Aquatic and terrestrial invertebrate community responses to drying in chalk streams

Temporary streams are dynamic ecosystems that shift between wet and dry states and include the ‘winterbourne’ chalk streams of south England. Our understanding of temporary stream biodiversity is biased, with most research to date exploring aquatic invertebrate communities in benthic sediments during flowing phases. We surveyed the invertebrate communities of the Candover Brook chalk stream, comparing aquatic (benthic, hyporheic) and terrestrial communities in reaches with different flow permanence regimes. We used kick and Bou–Rouch sampling methods to collect aquatic invertebrates, and compared the terrestrial communities characterised by pitfall traps and ground searches and in different seasons. Although aquatic taxa richness was lower in temporary compared to perennial reaches, the total biodiversity of temporary stream channels was enhanced by contributions from both aquatic and terrestrial species, including several of conservation interest. We recommend that both aquatic and terrestrial communities should be considered in research and monitoring to characterise the biodiversity and ecological quality of temporary streams.     

Multi-biochemical responses of benthic macroinvertebrate species as a complementary tool to diagnose the cause of community impairment in polluted rivers

Biological indexes, based on benthic macroinvertebrate taxa, are currently used worldwide to measure river ecological quality. These indexes assign a global ecological status of the biotic community, but not necessarily may detect specific effects of water pollutants. Conversely a large set of biochemical markers measured in macroinvertebrate benthic species can detect sublethal effects and inform us about additional environmental factors that are impairing benthic communities. This is especially interesting in moderately polluted sites, where other stressors are already affecting communities but not too strongly to be detected by biotic indexes. Up to ten different markers belonging to distinct metabolic paths and 42 contaminants measured in sample collections of the caddis fly Hydropsyche exocellata were assessed across a polluted gradient in the industrialized Mediterranean River basins of Besós and Llobregat (NE, Spain). Twenty four sample collections were selected to include macroinvertebrate communities representing the five impairment degrees defined by the Spanish Environmental authorities using the biotic metrics. Results evidenced a clear deterioration of the ecological water quality parameters and benthic communities towards downstream reaches. Biochemical responses varied significantly across the studied samples and were able to differentiate samples within communities having a good and deteriorated ecological stage. Principal Component Analyses indicated that salinity was one of the major stresses affecting macroinvertebrate assemblages, whereas antioxidant and metabolizing enzymes responded differently and were closely related to high and presumably toxic levels of accumulated organic pollutants. Therefore these results indicate that the use of multiple -markers sensitive to water pollution may provide complementary information to diagnose environmental factors that are impairing macroinvertebrate communities.     

Living in the big city: Effects of urban land-use on bird community structure, diversity, and composition

Cities represent an important threat to biodiversity at different scales. Nevertheless, little is known on the processes underlying such effects. In this paper we describe bird diversity, structure, and composition patterns in different urban land-use categories. For this, we surveyed resident bird communities in four representative land-use categories of southwestern Mexico City. Our results show that bird communities vary greatly along the different studied urban land-uses, which represent an urbanization development gradient. Bird communities were highly dominated by few generalist species in areas with commercial components, while showed to have higher evenness values in green areas. Bird species richness decreased and bird abundances increased with urbanization intensity. Also, our results indicate that bird species richness and abundance values are sensible to site-specific habitat characteristics. Although we did not find a clear pattern of taxonomic homogenization related to urbanization, our results show that urbanization development entails the functional homogenization of bird communities. Thus, based on our results, we suggest three urban planning and management activities: (1) regulate land-use change related to urbanization; (2) increase the number of green areas within the city; (3) establish bird monitoring programs to identify focal areas that need management and assist with ecological data for urban planning.     

塘类海绵生境鸟类多样性特征及其影响 因素研究

目前国内对海绵生境生物多样性方面的研究还较为欠缺,有蓄水功能的塘类海绵生境可作为鸟类觅食及栖息之地。为了探究塘类海绵生境的鸟类特征,以及生境中的设计与环境因子是如何影响鸟类群落多样性特征的,对重庆悦来会展城的干塘与湿塘进行调查,采集生境中的鸟类、植被、面积特征与环境干扰特征数据。采用聚类分析的方法明确鸟类群落组成特征,通过构建结构方程模型,探究塘类海绵生境特征因子对鸟类群落多样性特征的影响。经过四季监测实地调研,总共观测到64种鸟类,可划分为4种鸟类集团,整体鸟类群落多样性特征受到生境面积、蓄水层面积、乔木多样性、灌木多样性、乔木胸径、乔木盖度、噪声、距林地距离和距非绿地建设用地距离的显著影响。通过合理的设计策略可以提升塘类海绵生境鸟类多样性特征。本研究对于探索城市绿地小微生境的生物多样性效益,促进海绵城市精细化营建具有重要价值。     

Low concentrations of selenium in stream food webs of eastern Canada

Herbivorous and predatory invertebrates and two species of fish (brook trout and blacknose dace) were collected from 49 streams in New Brunswick, Canada to determine whether concentrations of selenium (Se) in the biota were affected by a point source (a coal-fired power plant), and stream water chemistry (pH, sulphate, conductivity, and total organic carbon), and to determine the trophic transfer of Se through these food webs. Total Se concentrations in the biota were generally low (0.2 to 4.8 μg g^− 1 dry weight) across sites and there was no relationship between distance from the coal-fired power plant and Se concentrations in invertebrates or fishes. Water chemistry was an equally poor predictor of Se concentrations in invertebrates and fish. Trophic position (determined using δ¹⁵N) was a significant predictor of Se concentrations in only five of the stream food webs, and two of these had negative slopes, indicating little or no trophic magnification across most systems; many fishes had lower concentrations than their invertebrate prey and trophic transfer was higher at sites with low invertebrate Se concentrations. Variability in Se concentrations in fishes was explained more by site of capture than microhabitat use within the site (as measured with δ¹³C), suggesting among-site differences in geological sources of Se. Because concentrations were below known toxicity thresholds for fish and other consumers, these results suggest that Se is not an environmental issue in New Brunswick streams that do not receive direct inputs from mining activities.     

The influence of coniferous afforestation on lowland farmland bird communities in Ireland: different seasons and landscape contexts

Current governmental policy in Ireland is encouraging afforestation, 80% of which is likely to consist of exotic conifer species, in low-lying agricultural areas. Whereas most studies of bird diversity in forest/farmland mosaic landscapes have focused on high quality woodland remnants in a hostile agricultural matrix, this study has considered the influence of man-made plantations in a less intensively farmed context. Bird communities of three lowland agricultural landscapes (each 2000 ha in area) with intermediate or low levels of coniferous forest cover (33% or 8% approximately) were sampled in winter and summer. Though total abundance and species richness of birds of farmland habitats in the partially forested and open sites did not differ, the presence of trees in the surrounding landscape did influence abundance of some common species such as Blue Tit Parus caeruleus, Robin Erithacus rubecula and Blackbird Turdus merula. In winter, species composition of farmland habitats with and without hedgerow trees differed between forested and open landscapes. Also, the abundance of certain species varied between farmland adjacent to and remote from forest edges, in both seasons. In these landscapes, coniferous plantations did not greatly affect the mainly generalist farmland bird community, either positively or negatively. However, if the proportion of land-use occupied by forestry were to increase, reducing the available hedgerow habitat and forest edge/area ratio, diversity and abundance of declining farmland bird species might be negatively affected.     

Analyzing trophic transfer of metals in stream food webs using nitrogen isotopes

This study examines detrimental effects of acid mine drainage (AMD) on stream invertebrate communities and tests for a direct relationship between trophic position and accumulation of three metals (Fe, Cu, Zn) by stream invertebrates in situ. On two dates in each of seven stream sites, we measured food chain length, mean trophic level, taxa richness, and trophic position of stream macroinvertebrates comprising the food webs using stable nitrogen isotope ratios. Metals in tissue of representatives of 35 taxa were measured by ICP-OES. Our results are the first direct comparison of uptake of these metals in stream invertebrate taxa according to trophic position as identified by delta15N. As predicted, metal concentrations were generally greater in water and insects from sites adjacent to mining activity and invertebrate taxa richness was significantly lower. Taxa richness increased with distance away from contaminated headwaters. Despite reductions in diversity at sites nearest AMD, food chain length and mean trophic level did not differ between streams. The relationship between trophic position and metal accumulation differed considerably among metals. Specifically, Fe declined (biodilution) and Zn increased (biomagnification) with trophic level, but trophic position had no effect on Cu levels in these insects. Our results highlight fundamental differences in trophic transfer of specific metals through aquatic food webs and identify ecologically important impacts of AMD on stream invertebrates.     

How do habitat variability and management regime shape the spatial heterogeneity of birds within a large Mediterranean urban park?

Large urban parks can support a diverse bird community. However, the effects of variability among habitats and of park management on bird assemblages are poorly understood. We studied bird communities within the Yarkon Park, Tel Aviv, the largest urban park in Israel. We examined species richness, abundance and community composition across 20 locations that differ in levels of park management to identify habitat variables responsible for variation in bird richness and composition. Of 91 recorded bird species, 13 were aliens (14%), 4 were urban exploiters (4%), 54 were urban adapters (60%) and 20 were migrants (22%). Management had a significant effect on native bird richness and bird community structure varied among areas with different management regimes. Species richness of all the above species’ groups was lowest in intensively managed areas. Areas with intermediate levels of management had higher or equal richness compared to unmanaged areas. The majority of urban exploiters were found at all locations within the park reaching their highest abundances in intensively managed areas. Species richness of alien birds did not vary across levels of management. Bird species richness was negatively associated with lawn cover and with distance from nearest water source and was positively associated with the number of woody plant species. We suggest that urban parks should be designed such that the heterogeneity of native vegetation is preserved, if we aim to maintain native bird species diversity and minimize urban exploiter and alien species. When lightly managed or unmanaged, urban parks can retain large remnants of sub-natural habitats and can serve as important contributors to the conservation of native biodiversity within a large urban metropolis.     

城市用地紧凑变化对河岸带生境的影响 ——以汉江小流域武汉段为例

流域尺度上的城市扩张会对河岸带生境产生显著的 负面影响,目前还不清楚何种用地模式能更有效地支持河岸带 生物多样性。以汉江小流域武汉段为研究对象,从用地强度、 形态和布局3个维度构建了城市用地紧凑度评价指标体系。根 据河岸带生境结构及其联系构建城市河岸带生境质量评价体 系。运用Spearman相关性分析和RDA分析探究子流域水平 上的城市用地紧凑变化对河岸带生境的影响。结果表明：随用 地紧凑度提升,河岸带综合生境质量显著降低;开发利用强 度、居住用地占比及土地利用混合度是致使河岸带生境变差的 主导因子;用地形态与布局的紧凑变化对河岸带生境质量的影 响不显著,且分形维度指数与河岸带生境质量呈正相关关系。 研究证明了在同等开发强度下,提升城市用地形态与布局紧凑 度是协同城市化与河岸带生物多样性提升的有效策略。