Skip to main content

Currently Skimming:

5 The Impact of Invasions
Pages 95-110

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 95...
... 2000) of invasions by species of plants, animals, and microorganisms generally do not include the displacement or extinction of native species that are of no immediate economic concern or the effects on native ecosystems, such as changes in fire regimes, nutrient cycling, or hydrology.
From page 96...
... Some support for that prediction comes from well-studied natural enemies released for biological control, in which suppression of target plant species increases with the number of control species established (Hoffmann and Moran 1998~. A second is that the more geographically isolated the biota of a region is, the more vulnerable it is to invasion.
From page 97...
... Impact can be represented as a linear combination of factors in the equation I = R x A x E If a nonindigenous species is widespread and abundant, prediction and comparison of the impacts of invaders rest with forecasting the per capita effect, E
From page 98...
... , especially if the invader becomes much more common than the native species; this seemingly hypothetical threat is both real and serious: three species federally listed as endangered in the United States have gone extinct since enactment of the Endangered Species Act because of hybridization with nonindigenous species (McMillan and Wilcove 1994~. Finally, hybridization among plants may spawn invasion by plant pathogens.
From page 99...
... Introduced biological controls can become less effective because of evolved changes in the virulence of control organisms or changes in the resistance of target organisms. Myxoma virus was released in Australia to control the introduced European rabbit Oryctolagus cuniculus.
From page 100...
... Population and Community Effects Invaders can cause reduction in the biological diversity of native species and the size of populations; next to land transformation, they are the most important cause of extinction (Vitousek et al.1996~. After habitat destruction (which affects 81% of imperiled plant species)
From page 101...
... Predictions of loss of regional biodiversity accompanying plant invasions have been based on observations of diversity decreasing with the extent of an invasion. For example, the impact of nonindigenous plants on native plants has been documented for fynbos vegetation on the Cape Peninsula in South Africa.
From page 102...
... Likewise, beech bark disease, caused by a nonindigenous scale insect and a pathogen, has led forests once composed of beech thickets or sites to be transformed to grass or shrub land-a change that can alter fire regimes (Oak 1998~. Both maladies have affected wildlife populations that depend on beech nuts (Martin et al.
From page 103...
... Examples of such species are natural enemies of pests for biological control; aesthetically pleasing, fast-growing, pollution-resistant horticultural plants; fish communities in reservoirs; and grasses that can reclaim strip-mined land in arid regions. The danger arises from nonindigenous species that either play no constructive role or play unexpected roles in their new ranges.
From page 104...
... Researchers found that increased abundance of acorns was associated with lower gypsy moth survival but higher densities of mice and host-seeking deer ticks, which presumably increase the incidence of Lyme disease. Such chain reactions are difficult to identify, let alone predict or manage.
From page 105...
... A brief examination is warranted of how chestnut blight and gypsy moths have created cascading events to alter forest organization rapidly. Chestnut blight resulted in the most profound set of changes ever recorded in a North American forest ecosystem.
From page 106...
... The dynamics of beech bark disease begin as infestations by the scale insect and fungal infections of the bark occur along the killing front. As native beeches dies, the remaining beech trees are riddled with nonlethal infections that grotesquely deform them.
From page 107...
... The chief reason for the difficulty in evaluating the impact of invasions, however, is the lack of sufficiently detailed data on the species composition, structure, and function of ecosystems before they are invaded. That is clearly the case with the introduction of the chestnut blight fungus: the only information that exists about preblight forests is anecdotal or comes from postblight studies (Stephenson 1986~.
From page 108...
... 108 PREDICTING INVASIONS OF NONINDIGENOUS PLANTS AND PLANT PESTS We are unlikely to obtain such quantitative information on patterns of variation and correlation among abundances of species in a community, so it is reassuring that simple qualitative analysis and modeling can further our understanding of potential ecological effects of nonindigenous species and serve as a practical tool for adaptive management (Li et al.
From page 109...
... · Effects or impacts of invasive species are often hard to measure and even harder to predict, because scientific uncertainty arises in quantifying each step in the invasion process. Moreover, data are lacking on species composition and species abundance in many ecosystems before the arrival of invasive species.
From page 110...
... . Invasive species often exert their influence by initiating a cascade of changes in the biotic and abiotic components of the ecosystem; examples are chestnut blight and gypsy moths in eastern North America.


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.