Presença de espinhos em plantas de fitofisionomias do Cerrado: resquícios da megafauna extinta brasileira?

Abstract

Large herbivorous mammals (here referred to as megafauna) are important ecosystem engineers, altering the structure of vegetation and favoring plant species that have defense mechanisms (e.g., spines). Ecosystems rich in resources (e.g., in fertile soils or close to watercourses) are preferred by large mammals due to the greater ease in obtaining these resources. Thus, in regions that have a preserved megafauna assemblage tend to be maintained in a savanna state by these animals due to consumption and related disturbances, even when the climate favors the development of forests. At the same time, the disturbance caused on plants in these ecosystems favors the dominance of species with defenses, such as thorns. Large herbivorous mammals are currently restricted to the African and Asian continents, but evidence indicates that approximately 10,000 years ago, these animals were also abundant in South America, that is, biomes in this continent evolved in the presence of megafauna. With the extinction of this megafauna, several savanna ecosystems became forested. However, even today some specific forests have thorns as an anachronistic feature and these thorns can be used to understand the interaction of these ecosystems with large herbivores in the past. In this work we tested the hypothesis that Cerrado physiognomies characteristic of fertile soils, such as Seasonal Deciduous Forest (SDF) and Semideciduous Forest (SSF), and with watercourses, such as Riparian Forests (RF), were more used than other phytophysiognomies by large herbivorous mammals, leaving a legacy of species with thorns in this vegetation in relation to other phytophysiognomies in the region. To do this, we used flora surveys from work carried out in the Uberlândia region in different phytophysiognomies and sought information about the presence of thorns in the recorded species. Finally, we used Pearson's chi-square test (χ2) to check whether there was a significant difference in the proportion of species with thorns in the SDF, SSF and RF in relation to the other phytophysiognomies. The phytophysiognomies that had higher frequency of species with thorns (significant difference; p ≤ 0.05) were: RF, SDF and SSF for thorns on the stem, and RF and SDF for thorns on the leaf. The phytophysiognomies that did not obtain a significant difference for thorns on the stem were Savanna and Cerradão Forest (CF), and, for thorns on the leaves, Savanna, CF and SSD. These results suggest that SDF, SSF and RF functioned as islands that concentrated large herbivores during the Pleistocene in the Cerrado region.