Sampling spatial and temporal variation in soil nitrogen availability

There are few studies in natural ecosystems on how spatial maps of soil attributes change within a growing season. In part, this is due to methodological difficulties associated with sampling the same spatial locations repeatedly over time. We describe the use of ion exchange membrane spikes, a relatively nondestructive way to measure how soil resources at a given point in space fluctuate over time. We used this method to examine spatial patterns of soil ammonium (NH⁺ ₄) and nitrate (NO⁻ ₃) availability in a mid-successional coastal dune for four periods of time during the growing season. For a single point in time, we also measured soil NH⁺ ₄ and NO⁻ ₃ concentrations from soil cores collected from the mid-successional dune and from an early and a late successional dune. Soil nitrogen concentrations were low and highly variable in dunes of all ages. Mean NH⁺ ₄ and NO⁻ ₃ concentrations increased with the age of the dune, whereas coefficients of variation for NH⁺ ₄ and NO⁻ ₃ concentrations decreased with the age of the dune. Soil NO⁻ ₃ concentration showed strong spatial structure, but soil NH⁺ ₄ concentration was not spatially structured. Plant-available NH⁺ ₄ and NO⁻ ₃ showed relatively little spatial structure: only NO⁻ ₃ availability in the second sampling period had significant patch structure. Spatial maps of NH⁺ ₄ and NO⁻ ₃ availability changed greatly over time, and there were few significant correlations among soil nitrogen availability at different points in time. NO⁻ ₃ availability in the second sampling period was highly correlated (r = 0.90) with the initial soil NO⁻ ₃ concentrations, providing some evidence that patches of plant-available NO⁻ ₃ may reappear at the same spatial locations at irregular points in time. Received: 20 February 1998 / Accepted: 23 November 1998     

Golden monkey ranging in relation to spatial and temporal variation in food availability

Understanding the determinants of a species’ range use aids in understanding their ecological requirements, which in turn facilitates designing effective conservation strategies. The ranging behaviour of golden monkeys (Cercopithecus mitis kandti) in Mgahinga Gorilla National Park, Uganda was studied from January 2003 to February 2004 to establish habitat preferences. In each 0.25 ha grid cell in the group’s home range we quantified the basal area of food trees (n = 12,133 trees), measured bamboo (Arundinaria alpina) stems (n = 103,548), and estimated vine and shrub coverage. The evaluation of habitat preferences was facilitated by the fact that only five plant species, plus invertebrates (7.5%) constituted 96.4% of the group’s foraging effort; this included bamboo (59.9%), Maesa lanceolata (18.7%), Hypericum revolutum (6.8%), Galiniera saxifraga (2.1%) and Ilex mitis (1.4%). Phenology data were collected for all five food tree species, three vines, and two shrubs. Range use generally followed food tree basal area distribution and not the distribution of bamboo, with the abundance of M. lanceolata being more closely associated with home range use than any other food plant. Bamboo was ubiquitous in distribution and a vital year‐round resource for golden monkeys, which they combined with other food items to meet their nutritional requirements. Illegal bamboo or tree extraction both pose a serious threat to the conservation of the golden monkey, but activities that affect food tree abundance will likely have the most influence on monkey persistence.     

Reproductive responses of temperate and boreal Tengmalm's Owl Aegolius funereus populations to spatial and temporal variation in prey availability

Environmental variation across space and time can strongly influence life‐history strategies in vertebrates. It has been shown that the reproductive success of birds of prey is closely related to food availability. However, relatively little is known about intraspecific differences in reproductive success of birds in relation to varying ecological conditions across environmental gradients. We investigated the reproductive performance of Tengmalm's Owls Aegolius funereus in a temperate (Czech Republic, 50°N) and a boreal (Finland, 63°N) population in relation to long‐term variations in the abundance of their main prey (small rodents). Prey densities at the northern site were much higher, but there were also large inter‐annual fluctuations and years with steep summer declines of vole densities. Northern owls laid larger clutches but offspring production per nest was similar at both study sites. This resulted from higher nestling mortality in the northern population, especially in nests established later in the season. Despite much greater nesting losses due to predation by Pine Martens Martes martes, productivity at the population level was about four times greater at the temperate site, mainly due to the much higher breeding densities compared with Finland. Tengmalm's Owls at the temperate study site may benefit from relatively stable prey abundance, a more diverse prey community that offers alternative prey during vole scarcity, longer nights in summer that allow more time for foraging, and a lower level of interspecific competition with other vole‐specialized predators.     

A nitrogen budget of mainland China with spatial and temporal variation

The present study evaluated nitrogen (N) input and output in mainland China using updated data of temporally and spatially-based land use maps and statistical data at national and provincial scales. The total N inputs increased from 3,081 kg km^?2 in 1985 to 5,426 kg km^?2 in 2007. Chemical fertilizer dominated the N input and showed an increasing trend. Biological N fixation was the second important N input till 1990 and atmospheric deposition became the second most important source after that, accounting for 24.0% in 2007. There was no net N input through food/feed import in 1985, but it accounted for 3.5% of the total N input in 2007. According to a mass balance model, we assumed total N input equal to output. The results showed that more than half of the total N was denitrified or stored in the system. Ammonia volatilization accounted for 18.9–22.9% of the total N input, and N export to water bodies accounted for 17.9–20.7%. About 5.1–7.7% of the N input was emitted to the atmosphere through biomass burning. When calculated per unit area, total N input, N export to water bodies, denitrification and storage could be very well explained by human population density. Nitrogen input and major outputs were also positively related to per capita gross domestic product and the percentage of total land area used as cropland. The N budget is compared to that of some other countries and the environmental impacts of the N cycle is discussed.     

Spatial and temporal variations in floral resource availability affect bumblebee communities in heathlands

Modifications of landscape structure and composition can decrease the availability of floral resources, resulting in the decline of many pollinator species, including bumblebees. These declines may have significant ecological consequences, because bumblebees pollinate a large range of plant species. Our study was carried out in heathlands, open semi-natural habitats that have decreased considerably due to human activities. We analysed how floral resources affect bumblebee communities throughout the colony lifetime at three scales: plot scale, heathland patch scale, and landscape scale. Floral density at the plot scale and spruce plantations at the landscape scale influenced bumblebee communities. The abundance of bumblebees on ericaceous species was higher when the landscape included a substantial proportion of unsuitable foraging habitat (i.e., spruce plantations). Both life history traits and colony life cycle stage influenced bumblebee responses to the availability of floral resources. Bumblebees were more affected by floral resources during the colony development phase than during the nest-foundation or mating phases. Moreover, bumblebees of species that form large colonies needed larger quantities of favourable foraging habitat, compared with small-colony bees, and their proportion decreased in habitats dominated by spruce plantations. In conclusion, the conservation of plant–bumblebee interactions will require management at a larger spatial scale than the restricted protected habitats. Moreover, at the landscape scale, both quantity of favourable foraging patches and their ecological continuity are important to conserve both small- and large- colony species.     

A graphical theory of competition on spatial resource gradients

Resource competition is a fundamental interaction in natural communities. However, little remains known about competition in spatial environments where organisms are able to regulate resource distributions. Here, we analyse the competition of two consumers for two resources in a one-dimensional habitat in which the resources are supplied from opposite sides. We show that the success of an invading species crucially depends on the slope of the resource gradients shaped by the resident. Our analysis reveals that parameter combinations, which lead to coexistence in a uniform environment, may favour alternative stable states in a spatial system, and vice versa. Furthermore, differences in growth rate, mortality or dispersal abilities allow a consumer to coexist stationarily with - or even outcompete - a competitor with lower resource requirements. Applying our theory to a phytoplankton model, we explain shifts in the community structure that are induced by environmental changes.     

Fecundity of Baltic cod: temporal and spatial variation

Potential and relative potential fecundity of 701 cod Gadus morhua caught in the Bornholm Basin (ICES Sub-division 25) during 1987–1996 and 106 from the Gdansk Deep (ICES Sub-division 26) in 1995 and 1996 varied significantly between years but neither between different spawning grounds nor between different sampling months within one spawning season. Growth and water temperature are factors identified to influence the mean relative fecundity explaining 66% of the variance between years.     

Effects of spatial aggregation on competition,complementarity and resource use

Abstract The spatial distributions of most species are aggregated to varying degrees. A limited number of studies have examined the effects of spatial aggregation on interspecific and intraspecific interactions, generally finding that spatial aggregation can enhance coexistence between species by reducing the capacity for interspecific competition. Less well studied are the effects of spatial aggregation on complementarity (i.e. differences in resource use strategies) and resource use. Our primary hypothesis was that spatial aggregation reduces the complementarity between species owing to: (i) less interspecific interactions as a result of spatial separation; and (ii) less differences between species as a result of phenotypic plasticity. We further postulate that these negative effects of spatial aggregation on complementarity will reduce resource use by the community. Here we test these hypotheses in a pot experiment in which we applied three levels of spatial aggregation to three sets of two‐species mixtures of herbaceous perennial plant species from native grasslands of south‐eastern Australia. Both root and shoot biomass were significantly affected by spatial aggregation, although the nature of these affects depended upon the species involved, and the relative strengths of interspecific versus intraspecific competition. Complementarity between species in the distribution of their green leaves decreased significantly as spatial aggregation increased for one of the species mixtures, providing some evidence in support of our hypothesis that aggregation reduces complementarity through phenotypic plasticity. Spatial aggregation also altered light interception and use of soil moisture resources, although these effects were dependent on the species involved. We suggest that clear effects of spatial aggregation on complementarity and resource use may be obscured by the idiosyncratic way in which neighbour identity influences plant growth and hence plant size, limiting the ability to generalize, at the community level, any underlying effects of spatial pattern on ecological process.     

Nitrogen and carbohydrate storage in biennials originating from habitats of different resource availability

Four biennial species (Arctium tomentosum, Cirsium vulgare, Dipsacus sylvester and Daucus carota) which originate from habitats of different nutrient availability were investigated in a 2-year experiment in a twofactorial structured block design varying light (natural daylight versus shading) and fertilizer addition. The experiment was designed to study storage as reserve formation (competing with growth) or as accumulation (see Chapin et al. 1990). We show that (i) the previous definitions of storage excluded an important process, namely the formation of storage tissue. Depending on species, storage tissue and the filling process can be either a process of reserve formation, or a process of accumulation. (ii) In species representing low-resource habitats, the formation of a storage structure competes with other growth processes. Growth of storage tissue and filling with storage products is an accumulation process only in the high-resource plant Arctium tomentosum. We interpret the structural growth of low-resource plants in terms of the evolutionary history of these species, which have closely related woody species in the Mediterranean area. (iii) The use of storage products for early leaf growth determines the biomass development in the second season and the competitive ability of this species during growth with perennial species. (iv) The high-resource plant Arctium has higher biomass development under all conditions, i.e. plants of low-resource habitats are not superior under low-resource conditions. The main difference between high- and low-resource plants is that low-resource plants initiate flowering at a lower total plant internal pool size of available resources.     

Impacts of temporal variation on apparent competition and coexistence in open ecosystems

The natural world is variable both in space and in time, but little ecological theory has been explicitly devoted to analyzing the consequences of both kinds of variability operating simultaneously. This issue is examined relative to the indirect interaction of apparent competition, which can limit the membership of prey communities. One limiting case that provides a useful starting point is to imagine that a local community is influenced by coupling with an external source landscape, but has little reciprocal influence on that landscape. There usually will be some rate of input of a locally inferior species that suffices to 'swamp' a superior species and drive it to extinction. We use simple models of apparent competition to show that when one superimposes upon this scenario temporal fluctuations, mediated through shifts in parameter values, such variation can either magnify the importance of the external input, or reduce it, depending on which component of the system experiences variation. We examine this in the case of both slow variation (for which we suggest a protocol that may be useful in a wide range of ecological models), and fast variation. The theoretical studies presented here provide examples of the rich range of outcomes that may arise due to temporal variability in spatially heterogeneous landscapes.     

Resource quality,resource availability,and intraguild predation among omnivorous mirids

Intraguild predation (IGP) among predatory species can influence many plant-arthropod associations. However, the relevance of IGP is poorly understood for truly omnivorous species such as those that can complete development on both animal and plant diets. Here we test the hypothesis that IGP among two omnivorous mirids is more common when extraguild food is either absent or not suitable. Laboratory experiments were performed in experimental cages in order to determine the effect of intraguild prey densities and diet availability on direction and intensity of IGP between Dicyphus tamaninii and Macrolophus caliginosus (Heteroptera: Miridae). Intraguild predation was symmetrical between the two mirid species in the absence of alternative food. Increasing densities of intraguild prey enhanced drastically the incidence of IGP. Intraguild predation was reduced when mirids were in the presence of green or red tomato fruits, but the presence of any other extraguild resources had no impact on IGP level. However, when given before the experiments, all resources with the exception of tomato leaves significantly reduced IGP. A second experiment was performed on live plants to compare the results of the previous trials with that obtained in a more natural setting. No IGP was observed when both mirid species were present on a plant. However, development of the intraguild prey (the more vulnerable stage) was hindered by the presence of the intraguild predator. The potential of such results is discussed from community ecology and biological control perspective.     

Sharp changes in resource availability may induce spatial nearly periodic population abundances

For many years, scientists have tried to understand the ubiquitous discrete nature of traits. As the emergence of nonuniform patterns in space via instability of the uniform pattern to spatial perturbations is well-understood in reaction–diffusion systems, several studies have suggested that a similar instability underlies discrete distributions of traits. In contrast, here we suggest that a different mechanism may underly species’ discrete distributions of trait values. We show that a point where niche availability changes sharply along the continuous niche axis promotes the discretized distribution of trait values even far from that point. In certain cases, this mechanism may apply also to patterns of population densities over space, such as patterns that were observed in vegetation biomass, as locations where environment changes sharply may promote spatially, nearly periodic stationary patterns.     

Community structure in north temperate ants: temporal and spatial variation

Summary Ant communities in Vermont and New York woods were sampled in four time periods to determine species composition, relative abundances, and nest locations in space. The Vermont community was richer, containing more species and higher nest densities than New York. Both communities followed the geometric distribution of species abundances, suggesting that a single resource was mediating competition. The resource most clearly implicated was suitable nest sites, principally pre-formed plant cavities. Nonrandom species associations, underdispersion in every season, and the occurrence of incipient nests overwintering aboveground all implicated shortage of such cavities. Furthermore, microhabitat differences which produce suitable nest sites occur over a very small scale in these communities.     

Pollen availability for predaceous mites on apple: spatial and temporal heterogeneity

It has been suggested that an abundance of alternate food early in the spring may be critical to the ability of generalist predaceous mites to suppress spider mite pests. One alternate food that is typically very abundant in spring is wind-dispersed pollen. Here we investigate, at several spatial scales, the heterogeneity in the availability of pollen to predaceous mites on apple. We found pollen to be abundant on apple leaves very soon after they opened (>100 grains/cm 2 ), and that the dominant pollen types at this time were wind-dispersed tree pollens (Betulaceae and Pinaceae). We found that most of the spatial variation in pollen abundance occurred at either small spatial scales (within trees) or very large spatial scales (among orchard blocks). Variability among orchards was clearly influenced by the surrounding vegetation, and probably also by the management regime (frequency of mowing). Spatial heterogeneity in pollen availability may affect the build-up of predatory mite populations in the spring, as we found early season abundances of Typhlodromus pyri (Phytoseiidae) and Zetzellia mali (Stigmaeidae) to be better correlated with early season pollen density than with abundance of mite prey (Aculus schlechtendali).     

Lifelong foraging and individual specialisation are influenced by temporal changes of resource availability

Resource availability largely determines the distribution and behaviour of organisms. In plant–pollinator communities, availability of floral resources may change so rapidly that pollinator individuals can benefit from switching between multiple resources, i.e. different flowering plant species. Insect pollinator individuals of a given generation often occur in different time windows during the reproductive season. This temporal variation in individual occurrences, together with the rapidly changing resource availability, may lead individuals of the same population to encounter and use different resources, resulting in an apparent individual specialisation. We hypothesized, that 1) individual pollinators change their resource use (flower visitation) during their lifetime according to the changing availability of floral resources, and that 2) temporal variation in individual occurrences of pollinators and in resource availability will partly explain individual specialisation. To test these hypotheses, we observed flower visitations of individually marked clouded Apollo butterflies Parnassius mnemosyne during one reproductive season. We found temporal changes in lifetime individual resource use that followed the changes in resource availability, indicating that butterflies can adjust foraging to varying resource availability. Individuals differed considerably in their resource use. This variation was partly explained by temporal variation in both floral resource availability and temporal occurrence of individual butterflies. We suggest the butterfly as a sequential specialist, i.e. short‐term specialist and long‐term generalist. This foraging plasticity can be essential for short‐living insect pollinators in rapidly changing environments. Although flowering dynamics do not fully explain the variability in foraging, our results highlight the importance of temporal dimension in resource use studies. Ultimately, the relative pace of environmental change compared to individual lifespan may be a key factor in resource use plasticity.     

基于信息熵的新疆降水时空变异特征研究

基于信息熵理论对新疆降水序列的时空变异性进行研究。利用边际熵研究不同时间尺度降水序列的变化特征。利用分配熵和强度熵分别研究降水量和降水天数年内和年代际(10a)分配情况。利用改进的Mann-Kendall趋势检验法分析新疆降水过程不确定性变化趋势。研究表明:(1)新疆降水量与降水天数年内分配不均匀性主要表现为由南向北减小的空间分布特征;(2)新疆不同尺度的降水序列不确定性具有明显空间特征;(3)越降水越稀少的地区,降水量与降水天数变异性就越大。本研究对该区域降水时空变异研究与水资源规划具有重要意义。     

Reproductive responses to spatial and temporal prey availability in a coastal Arctic fox population

1.?Input of external subsidies in the Arctic may have substantial effects on predator populations that otherwise would have been limited by low local primary productivity. 2.?We explore life-history traits, age-specific fecundity, litter sizes and survival, and the population dynamics of an Arctic fox (Vulpes lagopus) population to explore the influence of the spatial distribution and temporal availability of its main prey; including both resident and migrating (external) prey resources. 3.?This study reveals that highly predictable cross-boundary subsidies from the marine food web, acting through seasonal access to seabirds, sustain larger local Arctic fox populations. Arctic fox dens located close to the coast in Svalbard were found to have higher occupancy rates, as expected from both high availability and high temporal and spatial predictability of prey resources (temporally stable external subsidies). Whereas the occupancy rate of inland dens varied between years in relation to the abundance of reindeer carcasses (temporally varying resident prey). 4.?With regard to demography, juvenile Arctic foxes in Svalbard have lower survival rates and a high age of first reproduction compared with other populations. We suggest this may be caused by a lack of unoccupied dens and a saturated population.     

Influence of dietary specialization and resource availability on geographical variation in abundance of butterflyfish

Empirical evidence indicates that both niche breadth and resource availability are key drivers of a species' local abundance patterns. However, most studies have considered the influence of either niche breath or resource availability in isolation, while it is the interactive effects that are likely to influence local abundance. We examined geographic variation in the feeding ecology and distribution of coral-feeding butterflyfish to determine the influence of dietary specialization and dietary resource availability on their local abundance. Dietary composition and abundance of five butterflyfish and coral dietary resource availability were determined at 45 sites across five locations (Lizard Island and Heron Island, Great Barrier Reef; Kimbe Bay, Papua New Guinea; Noumea, New Caledonia; and Moorea, French Polynesia). Multiple regression models using variables representative of total dietary resource availability, availability of specific dietary resources, and interspecific competition were used to determine the best predictors of local abundance across all sites and locations for each species. Factors influencing local abundance varied between butterflyfish with specialized and generalized diets. Dietary resource availability had the strongest influence on the abundance of Chaetodon trifascialis-the most specialized species. Local abundance of C. trifascialis was best predicted by availability of the Acropora corals that it preferentially feeds on. In contrast, abundance of generalist butterflyfish was poorly described by variation in availability of specific resources. Rather, indices of total dietary resource availability best predicted their abundance. Overall, multiple regression models only explained a small proportion of the variation in local abundance for all five species. Despite their relatively specialized diets, dietary resource availability has limited influence on the local abundance of butterflyfish. Only the most specialized species appear to be consistently limited by prey availability. Local and total abundance of species are influenced by a wide range of different factors and there is definite need to conduct independent species assessments.     

苏干湖湿地植被覆盖度时空变化格局

植被覆盖度是反映群落外貌特征和影响植被生态系统稳定性的重要因子,其时空异质性演化规律研究有助于认识湿地群落的结构功能及其环境响应机制。采用湿地群落学调查和遥感技术相结合的方法,分析了苏干湖内陆盐沼湿地近30年植被覆盖度的时空变化及其影响因素。结果表明:像元二分模型在内陆盐沼湿地植被覆盖度研究方面具有较高的模拟精度;苏干湖湿地的植被覆盖度在1987—2017年间总体呈上升趋势,年际增幅为0.162%/5a,与气温和降水呈正相关关系;在空间上植被覆盖度与地下水位埋深呈正相关,与土壤全盐量呈负相关,但不同等级植被覆盖度与地下水位埋深、土壤全盐量间的相关性各有差异。苏干湖湿地植被覆盖度受地下水位埋深、土壤全盐量空间异质性的影响,呈现出斑块状镶嵌分布。