Across-shore distribution of Ocypode quadrata burrows in relation to beach features and human disturbance

Spatial distribution patterns of the ghost crab Ocypode quadrata were analysed using different approaches at one disturbed and two preserved reflective sandy beaches of the Mexican Caribbean. We used spatial correlation analysis to describe the across-shore distribution of O. quadrata and their patch dynamics by beach and sampling time. In addition, we analysed the across-shore variability of habitat extent of O. quadrata (habitat envelope) and its relation to human disturbance and beach features. The spatial structure of burrow density was consistent through time, showing a bimodal distribution with very low abundance in the mid distribution range and a discrete increment of burrows to landward. Nonetheless, the size of patches varied temporally for the three beaches. Burrow size increased from seaward to landward. The location of the first burrow and the habitat envelope varied among sampling times and beaches. The location of the first burrow is mostly mediated by the swash climate, while the habitat envelope is mainly controlled by the level of human disturbance. Despite the low number of disturbed and control beaches, our results suggest that the habitat envelope could be included in future studies when using ghost crabs as indicators of human disturbance. Polynomial models and variographic analysis proved to be useful tools to describe the across-shore distribution and patch dynamics of the ghost crab.     

高岩子林场天然林分中主要树种的空间格局研究

通过对天然林分中3个主要树种的地统计学分析，发现马褂木(Lirlodendron chinese)、华山松(Pinus armandi)的变异函数理论模型为指数型，呈聚集分布，华山松的聚集强度最大，区域空间连续性强度分别为50．1％、71．3％，均大于50％；杉木(Cunningharnia Lanceolata)为纯金块模型，呈随机分布，空间异质性最低，主要由随机部分组成，分数维最大，空间分布结构复杂；变程以马褂木最大，分数维最小，空间分布结构简单，说明3树种虽然生长在同一林分中，其空间格局是有差异的．