Spatial pattern and cover effect on the abundance of a currently obliterated population of Melocactus violaceus: a threatened species in Brazilian sandy coastal plain

Abstract

Environmental factors generally exhibit non-random patterns, and the spatial distribution of a species should, ideally, be translated into environmental patterns associated physiology and life-history constraints. This study was carried out in a habitat patch in Brazilian sandy coastal plain with occurrence of Melocactus violaceus subsp. margaritaceus. I investigated the spatial association between size classes and perennial plant cover from Spatial Analysis by Distance Index (SADIE) coupled with correlation analysis, in order to evaluate whether M.v. margaritaceus is associated with perennial plant cover. More-than-expected abundance was associated with bare ground for all size classes and less less-than-expected abundance in the patch of the perennial plants. The algorithm SADIE detected a significant clumped pattern in the spatial distribution of juveniles and adults abundance. Correlation analysis showed the presence of strong associations between size classes, except for cover which showed strong dissociations. Based on these analyses, I suggest that the establishment of this cactus species occurs preferably in bare ground or with little cover, and the spatial association is similar between size classes.