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