Submitted to: Journal of Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2000
Publication Date: 2/1/2001
Citation: AGUIAR, M.R., LAUENROTH, W.K., PETERS, D.C. INTENSITY OF INTRA- AND INTERSPECIFIC COMPETITION IN COEXISTING SHORTGRASS SPECIES. JOURNAL OF ECOLOGY. 2001. V. 89. P. 40-47.
Interpretive Summary: Blue grama and buffalograss are important plant species that dominate or codominate throughout shortgrass steppe rangelands in Colorado, New Mexico, Oklahoma, Kansas, and Texas. We studied the response by these species to intra- and interspecific competition in order to better understand their patterns of coexistence in shortgrass steppe plant communities. We conducted an experiment at the Central Plains Experimental Range in northern Colorado to evaluate these responses. We placed plants of each species in a honeycomb design where the center target plant was either surrounded by plants of the same species (intraspecific competition) or by the other species (interspecific competition). We placed steel cylinders around half of the target plants in order to evaluate the effects of reduced belowground competition. We found that plants growing with reduced belowground competition had larger biomass and greater seed production than nplants growing with both above- and belowground competition. Intra- and interspecific competition were found to have similar affects on biomass for both species. Our results are important to our understanding of species dominance in shortgrass steppe rangelands and suggest that competition both within and between plants of blue grama and buffalograss is intense and important.
Technical Abstract: A previous study indicated photosynthesis of Bouteloua gracilis and Buchloe dactylaides has a similar response to temperature, achieving their maximum at high temperatures. Together, photosynthesis response and phenology determine no temporal segregation in growth for these 2 grasses. To study competitive abilities, we performed 2 experiments that combined both species to compare intra- and interspecific competition. One experiment was planted in a small homogeneous area and ran for 3 years; the other occupied an area 9-times larger and lasted 2 years. In each, we planted target plants of both species in a honeycomb design to get a combination of species, to control plant size and neighborhood asymmetries at the start of the experiment, and to represent field conditions. Steel cylinders placed around half the target plants reduced belowground competition. Plant biomass and seed production of plants growing inside the cylinders (reduced dcompetition) were higher than target plants growing in competition. In neither experiment was relative growth rate affected by competition in the last year. There was no difference between the two species in intra- and interspecific relative competition intensity (calculated with biomass); seed production was more variable than biomass. In some years, intra- and interspecific competition equally reduced seed production; in others, the interspecific competition effect was more intense. Competition theory predicts intraspecific competition must be greater than interspecific for 2 species with similar requirements to achieve coexistence. Results suggest intense competition between these 2 species with similar environmental requirements and, in general, these species are not affected differentially by intra- and interspecific competition.