Although the ecology of many exotic invaders has been intensively examined in the novel range, few studies have comparatively explored how population dynamics differ in native and novel parts of an invading plants' range. The population dynamics of mile-a-minute weed, Polygonum perfoliatum L., was explored in both the native (Japan) and novel (northeastern USA) portions of its range and evaluated using periodic matrix models. Projected per capita population growth rate (k) varied within and between native and novel range populations. Surprisingly, five of the six populations in the novel range were projected to fail to replace themselves (k<1) while only two of the four native range populations were projected to decline, although these projections had wider confidence intervals than in the novel habitat. While changes in germination, survivorship, fecundity and seed banking would have equivalent effects on population growth in the invasive habitat, small increases in plant survivorship would greatly increase k in native populations. The differences between native and novel population growth rates were driven by lower adult survival in the native range caused by annual flooding and higher fecundity. Simulation analyses indicated that a 50% reduction in plant survival would be required to control growing populations in the novel range. Further comparative studies of other invading species in both their native and novel ranges are needed to examine whether the high per capita population growth and strong regulatory effects of adult survival in the native habitat are generally predictive of invasive behavior in novel habitats.
In order to predict species‐specific potential to form persistent soil seed‐banks and to characterize the dynamics of their seed‐banks, the seed dormancy/germination traits of seven Persicaria (Polygonum s.lat.) species sharing lakeshore habitats in central Japan were examined. Strict light requirements for seed germination were not observed in any of the species examined. Although all species required moist chilling (0–6 weeks) to break seed dormancy and were sensitive to temperature fluctuation, the degree of both responses varied between species. Seed germination of Persicaria hydropiper (L.) Spach, Persicaria lapathifolia (L.) S.F. Gray, and Persicaria longiseta (De Bruyn) Kitag. was more accelerated by temperature fluctuation and required shorter chilling periods compared with Persicaria japonica (Meisn.) H. Gross, Persicaria maackiana (Regel) Nakai, Persicaria thunbergii (Sieb. et Zucc.) H. Gross, and Persicaria sieboldi (Maisn.) Onki. Secondary dormancy was induced in all species at higher temperatures (24 and 30°C). A persistent seed‐bank strategy suggested by the dormancy/germination traits of the studied species was also demonstrated by seedling emergence from surface soils collected from the natural habitat immediately before seed dispersal, as well as by viable seed persistence for 13 months in the field in a seed burial experiment. In the natural habitat, the species with longer chilling requirements occurred in various microhabitats, including the interior of moist tall grasslands, whereas the species having higher sensitivity to temperature fluctuation were most frequently found in sparsely vegetated microhabitats.
Summary 1.A simple experimental device was designed, in which seeds can be exposed to natural fluctuation of surface soil temperature under a constant soil moisture condition maintained by an automatic water supply system based on the principle of a Mariotte siphon. 2. Except for the period during summer drought, surface soil temperature at a depth of 5 cm and its fluctuation within the device were largely similar to the temperature of the surface soil subjected to natural fluctuation of moisture. 3. The seeds of Persicaria lapathifolia placed at the depth of 0·5 cm in the soil within the device germinated during the natural germination season of the species, while the seeds placed at the depth of 5 cm or beneath the 10 cm-thick layer of litter failed to germinate. 4. The ungerminated seeds retrieved in August did not germinate at the favourable alternating temperature in the laboratory test unless exposed to previous moist chilling, suggesting the induction of secondary dormancy. Therefore, higher summer temperatures but not summer drought or moisture fluctuation seem to have been responsible for the dormancy induction, because the dormancy was induced in the fully hydrated seeds.
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