Autecological investigations on marine diatoms 6:Rhizosolenia robusta Norman,Rhizosolenia imbricata Brightwell andRhizosolenia shrubsolei Cleve

The warm oligo-eurytherm diatomsRhizosolenia robusta Norman andRhizosolenia imbricata Brightwell were cultured to determine the temperature range for the best competitive position by growth. Comparison of their generation times with those of other diatoms indicate thatR. robusta reaches this position around 20 °C andR. imbricata above 25 °C. The temperature ranges for growth were 12 °C up to 28 °C forR. robusta and 12 °C to above 30 °C forR. imbricata. The use of both species as indicator species for warm water currents is discussed on account of their lower temperature limit. The cold oligo-eurytherm diatomRhizosolenia shrubsolei had a temperature range for growth of below –1.0 °C to 25 °C. Our experimental results demonstrate thatR. imbricata andR. shrubsolei can be considered separate species.     

Resource heterogeneity generated by shrubs and topography on coastal sand dunes

In early stages of primary succession, colonizing plants can create resource patches that influence the abundance and distribution of other species. To test whether different colonizing shrubs generate contrasting patches on coastal sand dunes, we compared soil characteristics and light availability under the nitrogen-fixing shrub Lupinus arboreus, under the non-nitrogen-fixing shrub Artemisia pycnocephala, and between shrubs on dunes at a site in northern California. Concentrations of inorganic nitrogen and net nitrogen mineralization rates were generally 1–10 times greater in soil under Lupinus than under Artemisia or between shrubs. Soil water content was mostly lower under shrubs. Mean photon flux density near ground level was reduced by at least 80% at 35 cm inside shrub canopies. Topography appeared to have more effect on soil moisture but less direct effect on nitrogen availability than did Lupinus. However, Lupinus probably increases nitrogen levels more on higher, drier dunes. Microhabitats under and between nitrogen-fixing shrubs constitute a mosaic of individually poor but complementary patches in which high levels of light and moderate levels of soil nitrogen are present but tend not to occur together.     

Immunohistochemical and radioautographic evidence of monoamine-containing cells in bioluminescent elytra of the scale-worm Harmothoe imbricata (Polychaeta)

Summary Elytra of the scale-worm Harmothoe imbricata were examined for the presence of monoamine-like immunoreactivities and radioautographic reactions. Serotonin (5-HT)-like immunoreactivity was widely distributed among the cellular constituents of the elytra, being present in epithelial cells including photocytes, in elytral nerves, clear cells and the loose neuronal plexus of the middle compartment. The distribution of [³H]5-HT labelling coincided with that of the immunoreactivity except for an additional reactive band extending through the upper cuticle layer. Tyrosine hydroxylase (TH)-like immunoreactivity was detected in epithelial cells, sensory papillae and elytral ganglion and nerves, with little or no staining in clear cells and plexus neurons of the middle compartment. Radioautographic labelling with [³H]noradrenaline and [³H]adrenaline overlaid many epithelial cells, elytral nerves and sensory papillae, but not the loose neuronal plexus or, apparently, clear cells. It is concluded that monoaminergic systems are widely distributed and that they must play important roles as neuroactive and/or paracrine substances in the elytral neuroectoderm. The distribution of [³H]5-HT label in photocytes also suggests the involvement of serotonergic mechanisms in luminescence control, luminescence being the only known effector activity of elytra.     

Cytoprotective and antioxidant activity of Rhodiola imbricata against tert-butyl hydroperoxide induced oxidative injury in U-937 human macrophages

The present study reports cytoprotective and antioxidant activity of aqueous and alcoholic extracts of Rhodiola imbricata rhizome on tert-butyl hydroperoxide (tert-BHP) induced cytotoxicity in U-937 human macrophages. There was an increase in cytotoxicity and apoptosis significantly in the presence of tert-BHP over control cells. The tert-BHP induced cytotoxicity can be attributed to enhanced reactive oxygen species (ROS) production which in turn is responsible for fall in reduced glutathione (GSH) levels; further there was a significant decrease in mitochondrial potential and increase in apoptosis and DNA fragmentation. Both aqueous and alcoholic extracts of Rhodiola rhizome at a concentration of 250 μg/ml were found to inhibit tert-BHP induced free radical production, apoptosis and to restore the anti-oxidant levels to that of the control cells. The alcoholic extract of Rhodiola showed higher cytoprotective activities than aqueous extract. These observations suggest that the alcoholic and aqueous extracts of Rhodiola have marked cytoprotective and antioxidant activities.     

Influence of resource abundance on the structure of the insect community attracted to fermented tree sap

There has been little or no documentation of the insect community attracted to fermented tree sap, despite our familiarity with it. This study describes the influence of resource abundance (exudate quantity) on species richness, insect abundance, and diversity at the patch level in order to elucidate the mechanisms responsible for community structure. Resource abundance was positively correlated with species richness and insect abundance, negatively correlated with the equitability index (J), and not significantly correlated with diversity (Simpsons index of diversity; 1/D). Both correlation analyses and canonical correspondence analysis based on taxonomic categories indicated that responses to resource abundance were much greater in parasitoid wasps (Ichneumonoidea), drosophilid flies (Drosophilidae), and rove beetles (Staphylinidae). Field experiments showed that patches with more of the resource had greater species richness and greater hornet abundance. These results indicate that resource abundance is an important factor that affects community structure at the patch level, although it does not influence diversity directly, due to differences in the response to a resource across subgroups; drosophilid flies, the most abundant group that was heavily dependent on tree sap, make an especially large contribution to the change in J. Various factors influence the variation in the response to resource abundance, including population size, feeding habits, and resource utilization patterns (i.e. whether the species uses patches as habitat).     

Genetic assembly rules and community phenotypes

We present a conceptual construct for a genetic based community assembly rule where the genetic composition of a host plant, or resource, affects the structure of the dependent community. This is related to a genetic similarity rule that states that host plants with similar genetic compositions are hosts to similar arthropod communities. We present preliminary data from the Populus system to support this concept. We review the recent literature to evaluate the current state of the assembly rule concept and interpret a set of previous studies in the context of a genetic assembly rule. We suggest that by incorporating this concept into community ecology we can begin to bring an evolutionary perspective to this discipline.     

Spatial heterogeneity and structure of bird populations: a case example with the eagle owl

If individuals of the same population inhabit territories different in landscape structure and composition, experiencing habitat-specific demographic rates, then the landscape features become major determinants of the overall population characteristics. Few studies have tested how habitat-specific demography interacts with landscape heterogeneity to affect populations of territorial species. Here we report a 29-year study of an eagle owl (Bubo bubo) population in southern France. The aim of this study was to analyse how habitat heterogeneity could affect density and breeding performance. Mean productivity for the overall sample was 1.69±0.76 fledglings per breeding pair and, after controlling for year effect, significant differences between territories were detected for productivity. A positive correlation was found between the percentage of pairs producing 50% of the annual fledged young (an index of the distribution of fecundity among nesting territories) and the mean reproductive outputs, that is the heterogeneous structure of the population determined that most/all pairs contributed to the annual production of young during good years, but the opposite during poor years (i.e. fewer pairs produced the majority of fledglings). Mean reproductive output was positively affected by percentage of open country and diet richness. Although other factors different to territory quality could affect demography parameters (e.g. quality of breeders), our results clearly showed a significant correlation between landscape features and population productivity.     

Light field heterogeneity among tussock grasses: Theoretical considerations of light harvesting and seedling establishment in tussocks and uniform tiller distributions

Although the tussock growth form of caespitose graminoids is widespread, the effect of this growth form on light interception and carbon gain of tillers has received little attention. Daily incident photosynthetic photon flux density (PFD_inc) and carbon gain in monospecific stands of tussock grasses were compared with those of a hypothetical distribution with the equivalent tiller density per total ground area, but evenly distributed rather than clumped in tussocks. This was computed for two tussock grasses Pseudoroegneria spicata (Pursh) A. Löve (bluebunch wheatgrass) and Agropyron desertorum (Fisch, ex Link) Schult. (creasted wheatgrass) at different plant densities. Daily PFD_inc and net photosynthesis (A) were greater if tillers were distributed uniformly rather than clumped in tussocks, except when the density of tussocks was so great as to approach a uniform canopy. When tussock density per ground area was low, much of the difference between tussock and uniform tiller densities in PFD_inc and A was due to shading within the tussocks; up to 50–60% of the potential carbon gain was lost in A. desertorum due to shading within tussocks. In a matrix of tussocks, the light field for establishing seedlings was very heterogeneous; potential A ranged from 7 to 96% relative to an isolated seedling. The mean of daily PFD_inc and A for seedlings in a tussock stand were nearly identical to the values in corresponding stands of uniform tiller distributions. It is hypothesized that the loss of A resulting from clumping tillers into tussocks is offset by benefits of protecting sequestered belowground resources from invasion by seedlings of competitors.     

Influence of temporal heterogeneity in nitrogen supply on competitive interactions in a desert shrub community

Soil nutrients in arid systems are supplied to plants in brief pulses following precipitation inputs. While these resource dynamics have been well documented, little is known about how this temporal heterogeneity influences competitive interactions. We examined the impacts of the temporal pattern of N supply on competitive intensity and ability in an N-limited desert shrub community. At our field site, the three codominant shrubs, Atriplex confertifolia, A. parryi, and Sarcobatus vermiculatus, differ in seasonal growth patterns, with A. confertifolia and S. vermiculatus achieving higher growth rates earlier in the growing season than A. parryi. We predicted that these timing differences in maximum growth rate may interact with temporal variation in N supply to alter competitive abilities over time. Seedlings of the two Atriplex species were planted either individually in field plots or as target plants surrounded by neighbor seedlings. After one year of establishment, the same amount of ¹⁵N was applied to plots either as early spring pulses, mid spring pulses or continuously through the second growing season. Competitive effects were observed under continuous and pulsed N supply. Averaged across all target–neighbor treatments, competitive intensity was ∼1.8-fold greater when N was pulsed compared to when N was supplied continuously, but overall, the outcome of competitive interactions was not influenced by N pulse timing. While the timing of resource supply did not differentially influence the competitive abilities of coexisting species in this system, the temporal pattern of resource supply did alter the intensity of competitive interactions among species. While additional studies in other systems are needed to evaluate the generality of these results, this study suggests that competitive intensity may not necessarily be a direct function of productivity or resource availability as traditionally assumed. Instead, the intensity of competitive interactions in resource-poor systems may depend upon the temporal pattern of resource supply.     

Modeling density dependence in heterogeneous landscapes: Dispersal as a case study

Population models often pose density-dependent rates as relations between current population size on a habitat patch, n, and some threshold size defined by limiting resources, r. In fourteen recent modeling studies incorporating density-dependent dispersal, formulations of the density-dependent rate (or probability) fall into two distinct groups, expressing the rate as a function of n-r or n/r. These two depictions of the same process differ fundamentally: they can cause strikingly different dynamics in otherwise identical systems and they have different scaling properties in heterogeneous landscapes. Here I consider the implications of the two formulations under two broad ecological scenarios: scramble competition for an equally divided resource (e.g. food) and contest competition for an unequally divided resource (e.g. nest sites). In both cases, simple arguments show that the n/r form is preferable when density dependence is driven by individual access to resources. Other circumstances may require different formulations, but modelers must ensure that these have appropriate scaling and non-equilibrium behavior.     

Distribution,community structure and production of fishes in the upper Speed River,Ontario: a preimpoundment study

Synopsis The upper Speed River, on which a dam was under construction, was surveyed through fourteen qualitative and six quantitative collections to determine the distribution of fishes in the river above Guelph, Ontario and in a tributary, Luteral Creek. At the quantitative localities the removal method was used to estimate density and standing crop of all species. At three of these localities age and growth of the dominant species were determined and total ecological production calculated. Two approaches to the estimation of production for the 0–1 age class were compared and found to result in differences of 33–39% in the estimates of total production, thus illustrating the extent to which methodology may affect such estimates The dominant species in the river were, Semotilus atromaculatus, Notropis cornutus, Pimephales notatus, Rhinichthys atratulus, Hypentelium nigricans, Catostomus commersoni, Ambloplites rupestris, Micropterus dolomieui and Etheostoma flabellare. Density ranged from 11126 to 74765 individuals per hectare and standing crop from 32.4 to 190.0 kg ha⁻¹. Production values at the three localities were 15, 19 and 54 kg ha⁻¹ yr⁻¹ , and are low compared with estimates for other fluvial systems. Comparison with a 1951 survey of the Speed River revealed considerable changes in the composition and distribution of fish species. The ranges of several cold-water species had contracted towards the headwaters, whereas several warm-water species had extended their ranges up the river     

Niche partitioning and stochastic processes shape community structure following whitefly invasions

One of the most detrimental impacts of invasive species is the exclusion of native species, which reduces biodiversity and can alter community structure. Coexistence between invaders and native species across large scales, however, might be promoted by niche partitioning and/or stochastic processes, even when one species is excluded in some habitats. Here, we examined the effects of species traits, stochastic processes, and niche partitioning on coexistence of two morphocryptic whitefly species in the Bemisia tabaci complex: the invasive Mediterranean (MED) species and the native Middle East-Asia Minor 1 (MEAM1) species. These species engage in intense reproductive interference, which can result in the exclusion of one species or the other in shared habitats. Both species, however, have coexisted in sympatry in Israel for many years, where MED is invasive and MEAM1 is native. Using a spatially explicit model, we show that both stochastic processes and niche partitioning can promote coexistence between MEAM1 and MED, although predicted community structure differs drastically in each scenario. Comparison of field observations with model results indicated that variation in habitat use leading to niche partitioning was a primary factor driving coexistence between MEAM1 and MED across landscapes, although stochastic processes affected the establishment of rare species within habitats. In many systems, combining models with field surveys can be used to isolate and test mechanisms underlying patterns of community structure following invasions.     

戴云山黄山松群落生态（火用）空间异质性

热力学指标生态（火用）作为传统群落结构指数的补充,通过衡量物种包含的遗传信息量化群落生物热力学空间结构,评估其群落稳定性和健康程度。基于生态（火用）理论研究了戴云山黄山松（Pinus taiwanensis）群落乔木层、灌木层生态（火用）和结构（火用）的空间异质性及分布规律。主要结果如下：（1）乔木层和灌木层分别是群落生态（火用）和结构（火用）的主要贡献者。（2）黄山松种群在群落中具有更高的竞争能力和生存概率,群落生态（火用）贡献率为98.39%,对维持群落结构稳定性具有关键作用。（3）乔灌层的生态（火用）和结构（火用）在研究尺度上均具有强烈空间自相关,其空间异质性主要由结构性因素引起,所占比例大于75%。（4）乔灌层的生态（火用）和结构（火用）均呈明显条带状及斑块状分布,有多个明显高值区,等值线较弯曲且密集,空间异质性程度较高。研究确定了戴云山黄山松种群的热力学地位,黄山松在维系戴云山群落结构稳定和群落健康中发挥着重要作用,结果可为黄山松群落演替动态和可持续管理提供科学依据。     

Biomass responses to elevated CO<Subscript>2</Subscript>, soil heterogeneity and diversity: an experimental assessment with grassland assemblages

While it is well-established that the spatial distribution of soil nutrients (soil heterogeneity) influences the competitive ability and survival of individual plants, as well as the productivity of plant communities, there is a paucity of data on how soil heterogeneity and global change drivers interact to affect plant performance and ecosystem functioning. To evaluate the effects of elevated CO₂, soil heterogeneity and diversity (species richness and composition) on productivity, patterns of biomass allocation and root foraging precision, we conducted an experiment with grassland assemblages formed by monocultures, two- and three-species mixtures of Lolium perenne, Plantago lanceolata and Holcus lanatus. The experiment lasted for 90 days, and was conducted on microcosms built out of PVC pipe (length 38 cm, internal diameter 10 cm). When nutrients were heterogeneously supplied (in discrete patches), assemblages exhibited precise root foraging patterns, and had higher total, above- and belowground biomass. Greater aboveground biomass was observed under elevated CO₂. Species composition affected the below:aboveground biomass ratio and interacted with nutrient heterogeneity to determine belowground and total biomass. Species richness had no significant effects, and did not interact with either CO₂ or nutrient heterogeneity. Under elevated CO₂ conditions, the two- and three-species mixtures showed a clear trend towards underyielding. Our results show that differences among composition levels were dependent on soil heterogeneity, highlighting its potential role in modulating diversity–productivity relationships. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible to authorized users.     

Size structure and substitutability in an odonate intraguild predation system

Interactions between different size classes of predator species have the potential to influence survival of prey species in intraguild predation (IGP) systems, but few studies test for these effects. Using a substitutive design in a field setting, I measured the effects of two size classes of IG predators (large and small larvae of the dragonfly Anax junius) on the mortality of IG prey (larvae of the dragonfly Pachydiplax longipennis). I also examined whether combinations of large A. junius and P. longipennis and small A. junius and P. longipennis had substitutable effects on shared prey (larvae of the damselfly Ischnura verticalis). The presence of both size classes of A. junius, when alone and in combination with P. longipennis, significantly increased mortality of I. verticalis. In the presence of P. longipennis, large and small A. junius had similar effects on the mortality of I. verticalis, and effects of size-structured assemblages of A. junius were similar to the effects of each size class alone at the same density. The effects of the two size classes of A. junius on P. longipennis differed, and P. longipennis mortality was lower when exposed to size structured assemblages of A. junius than when exposed to only large A. junius at the same density. Results were similar to those in a laboratory study, although the effect of P. longipennis on I. verticalis was much lower in the field setting. These results demonstrate that interactions between different size classes of IG predators promote the survival of IG prey and highlight the importance of within-species size structure as a characteristic that may promote the coexistence of predators in IGP systems.     

Predator-prey interactions and community structure: chironomids,mosquitoes and copepods in Heliconia imbricata (Musaceae)

Summary Evidence from both field observations and experimental work indicates that predation by larvae of a midge, Pentaneura n. sp. (Chironomidae), causes the low densities of mosquito larvae (Culicidae) found in the water filled bracts of Heliconia imbricata (Musaceae), microhabitats typically colonized by mosquitoes. This predation affects 2 species of mosquitoes, Wyeomyia pseudopecten, a resident species, and Trichoprosopon digitatum, a non-resident species. Predation keeps resident mosquito densities low while completely excluding the nonresident mosquito from the habitat. Both these effects of predation depend on the presence of an abundant alternative prey, an undescribed species of harpacticoid copepod found in the bracts. These copepod prey sustain chironomids when resident mosquito densities are low, permiting predator densities to remain high enough to exclude the non-resident mosquito. I discuss the evolutionary and ecological implications of predation structuring communities.     

Plant genetic differences influence herbivore community structure: evidence from a hybrid willow system

To determine the influence of plant genetic variation on community structure of insect herbivores, we examined the abundances of 14 herbivore species among six genetic classes of willow: Salix eriocephala, S. sericea, their F₁ and F₂ interspecific hybrids, and backcross hybrids to each parental species. We placed 1-year-old plants, grown from seeds generated from controlled crosses, in a common garden. During the growing season, we censused gall-inducing flies and sawflies, leaf-mining insects, and leaf-folding Lepidoptera to determine the community structure of herbivorous insects on the six genetic classes. Our results provided convincing evidence that the community structure of insect herbivores in this hybrid willow system was shaped by genetic differences among the parental species and the hybrid genetic classes. Using MANOVA, we detected significant differences among genetic classes for both absolute and relative abundance of herbivores. Using canonical discriminant analysis, we found that centroid locations describing community structure of the insect herbivores differed for each genetic class. Moreover, the centroids for the four hybrid classes were located well outside of the range between the centroids for the parental species, suggesting that more than additive genetic effects of the two parental species influenced community formation on hybrid classes. Line-cross analysis suggested that plant genetic factors responsible for structuring the herbivore community involved epistatic effects, as well as additive and dominance effects. We discuss the ramifications of these results in regard to the structure of insect herbivore communities on plants and the implications of our findings for the evolution of interspecific interactions.     

The role of the hemiparasitic annual Rhinanthus minor in determining grassland community structure

Summary Rhinanthus minor (yellow-rattle) is a widespread hemiparasitic plant of grassland habitats throughout Great Britain. It is usually considered to be indicative of species-rich grassland, but in a survey of 14 habitats throughout Britain it was found that R. minor at the time of flowering normally occupied relatively low-diversity patches within areas of high diversity as determined by the number of species, Simpson's Index and the Shannon-Wiener Index. Following the death of adult plants of R. minor in the summer it was shown that the pattern of species diversity changed such that by the time R. minor germinated in the following spring the differences between the areas containing and not containing R. minor were much less distinct. A perturbation experiment in which R. minor was removed from four sites indicated that the effect of the removal of R. minor on the development of community structure over the next year was to increase species diversity on three of the sites and decrease it on the fourth. Those species which responded to the removal of R. minor by an increase in abundance were shown to be preferred hosts. All three lines of evidence point to the fact R. minor has a significant effect on the species diversity of the communities in which it grows by selectively parasitizing components of the flora and modifying the competitive relationships between plants. However, as the communities generally responded to the removal of R. minor by an increase in diversity and as the general survey indicated that R. minor is generally associated with areas of low diversity it would appear that the plants which are selectively parasitized are generally not the competitive dominants in the community.     

Yeast communities associated withDrosophila species and related flies in an eastern oak-pine forest: A comparison with western communities

Summary Intestinal yeast mycobiota were studied in 14 species ofDrosophila and in the drosophilid speciesChymomyza amoena, captured at Pinery Provincial Park, Ontario. Over 56 yeast species, some undescribed, were isolated. These yeast communities were compared with those from two similar surveys conducted in western portions of North America. The community structures were influenced significantly by the habitat rather than phylogeny of the flies. Geographic separation was a factor affecting yeast taxa frequencies in the fly species, but it was largely overshadowed by ecological factors when the communities were described physiologically. The notion that habitats are filled by yeasts which add up to a suitable physiological potential, more or less independently of their taxonomic affinities, was thus confirmed.This paper is dedicated to Professor Herman Jan Phaff in honor of his 50 years of active research which still continues.     

Demographic analysis of insect reproductive levels, patterns and heterogeneity: case study of laboratory strains of three Hawaiian tephritids

Reproductive data were collected on individually-held adult oriental fruit flies, Dacus dorsalis, melon flies, Dacus cucurbitae, and Mediterranean fruit flies, Ceratitis capitata including age-by-parity relations, birth interval, frequency distribution of individual egg production levels and the concentration of reproduction among females in a cohort. Specific findings include: i) delay in reproductive peaks in a cohort after eclosion is due almost entirely to the variance in attainment of reproductive maturity among individuals; ii) low reproductive output of reproductively mature melon flies is due mostly to long birth intervals; iii) high egg production in both the medfly and the oriental fruit fly is due to their consistency of egg laying levels and frequency (short birth intervals). Discussion stresses the importance of viewing reproduction, not as a singular and discrete life history trait, but as consisting of subcomponents of daily parity, cumulative parity and birth interval.

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Résumé Les informations sur la reproduction ont été obtenues à partir d'adultes de Dacus dorsalis, D. cucurbitae, C. capitata, élevés individuellement. Elles portent sur les paramètres suivants: distribution par âge en fonction de la fécondité, échelonnement des pontes, distribution des niveaux quotidiens de ponte, fréquence des pondeuses par cohorte.Différents caractères spécifiques ont été mis en évidence: 1) La variabilité de la date d'apparition de la maturité reproductive est pour l'essentiel responsable du retard dans les dates de reproduction maximale; 2) De 30 à 50% des femelles de D. dorsalis âgées de 10 jours pondent plus de 50 oeufs/jour pendant les deux semaines qui suivent, tandis que seulement 10 à 20% des femelles des deux autres espèces parviennent à pondre cette quantité d'oeufs à n'importe quel âge; 3) D. cucurbitae ayant atteint sa maturité pond environ pendant 40% des jours (c.à.d. chaque 2,5 j), tandis que les deux autres espèces pondent au moins quelques oeufs pendant 80% des jours (c.à.d. chaque 1,25 j); 4) La production élevée d'oeufs de C. capitata et de D. dorsalis est due à la régularité de leur niveau de ponte et à la fréquence (faible espacement); 5) Les fractions des effectifs qui ont pondu au moins 600 oeufs en 30 jours étaient approximativement de 0,8, 0,7, et 0,4 pour D. dorsalis, C. capitata, D. cucurbitae; 6) 50% des femelles de chacune des trois espèces contribuent en gros pour 65% à la ponte.