Competition and spacing in plant communities: the northern -Mohave Desert

Intraspecific and interspecific spacing and competition were studied in a diverse plant community in the northern Mohave Desert. Measurements of the sizes of nearest-neighbour plants and the distances between them were taken for three species, Opuntia acanthocarpa (acan), O. ramosissima (ramo) and Yucca schidigera (yucca). The following results were obtained. (1) Competition is occurring between all intraspecific and interspecific nearest-neighbour pairs. (2) No difference in the degree of competition could be detected between morphologically similar and dissimilar interspecific species-pairs (i.e. acan-ramo and acan-yucca). (3) Individuals of different species occur significantly closer together than individuals of the same species. (4) Despite the fact that ramo has a larger photosynthetic surface area (PSA) than acan in relation to bush diameter, for large sums of PSA ramo individuals are spaced closer together than acan individuals.