ABSTRACT
Disturbance gradients are particularly useful for understanding the relative influences of competition and dispersal. Shortly after disturbance, plant composition should be influenced more strongly by dispersal than competition; over time, this should reverse, with competition becoming more important. As such, we predicted that plant functional traits associated with high dispersal ability would be over-represented shortly after a disturbance event occurs, while those associated with high competitive ability would have increased representation as time progresses. Additionally, it has been suggested that competitive interactions may contribute to negative co-occurrence patterns; if this is the case, negative co-occurrence patterns should also increase as time-since-disturbance increases. Here, we examine how functional trait and co-occurrence patterns change over time following a herbicide-based disturbance, compared to undisturbed vegetation, in a temperate, old-field grassland dominated by herbaceous perennials. In our study system, negative co-occurrence patterns were most pronounced in disturbed plots one year after herbicide application, consistent with several lines of evidence that dispersal can strongly impact both composition and co-occurrence patterns. Over three years post-disturbance, co-occurrence patterns in disturbed plots decreased, becoming more similar to control plots. This pattern is inconsistent with the expectation that competition contributes to negative co-occurrence patterns, at least over three growing seasons. More pronounced negative co-occurrence patterns were associated with higher species evenness among plots. Functional traits related to increased dispersal (mean seed mass, and proportion of stoloniferous/rhizomatous species) and competitive ability (mean species height, and mean specific leaf area) did not differ significantly across treatments, with the exception of mean height in the third-year post-disturbance; however, the overall trajectory of this trait was inconsistent with theoretical expectations. Overall, co-occurrence patterns changed across the gradient of time-since disturbance, but not as expected; functional trait patterns (trait means, functional diversity measures) were not responsive to our experimental disturbance gradient.
Subject(s)
Herbicides , Plants , Seasons , SeedsABSTRACT
Introdução: A marcha é um evento bastante estudado, principalmente no que diz respeito às suas caracterísiticas espaço-temporais e angulares, no entanto, em se tratando de populações especiais, a exemplo dos cegos, estas variáveis ainda são pouco conhecidas. Objetivo: Avaliar as características espaço-temporais do andar no plano de portadores de deficiência visual e comparar com sujeitos norma-visuais, sem uso de alta tecnologia. Método: Participaram do estudo 20 sujeitos de ambos os sexos, divididos em dois grupos: portadores de deficiência visual - PDV (idade = 17,8 ± 2,8 anos; massa corporal = 56,6 ± 12,5 kg; estatura = 1,57 ± 0,06 m; IMC = 23,0 ± 0,7 kg/m2; altura da pelve = 87,8 ± 3,8 cm), composto por 10 sujeitos (6 homens e 4 mulheres) e norma-visuais - NV (idade = 22,5 ± 1,6 anos; massa corporal = 59,0 ± 16,7 kg; estatura = 1,63 ± 0,95 m; IMC = 22,2 ± 0,5 kg/m2; altura da pelve = 87,3± 4,1 cm), também composto por 10 sujeitos (3 homens e 7 mulheres). Os sujeitos caminharam sobre uma passarela de 7m e foram registrados os dados de variáveis espaço-temporais dos 5m centrais por meio do método Step Page. Para análise dos dados utilizou-se o SPSS (16.0), comparando-se as médias intra (teste t Student e Wilcoxon) e intergrupos (teste t Student, Mann-Whitney e ICe), adotando-se um nível de significância de 5% em todas as comparações. Resultados: Na comparação intra-grupos, não houve diferença estatística entre os membros para as variáveis de comprimento do passo (CP), comprimento da passada (CPas) e ângulo de rotação do pé (ARP) para ambos os grupos. Porém, na comparação entre os grupos (PDV x NV), houve diferença estatisticamente significante no comprimento do passo direito (CPD; p<0,05); comprimento do passo esquerdo (CPE; p
Introduction: The gait is an event well studied, especially with regard to their spatiotemporal and angular characteristics, however, when it comes to special populations, like the blind, these variables are still poorly known. Objective: The objective was to evaluate spatial and temporal gait characteristics of subjects with visual impairments and to compare them with normal vision subjects, without use of high technology. Method: The study included 20 individuaisof both sexes, divided into two groups: those with visual impairments - VIP (age = 17.8 ± 2.8 years, body weight =56.6 ± 12.5 kg, height = 1.57 ± 0.06 m, BMI = 23.0 ± 0.7 kg/m2; the pelvis = 87.8 ± 3.8 cm), composed of 10 subjects(6 men and 4 women) and normal visual - NV (age = 22.5 ± 1.6 years, body mass = 59.0 ± 16.7 kg, height =1.63 ± 0.95 m, BMI = 22.2 ± 0.5 kg/m2 ; the pelvis = 87.3 ± 4.1 cm), also composed of 10 subjects (3 men and 7 women). The subjects walked on a walkway of 7m and the data of spatiotemporal variables of the central 5m were recorded by the method Step Page. It was used the SPSS software (16.0) for the data analysis, the mean intra (Student t test and Wilcoxon) and between groups (Student t test, Mann-Whitney and ICe) were compared, adopting a significance levei of 5% for ali comparisons. Results: In comparison within groups there was no statistical difference between the members of the variables of step length (StL), stride length (SdL) and rotation angle of the foot (ARP) for both groups. But in the between groups analysis (VIP x NV), there was statistically significant difference for the variables right step length (RStL, p <0.05), left step length (LStL, p <0.01), right stride length (RSdL p <0.01), left stridelength (LSdL, p <0.01) and gait speed (p <0.01). Conclusion: According to the results of this study, we can inferthat the visually impaired patients group (VIP) moves more slowly and with shorter steps than the subjects with normal vision group (NV).
