Ecogeography of the herpetofauna of a northern California watershed: linking species patterns to landscape processes

Ecosystems are rapidly being altered and destabilized on a global scale, threatening native biota and compromising vital services provided to human society. We need to better understand the processes that can undermine ecosystem integrity (resistance‐resilience) in order to devise strategies to ameliorate this trend. We used a herpetofaunal assemblage to first assess spatial patterns of biodiversity and then to discover the underlying landscape processes likely responsible for these patterns. Reptiles and amphibians are a phylogenetically diverse set of species with documented sensitivity to environmental perturbations. We examined ecogeographic patterns of these taxa in aquatic and riparian environments across the landscape mosaic of the Mattole River watershed of northern California, USA. We analyzed species distributions relative to three primary vegetation types (grassland, second‐growth forest, late‐seral forest) and two hydrologic regimes (perennial vs intermittent). We sought evidence for the processes behind these patterns by modeling animal distributions relative to multi‐scale compositional, structural, and physical attributes of the vegetation or hydrologic type. Total herpetofaunal diversity was higher along perennial streams, with reptile diversity higher in mixed grassland. Amphibian and reptile richness, and reptile evenness, varied significantly among the three vegetations. Evidence indicated that distinct assemblages were associated with each end of a seral continuum. Four amphibians were more abundant in late‐seral forest, while two amphibians and two reptiles were more abundant in second‐growth forest, or mixed grassland, or both. Two amphibians were more abundant along intermittent streams. Models for predicting reptile richness, or abundances of the two amphibian assemblages, indicated water temperature was the best predictor variable. Based on these results and the physiological limits of several sensitive species, we determined the primary processes influencing faunal assemblage patterns on this landscape have been vegetation changes resulting from the harvesting of late‐seral forests and the clearing of forest for pasture. Comparing past with present landscape mosaics indicated that these changes have transformed the dominant amphibian and reptile species assemblage from a mostly cold‐water and cool forest‐associated assemblage to one now dominated by warm‐water and mixed grassland/woodland species.     

Habitat selection by a threatened desert amphibian

Habitat degradation and fragmentation are major drivers of amphibian declines. The loss of environmental features that allow for movement between water sources may be particularly detrimental for amphibians in arid environments. Climate changes will increase the importance of microhabitats to amphibians. Enhancing areas to facilitate movement may be a necessary conservation strategy for many animal species that depend on wetlands, including federally threatened Chiricahua leopard frogs (Lithobates chiricahuensis). Habitat preferences of this frog species are not well understood. We sought to better understand fine‐scale habitat selection, to inform conservation of Chiricahua leopard frogs. We conducted our study on the Ladder Ranch, a privately owned working bison ranch in New Mexico, USA that supports a large proportion of the remaining Chiricahua leopard frogs in the state. We attached radio transmitters to 44 frogs during summer 2014. We located each frog daily for up to 8 weeks (median = 30 days). We assessed fine‐scale habitat selection by comparing characteristics at each frog location and a random location 5 m away using conditional logistic regression. Frogs preferred features that likely reduce desiccation, even after accounting for the presence of water. Frogs selected areas with more low‐lying cover, especially aquatic vegetation and woody debris, a tree overstory, and a mud substrate. We recommend managing potential movement corridors for Chiricahua leopard frogs by ensuring the presence of muddy creek bottoms, woody debris, riparian overstory, low‐lying ground cover, and pools. Microclimates created by these features seem especially valuable given warming temperatures and modified precipitation regimes, resulting in decreased surface water, soil moisture, and vegetation cover. Retaining or creating preferred habitat features and microclimates in areas between water sources may increase connectivity among isolated populations of Chiricahua leopard frogs and could improve persistence and recovery of other water‐obligate species in arid landscapes.     

More than a barrier: The complex effects of ecotone vegetation type on terrestrial consumer consumption of an aquatic prey resource

Community structure and dynamics can be influenced by resource transfers between ecosystems, yet little is known about how boundary structure determines both the magnitude of exchanges and their effects on recipient and donor communities. Aquatic and terrestrial ecosystems are often linked by resource fluxes and riparian vegetation is commonly affected by anthropogenic alterations to land use or river hydrological regime. I investigated whether shrubs at the freshwater–terrestrial interface alter the supply, distribution and importance of aquatic prey resources to terrestrial consumers. Shrubs were predicted to alter the larval community composition of aquatic insects and the emergence of winged adults, thus affecting aquatic prey subsidies to terrestrial consumers. In addition, shrubs were hypothesized to alter the microclimatic suitability of the riparian zone for adult aquatic insects, act as a physical barrier to their dispersal and affect terrestrial community composition, particularly the abundance and type of predators that could benefit from the aquatic prey resource. Stable isotope dietary analyses and a survey of shrub‐dominated and open grassland riparian habitats revealed that larval densities of aquatic insects (EPTM: Ephemeroptera, Plecoptera, Trichoptera and Megaloptera) were higher in shrub than grassland habitats; however, reduced emergence and lateral dispersal in shrub areas led to lower densities of adults. The temperature and relative humidity of the riparian zone did not differ between the habitats. Ground‐active terrestrial invertebrate communities had a higher proportion of cursorial spiders in grassland, coinciding with greater abundances of aquatic prey. Aquatic prey contribution to cursorial spider diet matched adult aquatic insect abundances. Overall, riparian shrubs reduced the magnitude, or at least altered the timing, of cross‐ecosystem subsidy supply, distribution and use by consumers through mechanisms operating in both the aquatic and terrestrial ecosystems. Thus, the structure of ecosystem boundaries has complex effects on the strength of biological interactions between adjacent systems.     

Diet partitioning in sympatric Atlantic salmon and brown trout in streams with contrasting riparian vegetation

Prey intake by Atlantic salmon Salmo salar and brown trout Salmo trutta was measured across different riparian vegetation types: grassland, open canopy deciduous and closed canopy deciduous, in upland streams in County Mayo, Western Ireland. Fishes were collected by electrofishing while invertebrates were sampled from the benthos using a Surber sampler and drifting invertebrates collected in drift traps. Aquatic invertebrates dominated prey numbers in the diets of 0+ year Atlantic salmon and brown trout and 1+ year Atlantic salmon, whereas terrestrial invertebrates were of greater importance for diets of 1+ and 2+ year brown trout. Terrestrial prey biomass was generally greater than aquatic prey for 1+ and 2+ year brown trout across seasons and riparian types. Prey intake was greatest in spring and summer and least in autumn apart from 2+ year brown trout that sustained feeding into autumn. Total prey numbers captured tended to be greater for all age classes in streams with deciduous riparian canopy. Atlantic salmon consumed more aquatic prey and brown trout more terrestrial prey with an ontogenetic increase in prey species richness and diversity. Atlantic salmon and brown trout diets were most similar in summer. Terrestrial invertebrates provided an important energy subsidy particularly for brown trout. In grassland streams, each fish age class was strongly associated with aquatic, mainly benthic invertebrates. In streams with deciduous riparian canopy cover, diet composition partitioned between conspecifics with older brown trout associated with surface drifting terrestrial invertebrates and older Atlantic salmon associated with aquatic invertebrates with a high drift propensity in the water column and 0+ year fish feeding on benthic aquatic invertebrates. Deciduous riparian canopy cover may therefore facilitate vertical partitioning of feeding position within the water column between sympatric Atlantic salmon and brown trout. Implications for riparian management are discussed.     

Landscape genetics of an early successional specialist in a disturbance‐prone environment

Species that specialize in disturbed habitats may have considerably different dispersal strategies than those adapted to more stable environments. However, little is known of the dispersal patterns and population structure of such species. This information is important for conservation because many postfire specialists are at risk from anthropogenic changes to natural disturbance regimes. We used microsatellite markers to assess the effect of landscape variation and recent disturbance history on dispersal by a small mammal species that occupies the early seral stage of vegetation regeneration in burnt environments. We predicted that a postfire specialist would be able to disperse over multiple habitat types (generalist) and not exhibit sex‐biased dispersal, as such strategies should enable effective colonization of spatially and temporally variable habitat. We found significant differentiation between sites that fitted an isolation‐by‐distance pattern and spatial autocorrelation of multilocus genotypes to a distance of 2–3 km. There was no consistent genetic evidence for sex‐biased dispersal. We tested the influence of different habitat‐ and fire‐specific landscape resistance scenarios on genetic distance between individuals and found a significant effect of fire. Our genetic data supported recently burned vegetation having greater conductance for gene flow than unburnt habitat, but variation in habitat quality between vegetation types and occupied patches had no effect on gene flow. Postfire specialists must evolve an effective dispersal ability to move over distances that would ensure access to early successional stage vegetation. Natural disturbance and natural heterogeneity may therefore not influence population genetic structure as negatively as expected.     

Habitat microclimates drive fine‐scale variation in extreme temperatures

Most multicellular terrestrial organisms experience climate at scales of millimetres to metres, yet most species‐climate associations are analysed at resolutions of kilometres or more. Because individuals experience heterogeneous microclimates in the landscape, species sometimes survive where the average background climate appears unsuitable, and equally may be eliminated from sites within apparently suitable grid cells where microclimatic extremes are intolerable. Local vegetation structure and topography can be important determinants of fine‐resolution microclimate, but a literature search revealed that the vast majority of bioclimate studies do not include fine‐scale habitat information, let alone a representation of how habitat affects microclimate. In this paper, we show that habitat type (grassland, heathland, deciduous woodland) is a major modifier of the temperature extremes experienced by organisms. We recorded differences among these habitats of more than 5°C in monthly temperature maxima and minima, and of 10°C in thermal range, on a par with the level of warming expected for extreme future climate change scenarios. Comparable differences were found in relation to variation in local topography (slope and aspect). Hence, we argue that the microclimatic effects of habitat and topography must be included in studies if we are to obtain sufficiently detailed projections of the ecological impacts of climate change to develop detailed adaptation strategies for the conservation of biodiversity.     

Shifts in reciprocal river‐riparian arthropod fluxes along an urban‐rural landscape gradient

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鄱阳湖湖岸带景观变化

湖岸带是水陆生态系统过渡带,是人类活动最集中的区域之一,也是生态系统较为脆弱的区域。湖岸带具有重要的生态功能,湖岸带研究对于湖泊湿地生态系统保护具有重要意义。利用1995年,2000年,2005年和2010年4个时期的同水位条件下鄱阳湖湿地湖岸带遥感影像,对鄱阳湖湖岸带的景观进行了研究,结果表明,鄱阳湖湖岸带各种景观类型的面积变化显著,2010时期的水体面积较1995年、2000年和2005年时期减少近100km~2,绿地面积2010年较1995年减少近500km~2,建设用地和裸地面积2010年较1995年增加700km~2以上。景观指数变化明显,景观斑块数量逐年上升,最大斑块面积逐年减小,周长面积分形指数逐年加大,辛普森和香浓景观多样性指数逐年增大,表明湖岸带景观破碎化程度逐年加强。通过遥感影像解译结果综合分析,鄱阳湖湖岸带建设用地和裸地增加主要表现在沙化土地面积、交通建设用地面积和居民建筑建设用地的增加有关。     

Forest cover and heterogeneous pastures shape the diversity of predatory rove beetles in tropical riparian habitats

In tropical landscapes, forest remnants have been reduced to narrow strips of vegetation along rivers and streams surrounded by agricultural land that affects biodiversity, depending on the habitat and landscape characteristics. To assess the effect of riparian forest loss on the diversity of Staphylininae predatory rove beetles, we considered two habitat conditions (river sites with riparian vegetation and sites with heterogeneous pastures) within two micro-basin types (with >70% and <40% forest cover) in a tropical montane cloud forest landscape, Mexico. Beetles were collected using baited pitfall traps during the rainy season of 2014. No differences were found between micro-basin types and, although species richness (⁰D) was similar between habitat conditions, when the diversity of common (¹D) and dominant (²D) species was considered, sites with heterogeneous pastures were almost twice as diverse as those with riparian vegetation. All diversity measurements were greater in sites with heterogeneous pastures of either micro-basin type. Air temperature and canopy cover were the environmental variables that best explained the variation in beetle species composition. The greatest environmental differences related to species composition were detected between habitat conditions and were more evident in sites with heterogeneous pastures and low forest cover in the surroundings. The results suggest that replacing riparian vegetation with heterogeneous pastures, within micro-basins that lost between 30% and 60% of their forest cover, does not significantly reduce the diversity of predatory rove beetle but rather modifies the beetle composition. Effective formulation of management strategies to mitigate the impact of land use modification therefore requires an understanding of the interaction between vegetation remnants and landscape characteristics.     

Influence and value of different water regimes on avian species richness in arid inland Australia

Riparian habitats in arid landscapes are recognised for their structurally diverse vegetation and diverse bird species assemblages. In the extensive semi-arid and arid centre of Australia, riparian woodland habitats are impacted by pastoral land-use which may negatively influence vegetation structure and avian species composition. However, pastoralism has promoted the establishment of artificial water bodies, so that additional riparian vegetation may occur in the landscape. In this study, we surveyed the importance of different water regimes (i.e. artificial lakes, natural waterholes, desert sites) together with their associated vegetation on avian species richness in north-western New South Wales, Australia. Our results show that bird species richness was highest at water locations, in particular at artificial lakes. Avian species richness was negatively associated with distance to water bodies, both in desert vegetation types and in the riparian vegetation type along dry creeks. Moreover, riparian habitats supported larger avian assemblages and especially those of sedentary bird species compared to the surrounding shrub-steppe landscape. This indicates that artificial water bodies may be of significance for arid zone bird species and might gain in importance with changing water availabilities due to climatic changes.     

Spatio-temporal habitat assessment of the Gangetic floodplain in the Hastinapur wildlife sanctuary

Remote sensing provides multi-dimensional and multi-temporal information about habitat, insights into the significant drivers of change, and the key factors affecting landscape dynamics. Such information is crucial to provide perspective and a more profound understanding of ecological surveys. This study utilizes Google Earth Engine's capability to assess a riverine wetland grassland floodplain in Hastinapur Wildlife Sanctuary (HWS) along the Ganga River, which is a critical habitat for wintering migratory birds, the critically endangered gharial, turtles, aquatic mammals such as otters and dolphins, and cervid species such as swamp deer. We have developed a framework for regular monitoring through rapid habitat assessment, which visualizes the spatio-temporal change in land cover, the seasonal dynamics in water and vegetation, changes due to anthropogenic influences on the landscape, and finally, how these factors affect the habitat availability of species of concern in the HWS. The results show a dynamic river system with high seasonal variations. The vegetation trend shows increasing greenness, indicative of the conversion of grassland, scrubland, and herbaceous cover to more permanent vegetation, which will adversely affect the riparian habitat structure. A habitat suitability index generated through geospatial analysis using the weighted overlay method suggests that 40.07% of the HWS, nearly 767.12 km², comprising mainly the riverscape, wetland, and riparian grasslands, is suitable habitat for aquatic and semi-aquatic species. However, only 9.93% of the sanctuary comprising 197.27 km², is available as a core habitat. Further, the area is threatened by encroachment evident from the rapidly increasing land-use intensity and night light pollution, which puts the grasslands sheltered to swamp deer and other wildlife at higher risk leaving almost 27.9% of the area comprising 533.63 km² unsuitable for wildlife. Urban and agricultural land use has taken over 67% of the sanctuary. An increase in minimum radiance value representing ALAN, from 0.41 to 0.73 W/m²-sr in just six years from 2015 to 2021, shows a reduction in nocturnal darkness, reducing safe niches for wildlife. The study results provide critical baseline information for ecological surveys and a rapid assessment platform for future sanctuary management. Constant monitoring of anthropogenic activities such as farming, settlements, and transport routes threatening the habitat is essential for informed conservation management decisions.     

Effects of vegetation structure and landscape complexity on insect parasitism across an agricultural frontier in Argentina

Insect parasitism patterns are influenced by vegetation structure and landscape complexity. Our objective was to examine the effects of vegetation structure and landscape complexity on parasitism based on direct measurements of structure and diversity indices as well as on metrics based on remote sensing using Quickbird images. We collected 2266 lepidopteran larvae and pupae, including different families and habits, to estimate parasitism, and recorded vegetation characteristics in five 100-m² transects and 18 1 ha-plots in the dry Chaco, Northwest Argentina. We calculated landscape metrics and semivariograms in the plots from the image. The plots represented four “complexity groups”: agricultural, riparian/hedgerow, bare ground, and forest plots. Mean parasitism in the study sites was 10.7% (min: 0%, max: 23%). Parasitism was highest in agricultural plots, lowest in forest plots, and intermediate in riparian/hedgerow and bare ground plots. The landscape model explained parasitism more than the vegetation model. The landscape final model included Normalized Difference Vegetation Index (NDVI) Range, a measure of landscape heterogeneity, and Mean Shape Index, a measure of patch shape irregularity, and their interaction. The vegetation model included basal area and the Coefficient of Variation of tree density among transects, a measure of tree spatial distribution within a plot. Our results agree with previous studies that found higher parasitism in agricultural vs. non-agricultural environments in the subtropics, while riparian/hedgerow plots were important for conserving parasitism, as reported for temperate environments. We showed that under-explored tools such as the semivariogram and satellite band combinations were useful for the assessment of parasitism and that studying vegetation and landscape complexity simultaneously can help us examine mechanisms in detail. The identified variables related to high parasitism should be used for image classifications with a functional approach.     

Relationship between biodiversity and landscape structure in the Gyungan stream basin,central Korea

The relationship between landscape structure and biodiversity was investigated in the Gyungan stream basin, central Korea, in order to prepare a biodiversity conservation plan. The study area was divided into upstream, midstream, downstream and Gonjiam stream sub‐watersheds based on the land use pattern of each sub‐watershed. The quality of the terrestrial landscape was assessed by connectivity and percentages of deciduous broad‐leaved forest and urbanized area. The quality of the terrestrial landscape was the highest in the downstream sub‐watershed followed by Gonjiam stream, midstream and upstream sub‐watersheds. The quality of the riparian landscape assessed by percentages of the number and the area that the wetland vegetation elements occupy in the whole area showed a similar trend to that of terrestrial landscape. The diversity of all taxa including fish, reptiles and amphibians, birds, mammals and wetland vegetation except benthic macroinvertebrates was the highest downstream. The diversity of benthic macroinvertebrates was the highest in the Gonjiam stream sub‐watershed. Thus, biodiversity was shown to be the highest in the downstream sub‐watershed, followed, in order, by Gonjiam stream, midstream and upstream sub‐watersheds in proportion to landscape quality. On the other hand, the quality of the aquatic environment based on the ecological score of benthic macroinvertebrate (ESB) index was the highest downstream, followed, in order, by upstream, Gonjiam stream and midstream areas. This trend is different from that of biodiversity. In order to improve landscape quality degraded by excessive land use and to increase biodiversity, we recommended a restoration plan that addresses both ecosystem and landscape.     

城市化地区河岸带植被特征及其与河岸硬度的关系——以晋江市为例

确立了滨河河道硬度与滨河土地硬度两个指标,用以研究城市化地区河岸带的植物构成、多样性与均匀度、优势植物等特征与河岸硬度的关系。选定晋江市都市区12条主要河流作为研究对象,通过样地调查收集数据,并采用相应指数进行数据处理分析,结果表明:(1)调查河流的河岸带植被物种共计70科143属159种,其中乔木20科30属41种,灌木15科15属20种,草本35科98属98种,草本居主导地位,河流间种类分布不均衡;(2)河岸带植物乔灌草区系均以广义热带性成分居多,其次为世界性成分、温带性成分,无中国特有分布类型,乔木中广义热带成分占绝对主导,直观反映地带性特征,灌木与草本中的温带成分多于乔木中的温带成分,类型趋于多元,种类更丰富;(3)从河岸植被优势植物构成来看,主要优势乔木与灌木基本为本土植物,而主要草本中外来植物入侵严重,对地带性植物景观的指示显然不及乔木与灌木;(4)从河岸植被的人工美学属性来看,灌木优势植物中园林观赏植物的种类数显著多于乔木、草本优势植物,反映出晋江人工审美主导的滨河景观空间主要改变与塑造了灌木层植被景观;(5)从河岸植物的人居需求属性来看,龙眼、杨桃等多见于庭院林、水岸林的水果树种也在河岸植被中频繁出现,反映出人口密集区由于对植物生产用途的重视而对河岸植被产生的影响;(6)滨河土地硬度与河道硬度对河岸带灌木植物的影响最强烈,二者均对河岸带植物多样性造成威胁,且前者具有更大的影响力,而后者直接影响了河岸植物的分布形态,出于生产与审美目的的人为干扰对河岸带植物优势种的影响力随滨河硬度的增加而加强,低滨河硬度有助留存原生植被群落;(7)天然弯曲的河流形态对河流植被特征具有积极影响,有助于保留更多本土植被类型,并能在某种程度上丰富乔灌草的植物种类,但这种缓和作用无法根本扭转河岸硬化对植物多样性的胁迫影响。研究表明,城市化地区河流的岸带植被特征与沿线人为干扰类型和强度密切相关,恢复与塑造河岸生态景观要以乡土植被为主,通过乔木景观塑造地带性景观,并以灌木与草本丰富植被景观。     

Importance of low-flow and high-flow characteristics to restoration of riparian vegetation along rivers in arid south-western United States

1. Riparian vegetation in dry regions is influenced by low‐flow and high‐flow components of the surface and groundwater flow regimes. The duration of no‐flow periods in the surface stream controls vegetation structure along the low‐flow channel, while depth, magnitude and rate of groundwater decline influence phreatophytic vegetation in the floodplain. Flood flows influence vegetation along channels and floodplains by increasing water availability and by creating ecosystem disturbance. 2. On reference rivers in Arizona's Sonoran Desert region, the combination of perennial stream flows, shallow groundwater in the riparian (stream) aquifer, and frequent flooding results in high plant species diversity and landscape heterogeneity and an abundance of pioneer wetland plant species in the floodplain. Vegetation changes on hydrologically altered river reaches are varied, given the great extent of flow regime changes ranging from stream and aquifer dewatering on reaches affected by stream diversion and groundwater pumping to altered timing, frequency, and magnitude of flood flows on reaches downstream of flow‐regulating dams. 3. As stream flows become more intermittent, diversity and cover of herbaceous species along the low‐flow channel decline. As groundwater deepens, diversity of riparian plant species (particularly perennial species) and landscape patches are reduced and species composition in the floodplain shifts from wetland pioneer trees (Populus, Salix) to more drought‐tolerant shrub species including Tamarix (introduced) and Bebbia. 4. On impounded rivers, changes in flood timing can simplify landscape patch structure and shift species composition from mixed forests composed of Populus and Salix, which have narrow regeneration windows, to the more reproductively opportunistic Tamarix. If flows are not diverted, suppression of flooding can result in increased density of riparian vegetation, leading in some cases to very high abundance of Tamarix patches. Coarsening of sediments in river reaches below dams, associated with sediment retention in reservoirs, contributes to reduced cover and richness of herbaceous vegetation by reducing water and nutrient‐holding capacity of soils. 5. These changes have implications for river restoration. They suggest that patch diversity, riparian plant species diversity, and abundance of flood‐dependent wetland tree species such as Populus and Salix can be increased by restoring fluvial dynamics on flood‐suppressed rivers and by increasing water availability in rivers subject to water diversion or withdrawal. On impounded rivers, restoration of plant species diversity also may hinge on restoration of sediment transport. 6. Determining the causes of vegetation change is critical for determining riparian restoration strategies. Of the many riparian restoration efforts underway in south‐western United States, some focus on re‐establishing hydrogeomorphic processes by restoring appropriate flows of surface water, groundwater and sediment, while many others focus on manipulating vegetation structure by planting trees (e.g. Populus) or removing trees (e.g. Tamarix). The latter approaches, in and of themselves, may not yield desired restoration outcomes if the tree species are indicators, rather than prime causes, of underlying changes in the physical environment.     

Development, maintenance and role of riparian vegetation in the river landscape

1. Riparian structure and function were considered from a longitudinal perspective in order to identify multiscale couplings with adjacent ecosystems and to identify research needs. 2. We characterized functional zones (with respect to vegetation development in association with various biogeochemical processes) within geomorphological settings using a delineation based upon erosional, transitional and depositional properties. 3. Vegetation dynamics within the riparian corridor are clearly influenced substantially by hydrological disturbance regimes. In turn, we suggest that vegetation productivity and diversity may widely influence riverine biogeochemical processes, especially as related to the consequences of changing redox conditions occurring from upstream to downstream. 4. However, surface and groundwater linkages are the predominant controls of landscape connectivity within riparian systems. 5. The importance of riparian zones as sources and sinks of matter and energy was examined in context of structural and functional attributes, such as sequestering or cycling of nutrients in sediments, retention of water in vegetation, and retention, diffusion or dispersal of biota. 6. The consequences of interactions between different communities (e.g. animals and plants, micro-organisms and plants) on biogeochemical processes are notably in need of research, especially with respect to control of landscape features. Multiscale approaches, coupling regional and local factors in all three spatial dimensions, are needed in order to understand more synthetically and to model biogeochemical and community processes within the river-riparian-upland landscape of catchments.     

Benefits of habitat restoration to small mammal diversity and abundance in a pastoral agricultural landscape in mid-Wales

Changes in agricultural practice are predicted across the UK following agricultural reform driven by government policy. The suitability of agri-environment schemes for many species is currently debated because limited quantitative data are collected. In order to understand the changes to biodiversity due to agri-environment schemes, there is a need for studies to not just compare biodiversity and species composition in and out of agri-environment areas, but to factor in the influence of temporal habitat changes. In this study, we investigate the suitability of an agri-environment initiative to support and enhance a small mammal fauna among pastoral hill farms in mid-Wales. Grazed and ungrazed woodlands, riparian habitats, and broadleaf plantations, were compared for small mammal abundance and diversity following a trapping study. Mammal diversity was similar across habitats, though abundance varied significantly. A principle component analysis identified that mammal abundance clustered into three main habitat groups separated by seral stage (early, mid, late). No relationship between mammal abundance and stock grazing was found. A canonical correspondence analysis confirmed that vegetation structure was important in explaining the distribution of captures of mammal species across the landscape. The results for habitat type, and habitat context, suggest that a mix of vegetation seral stages, reflecting a varied vegetation structure, is important to maintain small mammal diversity and abundance across the study area. Heterogeneity in structural diversity at the landscape scale is important to maintain a variety of ground-dwelling mammal species, and particularly because trends in countryside surveys show that woodlands are skewed towards late seral stages. Habitat heterogeneity can be maintained because the hill farms neighbour each other, and the farmers co-operate as a group to manage the landscape. Habitat diversity is therefore possible. These results help us to advocate, and anticipate, the benefits of groups of farms within a landscape.     

Comparative landscape genetics reveals the evolution of viviparity reduces genetic connectivity in fire salamanders

Evolutionary changes in reproductive mode may affect co‐evolving traits, such as dispersal, although this subject remains largely underexplored. The shift from aquatic oviparous or larviparous reproduction to terrestrial viviparous reproduction in some amphibians entails skipping the aquatic larval stage and, thus, greater independence from water. Accordingly, amphibians exhibiting terrestrial viviparous reproduction may potentially disperse across a wider variety of suboptimal habitats and increase population connectivity in fragmented landscapes compared to aquatic‐breeding species. We investigated this hypothesis in the fire salamander (Salamandra salamandra), which exhibits both aquatic‐ (larviparity) and terrestrial‐breeding (viviparity) strategies. We genotyped 426 larviparous and 360 viviparous adult salamanders for 13 microsatellite loci and sequenced a mitochondrial marker for 133 larviparous and 119 viviparous individuals to compare population connectivity and landscape resistance to gene flow within a landscape genetics framework. Contrary to our predictions, viviparous populations exhibited greater differentiation and reduced genetic connectivity compared to larviparous populations. Landscape genetic analyses indicate viviparity may be partially responsible for this pattern, as water courses comprised a significant barrier only in viviparous salamanders, probably due to their fully terrestrial life cycle. Agricultural areas and, to a lesser extent, topography also decreased genetic connectivity in both larviparous and viviparous populations. This study is one of very few to explicitly demonstrate the evolution of a derived reproductive mode affects patterns of genetic connectivity. Our findings open avenues for future research to better understand the eco‐evolutionary implications underlying the emergence of terrestrial reproduction in amphibians.     

漓江水陆交错带不同植被类型的土壤酶活性

水陆交错带是内陆水生生态系统与陆地生态系统之间的功能界面区,其包含了高地到低地直到水体的区域,是土壤有机质源、汇和转换器。土壤中有机物的分解以及营养物质的转化不仅影响到植物的生长,也对水体质量产生间接影响。土壤酶几乎参与土壤中有机物质的分解与合成的全过程,直接或间接影响着土壤一系列的生物化学反应,对生态系统的物质循环产生重要影响。不少学者围绕农田土壤、林地土壤以及湿地土壤探讨了不同植被下酶活性的变异。水陆交错带植被种类丰富,周期性的淹水条件加剧了土壤性质变异的复杂性。但目前水陆交错带不同植被类型土壤酶活性差异的研究不多。以漓江水陆交错带土壤为研究对象,对苔藓、草本和灌丛3种植被类型下的土壤溶解性化学成分、4种土壤水解酶即糖苷酶、几丁质酶、亮氨酸氨基肽酶和磷酸酶以及2种氧化还原酶即酚氧化酶和过氧化物酶的活性,以及土壤性质与酶活性之间的关系进行了研究。结果表明,苔藓植被下土壤的糖苷酶和酚氧化酶活性显著高于草本和灌丛,草本植被下土壤的过氧化物酶活性显著高于苔藓和灌丛,灌丛植被下土壤几丁质酶活性显著高于苔藓和草本,但不同植被类型的土壤亮氨酸氨基肽酶活性无显著差异。相关分析表明,土壤水分含量与糖苷酶和酚氧化酶活性呈显著正相关,而与几丁质酶和碱性磷酸酶活性呈显著负相关。土壤有机碳和易氧化碳均与糖苷酶和酚氧化酶活性呈极显著负相关,与几丁质酶活性呈显著正相关。土壤溶解性有机碳与亮氨酸氨基肽酶和酚氧化酶呈显著正相关。综合认为,水陆交错带不同种类土壤酶在不同植被类型间的差异有别,土壤水分含量和土壤有机碳显著影响土壤酶活性的变化。不同植被类型土壤酶活性的差异不仅与植被类型有关,与水陆交错带微地形以及土壤性质的空间异质性也有密切关系,需运用长期控制试验手段开展研究。     

Drainage Size, Stream Intermittency, and Ecosystem Function in a Sonoran Desert Landscape

Understanding the interactions between terrestrial and aquatic ecosystems remains an important research focus in ecology. In arid landscapes, catchments are drained by a channel continuum that represents a potentially important driver of ecological pattern and process in the surrounding terrestrial environment. To better understand the role of drainage networks in arid landscapes, we determined how stream size influences the structure and productivity of riparian vegetation, and the accumulation of organic matter (OM) in soils beneath plants in an upper Sonoran Desert basin. Canopy volume of velvet mesquite (Prosopis velutina), as well as overall plant cover, increased along lateral upland–riparian gradients, and among riparian zones adjacent to increasingly larger streams. Foliar δ¹³C signatures for P. velutina suggested that landscape patterns in vegetation structure reflect increases in water availability along this arid stream continuum. Leaf litter and annual grass biomass production both increased with canopy volume, and total aboveground litter production ranged from 137 g m⁻² y⁻¹ in upland habitat to 446 g m⁻² y⁻¹ in the riparian zone of the perennial stream. OM accumulation in soils beneath P. velutina increased with canopy volume across a broad range of drainage sizes; however, in the riparian zone of larger streams, flooding further modified patterns of OM storage. Drainage networks represent important determinants of vegetation structure and function in upper Sonoran Desert basins, and the extent to which streams act as sources of plant-available water and/or agents of fluvial disturbance has implications for material storage in arid soils.