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European Starling
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How invasives move/spread
The European starling was first introduced to the United
States in New York City, in 1890. Inspired by William
Shakespeare's plays, Eugene Scheffland let loose one
hundred starlings in Central Park.
Cane toads in Australia
Cane toads were deliberately
introduced to Australia from Hawaii in
1935 in an attempt to stop French’s
Cane Beetle and the Greyback Cane
Beetle from destroying sugar cane
crops in North Queensland. The
Australian Bureau of Sugar
Experimental Stations made the
release of 101 cane toads at
Gordonvale in Queensland in 1935.
They were unsuccessful in controlling
the cane beetles.
Stow-aways
Commerce/Curiosity
Recreation
Aesthetics
Biological control
Biological control =
Introduction of predators to
control a prey species
Cane toads in Australia
How do invasives move/spread
Invasion and the evolution of speed in toads
Benjamin L. Phillips1, Gregory P. Brown1, Jonathan K. Webb1 and Richard
Shine1
Cane Toads An Unnatural
History
(1987)
Cane toads seem to have honed their dispersal ability to
devastating effect over the generations.
Cane toads (Bufo marinus) are large anurans (weighing up to 2
kg) that were introduced to Australia 70 years ago to control
insect pests in sugar-cane fields. But the result has been
disastrous because the toads are toxic and highly invasive. Here
we show that the annual rate of progress of the toad invasion front
has increased about fivefold since the toads first arrived; we find
that toads with longer legs can not only move faster and are the
first to arrive in new areas, but also that those at the front have
longer legs than toads in older (long-established) populations. The
disaster looks set to turn into an ecological nightmare because of
the negative effects invasive species can have on native
ecosystems1, 2; over many generations, rates of invasion will be
accelerated owing to rapid adaptive change in the invader3, with
continual 'spatial selection' at the expanding front favouring traits
that increase the toads' dispersal4, 5.
Pattern of a “typical” invasion
Latent phase (small population size)
Rapid population growth and spread
Opuntia
in
South-Africa
Effect of invasive species
Predation
Reconstructing 50 years of
Opuntia stricta invasion in the
Kruger National Park, South Africa:
environmental determinants
and propagule pressure
Llewellyn C. Foxcroft, Mathieu
Rouget, David M. Richardson
and Sandra Mac Fadyen
Diversity and Distributions, (2004)
10: 427–437
Brown tree snake
(Boiga irregularis)
on Guam
Threat to other species
Introduction
The brown tree snake
was first detected on
Guam in the 1950s near
the Naval Port (central
Guam), but may not have
become conspicuous
away from the port area
until the early 1960s.!
By the mid 1960s, the
snake had colonized over
half of the island.! In
1968, the snake had
reached the extreme
northern end of the
island and was present
throughout the island,
although its densities
varied widely from region
to region.
Status of forest species on Guam
Eradication and Detection
Other threats
Effect of invasive species
Predation
Competition (native vs House geckos in the Pacific)
http://www.fort.usgs.gov/Resources/Education/BTS/
Effect of invasive species
Effect of invasive species
Predation
Predation
Competition
Competition
Hybridization
Hybridization
Myrica faya on Hawaii
Environmental engineering
West slope cutthroat trout
Dr. Donald E. Gardner, University of Hawaii,
http://www.botany.hawaii.edu/faculty/gardner/biocontrol/myrica%20faya/myrica.htm
Effect of invasive species
Habitat invaded by Myrica faya
Myrica faya on Hawaii
Predation
Competition
Hybridization
Environmental engineering
N-fixing root nodules
Dr. Donald E. Gardner, University of Hawaii,
http://www.botany.hawaii.edu/faculty/gardner/biocontrol/myrica%20faya/myrica.htm
Effects of invasive species
Dr. Donald E. Gardner, University of Hawaii,
http://www.botany.hawaii.edu/faculty/gardner/biocontrol/myrica%20faya/myrica.htm
Factors affecting invasion
Predation
Competition
Basics
Hybridization
Factors affecting invasion
Environmental engineering
Introduction history
Economic effects
Invasive species is one of the major environmental issues of this century.
The economic cost to the US of invasive species is at least $137B/year.
(ESA 2000)
Each year, ~ $23 billion nationwide is lost to the effects of invasive plants
on agriculture, industry, recreation, and the environment. An estimated
1860 hectares (4600 acres) of land are invaded daily by invasive plants.
(Federal Highway Administration 2000)
Factors affecting invasion:
Introduction history
Time since introduction
Correlation of area and introduction date
Pathways of introduction
Ballast water
Propagule pressure
counteract small population challenges (e.g. genetic effects)
Time since introduction
Demographic processes
Adaptation
Opuntia invasion in South-Africa
Factors affecting invasion
Factors affecting invasion:
species characteristics
Basics
High dispersal rate
Factors affecting invasion
Persistence at low density and fast growth
!
e.g. asexual reproduction
Introduction history
Species characteristics
Good ecological match
large native range (can adapt to different habitats)
generalists
Associate with humans
Characteristics of invasive species
An example of a predictive trait from
the dayflower family
• Australian Weed Risk Assessment Model:
Predict what introduced species are likely to
become invasive based on species traits.
Jean Burns
Is self-compatibility associated with
invasiveness?
Murdannia nudiflora
invasive
Murdannia simplex
noninvasive
Self-compatibility is associated with
invasiveness.
Self-compatible
Self-incompatible
Invasive
Noninvasive
Pollen grain
Self-compatible
Self-incompatible
Pagel94: D = 3.60, P = 0.01
Self-compatibility is associated with
invasiveness.
Self-compatible
Self-incompatible
Invasive
Noninvasive
Factors affecting invasion: community
characteristics
Basics
Predicting invasions
Introduction history
Species characteristics
Characteristics of invasible ecosystems
Pagel94: D = 3.60, P = 0.01
Characteristics of invasible
ecosystems
Disturbed/Early in succession
good “Ecological Match”
Characteristics of invasible
ecosystems
Disturbed/Early in succession
good “Ecological Match”
Predators few or absent (=enemy release hypothesis)
Invasible ecosystems: Enemy
Release Hypothesis
Native Range
Introduced Range
herbivory
herbivory
plant abundance
plant abundance
Characteristics of invasible
ecosystems
Invasible ecosystems: low
diversity?
Disturbed/Early in succession
Islands are more invasible than mainlands (Elton 1958)
good “Ecological Match”
Low diversity local communities are less invasible (Levine
2000)
Predators few or absent (=enemy release hypothesis)
High diversity habitats are more invaded at large scales
(Stohlgren et al. 2003)
Low diversity?
Observations from islands, small-scale experiments, and mathematical models have generally
supported the paradigm that habitats of low plant diversity are more vulnerable to plant invasions
than areas of high plant diversity. We summarize two independent data sets to show exactly the
opposite pattern at multiple spatial scales. More significant, and alarming, is that hotspots of
native plant diversity have been far more heavily invaded than areas of low plant diversity in most
parts of the United States when considered at larger spatial scales. Our findings suggest that we
cannot expect such hotspots to repel invasions, and that the threat of invasion is significant and
predictably greatest in these areas.
Invasible ecosystems: low
diversity?
Invasive species
Basics
Predicting invasions
Introduction history
Characteristics of invasive species
Characteristics of invasible ecosystems
Managing Invasives
What to do about invasives?
Prevent entry
reduce human impact
Invasives: reduce human impact
What to do about invasives?
What to do about invasives?
Biological Control
Prevent entry
reduce human impact
public education
Host Specificity
border control (Australian Weed Risk Assessment)
Agent effectiveness
Removal of invasives
by hand vs pesticides
biological control
Biological Control: host specificity
Biological Control: host specificity
(Soberón 2002)
Biological Control: host specificity
Opuntia spinosissima
Opuntia triacantha
(Soberón 2002)
Biological Control: agent effectiveness
Rare in native habitat
lower chance of resistance in host
Environment matching
Using demographic models of evaluate effectiveness (remember PVAs?)
Biological Control: agent effectiveness
• Scotch broom
Ingrid Parker 2000, PVA
99.9% of seeds in prairies
and
70% of seeds in urban
populations
need to be destroyed to
stop invasion
of scotch broom
Biological Control: agent effectiveness
PVA: Elasticity analysis of how to stop Scotch broom
Characteristics of invasible ecosystems
Invasion front (fastest growing population)
Established population (slowest growing population
Disturbed/Early in succession
good “Ecological Match”
Predators few or absent (=enemy release hypothesis)
Low or High diversity?
Fragmentation