The effects of foliage damage on casebearing moth larvae, Coleophora serratella, feeding on birch

ABSTRACT.

• 1 Mechanical damage to birch (Betula pendula Roth) leaves leads to an increase in the concentration of phenolic compounds, which spreads throughout the leaf within 8 days.
• 2 Coleophora serratella L. (Lepidoptera: Coleophoridae) apparently responds to this chemical change over a similar time scale. Within 24 h of pin-pricking leaves the casebearer moves from the immediate vicinity of the damage, but is just as likely to move to an undamaged portion of the damaged leaf as to vacate the leaf entirely. After 8 days mines on undamaged portions of damaged leaves were significantly smaller than mines on undamaged leaves.
• 3 Furthermore, Coleophora serratella reared on damaged trees took an average of 3 days longer to develop than those reared on undamaged trees.
• 4 It has been suggested that increased movement in response to damage-induced chemical changes causes hyperdispersed damage on plant foliage. Both within and between-leaf casebearer damage patterns were shown to be aggregated on birch.
• 5 Thus although mechanical damage can induce chemical and behavioural changes in the field, these are not reflected in the observed damaged patterns. We speculate on several possible reasons for this.

     

华北落叶松鞘蛾和兴安落叶松鞘蛾形态学研究与再描述（鳞翅目：鞘蛾科）

对华北落叶松鞘蛾和兴安落叶松鞘蛾的形态特征进行了研究,与容易混淆的欧洲落叶松鞘蛾进行了比较。更正了兴安落叶松鞘蛾的学名,肯定了华北落叶松鞘蛾的分类学地位,并进行了重新描述。文中提供了以上3种落叶松鞘蛾的成虫、雌雄外生殖器等特征图,给出了它们的区别要点。     

Cascading effects of induced terrestrial plant defences on aquatic and terrestrial ecosystem function

Herbivores induce plants to undergo diverse processes that minimize costs to the plant, such as producing defences to deter herbivory or reallocating limited resources to inaccessible portions of the plant. Yet most plant tissue is consumed by decomposers, not herbivores, and these defensive processes aimed to deter herbivores may alter plant tissue even after detachment from the plant. All consumers value nutrients, but plants also require these nutrients for primary functions and defensive processes. We experimentally simulated herbivory with and without nutrient additions on red alder (Alnus rubra), which supplies the majority of leaf litter for many rivers in western North America. Simulated herbivory induced a defence response with cascading effects: terrestrial herbivores and aquatic decomposers fed less on leaves from stressed trees. This effect was context dependent: leaves from fertilized-only trees decomposed most rapidly while leaves from fertilized trees receiving the herbivory treatment decomposed least, suggesting plants funnelled a nutritionally valuable resource into enhanced defence. One component of the defence response was a decrease in leaf nitrogen leading to elevated carbon : nitrogen. Aquatic decomposers prefer leaves naturally low in C : N and this altered nutrient profile largely explains the lower rate of aquatic decomposition. Furthermore, terrestrial soil decomposers were unaffected by either treatment but did show a preference for local and nitrogen-rich leaves. Our study illustrates the ecological implications of terrestrial herbivory and these findings demonstrate that the effects of selection caused by terrestrial herbivory in one ecosystem can indirectly shape the structure of other ecosystems through ecological fluxes across boundaries.     

Interguild interactions between a non-native phloem feeder and a native outbreaking defoliator

1. Competitive and synergistic interactions directly or indirectly drive community dynamics of herbivorous insects. Novel interactions between non-native and native insects are unpredictable and not fully understood. 2. We used manipulative experiments on mature red spruce trees to test interactions between a non-native phloem feeding insect, the brown spruce longhorn beetle (BSLB), and an outbreaking native defoliator, the spruce budworm. We subjected treatment trees to defoliation by three densities of spruce budworm larvae. Treatment trees were: stressed by (i) girdling (to mimic beetle feeding) or (ii) girdling + BSLB before spruce budworm larvae were introduced on branches in sleeve cages. Budworm larvae then fed on foliage and developed to pupation. We assessed all branches for budworm performance, defoliation, shoot production and shoot growth. 3. Shoot length did not differ in response to stress from girdling or BSLB infestation. Neither stress from girdling, nor interactions with BSLB feeding affected spruce budworm performance or defoliation. Intraspecific impacts on performance and defoliation in relation to budworm density were stronger than the effects of tree stress. 4. Prior infestation of red spruce by BSLB in our experimental set-up did not influence spruce budworm performance. BSLB is a successful invader that has blended into its novel ecological niche because of ecological and phylogenetic similarities with a native congener, Tetropium cinnamopterum. 5. Outbreaks by BSLB will not likely impede or facilitate spruce budworm outbreaks if they co-occur. It would be useful to evaluate the reverse scenario of BSLB success after defoliation stress by spruce budworm.     

Effects of proteins on phospholipid vesicle aggregation and lipid vesicle-monolayer interactions

The effects of proteins on divalent cation-induced phospholipid vesicle aggregation and phospholipid vesicle-monolayer membrane interactions (fusion) were examined. Glycophorin (from human erythrocytes) suppressed the membrane interactions more than N-2 protein (from human brain myelin) when these proteins were incorporated into acidic phospholipid vesicle membranes. The threshold concentrations of divalent cations which induced vesicle aggregation were increased by protein incorporation, and the rate of vesicle aggregation was reduced. A similar inhibitory effect by the proteins, incorporated into lipid vesicle membranes, was observed for Ca²⁺-induced lipid vesicle-monolayer interactions. However, when these proteins were incorporated only in the acidic phospholipid monolayers, the interaction (fusion) of the lipid vesicle-monolayer membranes, induced by divalent cations, was not appreciably altered by the presence of the proteins.In contrast to these two proteins, the presence of synexin in the solution did enhance the Ca²⁺-induced aggregation of phosphatidylserine vesicles, but did not seem to affect the degree of Ca²⁺-induced fusion between phosphatidylserine/phosphatidylcholine (1:1) and phosphatidylserine vesicles and monolayer membranes.     

Bacteriocin‐mediated interactions within and between coexisting species

Bacteriocins are bacteriocidal toxins released by almost all bacteria. They are thought to have a narrow range of killing, but as bacteriocin‐mediated interactions have been rarely studied at biologically relevant scales, whether this narrow range of action falls mostly within or mostly between coexisting species in natural communities is an open question with important ecological and evolutionary implications. In a previous study, we systematically sampled Xenorhabdus bacteria along a hillside and found evidence for genotypic variability and bacteriocin‐mediated interactions within Xenorhabdus bovienii and X. koppenhoeferi colonies that were collected only a few meters apart. In contrast, colonies that were isolated from the same soil sample were always genetically similar and showed no inhibitions. Here, we conducted pairwise growth‐inhibition assays within and between seven X. bovienii and five X. koppenhoeferi colonies that were isolated from different soil samples; all seven X. bovienii colonies and at least three of the X. koppenhoeferi have been distinguished as distinct genotypes based on coarse‐grain genomic markers. We found signatures for both conspecific and heterospecific bacteriocin inhibitions in this natural community of Xenorhabdus bacteria, but intraspecific inhibitions were significantly more common than interspecific inhibitions. These results suggest that bacteriocins have a major role in intraspecific competition in nature, but also suggest that bacterocins are important in mediating interspecific interactions among coexisting species in natural communities.     

Negative interactions between Willamette mites and Pacific mites: possible management strategies for grapes

Willamette mites and Pacific mites are often negatively associated on grape vines. In particular, vineyards with early season infestations of the less damaging Willamette mite rarely develop high populations of the economically important Pacific mite. We report that Willamette mites had a negative effect on Pacific mite populations in both the greenhouse and field. In some experiments, the negative effect was more pronounced when vines had been damaged by previous feeding of Willamette mites and in other experiments concurrent feeding by both mite species was necessary to demonstrate a negative effect. Therefore, we cannot conclude if the mechanism of the response involves induced resistance against Pacific mites, more conventional interspecific competition, or both. Since predators were uncommon in our experiments, predator build up on Willamette mites did not cause the low Pacific mite population that we observed, although this mechanism may be important in many vineyards. Further, larger scale experiments are necesary to determine if growers can introduce Willamette mites to help control Pacific mites.

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Résumé E. willametti et T. pacificus sont souvent antagonistes dans les vignobles. En particulier, dans les vignobles contaminés tôt dans la saison par E. willametti,-dont les dégâts sont moins conséquents-, on observe rarement des populations élevées de T. pacificus, dont les dégâts sont économiquement importants. Nous avons constaté que E. Willametti a réduit les populations de T. pacificus, tant en serres qu'à l'extérieur. Dans quelques cas, l'effet antagoniste était plus marqué quand les vignes avaient été préalablement endommagées par l'alimentation de E. willametti. Dans d'autres expériences, la compétition alimentaire entre les deux espèces d'acariens était nécessaire pour produire un effet antagoniste. Cependant, nous ne pouvons pas en conclure que la réponse implique une résistance induite contre T. pacificus, ou une compétition interspécifique plus classique, ou les deux à la fois. Puisque les prédateurs étaient rares dans nos expériences, une explosion des prédateurs sur E. willametti n'a pu provoquer le faible niveau de population observé avec T. pacificus, bien qu'un tel méchanisme puisse être important dans certains vignobles. Quoi qu'il en soit, des expériences à plus grande échelle sont nécessaires pour déterminer si les vignerons peuvent introduire Eotetranychus willametti afin de limiter les populations de Tetranychus pacificus.

     

Interspecific complementary and competitive interactions between intercropped maize and faba bean

Interspecific complementary and competitive interactions between maize (Zea mays L. cv. Zhongdan No. 2) and faba bean (Vicia faba L. cv. Linxia Dacaidou) in maize/faba bean intercropping systems were assessed in two field experiments in Gansu province, northwestern China, plus a microplot experiment in one treatment of one of the field experiments in which root system partitions were used to determine interspecific root interactions. Intercropping effects were detected, with land equivalent ratio values of 1.21–1.23 based on total (grain+straw) yield and 1.13–1.34 based on grain yield. When two rows of maize were intercropped with two rows of faba bean, both total yield and grain yield of both crop species were significantly higher than those of sole maize and faba bean on an equivalent area basis. When two rows of pea (Pisum sativum L. cv. Beijing No. 5) were intercropped with two rows of faba bean, neither total yield nor grain yield of faba bean was higher than of sole faba bean on an equivalent area basis. Interspecific competition between maize and faba bean was relatively weak, with mean relative crowding coefficients of 0.99–1.02 for maize and 1.55–1.59 for faba bean. The microplot experiment in which partitions were placed between root systems showed a significant positive yield effect on maize when the root systems intermingled freely (no partition) or partly (400 mesh nylon net partition) compared with no interspecific root interaction (plastic sheet partition). This revised version was published online in June 2006 with corrections to the Cover Date.     

Low nutritive quality as a plant defence: Effects of herbivore-mediated interactions

Summary A plant may lower its nutritive quality, for herbivores, by using secondary compounds, morphological characters and/or having a lowered nutrient content. If such traits decrease the amount of resources lost through herbivory, then they act as antiherbivore defences. However, if herbivores compensate for the lowered nutrient availability, by increasing their intake rates or by prolonging their feeding periods, then this may render the defence useless. I analyse the conditions for evolution of this type of plant defences in a game theoretical model. The predictions of the model depend on the amount of compensatory feeding performed by the herbivores and on the herbivores' mobility in relation to the spatial structure of the plant population. When herbivores cannot compensate for a lowered nutritive quality, the defence can evolve irrespective of the type of herbivore. When herbivores can compensate for such defences, the outcome depends on how the herbivores compensate. In situations where herbivores compensate only on defended plants, which could correspond to immobile herbivores, this type of defence can evolve only if the level of compensation is lower than a certain critical value. When herbivores compensate more on defended than on undefended plants, e.g. because of low mobility, the outcome depends on the level of compensation performed on defended plants. If this level of compensation is high, then the model predicts a stable coexistence of defended and undefended plants and, if it is low, then the populations can consist of only defended plants. When herbivores compensate more on undefended plants than on defended ones, e.g. highly mobile herbivores, the result is populations consisting of either only defended plants, or only undefended plants. Consequently, the fact that herbivores may compensate for lowered nutrient quality does not, as such, nullify the notion of low nutrient quality as a plant defence. However, compensatory feeding may restrict the conditions for the evolution of such defences.     

The effect of spatial scale on interactions between two weevils and their parasitoid

1. The effect of spatial scale on the interactions between three hymenopteran parasitoids and their weevil hosts was investigated. The parasitoid Mesopolobus incultus (Walker) parasitised Gymnetron pascuorum Gyll.; the parasitoids Entodon sparetus (Walker) and Bracon sp. parasitised Mecinus pyraster Herbst. Both of these weevils develop inside the seedhead of Plantago lanceolata L. but occupy different niches. Seedheads were sampled annually from 162 plants at each of two experimental sites consisting of a series of habitat patches of two distinct sizes. Data were analysed from three site‐years. 2. Parasitoid densities at each site‐year were closely related to the abundance of their respective weevil hosts. The overall proportion of hosts parasitised was more variable for M. incultus than for E. sparetus and Bracon sp. 3. Changes in spatial scale affected the variability of parasitoid densities. For M. incultus, there was generally a greater degree of additional heterogeneity for all increases of scale; for E. sparetus, this was true only at the largest scales; for Bracon sp., all components of variance were negative. 4. The rate of parasitism was related to host density in different ways at different spatial scales. Mesopolobus incultus exhibited inverse density dependence at the finest (seedhead) scale, direct density dependence at the intermediate (plant) scale, and density independence at the large (habitat area 729 m²) scale. Entodon sparetus showed no response to variation in host density at any spatial scale. Bracon sp. showed direct density dependence only at the intermediate and largest scales. 5. Parasitoids E. sparetus and Bracon sp. seemed able to detect more than one M. pyraster individual in seedheads with multiple host occupancy; a greater incidence of conspecific parasitoids than expected emerged from such seedheads.     

Long-term dynamics of leaf miners, Eriocrania spp., on mountain birch: alternate year fluctuations and interaction with Epirrita autumnata

Abstract.

• 1 Abundance of leaf-mining larvae of the outbreak species Eriocrania spp. was monitored in northern Sweden in 1955–67 and 1984–92 in a mountain birch forest rejuvenated by an Epirrita autumnata outbreak in 1954–55.
• 2 Eriocrania mine density fluctuated in a regular biennial pattern, probably due to a semivoltine life cycle. The alternate year fluctuations had shifted phase between the two study periods.
• 3 The density fluctuated at a significantly higher mean level and with a lower amplitude in the c. 10-year-old forest in the 1960s than in the 30-year-old forest in the 1980s. However, no difference was found in mine density between c. 30- and >60-year-old stands in the 1980s.
• 4 Significant correlations between the density of mines in high-density years and date of budburst, and between rate of change between high-density years and the time between snow-melt and budburst indicate effects of weather. No correlation was found between yearly average mine density and date of budburst, precipitation or temperatures in May or June.
• 5 No correlation was found between the mean densities of Eriocrania mines and E.autumnata caterpillars in the same and the two preceding years. However, in the first (1955) and highest of three studied E.autumnata peaks a negative effect on population density of Eriocrania was indicated.
• 6 A significant, negative correlation between the number of Eriocrania mines and E.autumnata caterpillars on single branches was found in three out of eighteen years. The separation of caterpillars and mines at branch level indicates an effect of avoidance at intermediate population densities.

     

Effects of spatial scale of sampling on food web structure

This study asks whether the spatial scale of sampling alters structural properties of food webs and whether any differences are attributable to changes in species richness and connectance with scale. Understanding how different aspects of sampling effort affect ecological network structure is important for both fundamental ecological knowledge and the application of network analysis in conservation and management. Using a highly resolved food web for the marine intertidal ecosystem of the Sanak Archipelago in the Eastern Aleutian Islands, Alaska, we assess how commonly studied properties of network structure differ for 281 versions of the food web sampled at five levels of spatial scale representing six orders of magnitude in area spread across the archipelago. Species (S) and link (L) richness both increased by approximately one order of magnitude across the five spatial scales. Links per species (L/S) more than doubled, while connectance (C) decreased by approximately two‐thirds. Fourteen commonly studied properties of network structure varied systematically with spatial scale of sampling, some increasing and others decreasing. While ecological network properties varied systematically with sampling extent, analyses using the niche model and a power‐law scaling relationship indicate that for many properties, this apparent sensitivity is attributable to the increasing S and decreasing C of webs with increasing spatial scale. As long as effects of S and C are accounted for, areal sampling bias does not have a special impact on our understanding of many aspects of network structure. However, attention does need be paid to some properties such as the fraction of species in loops, which increases more than expected with greater spatial scales of sampling.     

生态学中的尺度问题：内涵与分析方法

尺度问题已成为现代生态学的核心问题之一.尺度问题主要涉及3个方面：尺度概念、尺度分析和尺度推绎.主要评述前两个方面.生态学尺度有三重概念：维数、种类和组分,其中每重概念又包含了多个定义,有必要进行澄清、分类和统一.尺度分析涉及尺度效应分析和多尺度空间格局分析.格局、过程及它们之间的关系,以及某些景观特性均表现出尺度效应,因此多尺度研究非常必要和重要.多尺度空间格局分析（尤其是特征尺度的识别）是进行尺度效应分析和跨尺度推绎的基础.多尺度分析需要特定的方法,景观指数法是最常用和最简单的方法,但也常产生误导;空间统计学方法（如半方差分析法、尺度方差分析法、空隙度指数法和小波分析法等）和分维分析法在最近十几年发展起来,并逐渐应用于生态学,在尺度分析上具有很大的应用潜力.各种方法在尺度分析上各有优势和不足,有必要同时使用两种或两种以上方法进行比较和评估.总之,有关尺度分析的研究需要进一步加强,从而为下一步的尺度推绎提供可靠的依据.     

Spatial interactions between sympatric carnivores: asymmetric avoidance of an intraguild predator

Interactions between intraguild species that act as both competitors and predator–prey can be especially complex. We studied patterns of space use by the black-footed ferret (Mustela nigripes), a prairie dog (Cynomys spp.) specialist, and the American badger (Taxidea taxus), a larger generalist carnivore that competes for prairie dogs and is known to kill ferrets. We expected that ferrets would spatially avoid badgers because of the risk of predation, that these patterns of avoidance might differ between sexes and age classes, and that the availability of food and space might influence these relationships. We used location data from 60 ferrets and 15 badgers to model the influence of extrinsic factors (prairie dog density and colony size) and intrinsic factors (sex, age) on patterns of space use by ferrets in relation to space use by different sex and age categories of badgers. We documented asymmetric patterns of avoidance of badgers by ferrets based on the sex of both species. Female ferrets avoided adult female badgers, but not male badgers, and male ferrets exhibited less avoidance than female ferrets. Additionally, avoidance decreased with increasing densities of prairie dogs. We suggest that intersexual differences in space use by badgers create varying distributions of predation risk that are perceived by the smaller carnivore (ferrets) and that females respond more sensitively than males to that risk. This work advances understanding about how competing species coexist and suggests that including information on both intrinsic and extrinsic factors might improve our understanding of behavioral interactions between sympatric species.     

地上-地下植食性天敌对入侵植物空心莲子草与本地种莲子草种间关系的影响

生物入侵是全球生物多样性的主要威胁,外来种与本地种的种间竞争能力会影响其能否成功入侵.本研究选用入侵植物空心莲子草和其本地同属种莲子草为对象,探究其专食性天敌莲草直胸跳甲与南方根结线虫对空心莲子草与莲子草的生长及种间关系的影响.结果 表明:与无天敌胁迫相比,线虫处理显著降低了莲子草的株高(28.1％),但显著增加了空心...