Incorporating Science, Economics, and Sociology in Developing Sanitary and Phytosanitary Standards in International Trade Proceedings of a Conference (2000) / Chapter Skim
Currently Skimming:
5 Biological Impacts of Species Invasions: Implications for Policy Makers
5 Biological Impacts of Species Invasions: Implications for Policy Makers
Pages 87-117
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 87... ...
GILBERT Department of Environmental Science, Policy, and Management, University of California, Santa Cruz The processes that control the transport, establishment, spread, and impact of invasive organisms underlie many of our concerns about sanitary and phytosanitary risk. In the United States and worldwide, our perception of risk has expanded from primarily economic and human health concerns to include risks to natural ecosystems.
|
From page 88... ...
Factors such as host range and dispersal ability can help gauge how big of a problem an invader will become. The prevalence of ecological idiosyncrasies, complex indirect effects and the possibility for synergistic effects among invaders, however, hinder our ability to predict ecological impacts.
|
From page 89... ...
Throughout, however, we focus primarily on ecological impacts, both in natural and agricultural ecosystems, because here the diversity of interactions and the complexity of the issues best inform us of the range of risks we face and the sources of uncertainty in predicting consequences of biological invasions. CASE STUDY 1: THE GRAPE ROOT LOUSE PHYLLOXERA THE IMPORTANCE OF RECOGNIZING AND REGULATING VECTORS The most devastating impacts of some invasive species have been economic and social, rather than environmental.
|
From page 90... ...
Had a more generalized pest been introduced or had phylloxera evolved the ability to use novel host plant species, its impacts may have extended to other agricultural systems or noncultivated ecosystems. To date, however, no research has looked for ecological impacts of the phylloxera invasion.
|
From page 91... ...
Identifying Patterns of Species Introductions and Impacts One of the most well-known examples of a vector for introducing nonindigenous organisms is ballast water. Ballast water taken on by ships in one part of the world, then expelled in another region, can efficiently transport a diversity of marine and freshwater organisms including bivalves, crustaceans,
|
From page 92... ...
TABLE 5-1. Counts of Plant Species Native to the United States That Have a Known Economic Importance Economic Importance Number of Species Food Construction Fuel Forage Weeds Alternate disease host 105 206 28 126 284 14 Source: USDA Agricultural Research Service 1999.
|
From page 93... ...
For example, brown tree snakes were introduced into Guam from New Guinea or Australia as stowaways in shipments of derelict war equipment shortly after World War II (Fritts and Rodda, 1998~. By the 1980s, these predators had extirpated or drastically reduced population sizes of most of the 10 species of native birds, as well as reduced the populations of native fruit bats and lizards ~ Fritts and Rodda, 1998; Savidge, 1987~.
|
From page 94... ...
IMPACT FROM AN ECOLOGICAL PERSPECTIVE Measuring the Ecological Impact of Invaders A biologist trying to determine the impact of an invader on native species and ecosystems faces a more difficult challenge than an economist evaluating that invader in financial ('pest") terms.
|
From page 95... ...
Extinction of native species is arguably the most dramatic impact of invasive species. Recall, for example, the brown tree snake that caused the extinction, or near extinction, of most of the native bird species of Guam (Savidge, 1987~.
|
From page 96... ...
When lnRR= 0, there was no change in density of the native species, when lnRR < 0 the native species density declined in the presence of the invader, and when lnRR > 0 the resident species increased in density in the presence of the invader. Arrows and numbers in white show means.
|
From page 97... ...
CASE STUDY 2: THE MOSQUITO FISH WHEN ANTHROPOCENTRIC AND ECOLOGICAL PERSPECTIVES CLASH The ecological impacts of some biological invasions contrast with their economic and social impacts. This situation characterizes some invaders that also serve as biological control agents.
|
From page 98... ...
To evaluate whether the net consequence of introducing mosquito fish turned out, on balance, positive or negative, one must weigh the ecological effects against the human health effects. To put the negative effects in perspective, it is instructive to compare the ecological impacts of using mosquito fish to control mosquitoes with those of alternative methods.
|
From page 99... ...
PREDICTING OUTCOMES OF SPECIES INTRODUCTIONS When we consider both economic and ecological impacts, the uncertainty involved in predicting the impacts of unplanned introductions can be overwhelming, even if we employ a vector-based approach to focus on a subset of potential invaders with similar impacts (e.g., ballast water introductions)
|
From page 100... ...
Their decision tree relies on information about the introduced species that is relatively easily obtained from the literature or herbarium records, which makes it a practical tool for managers. In validating their decision tree using all woody plant introductions, invasive and non-invasive, they correctly rejected 88 percent of the pest species and unconditionally accepted for admission only 7 percent of the invasive species.
|
From page 102... ...
The further development of such predictive models will depend on the creation, maintenance, and accessibility of large databases of invasive species worldwide. Experimental plantings of individual species into areas beyond their native range potentially offer an alternative to predictive models and show promise in determining if a particular species will become invasive in a region.
|
From page 103... ...
The process for evaluating or predicting impact seems complex for biological control agents, yet with other non-indigenous species the process becomes even more complex because we have to consider impacts on many more than just one target species, as well as community or ecosystem effects. Ecologists have made little progress in predicting which invaders will have a big impact (Parker et al., 1999~.
|
From page 104... ...
These generalizations are interesting and represent an important first step in defining what is a large impact, but they guide prediction only in a very limited context. That is, identifying the potential change in population dynamics of a target host plant, identifying the species ecologically most similar to the invader, or identifying novel functions can be done only in the context of a particular natural community.
|
From page 105... ...
All five species of native European crayfish show extreme susceptibility to crayfish plague. As the crayfish plague spread through Europe, reduced population sizes and local extinctions of native species occurred, causing a marked decline in overall crayfish densities.
|
From page 106... ...
In a Swedish lake, Signal crayfish outcompeted native Noble crayfish for shelter, leading to greater perch predation on the native species (Soderback, 1994~. The evidence suggests that the crayfish plague and the introduced Signal crayfish have synergistic impacts.
|
From page 107... ...
Also of intermediate predictability are impacts of species that attack not just one but rather a fairly restricted suite of hosts, such as biological control agents with undesirable effects on nontarget species (Louda et al., 1997; Louda, 1998~. We may not predict their impacts perfectly, but with good basic information about the likelihood of alternate host use, we should make reasonable assessments of the risks.
|
From page 108... ...
Although we should not be paralyzed by the apparent complexity of predicting invasions, perhaps a more realistic and optimistic short-term goal of invasion ecology lies in analyzing impacts of currently widespread invaders for broad taxonomic, trophic, or geographic patterns. Such a synthesis of empirical work may tell us something about how we should manage already widespread invasive species.
|
From page 109... ...
As a result of this shift, regulatory bodies now must strive to incorporate appropriate levels of protection for natural systems, as well as agriculture and human health, in the development of new policy. Key to understanding the risk that invasive species pose to natural environments is understanding what types of ecological effects current invaders have on natural ecosystems.
|
From page 110... ...
Today, these deficiencies are particularly crippling because the rate of introductions has greatly accelerated due to increased human traffic (Lover, 1997; Cohen and Carlton, 1998~. Several approaches may help both ecologists and policymakers make some sense of the complexity of ecological impacts.
|
From page 111... ...
1989. Can we expect mathematical models to guide biological control programs?
|
From page 112... ...
2000. Trophic and taxonomic patterns of impact of invasive species: a meta-analysis.
|
From page 113... ...
1997. Ecological effects of an insect introduced for the biological control of weeds.
|
From page 114... ...
1992. Ecological impact of crayfish plague in Ireland.
|
From page 115... ...
1990. Assessing the risk of invasive species in Pinus and Banksia in South African mountain fynbos.
|
From page 116... ...
1989. Biological invasions by Myrica faya in Hawaii: Plant demography, nitrogen fixation, ecosystem effects.
|
From page 117... ...
1996. Biological Invasions.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.