Invasive Species Study Notes

Invasive Species

Definitions and Types of Species

  • Introduced Species
    • Species which, due to human actions, occur in regions where they were historically absent.
    • Also referred to as:
    • Alien
    • Exotic
    • Nonnative
    • Nonindigenous
  • Naturalized Species
    • Introduced species that develop a self-sustaining population.
  • Native Species
    • A species that evolved in a region or arrived in a region by its own means.
  • Invasive Species
    • Introduced species that spread rapidly and outcompete, prey on, and otherwise reduce or eliminate populations of native species.

Types of Introductions

  • Alternative Introductions of Species
    • Cattle Egret: Native range expansion.
    • Horses in North America: Reintroduced species.
  • Introduction:
    • Species have overcome a biogeographic (dispersal) filter.
  • Naturalization:
    • Species have overcome a physiological/abiotic filter.
  • Invasion:
    • Species have overcome a biotic filter.

Ecological Impact and Public Awareness

  • Ecological Villains: Species that have impacted humans such that there is public awareness of their negative effects.

Intentional Introductions of Species

  • European Colonization:
    • Various purposes including:
    • Farming
    • Hunting
    • Fishing
    • Companion Animals
    • Nostalgia
    • Acclimatization Societies: Groups dedicated to the introduction of flora and fauna of their homeland.
    • Agriculture: Crops and livestock.
    • Horticulture: Garden and landscaping ornamentals, forestry.
    • Aquaculture: Escape of farmed fish.
    • Biological Control: Utilizing natural enemies of unwanted pest species including herbivores, predators, parasites, and diseases.

Unintentional Introductions

  • Mechanisms of Unintentional Introductions:
    • Ballast Water: Water carried in ships to improve stability, often contains invasive organisms.
    • Wheel Wells: Locations on airplanes that can transport pests.
    • Food Trade: Delivery of non-native species through the food industry.
    • Escaped Pets: Companion animals that escape can establish feral populations.
  • Risk of Ecosystem Invasion: Under suitable conditions, any species can invade effectively, and any ecosystem can be infiltrated.
    • Conditions for Risk:
    • An invasion pathway linking a community to species from well-matched climates and habitats (e.g. Hawaii, Florida, New Zealand, Australia).
    • Significant propagule pressure, where species introduced in large quantities are more likely to establish and persist (e.g. fire ants, mosquitoes).

Characteristics of Invasive Species

  • Common Traits of Successful Invaders:
    • Association with human activity (i.e., introduction efforts, disturbances).
    • Large pool of potential source populations: More specific traits may include:
    • Reproductive Advantages:
      • Rapid growth.
      • Short life cycle.
      • High reproductive potential (r-strategy).
      • Vegetative or clonal reproduction.
    • Good Dispersal:
      • Efficient local dispersal abilities.
      • Seed dormancy.
    • Being Well-Rounded:
      • Tolerance of a wide range of conditions.
      • A generalist diet.

Explanations for Species Invasions

  • Hypotheses for Species Invasion Success:
    • Disturbed habitat.
    • Species-poor habitat.
    • Missing enemies (predators, herbivores, etc.).
    • Novel ecosystems.
    • Rapid evolution of novel phenotypes.

Evolution Advantages

  • Superior Traits and Behaviors: Non-native species may exhibit traits or behaviors that enhance their chances of naturalization and spread including:
    • Cold Tolerance:
    • Example: Nonnative trees expanding into southern hemisphere islands.
    • Salt Tolerance:
    • Example: Coastal grassland dominance by iceplant in California.
    • Inundation Tolerance:
    • Example: Occupation of tidal mud-flats by cordgrass in Western USA.
    • Mating System and Cooperative Organization:
    • Example: Supercoloniality in invasive ant species (Argentine Ant, Invasive Garden Ant).

Impacts of Introduced Species

  • Invader-Based Extinction:
    • Many extinctions caused by humans, especially prevalent in island ecosystems.
    • 30 species of mammalian predators implicated in the extinction or endangerment of 738 vertebrates.
  • Ecosystem Transformation:
    • Altering fire cycles (e.g. Melaleuca).
    • Nitrogen fixation (e.g. Kudzu).
  • Native Extirpation and Suppression:
    • Numerous examples exist of native systems being disrupted by invasive species.
  • Biotic Homogenization:
    • Overlapping examples with all of the above.

Conservation Benefits of Invasive Species

  • More likely to persist in rapidly changing ecosystems.
  • May provide habitat, shelter, or food for native species (e.g. Tamarisk provides habitat for endangered southwestern willow flycatchers).
  • Could act as catalysts for the restoration of native species (e.g. guava trees supporting forest regeneration in Kenya).
  • Functional substitutes for extinct taxa (e.g. Aldabra giant tortoises as a source population for reintroductions).
  • Provide ecosystem services, such as bio-filtration by the nonnative Pacific oyster, which can reduce phytoplankton levels due to nutrient enrichment from anthropogenic sources.

Notable Invasive Species Examples

  • Purple Loosestrife (Lythrum salicaria):
    • Established in New England wetlands around 1830 via ship ballasts.
    • Now found in all US states except Florida; dries up wetlands and outcompetes native plants.
  • Kudzu (Pueraria lobata):
    • Introduced in 1876 at the Philadelphia Centennial Expo, propagates via runners.
    • Promoted for erosion control in the 1930-1950s.
  • Argentine Ant (Linepithema humile):
    • Native to Argentina; introduced inadvertently worldwide.
    • Forms supercolonies, displacing native ant species and harming local fauna.
  • Red Imported Fire Ant (Solenopsis invicta):
    • Native to South America; introduced in Alabama during the 1930s through ship ballast soil.
    • Infestations lead to significant economic costs, with estimates of $5 billion annually in infested areas.
  • Asian Tiger Mosquito (Aedes albopictus):
    • Native to Southeast Asia; introduced into the US in 1983 via used tires.
    • Acts as a significant vector for several viruses including West Nile, Yellow Fever, and Zika.
  • Emerald Ash Borer:
    • Native to Asia; found near Detroit in 2002, affecting all Native American Fraxinus species with 99% mortality.
  • Spongy Moth (Lymantria dispar):
    • Originated from Europe, first outbreak in Massachusetts in 1889; since then, has defoliated over 80 million acres, primarily affecting oak trees.
  • Water Hyacinth:
    • Native to Brazil; introduced in 1884 in New Orleans, now clogging waterways on five continents.
  • Zebra Mussel:
    • Native to the Black Sea; spread through European canals. Detected in the Great Lakes in 1988, causing a 90% decline in algae and phytoplankton.

Management of Invasive Species

Invasion Management Strategies

  • Prevention:
    • Limiting species spread and preventing establishment is critical.
    • Government regulations and legal penalties.
  • Early Detection and Mapping:
    • Identifying and eradicating new or outlying populations and predicting their spread.
  • Control:
    • Methods to reduce overall population sizes including herbicides, pesticides, hunting, and biological control.
  • Management (Containment):
    • Preventing the spread and re-emergence of invasives, as evidenced through the management of Amur (bush) honeysuckle.
  • Research:
    • Ongoing testing of manageably methods and increasing comprehension of invasives.
  • Communication, Education, Cooperation:
    • Educating the public on the ecological impacts and cultivating behaviors that contribute to biodiversity conservation.

Invasive Species and Human Health

Direct and Indirect Problems

  • Direct Problems:
    • Allergies stemming from pollen, insect stings, irritating/toxic plant compounds, and venomous/hazardous animals.
  • Indirect Problems:
    • Tick-borne diseases increased by deer populations around invasive honeysuckle (up to 10x increase in infected ticks).
    • Mosquito-borne diseases worsened by the Asian Tiger Mosquito as a vector for viruses.