Influência de fatores bióticos e abióticos na regeneração inicial de espécies com abundâncias distintas na caatinga

Abstract

A central question in ecology refers to the distribution and abundance of species, and how these attributes are influenced by biotic and abiotic factors. The regeneration niche expressed limits biotic and abiotic conditions tolerated and/or required during the regeneration process of a species. This process involves from producing seed until recruitment of juvenile, including seed dispersal, germination, and seedling establishment. Any factor that decreases the probability of survival at any stage of regeneration can reduce the size of the population, and this effect is known as demographic bottleneck. In this context, the aim of this study was to evaluate how biotic and abiotic factors can affect the natural regeneration process and to suggest possible predictors of species abundance. The focal species were Poincianella bracteosa (Tul.) LP Queiroz, who has a high abundance of adults in caatinga areas and Libidibia ferrea (Mart. Ex Tul.) LP Queiroz, who has low abundance in these areas and occurs preferentially on the banks temporary rivers. The choice of species is due to the contrast of abundance between them, which makes them good models for understanding the relationship between regeneration niche and abundance. In the manuscript I, studied factors were pre-dispersal predation and seed dormancy. The fruits were collected in caatinga area located at the Fazenda Experimental Vale do Curu/UFC in the city of Pentecoste-CE. In the predation experiment, conducted biometrics fruits (n=100/species), then fruits have benefited and the seeds were classified into three groups (healthy, malformed and preyed). For each species, we calculated the rate of predation and recorded the number of predator insects. In the dormancy experiment, healthy seeds of both species were subjected to six pre-germinative treatments. At the end of the test, was calculated the germination percentage, germination speed index and average germination time. L. ferrea showed the highest seed predation than P. bracteosa and low germination potential, since its seeds have strongly coat impermeability to water. Our results suggest that the factors can affect the regeneration of L. ferrea and seem to have no significant effects on P. bracteosa. In the manuscript II, the studied factor was water stress. We assess morphological and physiological characteristics of seedlings under different water regimes (10, 40, 70 and 100% of field capacity) for 85 days, in a greenhouse located at the Meteorological Station/ UFC, in the city of Fortaleza-CE. P. bracteosa showed features of species low-resource, which provide ecological benefits in conditions of stress, while L. ferrea showed features of species high-resource. Our results suggest that the attributes of "Stress resistance syndrome" may favor the high abundance of P. bracteosa in areas of caatinga. In the manuscript III the factors studied were water stress and herbivory. We evaluate the initial growth and survival of seedlings under natural conditions of seasonal water availability and attack insect herbivores on caatinga area located at the Fazenda Experimental Vale do Curu/UFC. Seedlings (two months of age) of species were submitted to two treatments, control and insecticide. Monthly, were performed measures of height, diameter and number of leaflets for one year (April/2013 - April/2014). Growth rates in height and diameter were calculated for different periods: rainy/2013, dry/2013 and rainy/2014. The herbivory was conducted during the rainy seasons (2013/2014), counting the number of leaflets with insect damage. Were also conducted measurements of gas exchange during the rainy season and dry/2013. The species showed no significant differences in growth rates, but L. ferrea was more susceptible to herbivory and drought than P. bracteosa. Our results suggest that during the seedling stage, water stress associated with cumulative damage of herbivory may affect the natural regeneration of L. ferrea in areas of caatinga and is little significant in the regeneration of P. bracteosa.