Competition between Bouteloua curtipendula and Bothriochloa ischaemum

Competition between species is one of the major factors that appear to control community composition. The results of competition between Bouteloua curtipendula (sideoats grama), an important prairie grass, and Bothriochloa ischaemum (King's ranch bluestem), an introduced grass are not known. These two species were studied to determine possible differences in competitive ability. Several competition experiments were carried out on B. curtipendula and B. ischaemum in a UTSA greenhouse during spring 2012. Intraspecific competition experiments were performed on each species separately to measure the effects of increasing plant density on above ground, below ground, and total drymass. Interspecific competition experiments were also carried out to measure effects of changing proportions of the two species at the same density, as well the added effects of soil nutrients and herbivory on each species separately. Density was 1, 2, 4, 8, and 16 plants per pot in the intraspecific competition experiments. Density was 20 plants per pot with proportions of 20:0, 15:5, 10:10, 5:15, and 0:20 (B. curtipendula:B. ischaemum) in the interspecific competition experiment. MANOVAs were used to compare mean plant height or total leaf length and basal diameter to all factors, and to compare above ground, below ground, and total drymass to all factors in each experiment. Mean plant height and mean basal diameter were compared to density or proportion and days since planting by using two factor ANOVAs. Mean total leaf length and basal diameter were compared to proportion, days since planting, and nutrient treatment by using three factor ANOVAs. Above ground, below ground, and total drymass was compared to density or proportion by using one factor ANOVAs, and compared to proportion and nutrient treatment using two factor ANOVAs. Results indicated that there were significant differences. Intraspecific competition experiments demonstrated that B. curtipendula and B. ischaemum mean above ground and total drymass both decreased as density increased. The interspecific competition experiment demonstrated that the mean below ground, and total drymass of B. ischaemum was increased when grown in competition with B. curtipendula, while the mean above ground, below ground, and total drymass of B. curtipendula was not significantly different among proportions. The added effects of nutrient levels and herbivory altered the response of B. ischaemum and B. curtipendula in the interspecific competition experiments. Simulated herbivory of B. curtipendula allowed B. ischaemum to increase when grown in interspecific competition, while B. curtipendula was inhibited. Simulated herbivory of B. ischaemum caused equal responses among B. ischaemum and B. curtipendula. The above ground, below ground, and total drymass of both species were reduced when B. ischaemum was subjected to simulated herbivory. Bothriochloa ischaemum appeared to out-compete B. curtipendula in the interspecific competition experiments, but the added effect of simulated herbivory of B. ischaemum equalized competitive abilities of both species. Further experimentation of herbivory of B. ischaemum coupled with other abiotic factors may demonstrate a course of management, in which B. curtipendula or other native species can out-compete introduced and potentially invasive species such as B. ischaemum.