NEIGHBORHOOD COMPETITION IN AN OLD-FIELD PLANT COMMUNITY'

A series of field neighborhood experiments was performed to compare the competitive effects of seven plant species on the performance of transplanted individuals of Solidago canadensis. The neighbor species included conspecifics and species of a variety of growth forms that co-occur with S. canadensis in old fields. There were strong competitive effects on the transplants; average S. canadensis growth was reduced 17-62% by the presence of neighbors growing at natural densities. The responses to gradients of increasing neighbor density or biomass appeared to be nonlinear, with decreasing effects of adding more neigh- bors at higher neighbor density or biomass. Competitive effects were compared among neighbor species at three levels: effects at natural densities, per-individual (population density) effects, and per-gram (biomass den- sity) effects. The magnitude of total effects at natural densities varied with the species of neighbor plants and was stronger for neighbor species with greater total biomass of plants per unit area. The magnitude of effects of each individual also varied with neighbor species and was stronger for neighbor species with larger mean biomass per individual. Conse- quently, per-gram competitive effects did not differ among the neighbor species. Thus, it appears that the differences in competitive effects among species were primarily due to differences in size or abundance, rather than to more subtle differences in aspects of resource use. The responses of target Solidago canadensis individuals to neighborhood competition were very variable. A maximum of 40% of the variance in individual performance was explained by any one of the measures of abundance of neighbors, and, in half of the neighbor species, < 100% of the variance in target performance was explained by abundance of neigh- bors. Competition intensity seems to limit the maximum potential growth of individuals, but actual growth was often below the boundary determined by competition.

[1]  W. Dixon,et al.  BMDP statistical software , 1983 .

[2]  J. E. Pinder.  Effects of Species Removal on an Old‐field Plant Community , 1975 .

[3]  J. P. Grime,et al.  Evidence for the Existence of Three Primary Strategies in Plants and Its Relevance to Ecological and Evolutionary Theory , 1977, The American Naturalist.

[4]  J. Silander,et al.  Analysis of interspecific interactions in a coastal plant community—a perturbation approach , 1982, Nature.

[5]  M. Caldwell,et al.  Competition for Phosphorus: Differential Uptake from Dual-Isotope—Labeled Soil Interspaces Between Shrub and Grass , 1985, Science.

[6]  P. Keddy,et al.  Measuring Diffuse Competition Along an Environmental Gradient: Results from a Shoreline Plant Community , 1986, The American Naturalist.

[7]  Jacob Weiner,et al.  A Neighborhood Model of Annual‐Plant Interference , 1982 .

[8]  J. Gurevitch.  Competition and the Local Distribution of the Grass Stipa Neomexicana , 1986 .

[9]  Thomas W. Schoener,et al.  Field Experiments on Interspecific Competition , 1983, The American Naturalist.

[10]  John L. Harper,et al.  INTERFERENCE IN DUNE ANNUALS: SPATIAL PATTERN AND NEIGHBOURHOOD EFFECTS , 1977 .

[11]  T. Fagerström,et al.  Limiting dissimilarity in plants: randomness prevents exclusion of species with similar competitive abilities , 1984 .

[12]  G. A. Mulligan.  The biology of Canadian weeds , 1979 .

[13]  D. Goldberg,et al.  Competitive effect and response in four annual plants , 1987 .

[14]  D. R. Strong,et al.  Density vagueness abiding the variance in the demography of real populations , 1986 .

[15]  S. Pacala,et al.  Neighborhood Models of Plant Population Dynamics. I. Single-Species Models of Annuals , 1985, The American Naturalist.

[16]  J. Harper,et al.  Studies in the dynamics of plant populations. 3. The influence of associated species on populations of Rumex acetosa L. and R. acetosella L. in grassland. , 1970 .

[17]  K. Gross.  Colonization by Verbascum thapsus (Mullein) of an old-field in Michigan : experiments on the effects of vegetation , 1980 .

[18]  N. Fowler.  Competition and coexistence in a North Carolina grassland. II. The effects of the experimental removal of species. , 1981 .

[19]  J. Connell.  Diversity and the coevolution of competitors, or the ghost of competition past , 1980 .

[20]  T. Miller,et al.  Competitive Effects and Responses Between Plant Species in a First‐Year Old‐Field Community , 1987 .

[21]  D. Goldberg.  Effects of Soil pH, Competition, and Seed Predation on the Distributions of Two Tree Species , 1985 .

[22]  D. Goldberg,et al.  Equivalence of competitors in plant communities: a null hypothesis and a field experimental approach. , 1983 .

[23]  D. Peart,et al.  Analysis and Prediction of Population and Community Change: A Grassland Case Study , 1985 .

[24]  R. Forman,et al.  Plant Species Removals and Old‐Field Community Structure and Stability , 1976 .

[25]  R. Moral.  COMPETITION AS A CONTROL MECHANISM IN SUBALPINE MEADOWS , 1983 .

[26]  J. Antonovics,et al.  Competition and Coexistence in a North Carolina Grassland: I. Patterns in Undisturbed Vegetation , 1981 .

[27]  J. Harper.  Population Biology of Plants , 1979 .

[28]  Stephen P. Ellner,et al.  Coexistence of plant species with similar niches , 1984, Vegetatio.

[29]  I. Bradbury,et al.  THE BIOLOGY OF CANADIAN WEEDS.: 45. Solidago canadensis L. , 1980 .