Bird assemblages on Amazonian river islands: Patterns of species diversity and composition

The principles of island biogeography are rarely applied to the animal assemblages of Amazonian river islands. Here, we compare bird assemblages of Amazonian river islands with a variety of mainland habitats. We also examine how bird species diversity and composition are related to island physical attributes. Birds were sampled with mist nets and qualitative censuses on 11 river islands and 24 mainland sites on the lower reaches of the Rio Negro in the Brazilian Amazon. Island bird assemblages were characterized by lower species richness and a higher abundance of a few dominant species. Additionally, the species composition of the islands was distinct from that of the mainland, including the nearby floodplain habitats. The number of bird species increased with island size and habitat diversity, and decreased with degree of isolation. In addition, small islands tended to harbor an impoverished subset of the species present on larger ones. Bird species diversity and composition on Amazonian river islands are likely influenced by the ecological succession and historical events affecting island formation. Considering their small total area across the Amazon basin, these insular fluvial communities could be disproportionately threatened by river channel disturbances related to climate change or hydroelectric dam development. Abstract in Portughese is available with online material.     

Grazing effects on plant diversity in the endemic Erica mackayana heathland community of north-west Spain

Background: Large areas of heathland landscapes in Galicia, north-west Spain, have traditionally been extensively grazed by free-ranging cattle and wild ponies. Recently, a large reduction in the number of these larger herbivores has been observed, with unknown consequences for the habitat.

Aims: To evaluate the effects of grazing and herbivore density on plant diversity, community composition and vegetation structure of the endemic wet heathlands dominated by Erica mackayana in Galicia.

Methods: Field sampling of vascular plants, generalised linear models (GLMs), non-metric multidimensional distance scaling (NMDS).

Results: Grazed sites had significantly higher total and rare species richness and diversity than ungrazed sites. Higher densities of cattle resulted in lower numbers of rare species, while wild pony density had no effect on rare species richness. In grazed sites, vegetation was lower with greater variation in height, resulting in greater heterogeneity of the habitat. Precipitation and summer temperatures were related to plant diversity, mainly beta diversity. Soil organic matter negatively correlated with rare species.

Discussion: Grazing, mostly by wild ponies, was demonstrated to be positively related to plant diversity and vegetation structure. Lack of grazing or high cattle densities resulted in a negative effect on total and rare species richness and diversity. Future climate change may negatively affect heathland plant diversity. Galician wild ponies represent a unique case of sustainable management of a wild species and an invaluable cultural heritage. Moreover, they have a significant role in maintaining the endemic E. mackayana heathlands, what would justify specific conservation actions for these large herbivores.     

Power and limitation of soil properties as predictors of variation in peak plant biomass in a northern mixed-grass prairie

Soil properties are thought to affect annual plant productivity in rangelands, and thus soil variables that are consistently correlated with plant biomass may be general indicators of rangeland health. Here we measured several soil properties (e.g. aggregate stability, organic carbon, total nitrogen) and tested each as a would-be predictor of local variation in peak aboveground grassland biomass. Individual properties explained a slight (≤10%) amount of variation in plant biomass. Plant biomass was mainly (negatively) associated with two soil properties, subsurface soil carbonate concentration and the stability of soil macroaggregates near the soil surface. Less important predictive variables included: elevation, plant community composition, surface soil organic carbon, and soil carbon:nitrogen. Plot-to-plot variation in plant biomass is seemingly difficult to predict based on soil properties, including popular indicators of soil and rangeland health and even root biomass. While protection of soil is critical to overall rangeland ecosystem function, our findings suggest that the relationship between soil properties and plant biomass in natural grasslands is complex. Thus, there may not be one or even several soil properties that consistently predict appreciable variation in peak grassland biomass, especially variation within an ecosystem independent of precipitation.     

Evaluating regional resiliency of coastal wetlands to sea level rise through hypsometry‐based modeling

Sea level rise (SLR) threatens coastal wetlands worldwide, yet the fate of individual wetlands will vary based on local topography, wetland morphology, sediment dynamics, hydrologic processes, and plant‐mediated feedbacks. Local variability in these factors makes it difficult to predict SLR effects across wetlands or to develop a holistic regional perspective on SLR response for a diversity of wetland types. To improve regional predictions of SLR impacts to coastal wetlands, we developed a model that addresses the scale‐dependent factors controlling SLR response and accommodates different levels of data availability. The model quantifies SLR‐driven habitat conversion within wetlands across a region by predicting changes in individual wetland hypsometry. This standardized approach can be applied to all wetlands in a region regardless of data availability, making it ideal for modeling SLR response across a range of scales. Our model was applied to 105 wetlands in southern California that spanned a broad range of typology and data availability. Our findings suggest that if wetlands are confined to their current extents, the region will lose 12% of marsh habitats (vegetated marsh and unvegetated flats) with 0.6 m of SLR (projected for 2050) and 48% with 1.7 m of SLR (projected for 2100). Habitat conversion was more drastic in wetlands with larger proportions of marsh habitats relative to subtidal habitats and occurred more rapidly in small lagoons relative to larger sites. Our assessment can inform management of coastal wetland vulnerability, improve understanding of the SLR drivers relevant to individual wetlands, and highlight significant data gaps that impede SLR response modeling across spatial scales. This approach augments regional SLR assessments by considering spatial variability in SLR response drivers, addressing data gaps, and accommodating wetland diversity, which will provide greater insights into regional SLR response that are relevant to coastal management and restoration efforts.     

氮素添加对内蒙古退化草原生产力的短期影响

不合理的土地利用方式以及气候变化导致我国草原生态系统普遍退化, 主要表现在土壤养分降低、植被覆盖度减少、生产力下降。外源氮素添加是促进退化草原尽快恢复的一项重要措施, 尤其是对那些退化较为严重的草原。该研究选取内蒙古东乌珠穆沁旗不同退化程度(轻度、中度和重度)的草原群落, 于2014-2015年开展连续两年的氮素添加实验, 设置对照(不添加)、低水平(5.0 g N·m^-2·a^-1)、中水平(10.0 g N·m^-2·a^-1)和高水平(20.0 g N·m^-2·a^-1) 4种氮素添加处理, 探讨退化草原群落生产力在恢复过程中对不同水平氮素添加的响应。结果显示: (1)高、中水平氮素添加显著提高了轻度退化群落的地上生物量, 分别比对照增加了53.1%、51.6%, 氮素各水平添加对中度、重度群落地上生物量无显著影响; (2)高、中水平氮素添加显著提高了轻度退化群落中多年生根茎型禾草地上生物量, 分别比对照增加了45.1%、47.7%, 而多年生杂类草地上生物量分别比对照减少了37.4%、42.1%, 但中度和重度退化群落各功能群生物量的响应不显著; (3)三种水平氮素添加对轻、中、重度退化群落物种丰富度在试验期间均没有显著影响。研究结果表明氮素添加有助于提高轻度退化草原中多年生根茎型禾草的生物量, 进而提高群落的生物量, 但多年生杂类草会被逐渐替代, 导致生物量降低, 可见施氮对草原恢复的影响取决于草原退化 程度。     

青藏高原草地产量与草畜平衡变化

深入了解青藏高原草地生产力与草畜平衡状态的变化,是青藏高原生态屏障建设和生态环境保护的基础.利用遥感植被指数和叶面积指数产品,基于VIP生态水文过程模型,模拟分析了青藏高原2000-2018年间草地生产力的时空格局,并结合同期农牧业统计资料,分析了青藏高原县域尺度草畜平衡状态的变化.结果表明:青藏高原草地多年平均净初级...     

On choice of substrate and habitat in bdelzoid rotifers

Information on the distributions of 77 bdelloid rotifers from diverse waters in south and central Sweden was analyzed to reveal their relationships to substrate and habitat. Only two species were reported from plankton, both in low frequency. An artificial substrate, white cotton, was utilized only by few bdelloids, mainly by species with eyes. Only one species occurred at higher frequency on the saprobic substrate Sphaerotilus. Most bdelloids prefer environments rich in oxygen, but some species may be found in soft-bottom sediments. Several species dwell preferentially in diverse habitats of bogs. Some bdelloids have an exceptionally broad ecological range, but even for these is it possible to distinguish a pattern of preference and avoidance.     

Two gerbils of the Negev: A long-term investigation of optimal habitat selection and its consequences

Optimal foraging theory has entered a new phase. It is not so much tested as used. It helps behavioural ecologists discover the nature of the information in an animals brain. It helps population ecologists reveal coefficients of interaction and their patterns of density-dependent variation. And it helps community ecologists examine niche relationships. In our studies on two species of Negev desert gerbil, we have taken advantage of the second and third of these functions. Both these gerbils prefer semi-stabilized dune habitat, and both altered their selective use of this habitat and stabilized sand according to experimental changes we made in their populations. Their changes in selectivity agree with a type of optimal foraging theory called isoleg theory. Isoleg theories provide examples of dipswitch theories – bundles of articulated qualitative predictions – that are easier to falsify than single qualitative predictions. By linking behaviour to population dynamics through isoleg theory, we were able to use the behaviour of the gerbils to reveal the shapes of their competitive isoclines. These have the peculiar non-linear shapes predicted by optimal foraging theory. Finally, when owl predation threatens, the behaviour of Gerbillus allenbyi reveals the shape of their victim isocline. As has long been predicted by predation theory and laboratory experiments, it is unimodal.