Effects of Grazing by a Chrysomelid Beetle, Gastrophysa Viridula, on Competition Between Rumex Obtusifolius and Rumex Crispus

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. This content downloaded from 169.230.243.252 on Tue SUMMARY(1) The effects of clipping (simulated grazing) and grazing by a chrysomelid beetle, Gastrophysa viridula, on plants of two species of Rumex were investigated.(2) Although Gastrophysa viridula feeds on both Rumex obtusifolius and Rumex crispus in the field, the preference is for R. obtusifolius.(3) Moderate levels of grazing or clipping had no significant effects on plants of either species when competing intraspecifically.(4) In the conditions of the experiments, R. obtusifolius grew better when competing interspecifically with R. crispus than when competing intraspecifically, whilst the reverse was found for R. crispus.(5) This advantage of R. obtusifolius was removed by moderate levels of clipping or grazing. Clipping removed the competitive disadvantage of R. crispus but moderate grazing enhanced it.(6) Heavy grazing significantly reduced leaf area, leaf dry weight, root dry weight and whole plant dry weight of R. obtusifolius and R. crispus grown alone.(7) Rumex obtusifolius responded to heavy grazing by an increase in the root: shoot ratio, whereas R. crispus responded by a decrease in this ratio.(8) There was a significant interference interaction between interspecific competition and heavy grazing in R. crispus. This was especially marked below ground.(9) The possible relevance of these findings to observations on the distribution of the two Rumex species in the field is discussed. It is concluded that there may be circumstances in which grazing by Gastrophysa viridula may affect the distribution of Rumex crispus, and that this is more likely to be the case if it is growing in the presence of R. obtusifolius.

Additive and nonadditive effects of herbivory and competition on tree seedling mortality, growth, and allocation

“…The intensity of herbivory may also affect the H ϫ C interaction. Bentley and Whittaker (1979) only found an H ϫ C interaction at high levels of herbivory, while no interaction existed at lower levels. Both species had a significant H ϫ C interaction for mortality in this study.…”

“…In the five terrestrial studies that found no interaction between competition and herbivory, four found competition to be more important (Fowler and Rausher, 1985;Steinger and Müller-Schärer, 1992;Rees and Brown, 1992;Reader and Bonser, 1998) and the other found herbivory to be more important (Maron, 1997). Similarly, of the studies that found an interaction between competition and herbivory for growth, herbivory was more important for one (Bentley and Whittaker, 1979) and competition more important for others (Müller-Schärer, 1991;Swank and Oechel, 1991;Steinger and Müller-Schärer, 1992;Frost and Rydin, 1997). This relationship may be further complicated as the relative strength of herbivory and competition may change temporally with environmental conditions (Ang et al, 1994).…”

“…Some studies have found no statistical interaction between herbivory and competition (Duggins and Dethier, 1985;Fowler and Rausher, 1985;Rees and Brown, 1992;Steinger and Müller-Schärer, 1992;Maron, 1997;Reader and Bonser, 1998), while others have found a H ϫ C interaction for plant mortality (Parker and Salzman, 1985;Müller-Schärer, 1991;Reader, 1992), growth (Bentley and Whittaker, 1979;Lee and Bazzaz, 1980;Cottam, Whittaker, and Malloch, 1986;Müller-Schärer, 1991;Swank and Oechel, 1991;Hjältén, Danell, and Ericson, 1993;McEvoy et al, 1993;McPherson, 1993;Ang et al, 1994;Shabel and Peart, 1994;Mutikainen and Walls, 1995;Frost and Rydin, 1997), population size structure (Weiner, 1993;Shabel and Peart, 1994), and reproduction (Lee and [Vol. 87 AMERICAN JOURNAL OF BOTANY Bazzaz, 1980;Müller-Schärer, 1991;Ang et al, 1994).…”

The effect of elevated CO2 and grazing by Gastrophysa viridula on the physiology and regrowth of Rumex obtusifolius

“…The herbivory treatments also reduced LAR, which might result from a reduction in the quantity of foliage, but in these experiments both leaf area and leaf d, wt were not affected by the herbivory treatments. It would seem likely that R. obtusifolius allocated less of its resources into parts which were eaten by Gastrophysa, thereby increasing RS and decreasing LAR, The tendency for R. obtusifolius to allocate resources to roots in response to herbivory provides a competitive advantage over R. crispus (Bentley & Whittaker, 1979), The large root system of R. obtusifolius accounts for its persistence as a weed, plants being able to develop from root fragments and regrow from mown stumps (Weaver & Cavers, 1979;Foster, 1989), By the final harvest the changes in LAR had largely disappeared, and this might indicate that on the termination of herbivore feeding the pattern of allocation tended to return the allometry of the plant to that of the controls. Responses of this kind have been observed in grasses, Oesterheld (1992) showing that allocation towards the restoration of basic allometric ratios was a major priority regardless of the intensity of defoliation, Herbivory caused a significant decrease in SLA, Impacts of herbivory on SLA have not been covered to any degree in the literature.…”

Experimental evidence for insect impact on populations of short-lived, perennial plants, and its application in restoration ecology

“…Exclusion of insects also illustrates that they can alter plant competitive ability (Windle & Franz 1979;Bentley & Whittaker 1979;Bentley, Whittaker & Malloch 1980;Fowler & Rausher 1985;Cottam et al 1986;Louda et al 1990a).…”