Predicting Invasions of Nonindigenous Plants and Plant Pests (2002) / Chapter Skim
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4 Biotic Invasion
4 Biotic Invasion
Pages 78-94
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From page 78... ...
From the case histories of individual invasions, it is apparent that the transition in each case has been propelled by a unique and accidental chain of events in which community dynamics and the resources of the environment interact with the biological characteristics of an established species in a way that fosters its proliferation (Crawley 1989a)
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From page 79... ...
(1997) compiled life tables for herbivorous insects and examined patterns in mortality caused by natural enemies to determine whether established nonindigenous species sustained lower mortality from resident natural enemies than did natives.
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From page 80... ...
Thus, information about the diversity, life history, and importance of natural enemies in the native habitat will be valuable in estimating the potential effects of the resident enemies on the dynamics of newly established nonindigenous insects. The longer a population is established and is expanding into a new range, the more likely it is to come into contact with a greater diversity of conditions and organisms (Strong et al.
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From page 81... ...
Shigesada and Kawasaki (1997) suggest that natural expansion of gypsy moth populations, which occurs when recently hatched larvae balloon on the wind, may exemplify a type 1 curve.
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From page 82... ...
Life history, morphology, and behavioral traits related to dispersal of a newly established species obviously play important roles in determining the rate of range expansion (Hastings 1996) , and knowledge of such characteristics would be useful in predicting the likelihood of invasion.
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From page 83... ...
1992~. In a simple diffusion model, the range of an immigrant expands solely by diffusion without population growth.
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From page 84... ...
Presence of an Allee effect or an increase in the diffusion coefficient will require the initial "beachhead" to be larger if the population is to avoid extinction. Even if an immigrant population initially arrives in a new area at a density above its critical Allee effect threshold, an Allee effect will increase the period before expansion begins (Veit and Lewis 1996)
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From page 85... ...
Continued research into and documentation of the spatial and temporal aspects of known invasions will be necessary if we are to improve our understanding of patterns of range expansion and of the mechanisms by which invasions progress. COMPETITION FOR RESOURCES Community Diversity and Resources Community diversity is viewed as the factor that most influences a community's susceptibility to invasion by nonindigenous species.
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From page 86... ...
Differential parasitism apparently shifted the competitive balance so that the native species was at a disadvantage compared with the nonindigenous species. Other studies have similarly shown that the establishment of a nonindigenous insect can be affected by complex interactions involving both potential competitors and resident natural enemies (Davis et al.1998, Muller and Godfray 1997~.
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From page 87... ...
In many invasive species, these competitive traits are revealed as the organism begins to proliferate. Evidence of interspecific competition among newly established insects or pathogens is scarce, but competition often plays a substantial role in plant invasions.
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From page 88... ...
An increase in the production of combustible fuel is perhaps the best-known environmental alteration caused by some invasive species. Some nonindigenous plants facilitate fire or alter the frequency or intensity of fires, whether by rapidly increasing fuel load or through the plant's chemical composition.
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From page 89... ...
, but this lack of diversity does not necessarily indicate that they lack genetic variation at all loci, particularly those governing quantitative traits related to fitness (Lewontin 1984, Brown and Burdon 1987~. Population differentiation within an invading population after range expansion should be expected, even in species with relatively low variation at neutral marker loci.
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From page 91... ...
1987, Burdon and Brown 1986~. Such diversity is likely to favor rapid evolution of local races, despite recent efforts at biological control.
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From page 92... ...
The rapidity with which a population can respond to selection will depend on the amount of additive genetic variation for fitness-related traits and the strength and direction of selection. Modern agricultural practices in which the grower makes every effort to eradicate unwanted plants, often including nonindigenous plantsprobably constitute some of the most intense selection pressures that introduced species encounter.
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From page 93... ...
Relevant dispersal components include the number of propagules available for movement, the opportunity for and mechanisms of dispersal, the distances that propagules are transported, and the spatial pattern of the dispersed propagules. · Although some invasions advance as a continuous wave front, most advance spatially by establishment of some minimal number of widely separated foci.
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From page 94... ...
The result is an increased probability of yielding an invading population. · Agricultural practices associated with a crop tend to provide intense and highly directional selection of invasive species which results in locally adapted races limited only by the area of the crop.
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