Predicting Invasions of Nonindigenous Plants and Plant Pests (2002) / Chapter Skim
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3 Establishment
3 Establishment
Pages 41-77
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From page 41... ...
Only an estimated 10% of all nonindigenous insect species that are introduced into a new range become established. Even when insects are carefully selected for intentional introduction as biological control agents, only about 33% become established (Williamson and Fitter 1996~.
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From page 42... ...
Even the planet's most abundant and widespread invasive species commonly began as "rare" species in their new ranges, compared with the size of their populations in their native ranges. (There are exceptions; see Eckert et al.
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From page 44... ...
, demographic stochasticity might well be viewed as "the immediate precursor of extinction." Environmental Stochasticity Environmental stochasticity usually reflects the impact of random variation in the environment as it influences a population. In its simplest form, the demographic effects of environmental perturbations are assumed to be equally distributed across all individuals in a particular age or stage class in a population.
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From page 45... ...
has suggested that when environmental stochasticity is present, expected population persistence time increases roughly as a linear function of population size. Given that the typical effect of increasing environmental stochasticity is to reduce the likelihood of population persistence, there should be selective value in the capacity of an organism to reduce the demographic impact of environmental variation.
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From page 46... ...
1984, Barrett and Shore 1989, Novak and Mack 1993~. Low diversity at the population and regional levels is especially evident in plant species that propagate by asexual reproduction, sometimes called selling.
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From page 47... ...
Influence of Allee effects on establishment has been addressed by examining the dynamics of populations of nonindigenous species released in biological control programs. Hopper and Roush (1993)
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From page 48... ...
A newly arrived immigrant species will persist, therefore, only if at least some subpopulations experience "good times" while other subpopulations suffer reduced population growth during "bad times". In contrast, spatially structured populations may be subject to inverse density dependence regardless of environmental conditions if subpopulations are diluted by dispersal.
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From page 49... ...
That approach has application for nonindigenous species: one can ask how nonindigenous species differ in their potential for becoming common. If we assume that immigrants initially consist of small, sparse populations.
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From page 50... ...
Avoiding Stochasticity: Multiple Introductions and Population Size Aside from the obvious inability of a population to survive under a climatic regimen that is well beyond its tolerance, stochasticity is the greatest threat to small populations. And as stated above, small numbers typify most unintentional introductions of nonindigenous species.
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From page 51... ...
In the Canadian biological control programs, nonindigenous species that were released in at least 10 episodes established in 70% of the cases; those released in fewer than 10 episodes established in only 10% of the cases (Bierne 1975~.
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From page 52... ...
Abiotic Factors The likelihood of establishment will be affected by the general climatic match between the donor habitat and the new habitat of the immigrant species. Moreover, the geographic distribution and range of climatic conditions known to have been suitable for the immigrant species in its native range or in previously invaded regions provide some indication of potentially suitable habitats.
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From page 53... ...
The influence of climate on the incidence of plant disease incidence has been studied for those indigenous and nonindigenous microorganisms that exist in the United States and infect agricultural crops (Coakley 1988~. Numerous climatic factors, particularly moisture and temperature, dictate where a microbe survives and whether it is able to infect a suitable host.
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From page 54... ...
Disturbance can reduce an immigrant population to such a low density that demographic stochasticity could cause extinction. It can also adversely affect population persistence if it increases environmental stochasticity or takes the form of natural or human-mediated catastrophes.
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From page 55... ...
The immigrants must be able to locate suitable host plants or come into contact with a suitable host through the deposition of spores and eggs or other dispersal units, survive interactions with newly encountered enemies, and compete with native species. A new nonindigenous insect or pathogen is often not detected for years or even decades (Carey 1996)
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From page 56... ...
Crawley (1986) analyzed establishment of insects released for the biological control of nonindigenous plants and concluded that the most common reason for their failure to establish was insect-plant incompatibility.
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From page 57... ...
Nonindigenous insects that are capable of feeding on a wide variety of hosts often can forage on novel hosts in their new range. Therefore, insects that are able to use many species as hosts in their native range could be less reliant on locating plants in a new range that are similar to their native diet; this lack of specificity could facilitate establishment.
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From page 58... ...
They suggested that a continent-wide conifer afforestation program in Europe has been a major factor in this host-range extension. Abundance and distribution of host plants may also be related to how Allee effects influence a low-density population of a newly introduced species.
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From page 59... ...
Evidence of the ability of indigenous species to prevent establishment of nonindigenous insects in its new range is scarce, and the topic deserves much further research. Much of the evidence stems from postrelease evaluations of herbivorous insects introduced for biological control.
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From page 60... ...
If resident enemies are more likely to prevent establishment of a nonindigenous species that is similar to their native prey, the converse prediction is that establishment should be more likely for species that are different from native prey species (Lawson and Brown 1986~. Lawton and Brown (1986)
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From page 61... ...
The hypoviruses appear to have their origin in eastern Asia with their fungal host (Peever et al., 1998~. Hypoviruses or their genetically modified variants eventually may prove useful as biological control agents for chestnut blight within chestnut's native North American range (Dawe and Nuss 2001~.
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From page 62... ...
Those examples involve spectacular action by resident pathogens, but we do not know how often such phenomena occur. Some generalist parasites thwart establishment of nonindigenous species.
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From page 63... ...
The authors attributed extinction of the ant to competition with aggressive native fire ants and extinction of the lizards to competition and predation by resident species. Introductions of herbivorous insects for the biological control of nonindigenous plants often provide little information, because interspecific competition is, by careful prerelease evaluation, minimal in such situations.
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From page 64... ...
Another difficulty in addressing how competition affects establishment arises because we cannot necessarily distinguish between effects of natural enemies and of competitors when a nonindigenous species arrives. An immigrant species and a native prey species can exhibit "apparent competition" through a shared enemya concept similar to the competition for enemy-free space described by Jeffries and Lawton (1984~.
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From page 65... ...
In the context of nonindigenous species' entry and survival, only one or neither species may be native to the new range (Simberloff and Von Holle 1999, Richardson et al.2000~. The scenarios by which this dependence can occur are well known and begin with the absence of an obligate pollinator.
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From page 66... ...
forces. However, no factor related to predicting the establishment of nonindigenous species has been pursued more assiduously or longer than a link between the life-history traits of species and their ability to become established in a new range.
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From page 67... ...
Dioecy does not, however, appear to be a major limitation for species establishment; there are dioecious invasive plant species, such as Rumex acetosella, Ailanthus altissima, and Ilex aquifolium. Uniparental sexual reproduction arises from self-fertilization and is facilitated by hermaphrodite sex expression.
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From page 68... ...
Their results suggest that an optimal mating system for a sexual invader should include the ability to alter selling rates according to local environmental and demographic conditions. When populations are small or individuals are at low density during the early phases of establishment in a new range, plants should be selfers to maximize fertility, thus increasing population growth rates.
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From page 69... ...
Length of the juvenile period can be difficult to determine accurately for woody species, for which several years can elapse before onset of reproduction. Length of the juvenile period has been used repeatedly to predict persistence of nonindigenous species (Rejmanek and Richardson 1996, Reichard and Hamilton 1997, Pheloung et al.
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From page 70... ...
in Hawaii and found that the invasive species were better suited to capturing and using light than a large group of natives. Pathogens Life-history traits important for the establishment of plant pathogens include reproductive strategies and genetic variability related to fitness, virulence, and host compatibility.
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From page 71... ...
The importance of variability in virulence for establishment tends to be greater among pathogen populations with narrow host ranges. High complexity for virulence is often found in clonally (asexually)
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From page 72... ...
Parthenogenesis does appear to be frequently associated with establishment of nonindigenous insects. A large fraction of the nonindigenous invertebrates that became established in Hawaii are parthenogenic or hermaphroditic (Howarth
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From page 73... ...
In a review of biological control projects Crawley (1986) found that arthropods with high fecundity, short generation time, or female-biased sex ratios were more likely to establish than comparable arthropods with lower population growth rates.
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From page 74... ...
Inbreeding in low-density populations can reduce the fitness of progeny. There are cases, however, where reduced heterozygosity resulting from a genetic bottleneck has enhanced the success of a nonindigenous species.
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From page 75... ...
. An Allee effect arising from low reproductive success or survival in lowdensity populations can strongly influence the ability of a newly arrived, nonindigenous species to persist.
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From page 76... ...
· Host plants must be temporally and spatially available to newly arriving nonindigenous insects and pathogens for their establishment in the new range. · A vector is necessary for the establishment of some pathogens; in these cases, abundance, spatial distribution, and temporal availability of the vector will affect establishment.
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From page 77... ...
· High intrinsic rate of increase, uniparental reproduction, and a dormant or resilient life stage that permits surviving temporally unfavorable conditions characterize many insect invaders. Other life-history strategies, such as long-lived adult stages, are common among established nonindigenous insects.
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