Invasive Species 3

Invasive Species

Course Information

  • Definitions

  • Community: A collection of 2 or more species interacting with one another (biotic interactions).

  • Ecosystem: Comprises nutrient cycling and energy flow within the environment.

Ecosystem Consequences of Invasive Species

  1. Ecosystem Interactions
       - Biotic and abiotic interactions within ecosystems.
       - Nutrient cycling: Movement of nutrients and water through ecosystems.
         - Biogeochemical cycles: The processes that move nutrients through biotic and abiotic components of ecosystems.
       - Productivity (Energy Flow): Associated with biomass production.
         - Primary productivity: Rate at which energy is converted by photosynthetic and chemosynthetic autotrophs to organic substances.
         - Net Primary Productivity (NPP): The rate of energy storage by autotrophs after accounting for respiration.
       - Disturbance Regime: Refers to predictable and unpredictable disturbances in ecosystems such as fire, drought, hurricanes, and human actions like bulldozing.
         - Fire frequency: The interval at which fires occur, known as fire return interval.
         - Erosion: Soil degradation resulting from water, wind, or human activities.
       - Biodiversity: Variability among living organisms, including diversity within species, between species, and of ecosystems.
         - Altered trophic web: Changes in predator-prey relationships due to invasive species.

  2. Nutrient Cycling/Biogeochemistry
       - Example Study: Morella faya (Faya Tree) in Hawaii
         - First major study linking nutrient cycling with invasive species.
         - Field Notes: Workers required new boots due to the abrasive nature of lava rock in the area.
         - Nitrogen Input: Sites with Morella faya demonstrated four times more nitrogen input due to its ability to fix nitrogen, being a legume.
           - In Hawaii, there are no native nitrogen-fixing trees, highlighting the role of Morella faya.
         - Ecological Effects:
           - Increased nitrogen availability benefits invasive species, thus decreasing native biodiversity and increasing invasive biodiversity.
         - Related Concepts:
           - Facilitation: The process by which one species increases the fitness of another.
           - Invasional meltdown: A scenario where invasive species facilitate the establishment and spread of other invasives.
           - Empty Niche: A situation where an absence of competitors allows invaders to thrive.
         - Nurse Plant Role: Morella faya functions as a nurse plant, aiding the establishment of other invasive species, including invasive earthworms and feral hogs.
         - Seed Proliferation: Seeds can germinate on fresh lava rock, benefiting from carbon fixation and nitrogen accumulation.
           - Seedlings improve area productivity; aggregate fruits contain thousands of seeds, creating a situation known as propagule pressure.

  3. Example of Invasive Species: Saltcedar (Tamarix species)
       - Eight species introduced, few are invasive.
       - Alters surface soil salt concentrations significantly.
       - Introduction to US: Brought in as a decorative tree in 1823, lacks native congeners in the US.
       - Characteristics:
         - High salinity tolerance with scale-like leaves and colorful flowers, which can excrete salt through specialized secretory glands.
         - Roots tap into groundwater, which is often salty (phreatophytes).
       - Invasive Behavior:
         - Spread across East and Southwestern US, particularly notably Tamarix ramosissima, known for rapid seed germination (24 hours), adventitious roots, and hybridization capabilities.
       - Landscaping Use: Attractive due to its flowers, salinity tolerance, and utility in soil stabilization.
       - Consequences of Saltcedar Invasion:
         - Alters stream flow due to solid stands affecting biodiversity, especially riparian cottonwood forests (Populus deltoides).
         - Limits germination sites for native cottonwood due to increased soil salinity, subsequently decreasing biodiversity.
         - Changes arthropod communities; many native species thrive on cottonwood but not saltcedar, indicating potential specialization.
         - At least six endangered species experience negative impacts from increased salinity, habitat alterations, and reduced vegetation.
         - Fire frequencies increase due to debris accumulation.
         - Leaf litter quality in streams is altered, impacting macroinvertebrate communities.
         - Despite the initial belief in high water usage (200 gallons/day), studies debunked this as an error without scientific basis.
         - Attention has shifted towards other ecological impacts directly resulting from saltcedar invasions.
         - Introduction of Tamarix beetle as a biocontrol measure faced regulatory roadblocks due to concerns for endangered species like the southwestern willow flycatcher that depends on saltcedar for survival.
     

Summary of Key Impacts from Saltcedar Invasion

  • Alters nutrient cycling, overall ecosystem productivity, and biodiversity.

  • Decreases habitat quality thereby reducing presence and diversity of native species.

  • Impacts recreational activities and alters community structure in related ecosystems.

  • Validates the need for ecological studies and interventions regarding invasive species impacts on ecosystems.