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Impacts of Invasive Species on Ecosystem Services 223
13.3 Mechanisms of Alteration
Ecosystems are characterized by their structure (composition and biological/physical
organization) and functions or processes, which lead to the production
and maintenance of ecosystem services. Invasive species alter the
production, maintenance, and quality of services by a variety of mechanisms.
As understanding of invasion biology has increased, so too has recognition
and comprehension of these mechanisms. The mechanisms are interrelated,
since they all affect aspects of the defining characteristics of ecosystem structure
and function. However, they can be grouped into three categories to
enhance ease in understanding (Fig. 13.2).
13.3.1 Species Extinctions and Community Structure
Invasive effects on native biodiversity and community structure are well
known, but few studies have examined the mechanisms that lead to these
effects (Levine et al. 2003). Invasive species may alter community structure
through exploitation competition (indirect interactions such as resource use),
and interference competition (direct interactions such as allelopathy in
plants; Callaway and Ridenour 2004). Invasive impacts on other species interactions,
including predation, herbivory, parasitism, and mutualisms, can
change the abundance of species with certain key traits that influence ecosys-
NATURAL ECOSYSTEMS (Ecosystem Structure & Function)
Biotic Factors
•Species diversity
•Community composition
& interactions
Natural Cycles
•Energy
•Nutrients
•Water
Other Abiotic Factors
•Disturbance regime
•Climate & Atmos. Comp.
•Physical habitat
Ecosystem
Goods & Services
Human Society
&
Impacts
- decrease biodiversity
- cause species extinctions
- alter trophic dynamics &
food webs
- change productivity
- change rate of decomposition
- alter soil resources
- alter species interactions
( e.g. competition, allelopathy,
predation, herbivory,
parasitism, mutualisms)
- change water use efficiency
- alter emission of VOCs,
- add functional group or guild
nitrogen gases, CO 2 , etc.
- community disassembly
- secrete salts, change pH, etc.
Spread of
Invasive
Species
- alter fire frequency
& intensity
- increase soil erosion
& change flooding regime
- change climate/microclimate
(e.g. albedo/canopy roughness)
Fig. 13.2 Mechanisms of ecosystem service alteration by invasive species