bluuebunny/crossref_metadata_2025 huggingface dataset:
A systematic review of guided tissue regeneration for periodontal furcation defects. What is the effect of guided tissue regeneration compared with surgical debridement in the treatment of furcation defects?
Authors: Jepsen Søren , Eberhard Jörg , Herrera David , Needleman Ian
Published: May 2003

Objectives:  To systematically review the evidence of effectiveness of guided tissue regeneration (GTR) for furcation defects.

Background:  The evidence for the effectiveness of GTR in furcation defects has not yet been systematically appraised.

Methods:  We searched for randomized controlled trials with at least 6 months' follow‐up comparing GTR with surgical debridement (open flap debridement, OFD). Data sources included electronic databases, hand‐searched journals and contact with experts. Screening, data abstraction and quality assessment were conducted independently by multiple reviewers. The primary outcome measure was reduction in open horizontal furcation depth, secondary outcomes were frequency of furcation closure, gain in horizontal and vertical probing attachment and reduction of vertical probing depth.

Results:  For the primary outcome, reduction in horizontal furcation depth assessed during re‐entry, the weighted mean difference between GTR and control was 1.51 mm (95% CI [0.39–2.62], chi‐square for heterogeneity 67.6 (df = 3), P < 0.001) in mandibular class II furcations, 1.05 mm (95% CI [0.46–1.64, chi‐square for heterogeneity 34.9 (df = 3), P < 0.001) in maxillary class II furcations, and 0.87 mm (95% CI [−0.08–1.82], chi‐square for heterogeneity 0.1 (df = 4), P = 0.991) in studies that had combined mandibular and maxillary class II furcations. For the secondary outcomes, GTR treatment led to significantly better results than open flap debridement. No meta‐analysis could be performed for frequency of furcation closure because of sparse data.

Conclusions:  Overall, GTR was consistently more effective than OFD in reducing open horizontal furcation depths, horizontal and vertical attachment levels and pocket depths for mandibular or maxillary class II furcation defects. However, these improvements were modest, variable and there was only a limited number of studies available to appraise the effects, thus limiting general conclusions about the clinical benefit of GTR. Future studies should aim to identify factors associated with achieving consistent and more pronounced benefits over open flap debridement.
Evolutionary aspects of host plant specialisation – a study on bruchids (Coleoptera: Bruchidae)
Authors: Jermy Tibor , Szentesi Árpád
Published: May 2003

We have studied the relationship of bruchids and their legume hosts by extensive field sampling throughout Hungary over 17 years and by rearing the beetles from the samples in the laboratory. The value of the system lies in the accuracy of host affiliations. A total of 138 species and subspecies of plants were sampled, representing approximately 87% of the Leguminosae in Hungary. Only 51 legume species (37.0%) harboured bruchids (12 Bruchus spp. and 15 Bruchidius spp). Bruchids occurred in 38.3% of the host plant samples. Thirty‐seven plant species congeneric with bruchid host species were unoccupied by bruchids.

The degree of host specificity ranged from monophagy (at least ecological monophagy) to oligophagy. On the basis of presence/absence data we tested the null hypothesis assuming that plant taxa and seed consuming bruchid species form congruent phyletic relations at the species level. We argue that the case for coevolution between the beetles and their hosts is weak. A comparison of the available taxonomic relationships (and presumed phylogenies) best fits a case of sequential evolution, with stronger phylogenetic conservatism in Bruchus species than in Bruchidius species. Bruchid and host plant taxa showed rough congruence only at the tribe level. We suggest that host shifts are best explained by the changes in the bruchids’ chemosensory system that determines the females’ host selection behaviour.
Seasonal energetic constraints in Mediterranean benthic suspension feeders: effects at different levels of ecological organization
Authors: Coma Rafel , Ribes Marta
Published: May 2003

The aim of this work is to examine the role of food as a constraining factor at different levels of ecological organization in benthic littoral ecosystems. In the search for patterns in ecological systems, it has recently been documented that seasonality in the dynamics of benthic suspension feeders (BSF) in the Mediterranean Sea is characterized by summer dormancy. We review recent studies on seston availability in the water column and feeding and respiration by BSF in the Mediterranean. The objective is to assess whether a pattern across particular studies exists that could provide evidence of food as a constraining factor. A pattern emerges from these organism‐level studies, one which indicates the seasonal occurrence of an energy shortage in the taxa exhibiting summer dormancy. This energy shortage is closely related to low food availability and suggests that an energetic constraint underlie the summer dormancy phenomenon. The seasonal occurrence of summer energy shortage also appears to affect the dynamics of BSF at population and community level. In this sense, in late summer 1999, a mass mortality event of BSF affected several hundreds of kilometers in the Ligurian Sea (NW Mediterranean). The fact that the mass mortality event occurred in late summer and especially affected the taxa that exhibit energy shortage – such as anthozoans and sponges – suggests, that energetic constraints may contribute to the understanding of the mass mortality event. The energy shortage phenomenon may provide a mechanism to understand how the occurrence of anomalous climatic conditions may have induced the mass mortality of some BSF taxa. This review points out the existence of a common energy shortage phenomenon mainly related to low food availability as an important determinant of the dynamics of most BSF taxa at organism level in the Mediterranean. But this determinant also affects the dynamics of BSF at population and community level. Therefore, the extant data point up the crucial role of food as a constraining factor for benthic littoral ecosystems in oligotrophic areas like the Mediterranean, with important seasonal variations in seston abundance and composition.
Experimental evidence of a tripartite mutualism: bacteria protect ant fungus gardens from specialized parasites
Authors: Currie C. R. , Bot A. N. M. , Boomsma J. J.
Published: May 2003

Symbioses shape all levels of biological organization. Although symbiotic interactions are typically viewed as bipartite associations, with two organisms interacting largely in isolation from other organisms, the presence and importance of additional symbionts is becoming increasingly more apparent. This study examines the importance of a third mutualist within the ancient symbiosis between leaf‐cutting ants and their fungal cultivars. Specifically, we experimentally examine the role of a filamentous bacterium (actinomycete), which is typically carried on the cuticle of fungus‐growing ants, in suppressing the growth of a specialized microfungal parasite (Escovopsis) of the fungus garden. We conducted two‐by‐two factorial design experiments crossing the presence/absence of actinomycete with the presence/absence of Escovopsis within small sub‐colonies of Acromyrmex octospinosus. In these experiments, infection by Escovopsis became much more extensive within fungus gardens and had a greater impact on the health of gardens in those sub‐colonies with the bacterium removed from workers as compared to gardens with the bacterium still present on the ants. We establish that the actinomycete bacterium is most abundant on those major workers tending the garden, providing further support that the bacterium is involved in garden hygiene. We also found a significantly higher abundance of actinomycete on workers in colonies experimentally infected with Escovopsis as compared to uninfected control colonies. We suggest that mutualisms between antibiotic‐producing microbes and higher organisms may be common associations that are mostly overlooked and that the role of symbionts in reducing the impact of parasites is likely an important aspect in the cost‐benefit assessment of mutualisms.
Within‐generation bet hedging: a seductive explanation?
Authors: Hopper K.R. , Rosenheim J.A. , Prout T. , Oppenheim S.J.
Published: May 2003

Bet hedging occurs when a single genotype shows a variety of phenotypes in the same environment, and each phenotype is successful only when the particular circumstances to which it is adapted occur. The time scale of between‐generation bet hedging ensures that all individuals with a given phenotype suffer the same fate – circumstances such as drought exert homogenous pressure on all members of a population. Under within‐generation bet hedging, however, individuals with the same phenotype are subject to heterogeneous selection pressure – predation, for example, will affect some individuals but not others. An important consequence of this difference is that conditions favoring the evolution of within‐generation bet hedging are very restricted. While a single lineage may realize increased fitness via within‐generation bet hedging, this fitness advantage varies inversely with population size and becomes vanishingly small at even modest population sizes. Although several reviews and analyses have highlighted the differences between these two types of bet hedging, confusion persists regarding their respective definitions and evolutionary justification. Bet hedging is a seductive explanation because most students of evolution are trained to focus on costs and benefits at the individual level, and tend to seek adaptive explanations for individual traits. Although this focus is often successful, it leads us astray in the case of within‐generation bet hedging. Only by assessing the fitness effects of a trait in the context of whole populations can one accurately identify traits that can and cannot be favored by within‐generation bet hedging.
Estimating rates of local extinction and colonization in colonial species and an extension to the metapopulation and community levels
Authors: Barbraud Christophe , Nichols James D. , Hines James E. , Hafner Heinz
Published: May 2003

Coloniality has mainly been studied from an evolutionary perspective, but relatively few studies have developed methods for modelling colony dynamics. Changes in number of colonies over time provide a useful tool for predicting and evaluating the responses of colonial species to management and to environmental disturbance. Probabilistic Markov process models have been recently used to estimate colony site dynamics using presence–absence data when all colonies are detected in sampling efforts. Here, we define and develop two general approaches for the modelling and analysis of colony dynamics for sampling situations in which all colonies are, and are not, detected. For both approaches, we develop a general probabilistic model for the data and then constrain model parameters based on various hypotheses about colony dynamics. We use Akaike's Information Criterion (AIC) to assess the adequacy of the constrained models. The models are parameterised with conditional probabilities of local colony site extinction and colonization. Presence–absence data arising from Pollock's robust capture–recapture design provide the basis for obtaining unbiased estimates of extinction, colonization, and detection probabilities when not all colonies are detected. This second approach should be particularly useful in situations where detection probabilities are heterogeneous among colony sites. The general methodology is illustrated using presence–absence data on two species of herons. Estimates of the extinction and colonization rates showed interspecific differences and strong temporal and spatial variations. We were also able to test specific predictions about colony dynamics based on ideas about habitat change and metapopulation dynamics. We recommend estimators based on probabilistic modelling for future work on colony dynamics. We also believe that this methodological framework has wide application to problems in animal ecology concerning metapopulation and community dynamics.
Strong and weak trophic cascades along a productivity gradient
Authors: Chase Jonathan M.
Published: May 2003

Variation in the strengths of predator effects, although commonly observed in natural communities, and predicted from theoretical models, remains poorly understood in the study of food web interactions and community structure. In this study, I first showed that prey species in benthic pond food webs were highly variable in their susceptibility to predators. Some were vulnerable throughout their lives, whereas others were vulnerable as juveniles, but able to grow to a size‐refuge. Next, I showed that herbivore and predator abundance increased along a natural productivity gradient among 29 ponds, and herbivore species composition shifted from dominance by vulnerable to dominance by invulnerable herbivore species along this gradient. However, there was a considerable amount of variation both in herbivore biomass and composition at intermediate productivity; some were dominated by small species and others by larger species. Finally, in in situ exclosure experiments, I found that predator effects were strong and cascaded to plants in a low productivity pond and in an intermediate productivity pond dominated by small herbivore species. Alternatively, in a high productivity pond and in an intermediate productivity pond dominated by larger herbivores, I found that predator effects on prey biomass were weak, and did not cascade to plants.
Effects of natural and simulated herbivory on spine lengths of Acacia drepanolobium in Kenya
Authors: Young Truman P. , Stanton Maureen L. , Christian Caroline E.
Published: May 2003

We present experimental evidence supporting the hypothesis that increased spine length in acacia species is a defense induced by herbivory. Acacia drepanolobium is the dominant tree over large areas of East Africa. Each individual tree is occupied by one of four ant species at our study site. Using two types of electric fences, we have effectively controlled herbivory by megaherbivores (elephants and giraffes) and other large mammalian herbivores at a field site in Laikipia, Kenya since 1995. Mean spine lengths of new spines on trees occupied by the most abundant ant species (presumed to be a defensive mutualist) have shown a slow and steady decline over the first five years of the experiment on branches protected from these herbivores. This reduction has been 35–40%, or approximately half of the reduction in spine length that we anticipate will eventually occur, based on trees that have been protected from herbivory for many years. In contrast, trees occupied by a resident ant species that systematically prunes shoots have shown no reduction in spine length associated with herbivore exclusion treatments. Experimental pruning of shoots similar to that carried out by this ant species resulted in longer spines on seedlings in a greenhouse setting. Simulated large mammal browsing in the field rapidly (re‐)induced greater spine lengths on trees that had been protected from large mammals for five years. The slow relaxation of spine length in the absence of herbivory, contrasted with its rapid induction after simulated browsing, suggests that there is a difference in the reliability of these two signals. Spine length responses to herbivory were extremely local (limited to individual branches). These branch‐specific responses are consistent with the hypothesis that induced defense in this system evolved in the context of within‐tree spatial variation in herbivore pressure, in particular variation in branch height.
Edge‐mediated effects on stand dynamic processes in forest interiors: a coupled field and simulation approach
Authors: Kupfer John A. , Runkle James R.
Published: May 2003

Researchers studying forest edge effects in fragmented landscapes have begun to move beyond merely documenting changes along the edge itself to examining the dynamic influences that edges may have on processes in adjacent areas. One such “edge‐mediated effect” is the influence that edges may have on canopy gap replacement processes within the forest interior by acting as seed sources for shade‐intolerant plant species. In this paper, we coupled analyses of woody species composition in gap and non‐gap areas within the interior of an Ohio hardwood forest with a simple cellular automata model of forest dynamics. Non‐gap composition was primarily correlated with disturbance history and site conditions (topographic position and slope) while a comparable analysis using a 24‐year time series of composition in gaps showed that gap composition was related most strongly to the proximity of edge communities for the first 10–15 years. However, after 15–20 years of gap succession, composition was correlated with essentially the same variables and to the same degree as non‐gap vegetation, suggesting that the influence of edge proximity on interior stand dynamic processes was transient. These results were used to develop a simple mathematical model of stand dynamics that showed that losses of interior forest area may be much greater than typically predicted by core‐area models, which do not consider dynamic, edge‐mediated effects. Further, our findings suggest the importance of considering disturbance interval in mediating edge‐interior relationships, particularly as it may interact with forest size and shape.
Crab spiders affect flower visitation by bees
Authors: Dukas Reuven , Morse Douglass H.
Published: May 2003

In a field experiment, the bumblebee, B. ternarius, visited milkweed patches harboring crab spiders, Misumena vatia, at a lower frequency than patches free of crab spiders, and honeybees showed a similar but non‐significant trend. Two other bumblebee species, B. terricola and B. vagans, did not avoid the spider patches. The latter two species are larger than B. ternarius and honeybees and suffer lower crab‐spider predation. As far as we know, this is the first field study documenting negative effects of predators on flower visitation rate by pollinator populations. Our study suggests that pollinator response to predation may influence pollinator‐plant interactions.
Survival during adverse seasons reveals size‐dependent competitive ability in a deposit‐feeding amphipod, Monoporeia affinis
Authors: Aljetlawi Albashir A. , Leonardsson Kjell
Published: May 2003

Previous food competition experiments indicated that small Monoporeia affinis (Lindström) amphipods are competitively superior to large conspecifics. If this is the case, large individuals such as adults should be more sensitive than their smaller conspecifics to food shortage during winter. Thus, our hypothesis was that the competitive relationships should be reflected in the winter survival between the different age‐ (size‐) classes. We investigated the effects of starvation on the survival and loss of mass of three age‐ (size‐) classes: juveniles (0+, young‐of‐the‐year) and (1+, one‐year‐old), and adults (2+, two‐year‐old) amphipods in a 10‐week experiment during the winter season. During the starvation period, the survival of the 0+ and 1+ age‐classes decreased gradually with no marked variation between the age‐classes over time, while that of the 2+ age‐class decreased dramatically after 4 weeks. The survival and swimming activity of adult (2+) amphipods were significantly lower than in the 0+ and 1+ age‐classes. The individual dry mass (W) of amphipods decreased with a rate equal to −0.0062W0.95 per day throughout the experiment, with no differences between age‐classes in the allometric scaling of the energetic costs. We found no dramatic decrease in the individual dry mass of 2+ age‐class similar to that in their survival. Using the survival results from our study to rank the age‐classes in terms of competitive ability gave the same rank order as from an earlier competition experiment. These results suggest that a starvation survival experiment prior to adverse seasons could be used to assess the competitive relationships within and between species exploiting the same resource.
Interactions among elk, aspen, galling sawflies and insectivorous birds
Authors: Bailey Joseph K. , Whitham Thomas G.
Published: May 2003

Using two years of observational and experimental data, we examined the hypothesis that browsing by elk on aspen indirectly affects the distribution of a leaf‐galling sawfly, which in turn affects insect diversity and foraging patterns of insectivorous birds. We found that: i) in an analyses of 33 arthropod species, the presence of sawflies significantly increased arthropod richness and abundance by 2 X and 2.5 X, respectively. ii) browsing by elk reduced sawfly gall abundance such that 90% of the galls were found on unbrowsed aspen ramets. iii) insectivorous birds attacked 60–74% of the galls on unbrowsed shoots compared to 11% on browsed shoots. When leaf‐galler abundance was experimentally held constant on browsed and unbrowsed shoots, predation by insectivorous birds did not differ significantly. This result suggests that browsing affects the patterns of avian predation by altering the distribution of a galling insect. These data argue that bottom‐up, top‐down, and lateral factors can act in concert to affect the distribution of a galler, structure arthropod communities and affect predation by insectivorous birds.
Response of plant‐pollinator communities to fire: changes in diversity, abundance and floral reward structure
Authors: Potts Simon G. , Vulliamy Betsy , Dafni Amots , Ne'eman Gidi , O'Toole Chris , Roberts Stuart , Willmer Pat
Published: May 2003

Globally, plant‐pollinator communities are subject to a diverse array of perturbations and in many temperate and semi‐arid systems fire is a dominant structuring force. We present a novel and highly integrated approach, which quantifies, in parallel, the response to fire of pollinator communities, floral communities and floral reward structure. Mt Carmel, Israel is a recognised bee‐flower biodiversity hotspot, and using a chronosequence of habitats with differing post‐fire ages, we follow the changes in plant‐pollinator community organisation from immediately following a burn until full regeneration of vegetation. Initially, fire has a catastrophic effect on these communities, however, recovery is rapid with a peak in diversity of both flowers and bees in the first 2 years post‐fire, followed by a steady decline over the next 50 years. The regeneration of floral communities is closely matched by that of their principal pollinators. At the community level we quantify, per unit area of habitat, key parameters of nectar and pollen forage known to be of importance in structuring pollinator communities. Nectar volume, nectar water content, nectar concentration and the diversity of nectar foraging niches are all greatest immediately following fire with a steady decrease as regeneration proceeds. Temporal changes in energy availability for nectar, pollen, total energy (nectar+pollen) and relative importance of pollen to nectar energy show a similar general decline with site age, however, the pattern is less clear owing to the highly patchy distribution of floral resources. Changes in floral reward structure reflect the general shift from annuals (generally low‐reward open access flowers) to perennials (mostly high‐reward and restricted access flowers) as post‐fire regeneration ensues. The impact of fire on floral communities and their associated rewards have clear implications for pollinator community structure and we discuss this and the role of other disturbance factors on these systems.
Fig choice by the pollinator of a gynodioecious fig: selection to rush, or intersexual mimicry?
Authors: Moore J. C. , Hatcher M. J. , Dunn A. M. , Compton S. G.
Published: May 2003

Due to selection to maximise the benefits accrued, conflicts of interest exist between mutualists. An extreme conflict occurs between gynodioecious fig trees and their pollinating wasps. Female wasps, which are required for pollination, cannot reproduce in female figs and should be selected to avoid them. We investigate fig choice in Liporrhopalum tentacularis, pollinator of Ficus montana. We show that entry rates are independent of fig sex and diameter, with wasps instead entering the first fig encountered (although significant between‐tree differences in entry rates to figs were observed). This suggests that wasps are unable to discriminate between the sexes because of selection for inter‐sexual fig mimicry. In conjuction with data on other species pairs, these findings imply that that the resolution of the conflict is ultimately under the tree's control, with the level of mimicry evolving in response to both the propensity of wasps to discriminate and the costs of them doing so.
Causes and consequences of individual variation in territory size in the American red squirrel
Authors: Steury Todd D. , Murray Dennis L.
Published: May 2003

For most territorial species that defend food or other resources, territory size is inversely related to resource density. However, in some food‐based territorial species, larger territories are known to contain greater absolute resource availability. For these latter species, both the specific determinants of territory size, and the relationship between territory size and fitness, remain unclear. We predicted that in American red squirrels (Tamiasciurus hudsonicus), where larger territories tend to hold increased food resources, survival should be correlated positively with territory size and that both individual (body mass, sex, duration of territory ownership) and habitat‐specific (population density) attributes would contribute to variation in territory size. We monitored survival and territory size of 58 squirrels during a two‐year period using live‐trapping and radio‐telemetry. Survival and territory size were correlated positively, with each 0.1 ha decrease in territory size typically resulting in a 16.6% increase in mortality risk; mortality risk for squirrels with the smallest versus largest territories differed by up to 23‐fold. Territory size was negatively related to local population density, but not to any attributes of individual squirrels, implying that, in this species, territory size may not be influenced strongly by individual quality. We conclude that while larger territories may confer a survival advantage to squirrels, territory size is unrelated to individual physical attributes, likely because costs associated with the acquisition of a larger or richer territory outweigh potential benefits of increased food access.
Mollusks as ecosystem engineers: the role of shell production in aquatic habitats
Authors: Gutiérrez Jorge L. , Jones Clive G. , Strayer David L. , Iribarne Oscar O.
Published: May 2003

Mollusk shells are abundant, persistent, ubiquitous physical structures in aquatic habitats. Using an ecosystem engineering perspective, we identify general roles of mollusk shell production in aquatic ecosystems. Shells are substrata for attachment of epibionts, provide refuges from predation, physical or physiological stress, and control transport of solutes and particles in the benthic environment. Changes in availability of these resources caused by shell production have important consequences for other organisms. Colonization of shelled habitat depends on individual shell traits and spatial arrangement of shells, which determine access of organisms to resources and the degree to which biotic or abiotic forces are modulated. Shell production will increase species richness at the landscape level if shells create resources that are not otherwise available and species are present that use these resources. Changes in the availability of resources caused by shells and the resulting effects on other organisms have both positive and negative feedbacks to these engineers. Positive feedbacks appear to be most frequently mediated by changes in resource availability, whereas negative feedbacks appear to be most frequently mediated by organisms. Given the diversity of species that depend upon resources controlled by shells and rapid changes in global shell production that are occurring due to human activities, we suggest that shell producers should not be neglected as a targets of conservation, restoration and habitat management.
Plant diversity and insect herbivores: effects of environmental change in contrasting model systems
Authors: Hartley S. E. , Jones T. H.
Published: May 2003

There is increasing concern over the potential impact of anthropogenic factors (e.g. increasing nutrient inputs, global climate change) on the rate of loss of diversity in ecosystems. Such losses may affect ecosystem processes. In addition, a change in diversity of one group of organisms may influence the diversity of species of the next trophic level. We examined the extent to which plant species richness influences that of insect herbivores in two systems: a long‐term field experiment on heather moorland and a model community in the Ecotron controlled environment facility. We examined the response of these two plant communities to environmental change, specifically increased levels of nutrients, grazing and atmospheric CO2. We measured the indirect effects of changes in these factors on insect herbivores, both above‐ and below‐ground. In the moorland system, grazing was the largest influence on plant community structure. The community was dominated by one species, Calluna vulgaris, and loss of cover under heavy grazing allowed competing species to invade. However, grazing regime was not a major influence on the species richness of the insect herbivore community. Site was more important: there were a greater number of Hemiptera species on sites with more mineral soils than on peat sites, possibly because a greater variety of grass and herb species was present on the former sites. In the Ecotron, below‐ground factors were also important drivers of community change: elevated CO2 increased carbon availability in the soil and there were simultaneous changes in the community composition of soil biota. Above‐ground, some plant species increased in abundance and others decreased, leading to interaction‐specific effects on the insect herbivores. In two very different studies of the effects of environmental change on the interactions between plants and their herbivores, several similar conclusions can be drawn: (1) effects are likely to be site‐ and interaction‐specific; (2) outcomes are likely to be strongly dependent on the initial state and the dominant species of the plant community; and (3) indirect effects, often mediated by below‐ground factors, may have a bigger influence on insect‐plant interactions than more direct effects of above‐ground factors.
Effects of landscape context on herbivory and parasitism at different spatial scales
Authors: Thies Carsten , Steffan‐Dewenter Ingolf , Tscharntke Teja
Published: May 2003

Local community structure and interactions have been shown to depend partly on landscape context. In this paper we tested the hypothesis that the spatial scale experienced by an organism depends on its trophic level. We analyzed plant‐herbivore and herbivore‐parasitoid interactions in 15 agricultural landscapes differing in structural complexity using the rape pollen beetle (Meligethes aeneus), an important pest on oilseed rape (Brassica napus), and its parasitoids. In the very center of each landscape a patch of potted rape plants was placed in a grassy field margin strip for standardized measurement. Percent non‐crop area of landscapes was negatively related to plant damage caused by herbivory and positively to the herbivores’ larval mortality resulting from parasitism. In a geographic scale analysis, we quantified the structure of the 15 landscapes for eight circular sectors ranging from 0.5 to 6 km diameter. Correlations between parasitism and non‐crop areas as well as between herbivory and non‐crop area were strongest at a scale of 1.5 km, thereby not supporting the view that higher trophic levels experience the world at a larger spatial scale. However, the predictive power of non‐crop area changed only slightly for herbivory, but greatly with respect to parasitism as scales from 0.5 to 1.5 km and from 1.5 to 6 km diameter increased. Furthermore, the effect of non‐crop area tended to be stronger in parasitism than herbivory suggesting a greater effect of changes in landscape context on parasitoids. This is in support of the general idea that higher trophic levels should be more susceptible to disturbance.
Herbivory and plant resource competition: a review of two interacting interactions
Authors: Hambäck Peter A. , Beckerman Andrew P.
Published: May 2003

This review discusses the prevalence and potential for interactive effects between herbivory and competition on plant growth and biomass, and it is apparent that such effects typically arise when there is a mismatch between the spatial scale of herbivore behaviour (food or patch choice) and the spatial heterogeneity of the plant community. Historically, such interactive effects have been examined using two approaches. Studies using the first approach have excluded plant neighbors and herbivores in a factorial experiment, and scored effects on plant biomass. Studies using the second approach have observed herbivore abundance or herbivory on plants with or without plant neighbors, and have identified a large number of mechanisms underlying such interactive effects. The two types of studies have produced somewhat conflicting results, where interactive effects have been commonly observed in studies using the second approach and only rarely in studies using the first approach. This is most likely a consequence of a biased choice of study systems, where studies using the first approach have primarily studied mammalian herbivory while studies using the second approach have been more focussed on insect herbivory. Moreover, studies using the first approach have typically been very small‐scale manipulations and this probably precludes most possible interactive effects in systems with mammalian herbivory. This points to the fact that studies examining interactive effects of herbivory and plant competition should more carefully consider the behaviour and life history of herbivores included in the study prior to the design of removal experiments.
Local adaptation and ecological genetics of host‐plant specialization in a leaf beetle
Authors: Ballabeni Pierluigi , Gotthard Karl , Kayumba Aline , Rahier Martine
Published: May 2003

The tendency of insect species to evolve specialization to one or a few plant species is probably a major reason for the remarkable diversity of herbivorous insects. The suggested explanations for this general trend toward specialization include a range of evolutionary mechanisms, whose relative importance is debated. Here we address two potentially important mechanisms: (i) how variation in the geographic distribution of host use may lead to the evolution of local adaptation and specialization; (ii) how selection for specialization may lead to the evolution of trade‐offs in performance between different hosts. We performed a quantitative genetic experiment of larval performance in three different populations of the alpine leaf beetle Oreina elongata reared on two of its main host plants. Due to differences in host availability, each population represents a distinctly different selective regime in terms of host use including selection for specialization on one or the other host as well as selection for utilizing both hosts during the larval stage.

The results suggest that selection for specialization has lead to some degree of local adaptations in host use: both single‐host population had higher larval growth rate on their respective native host plant genus, while there was no difference between plant treatments in the two‐host population. However, differences between host plant treatments within populations were generally small and the degree of local adaptation in performance traits seems to be relatively limited. Genetic correlations in performance traits between the hosts ranged from zero in the two‐host population to significantly positive in the single‐host populations. This suggests that selection for specialization in single host populations typically also increased performance on the alternative host that is not naturally encountered. Moreover, the lack of a positive genetic correlation in the two host‐population give support for the hypothesis that performance trade‐offs between two host plants may typically evolve when a population have adapted to both these plants. We conclude that although there is selection for specialization in larval performance traits it seems as if the genetic architecture of these traits have limited the divergence between populations in relative performance on the two hosts.
Impacts of temporal variation on apparent competition and coexistence in open ecosystems
Authors: Holt Robert D. , Barfield Michael
Published: May 2003

The natural world is variable both in space and in time, but little ecological theory has been explicitly devoted to analyzing the consequences of both kinds of variability operating simultaneously. This issue is examined relative to the indirect interaction of apparent competition, which can limit the membership of prey communities. One limiting case that provides a useful starting point is to imagine that a local community is influenced by coupling with an external source landscape, but has little reciprocal influence on that landscape. There usually will be some rate of input of a locally inferior species that suffices to ‘swamp’ a superior species and drive it to extinction. We use simple models of apparent competition to show that when one superimposes upon this scenario temporal fluctuations, mediated through shifts in parameter values, such variation can either magnify the importance of the external input, or reduce it, depending on which component of the system experiences variation. We examine this in the case of both slow variation (for which we suggest a protocol that may be useful in a wide range of ecological models), and fast variation. The theoretical studies presented here provide examples of the rich range of outcomes that may arise due to temporal variability in spatially heterogeneous landscapes.
Mixed blends of herbivore‐induced plant volatiles and foraging success of carnivorous arthropods
Authors: Dicke Marcel , De Boer Jetske G. , Höfte Marleen , Rocha‐Granados M. Carmen
Published: May 2003

Food webs are overlaid with infochemical webs that mediate direct and indirect interactions. Behavioural ecologists have extensively documented that carnivorous arthropods exploit herbivore‐induced plant volatiles during foraging for herbivorous arthropods. Most studies on the role of infochemicals in multitrophic interactions have been conducted against an odour‐free background, although field studies show that carnivores also use herbivore‐induced plant volatiles under more complex conditions. Here we investigated the effect of mixing the blends of volatiles emitted by two plant species on the foraging behaviour of the predatory mite Phytoseiulus persimilis. This was done in an olfactometer under laboratory conditions and in a semi‐field setup under greenhouse conditions. The olfactometer setup ensured directed mixing of the two odour blends, while odour mixing in the greenhouse setup was much less controlled and resulted from diffusion. In 4 out of 5 olfactometer experiments the behaviour towards volatiles from spider‐mite (Tetranychus urticae) infested Lima bean plants was not affected by mixing with volatiles from caterpillar (Pieris brassicae) infested Brussels sprouts plants. In the fifth olfactometer experiment the response shifted significantly towards the volatiles from infested Lima bean leaves without volatiles from infested cabbage leaves. In the greenhouse setup no effect of infested cabbage plants or their volatiles on the location of spider‐mite infested bean plants was recorded. The two odour blends used in this study, i.e. those from spider‐mite infested Lima bean leaves and from caterpillar‐infested Brussels sprouts plants, are very different and there is no overlap in compounds that are known to attract the predators. The results are discussed in the context of other types of odour‐blend mixing and the effects on food web interactions.
Dynamics of refuge use: diurnal, vertical migration by predatory and herbivorous mites within cassava plants
Authors: Onzo Alexis , Hanna Rachid , Zannou Ignace , Sabelis Maurice W. , Yaninek John S.
Published: May 2003

Plants may protect themselves against herbivorous arthropods by providing refuges to predatory arthropods, but they cannot prevent herbivores from taking countermeasures or even from reaping the benefits. To understand whether plants benefit from providing self‐made refuges (so‐called domatia), it is not only necessary to determine the fitness consequences for the plant, but also to assess (1) against which factors the refuge provides protection, (2) why predatory arthropods are more likely to monopolise the refuge, and (3) how herbivorous and predatory arthropods respond to and affect each other in and outside the refuge. In this article, we focus on the last aspect by studying the dynamics of refuge use of a predatory mite (Typhlodromalus aripo) and its consequences for a herbivorous mite (Mononychellus tanajoa) on cassava plants in Benin, West Africa. The refuge, located in‐between the leaf primordia of the cassava apex, is thought to provide protection against abiotic factors and/or intraguild predators. To test whether the predator waits for prey in the apex or comes out, we sampled predator‐prey distributions on leaves and in the apex at 4 hour‐intervals over a period of 24 hours. The predatory mites showed pronounced diurnal changes in within‐plant distribution. They were in the apices during the day, moved to the young leaves during night and returned to the apices the next morning. Nocturnal foraging bouts were more frequent when there were more herbivorous mites on the leaves near the apex. However, the foraging predators elicited an avoidance response by mobile stages of their prey, since these were more abundant on the first 20 leaves below the apex during late afternoon, than on the same leaves during night. These field observations on cassava plants show that (1) during daytime predatory mites monopolise the apical domatia, (2) they forage on young leaves during night and (3) elicit avoidance by within‐plant, vertical migration of mobile stages of the herbivorous mites. We hypothesize that cassava plants benefit from apical domatia by acquiring protection for their photosynthetically most active, young parts, because predatory mites (1) protect primordial leaves in the apex, (2) reduce the densities of herbivorous mites on young leaves, and (3) cause herbivorous mites to move down to less profitable older leaves.
Nutrient and microbiological characteristics of fine benthic organic matter in sediment settling ponds
Authors: Bonin H. L. , Griffiths R. P. , Caldwell B. A.
Published: May 2003

1. Fine benthic organic matter (FBOM, particles <1 mm) was collected eight times in 1995 and 1996 from settling ponds located at the base of five catchments, and assayed for total C, N and P, extractable ammonium, mineralisable N, organic P, labile polysaccharides, denitrification potential, acetylene reduction and respiration rates, and β‐glucosidase and phosphatase activities. The five catchments (10–101 ha in size) are located in the Pacific North‐west of the United States. They contain either old‐growth forests dominated by Douglas‐fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla) or stands that were harvested 30 years ago and replanted with Douglas‐fir, with riparian zones dominated by red alder (Alnus rubra), bigleaf and vine maple (Acer macrophyllum; A. circinatum) and understory herbaceous plants.

2. C : N ratios were significantly higher, and mineralisable N, extractable ammonium and labile polysaccharides were all significantly lower, in FBOM from old‐growth catchment sediment than in FBOM from catchments containing harvested stands, showing that the chemical characteristics of FBOM were influenced by forest harvest. C and N concentrations were greatest in sediment from old‐growth catchments, but microbial activities (respiration, denitrification potential, phosphatase and β‐glucosidase) tended to be greater in sediment from the harvested catchments.

3. Levels of certain chemical components of harvested‐catchment FBOM were elevated relative to those found in old growth; specifically, organic and total P, extractable ammonium, mineralisable N and labile polysaccharides, suggesting that stream FBOM from harvested basins is more biodegradable than stream FBOM from old‐growth basins.

4. In addition to effects of past timber harvest on FBOM characteristics, there were also significant seasonal differences in both logged and unlogged catchments in all variables except mineralisable N, labile polysaccharides and acetylene reduction rates.

5. The results indicate that past timber harvest in five river basins influenced both composition of and seasonal fluctuations in fine benthic organic matter (FBOM) collected from stream sediments in settling ponds, suggesting a linkage between forest harvest and stream productivity.

6. Comparisons between seasonal patterns in stream and settling pond sediment FBOM characteristics suggested that the readily decomposable organic matter entering sediments during a storm event are rapidly transported and decomposed during their movement through the catchment basin. It also showed the validity of studying settling pond sediments as a surrogate for mountain stream sediments.
A mixing model analysis of stream solute dynamics and the contribution of a hyporheic zone to ecosystem function*
Authors: Battin Tom J. , Kaplan Louis A. , Newbold J. Denis , Hendricks Susan P.
Published: May 2003

1. We monitored streamwater and streambed sediment porewaters from White Clay Creek (WCC), SE Pennsylvania, for dissolved organic carbon (DOC), dissolved oxygen (DO) and conductivity to investigate organic matter processing within the hyporheic zone. Dissolved organic carbon and DO concentrations were higher in the streamwater than in the porewaters and, in many cases, concentrations continued to diminish with increasing depth into the streambed.

2. Hydrological exchange data demonstrated that the permeability of the stream bed declines with depth and constrains downwelling, effectively isolating porewaters >30 cm from streamwater.

3. End‐member mixing analysis (EMMA) based on conductivity documented a DOC source and DO sink in the hyporheic zone. We calculated hyporheic streambed DOC fluxes and respiration from the EMMA results and estimates of water flux. Based upon our calculations of biodegradable DOC entering the hyporheic zone, we estimate that DOC supports 39% of the hyporheic zone respiration, with the remaining 61% presumably being supported by entrained particulate organic carbon. Hyporheic respiration averaged 0.38 g C m−2 d−1, accounted for 41% of whole ecosystem respiration, and increased baseflow ecosystem efficiency from 46 to 59%.

4. Advective transport of labile organic molecules into the streambed concentrates microbial activity in near‐surface regions of the hyporheic zone. Steep gradients in biogeochemical activity could explain how a shallow and hydrologically constrained hyporheic zone can dramatically influence organic matter processing at the ecosystem scale.