Abstract
We conducted an herbivore-exclusion plus neighbor-removal experiment to determine whether herbivory and competition had independent or interactive effects on a wetland plant, blue vervain (Verbena hastata). Eight-week-old plants were added to 1.5 m2 experimental plots with neighboring reed canary grass (Phalaris arundinacea) either left intact or removed and herbivores either not excluded or excluded. Neighbors were removed with herbicide and hand-weeding while herbivores were excluded by surrounding a plant with 6-mm wire mesh and spraying the plant weekly with a systemic insecticide. Treatment effects were determined by monitoring plant survival over two growing seasons and by measuring inflorescence mass in the second season. The two treatments had a synergistic, interactive effect on plant survival (G=25.7, P<0.001). Four of the five plants per treatment survived when exposed to herbivory alone or to competition alone, but no plants survived when exposed to both herbivory and competition. The two treatments had a substitutive, interactive effect on inflorescence mass (F=11.26, P<0.0005). Mean inflorescence mass was only 0–1 g plant−1 when plants were exposed to herbivory alone or to competition alone or to both herbivory and competition. Plants not exposed to either herbivory or competition had a mean inflorescence mass of 60 g plant−1. Since effects of herbivory and competition were interactive rather than independent, future studies measuring either herbivory or competition effects on wetland plants should include both herbivore-exclusion and neighbor-removal treatments.
Similar content being viewed by others
Literature Cited
Bazely, D. R. and R. L. Jefferies. 1986. Changes in the composition and standing crop of salt-marsh communities in response to the removal of a grazer. Journal of Ecology 74:693–706.
Belanger, L. and J. Bedard. 1994. Role of ice scouring and goose grubbing in marsh plant dynamics. Journal of Ecology 82:437–445.
Bertness, M. D. 1991. Interspecific interactions among high marsh perennials in a New England salt marsh. Ecology 72:125–137.
Burger, J. C. and S. M. Louda. 1994. Indirect versus direct effects of grasses on growth of a caetus (Opuntia fragilis): insect herbivory versus competition. Oecologia 99:79–87.
Chapman, A. R. O., 1990. Effects of grazing, canopy cover and substratum type on the abundances of common species of seaweeds inhabiting littoral fringe tide pools. Botanica Marina 33:319–326.
Collette, A. 1983. Effect of spring flooding on the structure of riparian communities along the Speed River in southern Ontario. MSc. Thesis. University of Guelph, Guelph. Ontario, Canada.
Crawley, M. J.. 1990. The population dynamics of plants. Philosophical Transactions of the Royal Society of London B: 330:125–140.
D’Antonio, C. M. 1993. Mechanisms controlling invasion of coastal plant communities by the alien succulentCarpobrotus edulis. Ecology 74:83–95.
Duggins, D. O. and M. N. Dethier. 1985. Experimental studies of herbivory and algal competition in a low intertidal habitat. Oecologia 67:183–191.
Ellison, A. M. 1987. Effects of competition, disturbance and herbivory onSalicornia europea. Ecology 68:576–586.
Gleason, H. A. and A. Cronquist. 1991. Manual of Vascular Plants of Northeastern United States and adjacent Canada. 2nd edition. The New York Botanical Garden, New York, NY, USA.
Grace, J. B. and R. G. Wetzel. 1981. Habitat partitioning and competitive displacement in cattails (Typha): experimental field studies. American Naturalist 118:463–474.
Harper, J. L. 1977. Population Biology of Plants. Academic Press, London, UK.
Hatcher, P. E. 1995. Three-way interactions between pathogenic fungi, herbivorous insects and their host plants. Biological Reviews 70:639–694.
Howe, H. F. 1990. Survival and growth of juvenileVirola surinamensis in Panama: effects of herbivory and canopy closure. Journal of Tropical Ecology 6:259–280.
Jensen, A. 1985. The effect of cattle and sheep grazing on salt-marsh vegetation at Skallingen, Denmark. Vegetatio 60:37–48.
Maron, J. L. 1997. Interspecific competition and insect herbivory reduce bush lupine (Lupinus arboreas) seedling survival. Oecologia 110:284–290.
McEvoy, P. B., N. T. Rudd, C. S. Cox, and M. Huso. 1993. Disturbance, competition, and herbivory effects on ragwortSenecio jacobaea populations. Ecological Monographs 63:55–75.
McPherson, G. R. 1993. Effects of herbivory and herb interference on oak establishment in a semi-arid temperate savanna. Journal of Vegetation Science 4:687–692.
Metcalfe, W. S., A. M. Ellison, and M. D. Bertness. 1986. Survivorship and spatial development ofSpartina alterniflora Loisel, (Gramineae) seedlings in a New England salt marsh. Annals of Botany 58:249–258.
Mulder, C. P. H. and R. W. Ruess. 1998. Effects of herbivory on arrowgrass: interactions between geese, neighboring plants, and abiotic factors. Ecological Monographs 68:275–293.
Parker, M. A. and A. G. Salzman. 1985. Herbivore exclosure and competitor removal: effects on juvenile survivorship and growth in the shrubGutierrezia microcephala. Journal of Ecology 73:903–913.
Pennings, S. C. and R. M. Callaway. 1992. Salt marsh plant zonation: the relative importance of competition and physical factors. Ecology 73:681–690.
SAS Institute. 1996. SAS Release 6.12. SAS Institute Inc., Cary, NC, USA.
Sinclair, A. R. E. and R. P. Pech. 1996. Density dependence, stochasticity, compensation and predator regulation. Oikos 75:164–173.
Smith, T. J. 1983. Alteration of salt marsh plant community composition by grazing snow geese. Holarctic Ecology 6:204–210.
Sokal R. R. and F. J. Rohlf. 1995. Biometry. 3rd edition. W.H. Freeman, New York, NY, USA.
Swank, S. E. and W. C. Oechel. 1991. Interactions among the effects of herbivory, competition, and resource limitation on chapparal herbs. Ecology 72:104–115.
Taylor, K. L. and J. B. Grace. 1995. The effects of vertebrate herbivory on plant community structure in the coastal marshes of the Pearl river, Louisiana, USA. Wetlands 15:68–73.
Taylor, K. L., J. B. Grace, and B. D. Marx. 1997. The effects of herbivory on neighbor interactions along a coastal marsh gradient. American Journal of Botany 84:709–715.
Tyler, C. M. 1995. Factors contributing to postfire seedling establishment in chapparal: direct and indirect effects of fire. Journal of Ecology 83:1009–1020.
Tyler, C. M. 1996. Relative importance of factors contributing to seedling establishment in maritime chapparal. Ecology 77:2182–2195.
Vila, M. and F. Lloret. 1996. Herbivory and neighbour effects on the sprout demography of the Mediterranean shrubErica multifiora (Ericaeae). Acta Oecologia 17:127–138.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Rachich, J., Reader, R. Interactive effects of herbivory and competition on blue vervain (Verbena hastata L.: Verbenaceae). Wetlands 19, 156–161 (1999). https://doi.org/10.1007/BF03161744
Received:
Revised:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF03161744