Determining the density dependence of immigration and emigration of benthic stream invertebrates: theoretical considerations

Simple mathematical models are formulated to describe density independent and density dependent dispersal. These models clarify hypotheses of density dependence and may be manipulated easily to suit particular applications. The models demonstrate that the initial composition of a species aggregate must be controlled before valid conclusions can be drawn about the density dependency of the aggregate's dispersal. Stochastic models of emigration are derived to assess the power of particular experimental designs and statistical techniques to discriminate a known form of density dependent emigration. Contribution No. 369, Great Lakes Research Division, University of Michigan Contribution No. 369, Great Lakes Research Division, University of Michigan     

Flight activity ofProstephanus truncatus (Horn) (Coleoptera: Bostrichidae) in relation to population density,resource quality,age, and sex

Higher flight activity has been observed in aged, high-density cultures ofProstephanus truncatus (Horn) (Coleoptera: Bostrichidae), but adults in new, lowdensity culture jars showed less flight activity. In order to understand this change in behavior, the effects of population density, age, resource quality, and sex on the flight ofP. truncatus were studied in a wind tunnel. While an immediate density on the release platform had no significant effect on flight, beetles from high-density cultures were more inclined to fly than those from low-density cultures. Resource quality exerted a major influence on flight; insects in food suitable for boring and oviposition seldomly exhibited flight, however, when food was absent or of inferior quality for boring and oviposition, the dominant behavior was flight. Also, insects maintained for a week in food suitable for boring and oviposition were less ready to fly than those maintained in food unsuitable for boring and oviposition. The optimum age range for flight activity was before the peak of reproduction and insects rarely flew before 4 days or after 32 days of emergence. There were no significant differences between the flight activity of males and that of females. Based on these results, we conclude that age and resource quality are major influences on the flight activity ofP. truncatus and a hypothesis is proposed in which reproductively active male and female beetles disperse from habitats of low resource quality to those that support their reproductive behavior. The practical implications of these results and the possible role of the male-produced aggregation pheromone are discussed.     

Differences in insect species richness and faunal composition of birch seedlings, saplings and trees: the importance of plant architecture

Abstract. 1. Data are presented on the species richness and faunal composition of herbivorous insects on birch seedlings, saplings and trees at one site in Northern England.
2. Species richness of insect herbivores in equal-sized samples from birch seedlings and trees was similar through most of the season.
3. Effects of plant architecture were confined to the first sampling date, when seedling faunas were species poor compared with trees – possibly due to safe overwintering sites on the extensive bark, twigs and buds of trees.
4. The faunal composition of birch seedlings, saplings and trees was also similar. Out of a total of 112 recorded species of herbivores, only one aphid species was confined to seedlings.
5. Similarly, no evidence for clear-cut vertical stratification of insects within trees was found.
6. Species turnover as host plants mature ('horizontal' stratification) and vertical stratification within trees add little to the high overall species richness of birch-feeding insects in Britain, contrary to the predictions of Lawton (1983).     

稻纵卷叶螟2010年的一次迁飞过程及其虫源分析

2010年6月10-12日, 我国华南、 江南南部稻区出现了稻纵卷叶螟Cnaphalocrocis medinalis （Guenée）的大范围同期突增。为了明确此次同期突增的虫源性质, 进一步揭示稻纵卷叶螟大规模降落的大气动力学机制, 我们利用HYSPLIT轨迹分析平台、 地理信息系统ArcGIS和气象图形软件GrADS, 对稻纵卷叶螟的迁飞过程及大气背景场进行了个例研究。结果表明： （1）粤北大范围的稻纵卷叶螟突增以外地迁入种群为主, 部分为本地繁殖种群; （2）西南低空急流为稻纵卷叶螟的远距离迁飞提供了运载气流, 稻纵卷叶螟迁飞种群的集中降落是降雨造成的, 主降区位于雨区边缘的曲江、 紫金、 佛冈等地区, 降雨区的空间分布直接导致了曲江、 南雄地区降虫量的巨大差别; （3）稻纵卷叶螟迁入峰的主要虫源地分布在广东西南部稻区, 6月上旬以阳春为代表的虫源地的双季早稻进入扬花灌浆期 乳熟期, 叶片营养恶化, 稻纵卷叶螟处于成虫盛发期, 存在为粤北大规模迁入提供虫源的可能。     

The scaling of leaf area and mass: the cost of light interception increases with leaf size

For leaves, the light-capturing surface area per unit dry mass investment (specific leaf area, SLA) is a key trait from physiological, ecological and biophysical perspectives. To address whether SLA declines with leaf size, as hypothesized due to increasing costs of support in larger leaves, we compiled data on intraspecific variation in leaf dry mass (LM) and leaf surface area (LA) for 6334 leaves of 157 species. We used the power function LM=alpha LAbeta to test whether, within each species, large leaves deploy less surface area per unit dry mass than small leaves. Comparing scaling exponents (beta) showed that more species had a statistically significant decrease in SLA as leaf size increased (61) than the opposite (7) and the average beta was significantly greater than 1 (betamean=1.10, 95% CI 1.08-1.13). However, scaling exponents varied markedly from the few species that decreased to the many that increased SLA disproportionately fast as leaf size increased. This variation was unrelated to growth form, ecosystem of origin or climate. The average within-species tendency found here (allometric decrease of SLA with leaf size, averaging 13%) is in accord with concurrent findings on global-scale trends among species, although the substantial scatter around the central tendency suggests that the leaf size dependency does not obligately shape SLA. Nonetheless, the generally greater mass per unit leaf area of larger than smaller leaves directly translates into a greater cost to build and maintain a unit of leaf area, which, all else being equal, should constrain the maximum leaf size displayed.     

Testing the resource concentration hypothesis with tarnished plant bug on strawberry: density of hosts and patch size influence the interaction between abundance of nymphs and incidence of damage

Abstract. 1. Attributes of patches with strawberry plants were manipulated experimentally to assess the impact of patch size and host density on the abundance of tarnished plant bug (Hemiptera: Miridae) and incidence of fruit damage.
2. The density of nymphs per inflorescence increased with patch size and host density for some but not all generations of plant bug, providing partial support for the resource concentration hypothesis, while emphasising the importance of replicating experiments across several generations of herbivore.
3. Increasing density of nymphs with increasing patch size and host density did not translate into a high incidence of damage, which may be due to the relatively low feeding impact of nymphs in patches with numerous fruits and to the relatively high perimeter-to-area ratio in small patches resulting in a relatively high proportion of damaged fruits.
4. The decreasing proportion of damaged fruits with increasing density of fruits per patch suggests that nymphs exhibit a saturating functional response to density of strawberry fruits. Functional responses of herbivores may be a critical yet overlooked component that influences interactions between insects and their host plant. In particular, concentrated plant resources may result in increased numbers of herbivores yet sill have a negligible influence on plant damage and/or fitness.     

Changes in plant species richness over the last century in the eastern Swiss Alps: elevational gradient, bedrock effects and migration rates

Areas of 2,800–3,000 m a.s.l. represent the alpine-nival ecotone in the Alps. This transition zone connecting the closed swards of the alpine belt and the scattered vegetation of the nival belt may show particularly strong climate warming driven fluctuations in plant species richness compared to the nival belt. To test this hypothesis, 12 summits within this range were investigated in the canton of Grisons, Switzerland in 2004. Complete lists of vascular plant species consisting of 5–70 species were collected on each summit and the elevation of the uppermost occurrence of each species was recorded. These data were compared to historical records over 120 years in age. Within this time, vascular plant species richness increased by 11% per decade on summits in the alpine-nival ecotone. Despite this considerable change, a comparison with nival summits did not support the hypothesis that species richness increase at the alpine-nival ecotone is higher than in the nival belt. A general trend of upward migration in the range of several metres per decade could be observed. Anemochorous species were more often found to be migrating than zoochorous or autochorous species and migration was higher on calcareous than on siliceous bedrock. A comparison between the summits with the adjacent slopes in our study revealed that changes in species number could be used as an indicator for climate-induced changes—if at all—only for the narrow summit areas.     

Two centuries of the Scandinavian wolf population: patterns of genetic variability and migration during an era of dramatic decline

The grey wolf (Canis lupus) was numerous on the Scandinavian peninsula in the early 19th century. However, as a result of intense persecution, the population declined dramatically and was virtually extinct from the peninsula by the 1960s. We examined historical patterns of genetic variability throughout the period of decline, from 1829 to 1979. Contemporary Finnish wolves, considered to be representative of a large eastern wolf population, were used for comparison. Mitochondrial DNA (mtDNA) variability among historical Scandinavian wolves was significantly lower than in Finland while Y chromosome variability was comparable between the two populations. This may suggest that long-distance migration from the east has been male-biased. Importantly though, as the historical population was significantly differentiated from contemporary Finnish wolves, the overall immigration rate to the Scandinavian peninsula appears to have been low. Levels of variability at autosomal microsatellite loci were high by the early 1800s but declined considerably towards the mid-20th century. At this time, approximately 40% of the allelic diversity and 30% of the heterozygosity had been lost. After 1940, however, there is evidence of several immigration events, coinciding with episodes of marked population increase in Russian Karelia and subsequent westwards migration.     

Field studies of seahorse population density,structure and habitat use in a semi-closed north-eastern Mediterranean marine area (Stratoni,North Aegean Sea)

The present study was carried out in the marine area of Stratoni, Greece, where two seahorse species are present (Hippocampus hippocampus and Hippocampus guttulatus). Two surveys were conducted (September 2016 and May 2019) to gather information regarding seahorse species' abundance, distribution and habitat characteristics. Four different seahorse natural and artificial habitat types were identified. The results revealed that the presence of H. hippocampus was relatively high, especially at sites with artificial structures, whereas the presence of H. guttulatus was rare. Data collected can provide baseline information for future population assessments.     

The effects of temperature and prey density on the development rates and growth of damselfly larvae (Odonata: Zygoptera)

Abstract. 1. The effects of prey density and temperature on the feeding and development rates of several late instars of the larvae of three common European damselflies ( Lestes sponsa (Hansemann), Coenagrion puella (L.) and Ischnura elegans van der Linden) were investigated in a laboratory experiment.
2. Functional responses were used to estimate maximum feeding rates. Maximum feeding rates were compared between species, instars and temperatures by expressing prey consumption in terms of prey biomass consumed per unit predator biomass. Lestes was capable of feeding at almost twice the rate of either Coenagrion or Ischnura.
3. Higher feeding rates led to faster development rates and there was an interaction between species and temperature. With the exception of those with very low feeding rates, larvae maintained at higher temperatures, but similar feeding rates, developed faster. Under similar conditions of temperature and feeding rate, Lestes larvae developed faster than larvae of either Coenagrion or Ischnura.
4. Faster development rates at similar rates of food intake were achieved at the cost of reduced size-increases between instars.
5. The differences in the responses of the three species are discussed in the light of their respective life histories, and with reference to a recent model of population regulation in damselflies.     

云南文山石漠化区车桑子叶脉密度与叶氮含量关系对生境的响应

植物叶脉特征和叶氮含量的变化影响着叶片经济谱的形成,为验证叶片结构中叶脉网络构建提供了理论依据。该文以单位质量叶氮含量(N_mass)和单位面积叶氮含量(N_area)分别表示叶氮含量,采取主成分分析、线性回归分析的方法,研究了云南文山石漠化区旷地(Ⅰ)、林缘(Ⅱ)和林下(Ⅲ)3种自然生境下车桑子的叶脉密度(Vein density,VD)与N_mass和N_area的异速关系。结果表明:从乔灌群落的旷地到林下,车桑子的比叶面积、叶绿素总含量、光能利用率和N_mass逐渐增大,光饱和点、光补偿点、水分利用效率、VD、N_area逐渐减小,净光合速率、蒸腾速率、气孔导度呈先增大后减小的趋势。VD与叶氮含量呈不同程度的相关性,在生境I和III,VD与N_mass和N_area分别具有显著的负相关(P<0.05)和正相关(P<0.05);在生境Ⅱ,VD与N_mass和N_area分别...     

On the elusiveness of enemy-free space: spatial, temporal, and host-plant-related variation in parasitoid attack rates on three gallmakers of goldenrods

Host shifting by phytophagous insects may play an important role in generating insect diversity by initiating host-race formation and speciation. Models of the host shifting process often invoke reduced rates of natural enemy attack on a novel host in order to balance the maladaptation expected following the shift. Such "enemy-free space" has been documented for some insects, at some times and places, but few studies have assessed the occurrence of enemy-free space across years, among sites, or among insect species. We measured parasitoid attack rates on three insect herbivores of two goldenrods (Solidago altissima L. and Solidago gigantea Ait.), with data from multiple sites and multiple years for each herbivore. For each insect herbivore, there were times and sites at which parasitoid attack rates differed strongly and significantly between host plants (that is, enemy-free space existed on one host plant or the other). However, the extent and even the direction of the attack-rate difference varied strongly among sites and even among years at the same site. There was no evidence of consistent enemy-free space for any herbivore on either host plant. Our data suggest that enemy-free space, like many ecological and evolutionary forces, is likely to operate as a geographic and temporal mosaic, and that conceptual models of host shifting that include enemy-free space as a consequence of host novelty are likely too simple.     

江苏扬州地区蔬菜烟粉虱寄主调查及种群动态

2002—2003年对江苏扬州地区露地蔬菜上的烟粉虱寄主植物、危害,及主要蔬菜上的烟粉虱种群动态进行了调查。共查到烟粉虱寄主植物10科39种(变种),主要分布在葫芦科、十字花科、豆科、茄科和菊科等蔬菜上,其中以黄瓜、豇豆、花菜和长茄发生较为严重;露地蔬菜上的烟粉虱发生在6月上旬至11月中旬,发生高峰期在8月下旬至9月上中旬;随着蔬菜的种类、季节和年份的不同,田间烟粉虱的发生为害也有所不同。     

Plants on small islands revisited: the effects of spatial scale and habitat quality on the species–area relationship

Understanding how species diversity is related to sampling area and spatial scale is central to ecology and biogeography. Small islands and small sampling units support fewer species than larger ones. However, the factors influencing species richness may not be consistent across scales. Richness at local scales is primarily affected by small‐scale environmental factors, stochasticity and the richness at the island scale. Richness at whole‐island scale, however, is usually strongly related to island area, isolation and habitat diversity. Despite these contrasting drivers at local and island scales, island species–area relationships (SARs) are often constructed based on richness sampled at the local scale. Whether local scale samples adequately predict richness at the island scale and how local scale samples influence the island SAR remains poorly understood. We investigated the effects of different sampling scales on the SAR of trees on 60 small islands in the Raja Ampat archipelago (Indonesia) using standardised transects and a hierarchically nested sampling design. We compared species richness at different grain sizes ranging from single (sub)transects to whole islands and tested whether the shape of the SAR changed with sampling scale. We then determined the importance of island area, isolation, shape and habitat quality at each scale on species richness. We found strong support for scale dependency of the SAR. The SAR changed from exponential shape at local sampling scales to sigmoidal shape at the island scale indicating variation of species richness independent of area for small islands and hence the presence of a small‐island effect. Island area was the most important variable explaining species richness at all scales, but habitat quality was also important at local scales. We conclude that the SAR and drivers of species richness are influenced by sampling scale, and that the sampling design for assessing the island SARs therefore requires careful consideration.     

Perspectives of data analysis of enzyme inhibition and activation,Part 3: Equations for calculation of the initial rates of enzymatic reactions

Equations for calculation of the initial rates of activated enzymatic reactions and the inhibited enzymatic reactions, unavailable in experimental enzymology, were obtained. Examples of practically using of these equations are given. © 2009 Wiley Periodicals, Inc. J Biochem Mol Toxicol 23:108–118, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jbt.20271     

Coevolution between crossbills and black pine: the importance of competitors,forest area and resource stability

Studies of predator‐prey interactions have found that geographically structured coevolution has played an important role in the adaptive diversification of crossbills (Loxia spp.). We extend those studies by considering common crossbills (L. curvirostra) in the Mediterranean where they rely on seeds in the cones of black pine (Pinus nigra). On the continent, where tree squirrels (Sciurus vulgaris) are present, enhanced defenses against crossbills were most evident in larger areas of pine forest. On islands in the absence of tree squirrels, crossbills and black pine have coevolved in a predator‐prey arms race on Cyprus but not Corsica. In contrast to other conifers that island endemic crossbills rely upon, black pine does not hold seeds in its cones year round. Consequently, key to the strong crossbill–pine interaction on Cyprus is likely the presence of an alternative conifer that provides seeds during early summer when black pine seeds are scarce.