Mathematical modeling of the native Mexican turkey’s growth

Little is known about the productive performance of Mexican turkey, so the objective of the present study was to characterize growth performance curves of backyard turkey under a confined system. Forty fertile eggs were artificially incubated and turkey weight was recorded at hatch. During growth performance weekly weight was measured until 385 days of age. Turkey commercial feed and water were offered ad libitum. To characterize growth curves, a fourth degree polynomial model regression and a Richards biological model were used, which were compared by determination coefficient (r2), to reach the best fit model. The best fit model was the fourth degree polynomial regression model from a mathematical standpoint of view. It was found that maximum tom growth was reached at 15.7 weeks with a weight gain of 259.3 g/week and in hens at 12.4 weeks with a weight gain of 112.0 g/week. Body weight reached by toms at 40 weeks was 6 kg and hens at 35 weeks with 3.6 kg.

墨西哥Huasteca Potosina地区Pujal-Coy项目区土地利用/土地覆被的空间配置

文章分析了墨西哥圣路易斯波托西州(San Luis Potosi)东部的Huasteca Potosina地区Puial-Coy项目区的土地利用/土地覆被的配置和空间重组的关系,同时分析了土地利用/土地覆被变化与该地区主要的环境状况间的相互关系。土地利用/土地覆被的变化是通过对不同日期的卫星图像的分析和解译确定的。不同研究阶段对于变化的确定与当前的主导自然因素相关。研究结果表明,农业活动的空间配置最初是由区域发展项目的实施造成的,并与诸如土壤类型,坡度和气候等制约因素密切相关。特别是前者所代表的因素导致了目前农业活动分布格局的建立。

Facilitation by nurse plants contributes to vegetation recovery in human-disturbed desert ecosystems

Aims Facilitation by nurse plants is a common interaction in harsh environments and this positive plant-plant interaction may promote vegetation recovery in ecosystems affected by human activities.Determining the relevance of this process,however,requires assessing how nurse plants influence the establishment of other species,as well as the proportion of species in the regional species pool that would benefit from the presence of nurse plants in human-disturbed areas.Further,since vegetation recovery is a time-dependent process,the community-level consequences of facilitation are likely to vary among landscapes with different disturbance history.Thus,an integrative perspective of the relevance of nurse plants for vegetation recovery could be obtained by measuring their effects across different human-disturbed landscapes of the target region.This study focuses on these issues and uses a regional-scale approach to assess the community-level effects of a widespread nurse plant of American deserts,the creosotebush(Larrea tridentata).Methods This study was conducted in the southernmost portion of Chihuahuan Desert because most floodplain valleys of this region have been affected by human activities during the past centuries.For this study,we selected 10 floodplain valleys differing in their age(i.e.the time elapsed after human activities were ceased).At each landscape,we measured the cover of creosotebushes and the proportion of plant species positively associated with them,as well as the density of seeds in the soil beneath creosotebush canopies.All these data were regressed against the age of the landscapes.Further,to assess whether positive association patterns were due to facilitation or other processes,we conducted field experiments and measured the ecophysiological performance of plant species established beneath and outside creosotebush canopies.Important Findings Most plant species from the target region were positively associated to creosotebushes,and our field experiments and ecophysiological measures indicated that these distribution patterns can be attributed to facilitative interactions.In most landscapes,the density of seeds was higher beneath creosotebushes than in the surrounding habitats,suggesting that these shrubs may also act as seed traps.The community-level effects of creosotebushes increased with landscape age and creosotebush cover,indicating that magnitude of these effects depends on the disturbance history of each site.These results highlight the relevance of performing large-scale assessments for identifying the consequences of facilitation on vegetation recovery across space and time.We then propose that this kind of large-scale approach should be taken into account in the development of conservation programs aimed at the recovery and preservation of plant biodiversity in harsh environments.

Patch isolation and shape predict plant functional diversity in a naturally fragmented forest

Aims It is known that taxonomic diversity can be predicted by the spatial configuration of the habitat,in particular by its area and degree of iso-lation.However,taxonomic diversity is a poor predictor of ecosystem functioning.While functional diversity is strongly linked to the func-tionality and stability of ecosystems,little is known about how changes in the spatial configuration of the habitat affect functional diversity.In this study,we evaluated whether the spatial configuration of forest patches predicts the functional diversity of plants in a fragmented forest.Methods Five functional leaf traits(leaf dry matter content,leaf punch force,specific leaf area,leaf size and leaf thickness)were measured for 23 dominant plant species in 20 forest patches in a naturally fragmented forest on the yucatan Peninsula.Abundance-weighted multivariate and individual trait metrics of functional diversity were calculated and cor-related with size,degree of isolation and the shape of forest patches.Important Findings Patch shape was negatively correlated with multivariate and individ-ual trait(leaf dry matter content and leaf size)metrics of functional diversity.Patch isolation measures were also negatively correlated with individual trait(leaf dry matter content,leaf punch force and leaf size)metrics of functional diversity.In other words,greater patch shape irregularity and isolation degree impoverish plant func-tional variability.This is the first report of the negative effects of patch shape irregularity and isolation on the functional diversity of plant communities in a forest that has been fragmented for a long time.