Lecture 13 The Ecological Effects of Invasions (cont’d)
Generally, the invasions that have the greatest impact are those that alter the way an
ecosystem works.
The main types of invasions that effect ecosystems are those that:
• (1) Alter trophic structure
• E.g. novel top predator (nile perch), or a new type of
plankton feeder (Asian carp). By altering food web
structure, they change the flow of energy in the
ecosystem.
• (2) Alter abiotic factors (some examples)
• Resource availability
• Nutrients (e.g., nitrogen fixers)
• Water (e.g., plants with high evapotranspiration
or dense growth in a water limited environment)
• Light (e.g., change light reaching forest floor –
invasive woody shrubs in temperate hardwood
forests)
• Disturbance frequency / intensity
• Fire (increase or decrease in fire return interval
and amplify or decrease the intensity of fire) e.g.,
cheat grass.
• Change physical environment
• Water flow eg., invasive beavers in Chile create
impoundments), nutria remove salt march
grasses allowing wave action to create larger
open areas and facilitate salt water intrusion into
coastal marshes.
• Sedimentation. Dense invasive plant growth can
change flow regimes in watersheds, leading to
increased sediment deposition (tamarisk,
phragmites, loosestrife)
• Earthworms change the structure and porosity
of soil columns thus alter nutrient and water
properties.