The role of clonal and sexual spread in cacti species dominance at the Brazilian Caatinga

Resumo

A large part of flowering plants have sexual and asexual propagation. The occurrence of these reproductive modes is probably related to adaptive responses to environmental conditions, species distribution, genetic variation and the maintenance of multiple biological interactions. Here we examined populations of eight cacti species from Brazilian Caatinga (Arrojadoa rhodantha, Cereus jamacaru ssp. jamacaru, Harrisia adscendens, Pilosocereus gounellei ssp. gounellei, Pilosocereus pachycladus ssp. pernambucoensis, Melocactus zehntneri, Tacinga inamoena and Tacinga palmadora) and verified how clonal and sexual spread contribute to these species’ dominance. We surveyed populations of these species in 30 plots of 50x20m in natural areas of Caatinga at Parnamirim municipality, in these plots adults and seedlings/saplings via sexual and asexual reproduction were recorded. We registered a total 2692 individuals from the eight studied species. The most abundant species were A. rhodantha, P. gounellei ssp. gounellei, M. zehntneri, T. inamoena and T. palmadora (> 200 individuals registered), while C. jamacaru ssp. jamacaru, H. adscendens and P. pachycladus ssp. pernambucoensis (< 100 individuals registered). We verified that the high investment in sexual, or in both propagation modes (clonal and sexual) explained the dominance of the cacti species. These results illustrate the vulnerability of some species with small populations, moreover the importance of both reproductive modes to understand the dominance of some cacti species. Cacti species with high investment in sexual reproduction or in both propagation modes (e.g., P. gounellei ssp. gounellei) could be considered less endangered because are able to keep locally and regionally their populations.