A trade-off between scale and precision in resource foraging

Summary There is widespread uncertainty about the nature and role of morphological plasticity in resource competition in plant communities. We have assayed the foraging characteristics of leaf canopies and root systems of eight herbaceous plants of contrasted ecology using new techniques to create controlled patchiness in light and mineral nutrient supply. The results are compared with those of a conventional competition experiment. Measurements of dry matter partitioning and growth in patchy conditions indicate a consistent positive association between the foraging characteristics of roots and shoots, supporting the hypothesis of strong interdependence of competitive abilities for light and mineral nutrients. Differences are identified in the abilities of dominant and subordinate plants to forage on coarse and fine scalcs. It is suggested that a trade-off exists in the scale (“high” in dominants) and precision (high in subordinates) with which resources are intercepted and that this trade-off contributes to diversity in communities of competing plants.     

Evaluation of alternative hypotheses to explain temperature-induced life history shifts in Daphnia

Negative correlations between environmental temperature andbody size are widespread in planktonic organisms, and ectothermsgenerally, but remain poorly understood. Here we evaluate experimentallytwo alternative hypotheses suggested to explain life historyshifts induced by raised temperature using parthenogenetic clonesfrom two Daphnia species. Explanation 1 proposes that the lifehistory shifts could be adaptive if increased temperature isused as an indirect cue to indicate increased risk from size-selectivepredators. Explanation 2 proposes that at larger body size energybecomes more limiting as temperature increases because of aless favourable assimilation: metabolism balance. In a factoriallaboratory experiment we examine the effects of three rearingtemperatures on the growth and reproductive traits of Daphniaraised in water with fish kairomone, Chaoborus kairomone, orin uncontaminated water. None of the three predictions of explanation1 were met by the data. In both D. pulex and D. curvirostris,and some other published studies, data suggested that at largerbody sizes the sum of growth and reproduction was lower at hightemperature, supporting our prediction from explanation 2. However,we propose a novel third explanation based on new evidence oftemperature-dependence in both reproductive effort and costin D. pulex.     

Using niche construction theory to generate testable foraging hypotheses at Liang Bua

Niche construction theory (NCT) has emerged as a promising theoretical tool for interpreting zooarchaeological material. However, its juxtaposition against more established frameworks like optimal foraging theory (OFT) has raised important criticism around the testability of NCT for interpreting hominin foraging behavior. Here, we present an optimization foraging model with NCT features designed to consider the destructive realities of the archaeological record after providing a brief review of OFT and NCT. Our model was designed to consider a foragers decision to exploit an environment given predation risk, mortality, and payoff ratios between different ecologies, like more‐open or more‐forested environments. We then discuss how the model can be used with zooarchaeological data for inferring environmental exploitation by a primitive hominin, Homo floresiensis, from the island of Flores in Southeast Asia. Our example demonstrates that NCT can be used in combination with OFT principles to generate testable foraging hypotheses suitable for zooarchaeological research.     

Vireo song repertoires and migratory distance: three sexual selection hypotheses fail to explain the correlation

Previous studies have found a relationship between migrationand the degree of elaboration of sexually selected traits,but investigators have differed in the mechanisms they proposedto account for this association. We examined the relationshipbetween song repertoire size and distance migrated among birdsin the genus Vireo. There is a strong positive relationshipbetween migratory distance and repertoire size in this genus,but our data do not support the specific predictions of anyof the three proposed mechanisms (the "rapid pairing," "goodmigrations," and "territory lottery" hypotheses). Migrationdistance is presumably correlated with other life-history characteristicsthat influence the development of sexually selected traits.     

Root allocation and foraging precision in heterogeneous soils

Root growth patterns respond to small-scale resource heterogeneity and the presence of roots of neighboring plants, but how a plant integrates its responses to these cues is not well understood. In the presence of neighbors, plants may shift allocation to roots as a consequence of plant size and root:shoot allometry, as a response to resource depletion by neighbors, or through a direct response to neighbor presence. The same response pathways also have the potential to alter proliferation in resource-rich patches in soil.Four species of grassland plants were grown in the greenhouse as single plants, monocultures, and mixtures. Root length allocation as a function of shoot mass was examined for background soil and fertilized patches. Plants grown with same-species neighbors followed the same allometric trajectory as single plants for root length in background soil, so any change in root allocation was due only to reduced plant size. Root proliferation in patches declined with neighbors, consistent with a response to resource depletion. Mixtures overproduced roots in both background soil and in patches, relative to plants of the same size in monocultures.     

植物根系养分捕获塑性与根竞争

为了更有效地从土壤中获取养分, 植物根系在长期的进化与适应中产生了一系列塑性反应, 以响应自然界中广泛存在的时空异质性。同时, 植物根系的养分吸收也要面对来自种内和种间的竞争。多种因素都会影响植物根竞争的结果, 包括养分条件、养分异质性的程度、根系塑性的表达等。竞争会改变植物根系的塑性反应, 比如影响植物根系的空间分布; 植物根系塑性程度差异也会影响竞争。已有研究发现根系具有高形态塑性和高生理塑性的植物在长期竞争过程中会占据优势。由于不同物种根系塑性的差异, 固定的对待竞争的反应模式在植物根系中可能并不存在, 其响应随竞争物种以及土壤环境因素的变化而变化。此外, 随着时间变化, 根系塑性的反应及其重要性也会随之改变。植物对竞争的反应可能与竞争个体之间的亲缘关系有关, 有研究表明亲缘关系近的植物可能倾向于减小彼此之间的竞争。根竞争对植物的生存非常重要, 但目前还没有研究综合考虑植物的各种塑性在根竞争中的作用。另外根竞争对群落结构的影响尚待深入的研究。     

Trade-offs of predation and foraging explain sexual segregation in African buffalo

1. Many studies have investigated why males and females segregate spatially in sexually dimorphic species. These studies have focused primarily on temperate zone ungulates in areas lacking intact predator communities, and few have directly assessed predation rates in different social environments. 2. Data on the movement, social affiliation, mortality and foraging of radio-collared African buffalo (Syncerus caffer) were collected from 2001-06 in the Kruger National Park, South Africa. 3. The vast majority of mortality events were due to lion (Panthera leo) predation, and the mortality hazard associated with being an adult male buffalo in a male-only 'bachelor' group was almost four times higher than for adult females in mixed herds. The mortality rates of adult males and females within mixed herds were not statistically different. Mortality sites of male and female buffalo were in areas of low visibility similar to those used by bachelor groups, while mixed herds tended to use more open habitats. 4. Males in bachelor groups ate similar or higher quality food (as indexed by percentage faecal nitrogen), and moved almost a third less distance per day compared with mixed herds. As a result, males in bachelor groups gained more body condition than did males in breeding herds. 5. Recent comparative analyses suggest the activity-budget hypothesis as a common underlying cause of social segregation. However, our intensive study, in an area with an intact predator community showed that male and female buffalo segregated by habitat and supported the predation-risk hypothesis. Male African buffalo appear to trade increased predation risk for additional energy gains in bachelor groups, which presumably leads to increased reproductive success.     

Two hypotheses to explain why RNA interference does not work in animal parasitic nematodes

RNA interference (RNAi) has been used extensively in model organisms such as Caenorhabditis elegans. Methods developed for RNAi in C. elegans have also been used in parasitic nematodes. However, RNAi in parasitic nematodes has been unsuccessful or has had limited success. Studies of genes essential for RNAi in C. elegans and of RNAi in Caenorhabditis spp. other than C. elegans suggest two complementary, and testable, hypotheses for the limited success of RNAi in animal parasitic nematodes. These are: (i) that the external supply of double stranded RNA (dsRNA) to parasitic nematodes is inappropriate to achieve RNAi and (ii) that parasitic nematodes are functionally defective in genes required to initiate RNAi from externally supplied dsRNA.     

An evaluation of hypotheses to explain the pattern of sap feeding by the yellow-bellied glider,Petaurus australis

Yellow-bellied gliders on occasion extensively incise the trunks of eucalypts to feed on sap but in doing so show strong preference for the species and number of trees utilized. Three hypotheses that may account for aspects of this behaviour were examined. They were: (i) sap feeding is related to the incidence of rain; (ii) sap feeding is influenced by the sap flow idiosyncracies of trees; and (iii) sap feeding is influenced by the availability of alternative food resources. Sap feeding at two sites occurred independent of ‘wet’ or ‘dry’ nights. Sap flow (measured as an index) in two species of eucalypt was highly variable among trees and among sample periods. This is the only hypothesis that accounts for the selectivity of the trees incised. Sap feeding at one site coincided with periods of high sap flow. However, at another site, sap feeding did not occur on measured trees despite their often high sap flow. At such times, flowering trees were abundant and gliders fed extensively on nectar. Thus, elevated sap flow may provide the necessary precondition conducive for sap feeding but may be ignored when other food types are available.     

Personality and problem-solving performance explain competitive ability in the wild

Competitive ability is a major determinant of fitness, but why individuals vary so much in their competitiveness remains only partially understood. One increasingly prevalent view is that realized competitive ability varies because it represents alternative strategies that arise because of the costs associated with competitiveness. Here we use a population of great tits (Parus major) to explore whether individual differences in competitive ability when foraging can be explained by two traits that have previously been linked to alternative behavioural strategies: the personality trait 'exploration behaviour' and a simple cognitive trait, 'innovative problem-solving performance'. We assayed these traits under standardized conditions in captivity and then measured competitive ability at feeders with restricted access in the wild. Competitive ability was repeatable within individual males across days and correlated positively with exploration behaviour, representing the first such demonstration of a link between a personality trait and both competitive ability and food intake in the wild. Competitive ability was also simultaneously negatively correlated with problem-solving performance; individuals who were poor competitors were good at problem-solving. Rather than being the result of variation in 'individual quality', our results support the hypothesis that individual variation in competitive ability can be explained by alternative behavioural strategies.     

A method to optimize precision and scale in grassland monitoring

Abstract. Methods for monitoring and survey of plant species abundance which do not account for variation in scale are often insensitive and imprecise. In monitoring, repeated observations are usually made within a fixed unit. Counts of species' presence must be made in a range of subunit sizes to accommodate the range of scales at which different species occur. A method comprising a rectangular fixed unit containing an 8 × 4 grid of square subunits has been developed and tested. Each subunit comprises a series of nested cells of increasing size, within which species are recorded cumulatively. Using this method, the concept of optimum scale is introduced. The optimum scale for a species is that for which its frequency count is closest to the midpoint. Two characteristics, sensitivity (absolute change detected) and blindness (failure to detect change in a species) were calculated for 24 plots from lowland grazing marsh which had been partially flooded between the time of two surveys. Optimum scale had greater sensitivity and lower blindness than any single scale in the majority of plots. Combining sensitivity and blindness, optimum scale was always superior. For the whole sample, optimum scale was less likely to cause Type I or Type II errors. The method is recommended for monitoring grasslands and allied plant communities in large geographical areas.     

Contrasting bee foraging in response to resource scale and local habitat management

It is hypothesized that two main factors drive the foraging patterns of native and exotic species: food resource availability and habitat composition. These factors are particularly relevant for native bees and exotic honeybees, essential crop pollinators that are sensitive to floral resources and habitat management, and that have recently exhibited alarming population declines. Mechanisms driving native and exotic bee foraging patterns may critically depend on floral resource availability and habitat composition, yet the impacts of these factors on bee foraging have never been simultaneously analyzed. In a coffee producing region in southern Mexico, we investigated the influence of coffee floral resource levels and habitat management on native and exotic bee foraging. We measured the amount of flowering coffee available at multiple spatial scales within two distinct agroforestry habitat types (high-shade and low-shade coffee) and recorded visits to coffee flowers, documenting bee species, visit duration and visit frequency. We observed a significantly greater number of visits in high-shade coffee habitats than in low-shade coffee habitats for both native and exotic bees. In high-shade coffee habitats, native solitary bee and native social bee visitation decreased significantly in response to increasing floral resource availability, exhibiting a 'dilution effect' at the smallest spatial scale. In contrast, in low-shade coffee habitats, Africanized honeybees exhibited a 'concentration effect', increasing visitation significantly in response to increasing floral resource availability at the largest spatial scale. This study is the first to show that foraging patterns of native bees and exotic honeybees contrast in response to floral resource level and scale and that this response is mediated by the vegetation management of the local habitat.     

Links between root developmental traits and foraging performance

We designed a simple dynamic and stochastic architectural model with six parameters to link the foraging performance of root systems to their developmental processes. Soil foraging was quantified by the volume enveloping the roots until a given uptake distance. Many simulated architectures were obtained by combining four different values for each parameter. The rate of soil colonization was mainly defined by individual root elongation rates and interbranch distances. Less intuitively, we showed that differentiation of elongation rates among the roots increased this colonization rate. Uptake efficiency--the ratio of the actual colonized volume to the volume of a unique cylinder with the same length and a radius corresponding to the uptake distance--declined with root system size. Nevertheless, large variations in efficiency existed among root systems for a given size, typically in a 4- to 10-fold range. Therefore, the 'efficiency gain' was defined as the deviation from the average trend in efficiency versus size. Between-root differentiation in elongation rates increased this gain. The level of hierarchy between mother and lateral roots, as well as the variation of elongation rates among lateral roots, was also shown to contribute to this optimization. Several parameter combinations could lead to similar efficiency gains.     

Colonization and persistence ability explain the extent to which plant species fill their potential range

Aim How species traits and environmental conditions affect biogeographical dynamics is poorly understood. Here we test whether estimates of a species’ evolutionary age, colonization and persistence ability can explain its current ‘range filling’ (the ratio between realized and potential range size). Location Fynbos biome (Cape Floristic Region, South Africa). Methods For 37 species of woody plants (Proteaceae), we estimate range filling using atlas data and distribution models, evolutionary age using molecular phylogenies, and persistence ability using estimates of individual longevity (which determines the probability of extinction of local populations). Colonization ability is estimated from validated process‐based seed dispersal models, the arrangement of potential habitat, and data on local abundance. To relate interspecific variation in range filling to evolutionary age, colonization and persistence ability, we use two complementary model types: phenomenological linear models and the process‐based metapopulation model of Levins. Results Linear model analyses show that range filling increases with a species’ colonization and persistence ability but is not affected by species age. Moreover, colonization ability is a better predictor of range filling than its component variables (local abundance and dispersal ability). The phylogenetically independent interaction between colonization and persistence ability is significant (P < 0.05) for 97% of 180 alternative phylogenies. While the selected linear model explains 42% of the variance in arcsine transformed range filling, the Levins model performs more poorly. It overestimates range filling for realistic parameter values and produces unrealistic parameter estimates when fitted statistically. Main conclusions Colonization and local extinction seem to shape Proteaceae range dynamics on ecological rather than macroevolutionary time‐scales. Our results suggest that the positive abundance–range size relationship in this group is due primarily to the effect of abundance on colonization. In summary, this study contributes to a process‐based understanding of range dynamics and highlights the importance of colonization for the future survival of Fynbos Proteaceae.     

在“微生物学”课堂教学中立德树人

立德树人是高等教育的中心环节,思想政治工作应贯穿教育教学全过程。微生物学是一门与人类日常生活密切相关的学科。本文通过若干具体案例,介绍如何在"微生物学"课堂教学过程中立德树人。在传授微生物学专业知识的同时不断加强思想政治教育,从而提高学生的思想水平、政治觉悟、道德品质、文化素养,让学生成为德才兼备、全面发展的人才。此外,为其他自然科学类课程教学实现立德树人提供借鉴和参考。     

巴氏新小绥螨对猎物搜寻能力的研究

巴氏新小绥螨Neoseiulus barkeri(Hughes)是一种多食性捕食螨,主要捕食叶螨和蓟马等。因其捕食范围广,捕食量相对较大,且易人工繁殖,因此,被广泛应用于农业生物防治中。本文利用温室的释放-回收实验研究了巴氏新小绥螨对截形叶螨Tetranychus truncatus和西花蓟马Frankliniella occidentalis(Pergande)的搜寻能力。实验共设3个处理:(1)叶螨为害植株与清洁植株;(2)蓟马虫害植株与清洁植株;(3)蓟马、叶螨混合为害植株与清洁植株。当捕食螨释放于清洁黄瓜植株和虫(螨)害黄瓜植株交替排列的六角结构的中心时,2种害虫(螨)不论是单独危害还是混合危害,巴氏新小绥螨回收比例随着时间的延长逐渐趋于平缓。释放后1 d之内,叶螨、蓟马及混合猎物处理中回收到的捕食螨分别占释放总量的65.25%±1.61%、62.75%±1.31%和81.75%±2.14%,并且虫(螨)害植株上回收到的捕食螨数量明显比清洁植株多,叶螨、蓟马及混合猎物危害植株回收的捕食螨量分别占释放总量的53.5%±5.6%、49.5%±3.6%和74.0%±2.7%。因此,巴氏新小绥螨对这2种猎物及其混合物均有较强的搜寻能力,能够有效定位作物中有猎物的植株。同时对利用一种捕食螨生物防治温室中同时发生的2种害虫(螨)的可能性进行了讨论。     

Plant root distributions and nitrogen uptake predicted by a hypothesis of optimal root foraging

CO(2)-enrichment experiments consistently show that rooting depth increases when trees are grown at elevated CO(2) (eCO(2)), leading in some experiments to increased capture of available soil nitrogen (N) from deeper soil. However, the link between N uptake and root distributions remains poorly represented in forest ecosystem and global land-surface models. Here, this link is modeled and analyzed using a new optimization hypothesis (MaxNup) for root foraging in relation to the spatial variability of soil N, according to which a given total root mass is distributed vertically in order to maximize annual N uptake. MaxNup leads to analytical predictions for the optimal vertical profile of root biomass, maximum rooting depth, and N-uptake fraction (i.e., the proportion of plant-available soil N taken up annually by roots). We use these predictions to gain new insight into the behavior of the N-uptake fraction in trees growing at the Oak Ridge National Laboratory free-air CO(2)-enrichment experiment. We also compare MaxNup with empirical equations previously fitted to root-distribution data from all the world's plant biomes, and find that the empirical equations underestimate the capacity of root systems to take up N.     

Root foraging traits and competitive ability in heterogeneous soils

The responses of plant roots to nutrient patches in soil may be an important component of competitive ability. In particular, the scale, precision, and rate of foraging for patchy soil resources may influence competitive ability in heterogeneous soils. In a target–neighbor experiment in the field, per-individual and per-gram competitive effects were measured for six old-field species with known root foraging scale, precision, and rate. The presence and number of nutrient patches were also manipulated in a full factorial design. Number and presence of patches did not influence the outcome of competition. Competitive ability was not related to total plant size, growth rate, or root:shoot allocation, or to root foraging precision. Per-individual competitive effects were marginally correlated with root foraging scale (biomass of roots) and root foraging rate (time required to reach a patch). Therefore, competitive ability was more closely related to ability to quickly fill a soil volume with roots than to ability to preempt resource-rich patches.     

外来入侵植物的根系觅养行为研究进展

土壤养分分布具有高度空间异质性, 植物的根系觅养行为是其对土壤养分异质性的一种适应。不同植物为了适应养分异质性会产生不同的根系觅养行为, 通过调整自身的根系觅养范围、觅养精度和觅养速度来更好地吸收利用土壤中的养分。外来植物与本地植物的竞争是决定其成功入侵的重要因素, 土壤养分等环境因素会影响它们之间的竞争关系。近年来, 外来入侵植物的觅养行为逐渐受到人们的关注, 关于入侵植物根系觅养行为的研究成果陆续出现: (1)总体来看, 外来入侵植物具有较强的根系觅养能力, 但根系觅养范围与觅养精度之间的权衡关系还不确定; (2)营养异质性会影响入侵植物与本地植物之间的竞争, 反过来, 二者之间的竞争也会影响根系觅养行为对营养异质性的响应; (3)丛枝菌根真菌(arbuscular mycorrhizal fungi, AMF)能够提高入侵植物的根系觅养能力, 外来植物入侵能够改变入侵植物对AMF的偏好性, 形成AMF对入侵的正反馈作用, 而本地植物与AMF的相互作用也会影响入侵植物的竞争力。未来还应加强营养异质环境下种间竞争和AMF共生对入侵植物根系觅养行为的影响机制研究, 以及全球变化背景下入侵植物根系觅养行为的变化与机制方面的研究, 可以更深入地认识外来植物的觅养行为在其成功入侵中的作用, 并为利用营养调控来防控入侵植物提供理论依据。