Invasive species are organisms introduced to new ecosystems, causing harm to the environment, economy, or human health. They spread rapidly, outcompete native species, and disrupt ecosystems. The invasion process involves introduction, establishment, naturalization, and spread, with only a small percentage becoming truly invasive.

These non-native invaders impact biodiversity, alter ecosystems, and cause economic losses in agriculture, forestry, and fisheries. They spread through intentional releases, accidental introductions, and natural dispersal. Human activities, like global trade and habitat changes, accelerate their spread and create new invasion opportunities.

Invasive Species: Definition and Distinction

Defining Invasive, Native, and Non-Native Species

• Invasive species introduce to ecosystems outside their native range and cause harm to the environment, economy, or human health
• Native species occur naturally in specific ecosystems or regions, evolving there over time
• Non-native (exotic) species introduce to areas outside their native range but may not cause harm or spread rapidly
• Invasive species characteristics include rapid reproduction, high dispersal ability, phenotypic plasticity, and outcompeting native species for resources

Invasion Process and Success Rates

• Invasion process follows sequence: introduction, establishment, naturalization, and invasion (spread)
• Estimated 10% of introduced species successfully establish, smaller percentage become invasive
• "Tens rule" in invasion biology suggests:
  • 10% of imported species appear in the wild
  • 10% of those establish
  • 10% of established species become pests

Impacts of Invasive Species

Ecological Impacts

• Biodiversity loss results from invasive species outcompeting or preying on native species
• Ecosystem functions alter through disruption of food webs and nutrient cycles
• Extinctions of native species occur through:
  • Predation by invasive species
  • Competition for resources
  • Alteration of habitat structure
• Severe impacts on islands and isolated ecosystems with high endemism levels (Hawaii, Galapagos Islands)

Economic and Human Health Impacts

• Economic costs include damage to:
  • Agriculture (crop losses from invasive pests)
  • Forestry (destruction of timber resources)
  • Fisheries (disruption of native fish populations)
• Control and eradication efforts incur significant expenses
• Annual global economic cost estimates in hundreds of billions of dollars
• Human health effects:
  • Invasive species serve as disease vectors (mosquitoes carrying West Nile virus)
  • Cause allergic reactions (ragweed pollen)
• Ecosystem services alteration indirectly affects human well-being:
  • Water purification disruption (invasive zebra mussels in Great Lakes)
  • Pollination changes (displacement of native pollinators)
  • Erosion control modification (invasive plants altering soil stability)

Pathways of Invasion

Introduction Methods

• Intentional release for:
  • Agriculture (kudzu for erosion control)
  • Ornamental purposes (water hyacinth in ponds)
• Accidental release:
  • Pet escapes (Burmese pythons in Florida Everglades)
  • Agricultural contaminants (seeds mixed with crop shipments)
• Natural dispersal:
  • Wind-carried seeds or spores
  • Water-borne organisms
  • Animal-mediated transport (birds carrying seeds)

Transportation and Industry Vectors

• Ships transport invasive species through:
  • Ballast water (zebra mussels in the Great Lakes)
  • Hull fouling (marine organisms attached to ship hulls)
• Airplanes carry insects and plant materials
• Vehicles spread seeds and small organisms along roads
• Pet trade introduces exotic animals (red-eared slider turtles)
• Horticulture industry spreads invasive plants (Japanese knotweed)
• Aquaculture operations release non-native fish (Asian carp in North American rivers)

Invasion Dynamics

• Propagule pressure concept explains invasion success:
  • Higher number of individuals introduced increases establishment likelihood
  • More frequent introduction events boost invasion chances
• Lag phases occur between introduction and invasion:
  • Early detection crucial for effective management
  • Rapid response necessary to prevent establishment
• Invasive species traits enhancing spread:
  • High reproductive rates (rabbit populations in Australia)
  • Generalist habitat requirements (cane toads adapting to various Australian ecosystems)
  • Allelopathic capabilities (garlic mustard suppressing native plant growth)

Human Role in Invasion

Globalization and Trade Impacts

• International trade accelerates species introductions worldwide
• Examples of trade-related invasions:
  • Asian long-horned beetle in North American hardwood forests
  • Red imported fire ants spreading through global shipping
• Climate change alters geographic ranges of species:
  • Creates new invasion opportunities in previously unsuitable habitats
  • Allows tropical species to establish in warming temperate regions

Anthropogenic Environmental Changes

• Habitat fragmentation favors establishment of invasive species over natives:
  • Edge effects create disturbed areas for colonization
  • Reduced native biodiversity decreases ecosystem resistance
• Land-use changes create novel ecosystems susceptible to invasion:
  • Urbanization introduces non-native ornamental plants
  • Agricultural expansion creates monocultures vulnerable to pests
• Construction of corridors facilitates invasive species spread:
  • Canals connect previously isolated water bodies (Suez Canal allowing Red Sea species into Mediterranean)
  • Roads provide pathways for terrestrial species movement

Synergistic Effects and Global Patterns

• Human-mediated introductions lead to biodiversity homogenization:
  • Certain invasive species become widespread across continents (water hyacinth in tropical regions worldwide)
• Multiple anthropogenic stressors weaken native ecosystems' invasion resistance:
  • Pollution stress on native species
  • Overexploitation of natural resources
  • Habitat destruction
• Cumulative effects of human activities create global invasion patterns:
  • Invasive species hotspots in areas of high human activity
  • Similar invasion profiles in regions with comparable climate and trade patterns