek new species, importing plants from broad geographic range. Modern trade routes are faster,
more direct, & transport larger numbers of specimens than in past, making “never-ending search for novelty”
persistent driver of introductions.
• Pet Trade => Many alien species enter through exotic pet trade. Unwanted pets (such as turtles won at fairs or
ornamental fish) are released into wild, where they may establish. Example: Parakeets from Melipark in
brussels, have limited impacts since they remain largely within cities.
• Unintentional Transport
o Resting stages of organisms (such as zooplankton eggs, insect larvae) can travel unnoticed in soil, plant
material, or on equipment moved across borders.
o Migratory birds can bring parasites across regions => not considered alien unless human activity facilitates
their dispersal.
• Global Shipping & Ballast Water => International shipping has increased 10x in recent decades, with
over 12 billion tons of ballast water are moved each year across coastal & oceanic systems. Each
day more than 3000 species are transported in ballast water (number that is still underestimated).
Sessile species (barnacles, mussels, algae) can attach to ship hulls & mobile species (crabs, small
fish) may live within these communities & be carried globally. Best practice involves “Check, Clean,
Dry” protocol before moving between water bodies, but this is not always followed.
Examples of:
• Deliberate introductions = Ornamental & horticultural plants, Pets & aquarium species, Biological control
agents, Species for zoos & botanical gardens, Agriculture, forestry, game species
• Accidental introductions (hitchhikers) = Contaminants in grain & seed imports, Transport in ballast water, Soil &
substrate contaminantion, Hidden transport in commercial products
o Example: Tiger mosquito introduced via used tire trade (larvae survived in pooled water)
Pathway Categories from intentional to unintentional:
• Release = intentional introduction as commodity for release into wild
o Example: restocking game animals, plants for erosion control, biocontrol agents
• Escape = intentional introduction as commodity, but escapes unintentionally captivity or cultivation.
o Example: feral crops & livestock, pets, garden plants, live baits => happens often via flooding or neglect
• Contaminant = unintentional introduction with specific commodity
o Example: parasites, pests commensals of traded plants/animals (such as seeds in crop imports)
• Stowaway = unintentional introduction attached to or within transport vector
o Example: Species hiding in transport vehicle, ship, train, aircraft, truck (such as barnacles on ships or in
ballast water)
• Corridor = unintentional introduction via human infrastructures linking previously unconnected parts
o Example: such as canals, tunnels, bridges
H1: Introduction to invasion science
Alien / Exotic / Non-indigenous / Non-native / Introduced / Noxious Species = species living outside its native
distributional range, & has arrived there due to human activity (intentionally or accidentally).
• Natural range of species is determined by their inherent dispersal mechanisms & biogeographical barriers
Invasive Species = species able to establish in new environment & to spreads & reproduces. Causing ecological,
economic, or health impacts
=> All invasive species are alien, but not all alien species are invasive.
Invasion science = focus lies on social-ecological systems (= socio-economic & biophysical
context) with research on
• Ecology, evolution, & biogeography of non-native species (animals, plants, fungi, &
microorganisms)
• Mechanisms driving introduction, establishment, & spread
• Economic, & other consequences of invasions
• Management of biological invasions
• Ethical, social, legal, & policy dimensions related to invasive species
It integrates multiple disciplines => ecology, evolutionary biology, geography, climatology, socio-political sciences &
conservation biology
Invasion biology/ecology = focuses on biological & physiological aspects of non-native species
Both invasion science & biology employs diverse range of approaches & methodologies => observational &
experimental studies, citizen-science initiatives, surveys & questionnaires, satellite data, modeling, & meta-analyses.
Charles Elton is considered founding figure of invasion biology. Elton’s work was pioneering because he:
• Examined biological invasions as global phenomenon across both terrestrial & marine ecosystems
• Identified invasions as serious threat to natural world
• Explored factors that promote or inhibit invasions
• Highlighted human activities as major drivers reshaping species distributions
• Proposed hypotheses that continue to guide modern research (many of which are still being tested today)
• Emphasized importance of understanding what drives biological invasions & developing general theoretical
framework to explain them.
Citation data over time shows that it took ca 35 years for this field to establish itself as recognized scientific discipline,
but since 2015 scientific journals have increasingly publishing studies on invasive species (was rare before). Making
invasion biology young but rapidly expanding branch of biology, with growing scientific & societal interest in impacts
& management of biological invasions. Field now has:
• Its own handbook (1st edition published in 2007)
• Dedicated peer-reviewed journals => Biological Invasions, Aquatic Invasions, NeoBiota, …
• Coverage in major high-impact scientific journals
Publication of unsuccessful management attempts are often excluded in other disciplines, but in this field these are
considered essential to prevent repetition of ineffective strategies.
1.1: Global Threat of Invasive Alien Species
Example: Northern Snakehead Fish (Channa argus) has
• Native range = China, possibly Korea & Russia
• Invasive range = Across US => part of 1st well-documented fish invasion in US. It started when local fishermen
caught unfamiliar fish & took photographs to show scientists. By time it was identified, it had already spread
, extensively. Northern snakehead introduced in US via private individual who bred this fish & released it into
local waterways (intentionally to establish local food source for fishermen or accidentally). This fish introduction
has ecological impact, as it’s top predator that exerts strong top-down effect on aquatic ecosystems & thus
disrupts natural food webs, alters community structure, & competes with native species for resources.
=> This illustrates how new invasive species are often discovered today, by people encountering unfamiliar
organisms, take photographs, & send them to scientists for identification.
Invasive alien species are severe global threat that has long been underappreciated, underestimated, &
unacknowledged. It was only in 2019 that global scientific community formally recognized invasive species as major
global issue. This is late & other ecological problems had received more attention. Some countries have implemented
strong anti-invasive species policies, others show minimal concern.
Despite importance of Intergovernmental Science-Policy Platform on Biodiversity & Ecosystem Services (IPBES) report
(resembles IPCC reports in scale & scope) it received very little media coverage. 2019 IPBES Global Assessment
Report identified invasive alien species as 1 of 5 primary direct drivers of biodiversity loss, along with:
• Changes in land & sea use
• Direct exploitation of species
• Climate change
• Pollution
Governments requested IPBES to provide best scientific evidence & policy options to address biological invasions.
Resulting report involved 86 experts from 49 countries working over 4,5 years, drawing on more than 13,000
references, & with contributions from indigenous peoples & local communities. Making it most comprehensive
assessment conducted on invasive alien species worldwide.
Invasion Process is not 1 single event but multi-stage process, where each stage corresponds to crossing specific
barrier & is linked to different management strategies. => Unified Framework & Categorization of Alien Populations
created risk assessment classifying populations according to their invasion stage (from A to E), which gives
categorization scheme for populations in unified framework.
Invasion process:
A. Transport stage = not transported beyond limits of
native range.
=> barrier = geography ➔ species must be moved
across natural geographic boundaries (usually by
humans) to get into next stage.
B. Introduction stage = individuals transported beyond
native range limits & are
o B1 = in captivity or quarantine (such as individuals
provided with conditions suitable for them, but
explicit measures of containment are in place).
o B2 = in cultivation (such as individuals provided with conditions suitable for them but explicit measures to
prevent dispersal are limited at best).
o B3 = directly released into novel environment
=> barrier = captivity/containment barrier ➔ Individuals must escape from confinement (such as aquariums,
zoos, gardens) to get into next stage.
C. Establishment = individuals released into wild in location where introduced &
o C0 = introduction is for significant period
o C1 = no reproduction (cross ½ barriers)
o C2 = reproduction occurring, but population not self-sustaining (failed to cross 2nd barrier)
o C3 = population self-sustaining (crossed 2/2 barriers)
=> 2 barriers = Survival & reproduction barrier ➔ individuals must survive & reproduce successfully under new
environmental conditions to get into next stage.
D. Spread stage = self-sustaining population in wild, with individuals
o D1 = surviving significant distance from original point of introduction
, o D2 = surviving & reproducing significant distance from original point of introduction
=> barrier = dispersal ➔ individuals must spread beyond initial introduction site.
E. Final stage = fully invasive species with individuals dispersing, surviving & reproducing at multiple sires across
spectrum of habitats & extent of occurrence
Terminology at different stages
• B1–E stages = Alien species => has crossed geographic barrier through human activity
• C0–C2 = Casual/Introduced alien species => may survive or reproduce but cannot sustain populations
• C3–E = Naturalized/Established species => self-sustaining & reproducing over several generations
• D1–E = Invasive species => capable of long-distance spread & significant impacts
=> Human-mediated dispersal created new categories (B1, B2) & extended persistence of populations in C0–C2
stages.
According to 10% hypothesis (still being tested), ca 10% of species advance from 1 stage to next stage.
In European Union, ca 4000 species enter at 1st barrier => Effective border control is therefore crucial, but open-
border system in EU makes prevention difficult. (example: New Zealand has strict biosecurity measures & intensive
border inspections).
Examples: Species Categorization
• Sibinia fastigiata => Introduced in Australia for biological control of Mimosa pigra. Despite successful
host-range testing, it failed to establish (possibly due to differences in flower timing between native &
invasive ranges). → C0 (= released into wild but did not establish).
• Acacia species introduced to South Africa
o Acacia rostriformis was introduced & cultivated, but no naturalization → B2 (= cultivated, but
no spread).
o Acacia mearnsii (black wattle) spread widely across South Africa → E (= fully invasive).
• Budgerigar (Melopsittacus undulatus) => Native to Australia & often kept as pet.
o Escaped individuals in UK & did not survive long → C0.
o Small population on Tresco Island (1972–1975) survived due to supplemental feeding → C2
(= temporary, non-self-sustaining).
o In Florida populations expanded but later declined (“boom & bust”) → C3 to C0 transition
over time. (These show that invasion stage can vary across regions & time).
New species are often poorly understood, & thus comprehensive studies are required before management or
eradication can begin.
Each stage is linked to different management strategies, & prevention (= intervening at earliest stages) is most
effective & cost-efficient approach (AKA early detection & prevention are key). But different species vary in their
manageability & impact. Some invasions are easily contained, while others are persistent & complex. Diversity of
invasive species (in form, ecology, & behavior) makes management multidisciplinary challenge.
Invasion is gradual, multi-barrier process, not 1 single event. Human actions (both intentional & accidental) remain
main driver of biological invasions.
1.2 Transport and Introduction of Alien Species
Great Acceleration (in 1950) = time marked by explosive increase in human population &
spread of invasive species. This acceleration was driven by post–World War II economic
recovery, use of synthetic fertilizers, large-scale dam construction, & industrial expansion.
Anthropocene = era where human activities became dominant driver of planetary change,
including global redistribution of species => Scientists propose that Anthropocene started in
, 1950 & is current geological epoch defined by human dominance of Earth’s systems. This aligns with:
• Global dispersal of radioactive elements from nuclear bomb testing, leaving detectable geological signal.
• Major socio-economic changes, including industrialization of agriculture, notably industrial-scale breeding of
chickens.
Alien species is nothing new & introduction has long history. Many crops &
domestic species in Europe originated elsewhere. Example: Tomato, potato,
maize, vanilla were all introduced after Columbus’ voyages (= Columbian
Exchange) between Europe, Africa, & Americas. Potato originated in Peru &
reached Belgium in the 1500s.
Introductions after 1500 CE are considered biological invasions, but:
• Introductions before 1500 CE are not considered biological invasions.
• If species is reintroduced to region where it was native but locally extinct, it is not considered invasive.
Species are introduced into new regions through variety of intentional or unintentional pathways:
• Horticulture & Ornamental Plants => Use of alien plants in horticulture is major introduction route. Nurseries
continuously seek new species, importing plants from broad geographic range. Modern trade routes are faster,
more direct, & transport larger numbers of specimens than in past, making “never-ending search for novelty”
persistent driver of introductions.
• Pet Trade => Many alien species enter through exotic pet trade. Unwanted pets (such as turtles won at fairs or
ornamental fish) are released into wild, where they may establish. Example: Parakeets from Melipark in
brussels, have limited impacts since they remain largely within cities.
• Unintentional Transport
o Resting stages of organisms (such as zooplankton eggs, insect larvae) can travel unnoticed in soil, plant
material, or on equipment moved across borders.
o Migratory birds can bring parasites across regions => not considered alien unless human activity facilitates
their dispersal.
• Global Shipping & Ballast Water => International shipping has increased 10x in recent decades, with
over 12 billion tons of ballast water are moved each year across coastal & oceanic systems. Each
day more than 3000 species are transported in ballast water (number that is still underestimated).
Sessile species (barnacles, mussels, algae) can attach to ship hulls & mobile species (crabs, small
fish) may live within these communities & be carried globally. Best practice involves “Check, Clean,
Dry” protocol before moving between water bodies, but this is not always followed.
Examples of:
• Deliberate introductions = Ornamental & horticultural plants, Pets & aquarium species, Biological control
agents, Species for zoos & botanical gardens, Agriculture, forestry, game species
• Accidental introductions (hitchhikers) = Contaminants in grain & seed imports, Transport in ballast water, Soil &
substrate contaminantion, Hidden transport in commercial products
o Example: Tiger mosquito introduced via used tire trade (larvae survived in pooled water)
Pathway Categories from intentional to unintentional:
• Release = intentional introduction as commodity for release into wild
o Example: restocking game animals, plants for erosion control, biocontrol agents
• Escape = intentional introduction as commodity, but escapes unintentionally captivity or cultivation.
o Example: feral crops & livestock, pets, garden plants, live baits => happens often via flooding or neglect
• Contaminant = unintentional introduction with specific commodity
o Example: parasites, pests commensals of traded plants/animals (such as seeds in crop imports)
• Stowaway = unintentional introduction attached to or within transport vector
o Example: Species hiding in transport vehicle, ship, train, aircraft, truck (such as barnacles on ships or in
ballast water)
• Corridor = unintentional introduction via human infrastructures linking previously unconnected parts
o Example: such as canals, tunnels, bridges
