基于耕地连片度的高标准基本农田建设划区

为提高高标准基本农田划定区域的耕地连片性,在耕地综合质量评价和耕地连片网络基础上,提出了局部耕地连片度计算公式来评价耕地的连片性,并采用四象限法空间耦合耕地质量和连片度2个时空属性。结果表明:献县高标准基本农田优先建设区域面积为24 803.45 hm~2,重点建设区域面积为19 688.77 hm~2,有条件建设区域面积为19 538.64 hm~2,与面积累加方法相比,优先建设区域连片度提高了15.55%,而有条件建设区域连片度减小了37.82%,表明该方法明显提高了高标准基本农田建设划区的耕地连片度。     

Beyond the least-cost path: evaluating corridor redundancy using a graph-theoretic approach

The impact of the landscape matrix on patterns of animal movement and population dynamics has been widely recognized by ecologists. However, few tools are available to model the matrix’s influence on the length, relative quality, and redundancy of dispersal routes connecting habitat patches. Many GIS software packages can use land use/land cover maps to identify the route of least resistance between two points—the least-cost path. The limitation of this type of analysis is that only a single path is identified, even though alternative paths with comparable costs might exist. In this paper, we implemented two graph theory methods that extend the least-cost path approach: the Conditional Minimum Transit Cost (CMTC) tool and the Multiple Shortest Paths (MSPs) tool. Both methods enable the visualization of multiple dispersal routes that, together, are assumed to form a corridor. We show that corridors containing alternative dispersal routes emerge when favorable habitat is randomly distributed in space. As clusters of favorable habitat start forming, corridors become less redundant and dispersal bottlenecks become visible. Our approach is illustrated using data from a real landscape in the Brazilian Atlantic forest. We explored the effect of small, localized disturbance on dispersal routes linking conservation units. Simulated habitat destruction caused the appearance of alternative dispersal routes, or caused existing corridors to become narrower. These changes were observed even in the absence of significant differences in the length or cost of least-cost paths. Last, we discuss applications to animal movement studies and conservation initiatives.     

A new measure of longitudinal connectivity for stream networks

Habitat connectivity is a central factor in shaping aquatic biological communities, but few tools exist to describe and quantify this attribute at a network scale in riverine systems. Here, we develop a new index to quantify longitudinal connectivity of river networks based on the expected probability of an organism being able to move freely between two random points of the network. We apply this index to two fish life histories and evaluate the effects of the number, passability, and placement of barriers on river network connectivity through the use of simulated dendritic ecological networks. We then extend the index to a real world dendritic river system in Newfoundland, Canada. Our results indicate that connectivity in river systems, as represented by our index, is most impacted by the first few barriers added to the system. This is in contrast to terrestrial systems, which are more resilient to low levels of connectivity. The results show a curvilinear relationship between barrier passability and structural connectivity. This suggests that an incremental improvement in passability would result in a greater improvement to river network connectivity for more permeable barriers than for less permeable barriers. Our analysis of the index in simulated and real river networks also showed that barrier placement played an important role in connectivity. Not surprisingly, barriers located near the river mouth have the greatest impact on fish with diadromous life histories while those located near the center of the river network have the most impact on fish with potadromous life histories. The proposed index is conceptually simple and sufficiently flexible to deal with variations in river structure and biological communities. The index will enable researchers to account for connectivity in habitat studies and will also allow resource managers to characterize watersheds, assess cumulative impacts of multiple barriers and determine priorities for restoration.     

江苏省耕地集聚连通性时空特征与分类优化策略

耕地的集中连片和空间连通对农业现代化发展至关重要。该研究基于“像元—邻域—连片”三级尺度嵌套视角,综合考虑耕地面积、形状、结构和连通性等特征,构建耕地集聚度和连通性特征测算体系,探究了2000—2020年江苏省耕地格局时空演化规律和分类优化策略。研究结果表明：1）江苏省耕地集聚度从中部向北部和南部递减,98.94%的县域以不同程度下降。2）江苏省耕地连通性从中部至北部形成以宝应县和宿豫区为中心的连通性优势带,南部区域则有所下降。3）根据耕地集聚度和连通性的现状和变化趋势,可将江苏省划分为6个类型区,并提出相应的耕地利用和改善策略。该研究为综合测算耕地的集聚度和连通性特征提出了新的研究视角,明确了耕地优化管理的策略,对于指导区域耕地保护与高效利用、推动农业现代化具有参考价值。     

Dispersal dynamics of post-larval blue crabs, Callinectes sapidus, within a wind-driven estuary

We examined how post‐larval blue crab (Callinectes sapidus) dispersal occurs within Pamlico Sound, NC, USA, a predominantly wind‐driven system. We sampled during multiple 24‐h periods over 2 years (2000–01) to relate the spatial distribution of post‐larvae in the water column with circulation patterns. A hydrodynamic model of the region was used to recreate dispersal trajectories and to assess potential transport mechanisms and pathways that link near‐inlet and across‐Sound nursery habitats. Most post‐larval blue crabs were collected in surface waters at night, and were consistently distributed within the north‐western region of Pamlico Sound. Particle‐tracking simulations suggested that dispersal from the inlets to across‐Sound nursery habitats only resulted from the combination of tidal and wind‐driven currents. Our simulation results further indicated that the northernmost inlet (Oregon Inlet) was the primary supplier of post‐larval blue crabs throughout the northern basin of Pamlico Sound, as crabs ingressing through Hatteras Inlet to the south were not retained within our study area. A dispersal pathway connecting Oregon Inlet and across‐Sound settlement habitats was evident from field observations. Collectively, our results indicate how multiple forcing agents, coupled with post‐larval vertical positioning within the water column, drive estuarine dispersal and connect spatially separated nursery habitats.     

白洋淀流域水文连通对浮游植物群落的影响

为探究水文连通对白洋淀流域浮游植物群落分布特征的影响,并揭示其关键影响因子,于2019年6月27日—7月4日在白洋淀流域开展了水文水质及浮游植物调查,结合流域内闸坝空间分布,计算了白洋淀流域河湖水系的连通性强度指数(Longitudinal connectivity index, LoC);利用多元统计分析方法,如非度量多维尺度分析和冗余分析等方法,探究了水文连通对白洋淀流域浮游植物群落结构、优势种物种丰度变化的影响。结果表明:王快水库上游河流的LoC指数最高(0.84),府河、白沟引河及孝义河等入淀河流LoC指数较低(0.06～0.08)。白洋淀流域浮游植物生物量及物种丰度呈现空间差异,其中,孝义河浮游植物的生物量最大,约为3.07 mg·L~(-1),西大洋水库上游河流最小(0.30 mg·L~(-1));白洋淀淀区浮游植物的物种丰度最大,为5.13×10~6cell·L~(-1),王快水库上游河流最小(1.62×10~5cell·L~(-1))。多元统计分析结果表明,按浮游植物相似性特征,白洋淀流域可分为水库上游河流、入淀河流及淀区3个区域;且影响各个区域浮游植物群落特征的关键因子有所不同,其中水库上游河流浮游植物受COD、TP及流速的影响,入淀河流受COD、TN及流速的影响,而淀区则受DO、TP和COD的影响。     

Fish species incidence patterns in naturally fragmented Chihuahuan Desert streams

We investigated how stream fragmentation affects local fish species persistence and extinction from three Rio Grande systems (Texas, USA) stream reaches with different levels of natural fragmentation. We examined species–volume (SV) relationships of fish assemblages in 42 pools across the watersheds and predicted greater fragmentation would correspond to an increase in the slope of the SV relationship due to decreased within‐reach rescue effects. In addition, we examined relationships among tributary‐specific nested subset patterns, local habitat features and spatial position of the reaches relative to the Rio Grande mainstem to better understand the importance of local and regional processes on fish species richness patterns in the stream reaches. Slopes of the SV curves did not differ among the stream reaches, but the intercepts of the SV curves were significantly different. These results indicated rescue effects among habitats within a stream reach were not apparent; however, rescue effects from the mainstem largely determined the species richness of a given stream reach. The nested subset patterns in all stream reaches were related to several local environmental factors, and large, deep pools provided important aquatic refugia in all three systems. We suggest declines in mainstem and tributary flows will likely continue to impact local and regional fish assemblage attributes. High flow events are important for dispersal and can reset tributary fish communities for the next extinction‐driven, successional cycle.     

Microgeographic genetic isolation in chub (Cyprinidae: Squalius cephalus) population of the Durance River: estimating fragmentation by dams

Dehais C, Eudeline R, Berrebi P, Argillier C. Microgeographic genetic isolation in chub (Cyprinidae: Squalius cephalus) population of the Durance River: estimating fragmentation by dams.
Ecology of Freshwater Fish 2010: 19: 267–278. © 2010 John Wiley & Sons A/S Abstract – Weirs and dams are wide spread throughout the world’s river systems. The most direct effect of these barriers is the limitation of organism movements, i.e., the alteration of connectivity by fragmentation of the aquatic habitat. Whereas the impact of fragmentation on migratory fish species has been well studied, insights on nonmigratory species are still needed. In particular, knowledge on the effects of dams on cyprinid populations at the watershed scale is lacking. Therefore, we studied the genetic structure of eleven chub (Squalius cephalus) samples lined up in the highly fragmented Durance River (France). Using five microsatellite loci, we show that even if the overall genetic differentiation is low, isolation by distance does occur and that genetic diversity increases from upstream to downstream. Dams seem to participate jointly with waterway distance in the explanation of this pattern. However more precise conclusions cannot be made. Guidance for future studies are given.     

极端降雨条件下植被恢复流域结构和功能连通性间的关系

探明极端降雨条件下流域水文和泥沙连通性的相互关系，对新形势下黄土高原植被恢复流域水沙调控与水土保持高质量发展具有重要作用。该研究在泥沙连通性指数(index of connectivity,IC)的基础上，采用地形位置指数和植被覆盖因子改进的结构连通性指数(structural sediment connectivity,SC_st)，累计地表径流深因子改进的功能连通性指数(functional hydrological connectivity,HC_fn)，研究了极端降雨和植被恢复对流域水沙连通性的影响及输沙潜力的表征能力。结果表明：植被恢复流域归一化植被指数均值由2000年的0.29剧增到2020年的0.70，显著影响SC_st，其均值由2000年的-6.49下降到2020年的-10.03,Pearson相关系数-0.93；降雨径流显著影响HC_fn，年月尺度上HC_fn均值与降雨径流深的相关系数均大于0.70。HC_fn可动态反映流域径流输沙情况，平水年流域实...     

Increasing connectivity of Great Lakes tributaries: Interspecific and intraspecific effects on resident brook trout and brown trout populations

Understanding resident fish population responses to restored connectivity would enhance decision-making on dam removal and fish passage. Since such evaluations are limited in the Great Lakes region of North America, we compared abundance, survival, and growth of resident brook trout and brown trout between sets of Michigan streams where populations were or were not interacting with salmonid species that might be present if connectivity existed. We analysed data from 34 electrofishing index sites to compare resident trout populations between streams without versus with Great Lakes access (and migratory Pacific salmonids), and brook trout populations in Great Lakes inaccessible (land-locked) streams where brown trout were present versus absent. Great Lakes accessibility effects on fish density became increasingly positive for older age groups of brown trout while generally negative for all age classes of brook trout. Brown trout had consistently negative effects on brook trout density in land-locked streams. Increased connectivity had significant effects on annual survival for only one of seven trout age classes modelled, while intraspecific density-dependent effects on survival were significant in six models. Significant intraspecific effects on resident trout growth occurred for seven of eleven age classes examined. Negative interspecific effects of Great Lakes access on resident trout growth were most noticeable for age-0 and age-1 resident trout, age classes that likely compete with juvenile Pacific salmonids. Our findings provide a more robust understanding of how Great Lakes connectivity affects resident trout populations, highlighting negative influences of brown trout on brook trout and intraspecific density-dependent effects.