Reproductive systems and colonization in Canadian weeds
TL;DR: It was concluded that self-fertilization in annual, biennial, and caespitose perennial weeds, and in a few instances, agamospermy in caesp itose perennials, are factors that help make them successful weeds.
Abstract: Flowers of 65 Canadian weeds were bagged to determine if external pollinators were needed for seed set. All of the 33 annual weeds studied, and 21 of the 23 biennials and caespitose perennials, set...
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TL;DR: This study compares individual phenotypic plasticity for components of fitness in four congeneric annual plant species with contrasting ecological distributions to reveal highly complex differences among the species in patterns of plastic response.
Abstract: The ecological distribution of species is influenced by individual patterns of response to environment for traits that contribute to fitness. Comparative data on fitness responses to complex environments are particularly valuable for understanding the relation of plasticity to ecological breadth. This study compares individual phenotypic plasticity for components of fitness in four congeneric annual plant species with contrasting ecological distributions (Polygonum cespitosum, P. hydropiper, P. lapathifolium, and P. persicaria). Replicate seedlings of 32 inbred lineages drawn from five natural populations per species were grown to maturity under controlled conditions in all 12 possible combinations of low and high light; dry, moist, and flooded soil; and poor vs. rich nutrients. Timing of reproduction, total reproductive output, offspring size, and allocation to reproduction were determined for each plant. The data revealed highly complex differences among the species in patterns of plastic response for f...
304 citations
TL;DR: It is a weed of orchards, vineyards, roadsides, and arable fields where tillage has been reduced or eliminated and serves as a wild host of the tarni shed plant bug and of aster yellows, a mycoplasma disease transmitted by the aster leaf hopper.
Abstract: Conyza canadensis (L.) Cronq. (Canada fleabane, horseweed, mare’s-tail) is a winter or summer annual, native to North America, and found in all provinces of Canada except Newfoundland. It is a weed of orchards, vineyards, roadsides, and arable fields where tillage has been reduced or eliminated. Most seedlings emerge from late August through October and form rosettes which overwinter. Large numbers of small, wind-dispersed seeds, ranging to over 200 000 seeds per plant, are produced in late summer. Populations of C. canadensis in more than ten countries have evolved resistance to herbicides such as paraquat, atrazine, chlorsulfuron or glyphosate. Several paraquat resistant populations were found in orchards in Essex Country, Ontario. It serves as a wild host of the tarni shed plant bug, and of aster yellows, a mycoplasma disease transmitted by the aster leaf hopper. Key words: Canada fleabane, ERICA, Conyza canadensis, Erigeron canadensis, horseweed
238 citations
TL;DR: Results from experimental pollinations suggest that seed production of S. juncea was at its potential maximum throughout the flowering season, and the major factor influencing the relative abundances of honeybees on these four species of goldenrod seemed to be overlap among the flowering periods of the goldenrods and those of several introduced plant species.
Abstract: Four co-occurring species of goldenrod bloom at different times with varying degrees of overlap; in order of peak flowering they are Solidago juncea, S. graminifolia, S. canadensis, and S. nemoralis. All four species are self-incompatible and require an insect vector for successful seed- set. First, the relationship between flowering time and seed-set of individual plants of these four species was determined. All four species of Solidago had significant differences in both the percentage of filled seeds and the total seed-set of clones that flowered at different times. Early-flowering clones had lower seed-set than did late-flowering clones in S. canadensis, S. graminifolia, and S. nemoralis. In contrast, early-flowering ramets of S. juncea had significantly greater seed-set than did late-flow- ering ramets. Secondly, the underlying factors limiting seed-set were investigated by observational and experimental techniques, in order to lend insight into the processes which can select for flowering time in natural plant populations. The abundance of pollinators on goldenrods and other plant species and the abundance of flower predators were monitored over the season. Experimental hand-pollina- tions were performed on individual plants of each species over the entire flowering season, to deter- mine if seed-set was limited by the amount of pollen reaching stigmas or by factors intrinsic to individual plants which flowered at different times. Apis mellifera, the introduced honeybee, is the major pollinator of goldenrods in this system. The major factor influencing the relative abundances of honeybees on these four species of goldenrod seemed to be overlap among the flowering periods of the goldenrods and those of several introduced plant species. Apis began visiting goldenrods at a point when the abundance of flowers in the weedy flora had declined greatly. The flowering period of S. juncea overlapped almost entirely with the flowering periods of several species in the weedy summer flora. This appears to explain the lack of Apis visits to S. juncea, which was visited only by small, native bees and beetles. However, the results from experimental pollinations suggest that seed production of S. juncea was at its potential maximum throughout the flowering season. In early-flowering clones of S. graminifolia, the natural seed-set was significantly lower (by 57%) than the maximum potential seed-set determined from experimental pollinations, but in late-flowering clones there was no difference between actual and potential seed-set. Of the reduction from potential seed-set in early-flowering clones, the low frequency of honeybee visits was estimated to account for most of the loss, and flower predation by the blister beetle, Epicauta pennsylvanica, accounted for the remainder. In S. canadensis, the seed-set of both hand-pollinated and control flowers was greater in late- relative to early-flowering clones of S. canadensis (i.e., late-flowering clones had greater physiological potential for seed production). The differences in the seed-set of clones flowering at different times were due to physiological or microenvironmental differences among clones. There was also some degree of pollen limitation of seed-set (17-34% of the potential maximum seed-set) at all times. Again, pollen limitation of seed-set was due mostly to pollinators, as opposed to flower predators. In S. neinoralis, the late-flowering clones had significantly higher seed-set than early-flowering
230 citations
01 Jan 1990
TL;DR: This chapter reviews the physiological, demographic and genetic attributes of invaders sensu stricto (excluding native weeds or colonists), and the need for an approach combining ecolological and evolutionary features of habitats and introduced species is emphasized.
Abstract: A unique attribute of invaders is that they thrive in a country in which they did not evolve. In this chapter, I review the physiological, demographic and genetic attributes of invaders sensu stricto (excluding native weeds or colonists). When compared to similar native species, invaders often have features likely to endow them with higher relative fitness. However, the few available comparisons may constitute a biased sample. Attempts to generalize show that the invasive flora of a country is composed of a large array of plant types and that there are no attributes with which to characterize invaders in general. More specific approaches of invasions, centered on the invaders or the recipient habitats, are reviewed. The need for an approach combining ecolological and evolutionary features of habitats and introduced species is emphasized.
196 citations