Life history traits of invasive species

1
Life history traits of invasive species
Baker 1965

• Reproduce sexually and asexually
• Rapid growth from seedling to sex. Maturity
• Phenotypic plasticity
• Tolerance to environmental heterogeneity
  (phenoytpic plasticity)

2
Life history traits of invasive species

• Few data exist to support or refute Bakers list
• Bakers list works for ruderals and does not
  include species that may establish in the
  understory
• Congenors with similar traits often differ in
  invasiveness
• Thebaud et al. 1996

3
Thebaud et al 1996
Two species of Conzya Conzya canadensis
restricted distribution Conzya sumatrensis wider
distribution

• Transplanted seedlings into 3 old field sites of
  different ages
• C. sumatrensis better in all fields
• C.sumatrensis better in presence of neighbors
• C. sumatrensis able to take up water and
  nutrients better than C. canadensis

4
Several attempts at analysis of Floras

• Pysek et al. 1995.
• Flora of Czech Republic since 1492
• Plant height
• Life form
• Competitiveness
• One family Asteraceae

5
Flora analysis

• Reichard and Hamilton 1997
• Post-hoc analysis of invading and non-invading
  woody plants
• Used discriminant analysis
• 86 correctly classified
• Traits
• Vegetative reproduction
• No special germination requirement
• Hermaphrodits
• Short period when fruit is on plant

6
Flora Analysis
Daehler 1998
Agricultural weeds conformed to Bakers
list Natural area invaders were Primarily
aquatic or semi-aquatic Grasses, Nitrogen
fixers Climbers Clonal trees
7
Other Taxa
Birds
Dispersal ability Large clutch size More than one
clutch per season Compete with native species for
resources Repeated introductions Association with
humans
8
Other taxa
Fresh-water Fish
Tolerance to broad range of envt.
Conditions Rapid dispersal Aggressive
behavior Good competitors Desirability to humans
9
Four stages necessary for a successful invasion

• Dispersal to new habitat
• Initial colonization
• Establishment
• Secondary spread

10
Dispersal

• Deliberate introductions
• Accidental introductions
• Wind, water and animal dispersal (for plants)

11
Initial Colonization

• Isolated individuals self-fertilize
• Plants can be sexual (hermaphrodites)
• Asexual (clonal)
• Insects and some vertebrates can store sperm
• 2. Multiple reproductive strategies
• 3. Phenotypic Plasticity (cope with envt.
  heterogeneity)

12
Establishment
Insects (biocontrol agents, Crawley 1986) High
intrinsic growth rate Small body size Fast time
to maturity Pines (Rejmanek and Richardson
1996) Small seed size Short juvenile period Short
interval between seed crops
13
Establishment
Competitive ability Life history theory predicts
a trade-off between fast reproductive rate and
competitive ability BUT this may not be true for
invasive species!!
14
Establishment
Competitive ability Example Purple
loosestrife Very high fecundity Capable of
suppressing the biomass of 3 indicator wetland
species when grown in competition (Keddy et al.
1994.)
15
Establishment
Example Purple loosestrife Blossey and Notzold
(1995) Hypothesize that invasive species have
been released from pressure of pests from their
native habitat Can reallocate biomass for defense
to reproduction and growth Compared biomass of
Purple loosestrife in native and non-native
habitat Biomass was greater in non-native habitat
16
Propagule Pressure Controlling propagule pressure
may prevent spread. Difficult to quantify Humans
modify Multiple introductions can increase spread