Changes of species richness pattern in mountain grasslands: abandonment versus restoration

Changes in plant species richness at various spatial scales were investigated by manipulative experiment in mountain grasslands. The aim of the research was to compare changes in species richness in newly abandoned sites and sites where restoration measures were applied after 20 years of abandonment. The plots were located in two vegetation types with different moisture regime. Species richness decreased significantly after abandonment, mainly at the finest spatial scale of 10 × 10 cm. There was significant increase of species richness on restored sites, but it was apparent mainly at a larger scale. However, even 4 years of regular mowing were not sufficient to restore species richness to the level typical for traditionally managed grasslands in the region. No significant difference was found in the performance of the 2 contrasting vegetation types (wet and dry) in relation to management measures. A significant difference in scale-dependent species richness was only observed. The dry type had a steeper species-area curve, with a lower number of species at the finest spatial scale. According to the results of the experiment, mountain grasslands are very vulnerable habitats, losing their conservation value quickly after abandonment. Restoration is possible due to an extensive species pool in the region, but return to the original species richness at all spatial scales is quite a long process.     

Separating the effects of number of individuals sampled and competition on species diversity: an experimental and analytic approach

1 Species richness typically increases with the number of individuals sampled, although many ecological processes that influence species richness are also well known to depend on density of individuals. We separated the effects of density on species richness that are due to sampling, from those due to density-dependent ecological processes such as competition or predation, by manipulating the density of an entire community.
2 A seed bank from a community of desert annual plants that occur on semi-stabilized sand dunes in Israel was collected from the field and sown in an experimental garden at a range of densities from 1/16 to eight times the natural density. The species pool observed in the lowest density plots was used as the null community, which was repeatedly sampled to calculate the species richness (and other diversity indices) in higher density plots that would be expected from sampling considerations alone. The significance of deviations of observed diversity from this expected diversity was then evaluated.
3 Both observed and expected number of species increased substantially with the experimental increase in density. However, observed species richness, the Shannon–Wiener diversity index and Simpson's diversity index were often significantly lower than that expected based on sampling considerations. The magnitude of the deviation from expected increased significantly with increasing density for richness and the Shannon–Wiener index. This provides some of the first direct experimental evidence from diverse natural assemblages that increasing competition among all the individuals in a community can lead to competitive exclusion.     

贺兰山木本植物群落物种多样性的海拔格局

 贺兰山位于中国温带草原和温带荒漠的过渡带,是研究干旱区山地物种多样性海拔格局的理想区域。该文通过样方法调查研究区的森林和灌丛群落,并运用广义可加模型分析物种多样性的海拔分布格局。结果表明：1）海拔是物种丰富度的重要影响因子,一般能解释原始数据30%～40%的变差。2）对于森林和灌丛群落,草本植物都是群落中比例最高的物种, 而且决定了群落总物种丰富度的海拔分布格局。3）森林群落的乔木层物种丰富度在中海拔区域最高,反映了中海拔区域相对优越的水热条件。灌木层和草本层的物种丰富度明显受到乔木层郁闭度的影响,有随海拔升高而降低的趋势。4）灌丛群落的灌木层和草本层物种丰富度均呈单峰格局,皆因低海拔的干旱和高海拔的寒冷抑制了多数物种的生存,仅气候条件适宜的中海拔区域能够生存丰富的物种。     

甘肃民勤连古城自然保护区优势种种群结构和动态研究

通过重要值、分布格局、年龄结构、静态生命曲线等方法研究了连古城自然保护区5种群落优势种群数量在时间上和空间上的变化趋势。研究结果表明：灌木荒漠群落中,优势种群或共优种群的重要值远远大于亚优势种群,在维持群落结构和功能方面占据十分重要的地位。除红砂群落外,其它类型的群落中,都具有相同的亚优势种群,即泡泡刺种群,表明泡泡刺种群具有较宽的生态幅是比较古老的种群,其它类型的种群是在这一种群基础上发展起来的。优势种群的分布格局由种群生物学特性和环境条件等诸多因子共同决定,膜果麻黄和绵刺种群呈集群分布,而其它种群呈随机分布。优势种群的年龄结构和静态生命曲线均呈现多样化,膜果麻黄、猫头刺和甘蒙锦鸡儿种群年龄结构为增长型锥体,静态生命曲线为凹型下降,均为稳定种群;绵刺种群的年龄结构为下降型锥体,静态生命曲线为反对角线型上升,但其营养繁殖策略决定了绵刺种群为稳定种群;珍珠猪毛菜种群年龄结构在整体上为稳定型锥体,但局部表现为下降型锥体,种群开始衰败,静态生命曲线为正态分布型;红砂种群的年龄结构为下降型锥体,静态生命曲线残缺并有许多空白区,种群严重退化。     

香溪河流域河岸带植物群落物种丰富度格局

通过不同海拔高度的样带调查来研究香溪河流域河岸植物群落物种丰富度格局,并探讨河岸带中生物多样性维持的生态学机制。结果表明：河岸植物群落总的物种丰富度、乔木层物种丰富度和草本层物种丰富度沿海拔梯度均表现出相似的格局特征,利用抛物线方程进行拟合,物种丰富度与海拔之间有显著的相关性。灌木层物种丰富度和藤本植物物种丰富度格局特征不明显,且物种丰富度与坡度相关,在流域尺度上,海拔对物种丰富度有着重要的控制作用;在局部尺度上,季节性洪水干扰导致的空间异质性和小地形对群落的生物多样性有着重要的影响,研究结果支在于总的物种多样性在原始河流的中间河段将达到最大值的预测。     

Functional responses of adaptive consumers and community stability with emphasis on the dynamics of plant-herbivore systems

A comparatively recent focus in consumer–resource theory has been the examination of whether adaptive foraging by consumers, manifested through the functional response, can stabilize consumer–resource dynamics. We offer a brief synthesis of progress on this body of theory and identify the conditions likely to lead to stability. We also fill a gap in our understanding by analysing the potential for adaptively foraging herbivores, which are constrained by time available to feed and digestive capacity, to stabilize dynamics in a single-herbivore/two-plant resource system. Because foraging parameters of the adaptive functional response scale allometrically with herbivore body size, we parameterized our model system using published foraging data for an insect, a small mammal and a large mammal spanning four orders of magnitude in body size, and examined numerically the potential for herbivores to stabilize the consumer–resource interactions. We found in general that the herbivore–plant equilibrium will be unstable for all biologically realistic herbivore population densities. The instability arose for two reasons. First, each herbivore exhibited destabilizing adaptive consumer functional responses (i.e. density-independent or inversely density-dependent) whenever they selected a mixed diet. Secondly, the numerical response of herbivores, based on our assumption of density-independent herbivore population growth, results in herbivores reaching densities that enable them to exploit their resource populations to extinction. Our results and those of studies we reviewed indicate that, in general, adaptive consumers are unlikely to stabilize the dynamics of consumer–resource systems solely through the functional response. The implications of this for future work on consumer–resource theory are discussed.     

河西走廊水生植物多样性格局、群落特征及影响因素

水生植物是湿地生态系统重要组成部分,研究水生植物多样性分布格局及其影响因素对地区水生植物资源保护具有重要意义。通过野外调查并结合气候等环境因素,研究了河西走廊主要水生植物群落类型、数量特征、水生植物多样性分布格局及影响因素,并对中域效应假说进行了验证。研究结果表明:(1)河西走廊地区共有水生植物29科42属84种,群落的聚类分析可将河西走廊水生植物群落划分为15个主要群落类型;(2)河西走廊水生植物群落类型主要受到水温、海拔、经纬度等环境因子影响,群落物种多样性指数与盐度以及溶解性固体总量呈显著性相关;(3)河西走廊水生植物多样性空间格局呈现出\"∩\"型的单峰格局,中域效应模型能较好地解释该地区水生植物多样性水平的纬度格局及海拔垂直分布格局,对该区域水生植物物种丰富度在纬度和海拔梯度上的变异解释率分别为57.56%、63.5%。分析表明,河西走廊水生植物物种丰富度格局由几何(边界)限制和随机过程及其他未知因素共同控制,且几何(边界)限制和随机过程贡献率较大;同时本研究中未考虑的环境异质性、气候、人为干扰等因素也对河西走廊水生植物多样性空间分布产生重要影响。     

Are island plant communities more invaded than their mainland counterparts?

Questions: Are island vegetation communities more invaded than their mainland counterparts? Is this pattern consistent among community types? Location: The coastal provinces of Catalonia and the para‐oceanic Balearic Islands, both in NE Spain. These islands were connected to the continent more than 5.35 million years ago and are now located <200 km from the coast. Methods: We compiled a database of almost 3000 phytosociological relevés from the Balearic Islands and Catalonia and compared the level of invasion by alien plants in island versus mainland communities. Twenty distinct plant community types were compared between island and mainland counterparts. Results: The percentage of plots with alien species, number, percentage and cover percentage of alien species per plot was greater in Catalonia than in the Balearic Islands in most communities. Overall, across communities, more alien species were found in the mainland (53) compared to the islands (only nine). Despite these differences, patterns of the level of invasion in communities were highly consistent between the islands and mainland. The most invaded communities were ruderal and riparian. Main conclusion: Our results indicate that para‐oceanic island communities such as the Balearic Islands are less invaded than their mainland counterparts. This difference reflects a smaller regional alien species pool in the Balearic Islands than in the adjacent mainland, probably due to differences in landscape heterogeneity and propagule pressure.