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

1979; Wiley; Volume: 67; Issue: 1 Linguagem: Inglês

10.2307/2259338

1365-2745

S. Bentley, J. B. Whittaker,

Ecology and Vegetation Dynamics Studies

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.