Seed production and predispersal seed predation in the biennial composite species, Arctium minus (Hill) Bernh. and A. lappa L.

Abstract

Comparison was made of the seed production of two species of burdock, Arctium minus (Hill) Bernh. and A. lappa L., which are found in a variety of recently disturbed habitats throughout Waterloo County, Ontario. The mean number of seeds per plant of A. minus was significantly greater, 13,400 compared with 8,200 seeds in A. lappa. The mean number of heads per plant was also greater for A. minus than for A. lappa, 338 versus 112 heads respectively. Above-ground biomass allocated to reproductive heads was similar in A. minus (44.2%) and A. lappa (43.7%). Significant variation in the mean number of seeds per head was observed in A. minus, ranging from 29.0 to 47.1. The between-plant variation in this character is significantly greater than the variation between populations from various sites.Predispersal seed predation by the microlepidopteran Metzneria lappella (Fam. Gelechiidae) resulted in 28% to 71% loss of seeds of A. minus at different sites. The observed loss in A. lappa was dramatically lower at 15.5%. The number of seeds attacked by one larval predator varied from 2 to 15 with means from 7 to 9. In addition, great variation in the number of seeds and the number of predators per head was observed. Larvae were randomly distributed among the heads at 4 of 7 sites and aggregated at the other sites. Seed predation per head greater than 60% was found with the aggregated larval distributions. Only rarely was the number of seeds attacked by a larva associated with the number of larvae in the head. The winter dispersal of heads of A. minus was much lower than that for A. lappa, 62.2% and 21.0% respectively. Also, the dispersal of seeds from heads differed between the two species. Only 21.8% of the seeds of A. minus were lost compared with a seed dispersal rate of 56.5% for A. lappa.

Differences in herbivore damage toArctium minusin open and forest habitats in its non-native range

“…These figures (~0.3-2.1 larvae/capitulum) are somewhat higher than those reported in Lee and Kotanen 2015 (~0.5-0.8 larvae/capitulum), potentially reflecting slow colonization by herbivores of common garden plants in that study. Kambo and Kotanen (2014) did not report the number of larvae per capitulum, but the fraction of seeds damaged in southern populations (~40%-90%, dropping further north) was higher than found in this study (17%-49%, excluding a 5% outlier), possibly reflecting interannual variation; another study in southern Ontario (Hawthorn and Hayne 1978) reported intermediate levels of seed loss (28%-71%). Straw (1991) also found that understory plants in the UK had greater losses of seeds than plants in openings, even though these were attributable to a different family of insects (Tephritidae).…”

Seed dispersal spectra of plant communities in the Iberian Peninsula

“…Most exozoochores are herbaceous (Rockwood 1985), generally with heights of 1 m or less (Sorensen 1986), which tends to maximize the number of their contacts with dispersal vectors (Hawthorn & Hayne 1978;Lacey 1981;Sorensen 1986); these characteristics are typical of the communities that we, like Sorensen (1986), found exozoochores to be most prevalent in, the nitrophile communities.…”

Bird behaviour on and entanglement in invasive burdock (<em>Arctium</em> spp.) plants in Winnipeg, Manitoba

“…The fresh green flowers or burrs are just as adherent as dried burrs (TJU, personal observation) and can entrap birds (e.g., Hinam et al 2004). By late summer, when fall migration begins, a fresh crop of burrs is available, but over the winter many of these burrs fall off, e.g., >60% of Arctium lappa burrs and >20% of A. minus burrs (Hawthorn and Hayne 1978), or entire plants may be knocked down. Thus, the environmental risk of entanglement peaks in late summer and fall when songbirds are migrating through southern Manitoba.…”

“…on 3 September 2003, we observed a yellow-rumped Warbler take a small insect larva, possibly M. lappella, from a burr, providing the first real evidence that birds are attracted to burrs to forage on insects. First-instar M. lappella larvae appear in burrs by late July, mature in fall, and overwinter as larvae in burrs (Hawthorn and Hayne 1978). Thus, the availability of insects on burrs remains high during fall, providing another link to the greater number of birds found entangled in the fall.…”