9.3 Invasive species

Invasive species are reshaping global biogeography, altering ecosystems and species distributions. These organisms impact native biodiversity and ecosystem functioning, often with significant ecological and economic consequences. Understanding invasive species is crucial for predicting and managing changes in world biogeography.

Rapid reproduction, high dispersal ability, and adaptability are key traits of invasive species. They often outcompete natives for resources and can quickly establish in new areas. While not all non-native species become invasive, those that do can dramatically alter ecosystems and pose management challenges.

Definition of invasive species

• Invasive species play a crucial role in shaping global biogeography by altering ecosystems and species distributions
• These organisms significantly impact native biodiversity and ecosystem functioning, often leading to ecological and economic consequences
• Understanding invasive species is essential for predicting and managing changes in world biogeography

Characteristics of invasive species

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• Rapid reproduction and growth allow quick population establishment
• High dispersal ability enables spread to new areas
• Phenotypic plasticity facilitates adaptation to various environments
• Generalist habitat requirements increase survival in different ecosystems
• Ability to outcompete native species for resources (food, space, light)

Native vs non-native species

• Native species evolved in a specific ecosystem over long periods
• Non-native (exotic) species introduced to areas outside their natural range
• Invasive species subset of non-native species causing harm to ecosystems
• Not all non-native species become invasive (approximately 10% do)
• Time since introduction often influences invasive potential (lag phase)

Pathways of introduction

• Invasive species introductions reshape biogeographic patterns globally
• Understanding introduction pathways is crucial for preventing new invasions
• Human activities have dramatically increased the rate of species introductions

Natural dispersal mechanisms

• Wind dispersal carries seeds and small organisms over long distances
• Water currents transport aquatic species across oceans and along rivers
• Animal-mediated dispersal through migration or attachment (burrs, seeds)
• Volcanic activity creates new habitats for colonization (island biogeography)
• Natural range expansion due to changing environmental conditions

Human-mediated introductions

• Intentional introductions for agriculture, horticulture, and pet trade
• Accidental transport through global trade (ballast water, shipping containers)
• Tourism and travel facilitate species movement across biogeographic barriers
• Habitat modification creates new niches for non-native species
• Climate change-induced range shifts blur lines between natural and human-mediated introductions

Ecological impacts

• Invasive species significantly alter ecosystem structure and function
• These impacts cascade through food webs and biogeochemical cycles
• Understanding ecological consequences is crucial for predicting biogeographic changes

Biodiversity loss

• Competitive exclusion of native species through resource monopolization
• Predation on native fauna, leading to population declines or extinctions
• Hybridization with closely related native species, diluting genetic diversity
• Habitat alteration rendering environments unsuitable for native species
• Disease transmission to native species lacking evolved immunity

Ecosystem disruption

• Alteration of nutrient cycling processes (nitrogen fixation, decomposition)
• Changes in fire regimes, affecting ecosystem structure and succession
• Modification of hydrological cycles through altered transpiration rates
• Soil chemistry changes impacting plant community composition
• Disruption of mutualisms (pollination, seed dispersal) between native species

Trophic cascades

• Top-down effects when invasive predators reduce herbivore populations
• Bottom-up impacts when invasive plants alter resource availability
• Mesopredator release following the introduction of apex predators
• Alterations in energy flow through food webs
• Indirect effects on non-target species through altered interspecific interactions

Economic consequences

• Invasive species have far-reaching economic impacts across various sectors
• These consequences often drive management decisions and policy development
• Economic costs of invasions influence biogeographic research priorities

Agricultural impacts

• Crop yield reductions due to competition with invasive weeds
• Increased pesticide use to control invasive pests, raising production costs
• Livestock health issues from toxic invasive plants or parasites
• Soil degradation leading to long-term productivity declines
• Market access restrictions due to invasive species quarantine measures

Infrastructure damage

• Structural damage to buildings from invasive termites or plants
• Clogging of waterways and irrigation systems by aquatic invaders
• Road and railway damage from root systems of invasive plants
• Power outages caused by invasive vines on electrical infrastructure
• Increased maintenance costs for public spaces and recreational areas

Management costs

• Surveillance and monitoring programs to detect new invasions
• Research and development of control methods (biological, chemical, mechanical)
• Implementation of eradication or containment strategies
• Public education and outreach campaigns on invasive species
• Economic losses from reduced ecosystem services provided by native species

Biological factors in invasion success

• Certain biological traits increase the likelihood of successful invasions
• Understanding these factors helps predict potential invaders and vulnerable ecosystems
• Biological adaptations of invasive species often challenge traditional biogeographic patterns

Rapid adaptation

• Genetic bottlenecks leading to rapid evolution in new environments
• Epigenetic changes allowing quick responses to novel conditions
• Hybridization between closely related species creating more robust genotypes
• Phenotypic plasticity enabling survival in diverse habitats
• Selection for traits that promote invasiveness (e.g., increased dispersal ability)

Lack of natural predators

• Enemy release hypothesis explains increased fitness in new environments
• Absence of co-evolved parasites and pathogens reduces population regulation
• Altered allocation of resources from defense to growth and reproduction
• Naive prey species lacking appropriate anti-predator behaviors
• Potential for invasive species to develop novel defenses over time

Competitive advantages

• Superior resource acquisition strategies (e.g., allelopathy in plants)
• Higher reproductive rates allowing rapid population growth
• Broader environmental tolerances compared to native species
• Ability to modify habitats to their advantage (ecosystem engineers)
• Exploitation of empty niches in recipient ecosystems

Geographic patterns of invasion

• Invasive species distributions reveal global patterns of biotic exchange
• These patterns inform our understanding of modern biogeography
• Identifying invasion hotspots helps prioritize conservation efforts

Global hotspots of invasion

• Mediterranean-type ecosystems highly susceptible to plant invasions
• Temperate grasslands vulnerable to both plant and animal invaders
• Tropical islands experiencing high rates of species introductions
• Coastal marine ecosystems impacted by shipping-related invasions
• Urban areas serving as entry points and habitats for many invasive species

Island vs continental invasions

• Islands more vulnerable due to isolated evolutionary history
• Higher endemism on islands increases risk of extinction from invaders
• Continental ecosystems often more resistant due to higher native diversity
• Differences in invasion success related to island size and isolation
• Human-mediated introductions blurring distinctions between island and continental invasion patterns

Case studies of invasive species

• Examining specific invasions provides insights into biogeographic processes
• Case studies illustrate the diverse impacts of invasive species across ecosystems
• These examples highlight the complexity of managing biological invasions

Terrestrial plant invaders

• Kudzu (Pueraria montana) rapid spread across southeastern United States
• Australian Acacia species altering fire regimes in South African fynbos
• Japanese knotweed (Fallopia japonica) damaging infrastructure in Europe
• Garlic mustard (Alliaria petiolata) disrupting forest understory communities
• Cheatgrass (Bromus tectorum) transforming western North American rangelands

Aquatic invasive species

• Zebra mussels (Dreissena polymorpha) altering Great Lakes ecosystems
• Water hyacinth (Eichhornia crassipes) clogging waterways in tropical regions
• Lionfish (Pterois volitans) impacting Caribbean coral reef fish communities
• Asian carp species threatening North American river systems
• Caulerpa taxifolia altering Mediterranean Sea benthic habitats

Invasive animals

• Cane toads (Rhinella marina) poisoning native predators in Australia
• European rabbits (Oryctolagus cuniculus) degrading Australian rangelands
• Brown tree snakes (Boiga irregularis) decimating Guam's bird populations
• Feral pigs (Sus scrofa) damaging ecosystems worldwide
• Argentine ants (Linepithema humile) displacing native ant species globally

Management and control strategies

• Effective management is crucial for mitigating invasive species impacts
• Strategies vary depending on invasion stage and ecosystem characteristics
• Management approaches influence the future biogeography of invaded regions

Prevention methods

• Risk assessment protocols to identify potential invasive species
• Strict quarantine measures at ports of entry (airports, seaports)
• Public education programs to reduce intentional introductions
• Development of invasion-resistant crop varieties
• Implementation of ballast water treatment technologies for ships

Eradication techniques

• Chemical control methods (herbicides, pesticides) for localized invasions
• Mechanical removal of invasive plants or animals
• Biological control using carefully selected natural enemies
• Genetic techniques (sterile male release, gene drive) for insect pests
• Integrated management combining multiple eradication approaches

Containment approaches

• Establishment of buffer zones to limit spread
• Use of physical barriers (fences, nets) to restrict movement
• Implementation of early detection and rapid response systems
• Habitat manipulation to favor native species over invaders
• Controlled burning to manage fire-adapted invasive plants

Policy and legislation

• Policy frameworks shape the global response to invasive species
• Legislation at various levels influences management and prevention efforts
• International cooperation is essential for addressing transboundary invasions

International agreements

• Convention on Biological Diversity addresses invasive species globally
• International Plant Protection Convention focuses on plant health and trade
• Ballast Water Management Convention targets marine invasions
• Cartagena Protocol regulates movement of living modified organisms
• Regional cooperation initiatives (e.g., European Strategy on Invasive Alien Species)

National invasive species programs

• Executive Order 13112 establishes U.S. National Invasive Species Council
• Australia's Weeds of National Significance program prioritizes management
• New Zealand's Biosecurity Act provides comprehensive invasion management framework
• South Africa's Working for Water program combines invasive control with job creation
• European Union Regulation 1143/2014 on Invasive Alien Species

Climate change and invasive species

• Climate change alters the dynamics of species invasions globally
• Shifting climatic zones create new opportunities for invasive species
• Understanding these interactions is crucial for predicting future biogeographic patterns

Range expansion predictions

• Poleward shifts in species distributions opening new invasion pathways
• Altitudinal range expansions in mountainous regions
• Changes in ocean currents affecting dispersal of marine invaders
• Increased frequency of extreme weather events facilitating long-distance dispersal
• Modeling approaches (species distribution models) to forecast future invasions

Altered invasion dynamics

• Changes in competitive relationships between native and invasive species
• Shifts in phenology affecting plant-pollinator interactions
• Increased stress on native ecosystems reducing resistance to invasion
• Altered fire regimes favoring fire-adapted invasive species
• Changes in host-parasite relationships affecting invasive species success

Positive impacts of invasive species

• While often harmful, some invasive species can have beneficial effects
• These positive impacts complicate management decisions and public perception
• Understanding potential benefits is important for comprehensive invasion biology

Ecosystem services

• Habitat provision for native species in degraded environments
• Soil stabilization and erosion control by invasive plants
• Carbon sequestration by fast-growing invasive trees
• Pollination services provided by introduced insects
• Bioremediation of contaminated sites by certain invasive plants

Economic benefits

• Commercial value of some invasive species (timber, food, ornamental)
• Job creation through invasive species management programs
• Ecotourism opportunities centered around charismatic invasive species
• Utilization of invasive biomass for biofuel production
• Development of novel products or medicines from invasive organisms

Future challenges in invasion biology

• Ongoing globalization and environmental change present new invasion risks
• Emerging technologies offer both challenges and opportunities for management
• Addressing these challenges is crucial for predicting and shaping future biogeography

Emerging invasive threats

• Climate change creating novel invasive species assemblages
• Increased risk from Arctic invasions due to melting sea ice
• Potential for invasive microorganisms to disrupt ecosystem processes
• Threats from novel genetically modified organisms escaping containment
• Invasive species benefiting from increased atmospheric nitrogen deposition

Novel ecosystems

• Formation of new ecological communities with no historical analogues
• Challenges in defining management goals for hybrid ecosystems
• Potential for increased ecosystem resilience through diverse species assemblages
• Ethical considerations in managing novel ecosystems
• Need for adaptive management approaches in rapidly changing environments