bluuebunny/crossref_metadata_2025 huggingface dataset:
Does grafting provide tomato plants an advantage against H2O2 production under conditions of thermal shock?
Authors: Rivero Rosa M. , Ruiz Juan M. , Sánchez Esteban , Romero Luis
Published: December 2004

Non‐grafted tomato plants (Lycopersicon esculentum L. cv. Tmknvf2) and grafted tomato plants (L. esculentum L. cv. Tmknvf2 × L. esculentum L. cv. RX‐335) were grown for 30 days at three different temperatures (10°C, 25°C and 35°C). In the leaves of these plants, the enzymatic activities of SOD, GPX, CAT, APX, DHAR and GR were analysed, as were the concentrations of total H2O2, ascorbate and glutathione as well as foliar DW. Regardless of whether the plant was grafted or not, our results indicate that the thermal stress occurred mainly at 35°C, with the following effects: (1) high SOD activity; (2) H2O2 accumulation; (3) foliar‐biomass reduction; (4) low GPX, CAT, APX, DHAR and GR activities; and (5) high concentrations of ascorbate and glutathione. In addition, our data show these effects to be much weaker in grafted than in non‐grafted plants, directly reflected in greater biomass production. Therefore, the use of grafted plants under excessively high temperatures may offer an advantage over non‐grafted plants in terms of resistance against thermal shock.
Growth of tomato and an ABA‐deficient mutant (sitiens) under saline conditions
Authors: Mäkelä Pirjo , Munns Rana , Colmer Timothy D. , Peltonen‐Sainio Pirjo
Published: December 2004

To determine whether ABA accumulation inhibits or promotes shoot growth under stress, an ABA‐deficient mutant tomato, sitiens, and its wild‐type, the cultivar Rheinlands Rhum, were exposed to moderate salinity stress. Plants were grown at 75 mM NaCl for 2 weeks under conditions of moderate or high relative humidity (70% and 95% RH, respectively). At 70% RH, shoot DW and relative growth rate were reduced more in sitiens than in the cultivar, but the major difference between genotypes was in the degree of injury suffered by older leaves. Most leaves of sitiens died after 2 weeks, but those of the cultivar remained alive. When plants were grown at 95% RH, to maximize the leaf water status of both genotypes, there was no significant effect of salt on shoot DW of either genotype. However, there was still considerable leaf death in sitiens whereas no visible injury appeared in the cultivar. Cl– accumulated to higher levels in leaf tissues than Na+, but to similar concentrations in both genotypes, and so could not explain the injury in the sitiens leaves. The results indicate that ABA maintains rather than inhibits new growth under stress, and has a major effect on preservation of older leaves.
Field testing of UV biological spectral weighting functions for higher plants
Authors: Flint Stephan D. , Caldwell Martyn M.
Published: December 2004

In biological research on the ozone depletion issue, action spectra are typically used as biological spectral weighting functions (BSWF). There has been little testing, however, of the appropriateness of different functions under realistic field conditions. Here we quantitatively evaluate a new BSWF for plant growth response to UV radiation, and other action spectra potentially usable as BSWF, in two seasons of field experiments. We utilized supplemental UV‐B radiation with various combinations of filtered solar UV‐A radiation. Our new BSWF, which we call the UV plant growth weighting function, indicates responses in the UV‐A waveband. In field tests it proved to be the most appropriate weighting function for the responses we measured in oat (Avena sativa L. cv. Otana) over the two field seasons in these studies. A 10‐day field experiment with canola, Brassica rapa L. cv. Goldrush, also suggested substantial effects of both UV‐B and UV‐A radiation on growth. If this new UV plant growth BSWF proves to be appropriate for many plant species, it represents a lower radiation amplification factor (RAF) than several previously used weighting functions for plants. This means less change in biologically effective UV for each increment of ozone column change. However, the lower RAF also means that experiments utilizing supplemental UV treatments have supplied milder doses of additional UV than intended, since they were based on BSWF that overemphasized UV‐B and ignored the UV‐A region. While we await continued field testing of BSWF on diverse taxa, we recommend: (1) reporting weighted irradiance with our new BSWF, and other appropriate functions; (2) continued reporting of the generalized plant weighted UV for continuity and comparative purposes, since it has been so widely used.
Diaspore ecology ofMertensia maritima: effects of physical treatments and their relative timing on dispersal and germination
Authors: Skarpaas Olav , Stabbetorp Odd E.
Published: December 2004

This paper reports an experimental study of water dispersal potential and germination of the shingle beach plantMertensia maritimain which we consider the effects of physical factors (cold treatment, mechanical wear of the pericarp and salt‐water exposure) on the diaspores. Our approach also includes testing effects of different orders of the treatments, in contrast to most earlier studies of diaspore ecology. A cold period was necessary to break seed dormancy, and prolonged cold treatment (stratification at 2°C) enhanced germination. Mechanical wear of the pericarp before cold treatment did not affect germination, whereas mechanical wear after cold treatment increased germination significantly. Seeds exposed to 6 weeks of cold treatment before floating in salt water for 6 weeks did not germinate. In contrast, for seeds given the same cold treatment after floating, the germination was more than 50%. Most undamaged and slightly damaged nutlets stayed afloat throughout the dispersal experiment (9 weeks) in 3% salt water, whereas seeds that fell out of damaged nutlets sunk immediately. Thus, the results suggest that the potential for long‐distance dispersal is high unless the diaspores (nutlets) are severely damaged, but the order of cold treatment and water dispersal seems to be of great importance for germination: seeds dispersed in autumn (before cold periods) have a much higher probability of germinating than seeds dispersed in winter or early spring (after a cold period). Similar effects of the relative timing of physical processes have hitherto only been reported for two other water‐dispersed beach plants. Future studies in diaspore ecology should consider such timing effects as they may be important determinants of the distribution and abundance of plants.
Dispersal behaviour of individuals in metapopulations of two British butterflies
Authors: Conradt L. , Roper T. J. , Thomas C. D.
Published: December 2004

Dispersal patterns are important in metapopulation ecology because they affect the dynamics and survival of populations. However, because little empirical information exists on dispersal behaviour of individuals, theoretical models usually assume random dispersal. Recent empirical evidence, by contrast, suggests that the butterfly Maniola jurtina uses a non‐random, systematic dispersal strategy, can detect and orient towards habitat from distances of 100–150 m, and prefers a familiar habitat patch over a non‐familiar one (‘homing behaviour’). The present study (1) investigated whether these results generalise to another butterfly species, Pyronia tithonus; and (2) examined the cause of the observed ‘homing behaviour’ in M. jurtina. P. tithonus used a similar non‐random, systematic dispersal strategy to M. jurtina, had a similar perceptual range for habitat detection and preferred a familiar habitat patch over a non‐familiar one. The ‘homing behaviour’ of M. jurtina was found to be context‐dependent: individual M. jurtina translocated within habitat did not return towards their capture point, whereas individuals translocated similar distances out of habitat did return to their ‘home’ patch. We conclude that butterfly ‘homing behaviour’ is not based on an inherent preference for a familiar location, but that familiarity with an area facilitates the recognition of suitable habitat, towards which individuals orient if they find themselves in unsuitable habitat. Contrary to conventional wisdom, we suggest that frequent, short ‘excursions’ over habitat patch boundaries are evolutionarily advantageous to individuals, because increased familiarity with the surrounding environment is likely to increase the ability of a straying animal to return to its natural habitat, and to reduce the rate of mortality experienced by individuals attempting to disperse between habitat patches. We discuss the implications of the non‐random dispersal for existing metapopulation models, including models of the evolution of dispersal rates.
Effects of soil decomposer invertebrates (protozoa and earthworms) on an above‐ground phytophagous insect (cereal aphid) mediated through changes in the host plant
Authors: Bonkowski Michael , Geoghegan Irene E. , Birch A. Nicholas E. , Griffiths Bryan S.
Published: December 2004

We investigated if the activity of soil invertebrates (protozoa and earthworms) affected the performance of barley and if effects propagated higher up the above‐ground food chain into herbivores (cereal aphid,Sitobion avenae). Barley plants were grown individually in microcosms containing defaunated soil and grass residues. Plants were grown in soil containing: a) no added fauna, b) protozoa, c) earthworms, or d) protozoa and earthworms. After 7 weeks growth at 20°C three adult cereal aphids were added to each plant on separate leaves. The aphids were allowed to grow and reproduce for another 2 weeks before the experiment was destructively sampled. Amounts of mineral N in the soil and leached from the microcosms were significantly reduced by the presence of soil animals. Correspondingly plant biomass and total plant N content were increased significantly by soil animals, protozoa in particular. The different mechanisms responsible for changes in nutrient turnover in presence of protozoa and earthworms are discussed. Aphid performance was strongly influenced by the presence of protozoa, but not by earthworms. In the presence of protozoa the numbers and biomass of adult and juvenile aphids were significantly increased. These effects are likely due to an increased N content in barley plants and consequently increased nitrogen availability to aphids. The results underline that the detritivore and herbivore systems are intimately linked.
Predators are rare even when they are small
Authors: Ahlering Marissa A. , Carrel James E.
Published: December 2004

A recent review of published studies revealed that predators generally have lower population densities than non‐predators in a variety of communities. We report here similar results for a highly replicated study of macroinvertebrates that colonized very uniform detrital microcosms in an old field. This pattern persisted even though predators usually were smaller than non‐predators, as determined by body length and volume.
Food hoarding behaviour of black‐capped chickadees (Poecile atricapillus ) in relation to forest edges
Authors: Brotons Lluís , Desrochers André , Turcotte Yves
Published: December 2004

In temperate forests, small birds avoid the use of forest edges in adverse winter weather suggesting high foraging costs in terms of energetic requirements. Since hoarding species will often retrieve caches during adverse winter weather, they may perceive forest edges, especially exposed ones, as low quality hoarding sites. We tested whether black‐capped chickadees (Poecile atricapillus) inhabiting fragmented forests modify and reduce hoarding activity near forest edges. We also tested whether hoarding behaviour will be most affected in sites with forest edges more exposed to extreme weather. Black‐capped chickadees taking food from a feeder 30 m from the nearest forest edges hoarded items mostly towards the forest interior, whereas no preference in hoarding location was observed with birds taking food from a feeder placed >100 m from the edge. Furthermore, birds avoided direct flights towards forest edges and, at sites exposed to prevailing winds, hoarding trips were shorter than at other locations. These results suggest that individuals avoid hoarding near forest edges and there, they lower their investment in terms of hoarding effort. The observed difference in hoarding behaviour was more evident near forest edges delimiting wide unforested areas than in edges delimiting narrower unforested areas. Edge exposure to prevailing winds influenced hoarding behaviour much less. We suggest that hoarding birds may partially overcome the ecological costs of habitat loss and fragmentation due to abiotic edge effects. By hoarding food away from forest edges in good weather, they may use forest interiors as low‐cost retrieval sites under adverse weather.
Host selection in phytophagous insects: a new explanation for learning in adults
Authors: Cunningham J. P. , West S. A. , Zalucki M. P.
Published: December 2004

Insect learning can change the preferences an egg laying female displays towards different host plant species. Current hypotheses propose that learning may be advantageous in adult host selection behaviour through improved recognition, accuracy or selectivity in foraging. In this paper, we present a hypothesis for when learning can be advantageous without such improvements in adult host foraging. Specifically, that learning can be an advantageous strategy for egg laying females when larvae must feed on more than one plant in order to complete development, if the fitness of larvae is reduced when they switch to a different host species. Here, larvae benefit from developing on the most abundant host species, which is the most likely choice of host for an adult insect which increases its preference for a host species through learning. The hypothesis is formalised with a mathematical model and we provide evidence from studies on the behavioural ecology of a number of insect species which demonstrate that the assumptions of this hypothesis may frequently be fulfilled in nature. We discuss how multiple mechanisms may convey advantages in insect learning and that benefits to larval development, which have so far been overlooked, should be considered in explanations for the widespread occurrence of learning.
On the conceptual basis of the self‐thinning rule
Authors: Torres José‐Leonel , Sosa Vinicio J. , Equihua Miguel , Torres Leonel
Published: December 2004

We show a widely accepted proof of the self‐thinning rule offered by Enquist et al. to be mathematically incomplete, as it does not identify the plant mass distributions that satisfy a condition implicitly used in the proof. We propose a method to guide the search for such mass distributions, based on a requirement of maximum mass diversity under the appropriate constraints. This generic method allows construction of a probability density that incorporates the available information on a given stochastic variable, and we illustrate its use through the calculation of a continuous mass distribution for the self‐thinning rule that satisfies the implicit condition mentioned above. We suggest a biological justification of maximum mass diversity, as a corollary to the random and unbiased nature of the source of diversity in Darwin's principle.
Seedling resistance to herbivory as a predictor of relative abundance in a synthesised prairie community
Authors: Burt‐Smith G. S. , Grime J. P. , Tilman D.
Published: December 2004

In a laboratory experiment seedlings of 24 perennial herbaceous prairie species were offered to the omnivorous cricket Acheta domestica in an extended feeding trial. Leaf damage was monitored daily allowing an index of palatability to be calculated for each plant species.  The index of palatability successfully predicted relative abundance within the same set of species in an independently‐conducted study involving community assembly from seed in low‐fertility plots.  These results support the hypothesis that resistance to herbivory may be an important component of plant fitness in unproductive vegetation. However, the correlation between palatability and community composition may be interpreted as a positive association between traits that lead to high competitive ability and herbivory resistance.  There is a need to establish whether the success of the dominant grasses at Cedar Creek arises from their superior ability to capture nitrogen from low external concentrations or is, rather, due to their superior ability to minimise nitrogen loss to herbivores.
The feeding behavior of the weevil, Exophthalmus jekelianus, with respect to the nutrients and allelochemicals in host plant leaves
Authors: Wright Geraldine A. , Simpson Stephen J. , Raubenheimer David , Stevenson Philip C.
Published: December 2004

The aim of this study was to relate nutritional and allelochemical variables in a living host plant to the feeding behavior of herbivorous insects in a field setting. We chose to study the foraging behavior of individual folivorous weevils (Exophthalmus jekelianus) while they were feeding on Central American mahogany (Cedrelaodorata) in plantation in Costa Rica. All leaves contacted by the weevils during each observation were subjected to chemical analysis, and the weevils' choice of leaves and their meal durations on those leaves were examined with respect to leaf chemical composition. Leaves that contained limonoids (allelochemicals present in the leaves) had fewer meals taken on them than did leaves without limonoids. Regression analysis and factor analysis were employed to investigate associations between leaf chemistry and meal duration. Univariate regressions indicated significant associations between meal duration and sucrose concentration, and between meal duration and nitrogen concentration. Factor analysis indicated that soluble sugars, nitrogen and limonoids were important variables that accounted for variation in meal duration. Sucrose and nitrogen concentrations were incorporated into a mathematical model that predicts the phagostimulatory power of foods in the context of the regulation of multiple nutrients. The model is shown to provide an effective framework for understanding the complex interactions among the chemical constituents of plants in determining foraging behaviour under field conditions.
The energetic equivalence rule rejected because of a potentially common sampling error: evidence from carabid beetles
Authors: Arneberg Per , Andersen Johan
Published: December 2004

Abundance data from pitfall traps are widely used to estimate the relationship between beetle body size and abundance. Such data probably overestimate densities of large bodied species and may overestimate slopes of size‐abundance relationships. Here, we test this idea by comparing size‐abundance patterns found using data from pitfall trapping with those found with data from a quantitative method of estimating abundance, quadrat sampling. We use data from a total of 47 communities. As expected, slopes of size‐abundance relationships are significantly more positive when estimated using data from pitfall traps compared to when using quadrat sampling data. This was seen when looking across different communities, within communities sampled by both methods and when focusing on the set of species found by both methods within a community. These results were also generally found regardless of method of analysis, which were done using regression with species values as independent data points and using the independent contrast method, and with slopes estimated using ordinary least square regression or the structural relation. Most important, slopes of size‐abundance relationships based on data from pitfall traps were on average significantly more positive than −0.75 on log–log scales, and thus inconsistent with the energetic equivalence rule. Slopes based on quadrat sampling, on the other hand, were on average not significantly different from −0.75. The rejection of the energetic equivalence rule based on data from pitfall traps here is therefore a sampling artefact. Similar problems may apply to abundance data from virtually all insect trapping methods, and should make us consider re‐examining many of the size‐abundance patterns documented so far. As a large proportion of all animal species are insects, and traps are widely used to estimate abundance, this is a potentially important problem for our general understanding of the relationship between species body size and abundance.
Increased risk of parasitism as ecological costs of using aggregation pheromones: laboratory and field study ofDrosophila‐Leptopilinainteraction
Authors: Wertheim Bregje , Vet Louise E. M. , Dicke Marcel
Published: December 2004

Information conveyance plays an important role in parasitoid‐host interactions. Several sources of information are available for searching parasitoids and exploitation of that information during the different phases of host location depends on its reliability, detectability and accuracy. One source of information especially suitable for exploitation by parasitoids is a host aggregation pheromone, because this often combines all three aspects. In laboratory and field experiments we studied the behavioural responses of the parasitoidLeptopilina heterotomato the aggregation pheromone of the fruit flyDrosophila melanogaster, both for substrate selection and the behaviour on host substrates. Our results show that substrates with increasing dose of the host's aggregation pheromone attract increasingly more parasitoids, whereas we found no significant effects of pheromone on parasitoid searching behaviour on the substrates. Parasitoid searching behaviour on substrates was influenced by other host cues (e.g.larval excrements, traces of adults other than aggregation pheromone), which is discussed in relation to the expectations from reliability‐detectability theory. The responses of the parasitoids were further influenced by substrate quality (i.e. yeast concentration) and the microscale distribution of pheromone. In several field experiments, the fraction of fruit fly larvae that was parasitised was significantly higher in substrates with aggregation pheromone than in control substrates, indicating an ecological cost to the use of aggregation pheromones in adultD. melanogaster.
Testing predictions of the lake food web theory on pelagic communities of Australian reservoirs
Authors: Matveev Vladimir
Published: December 2004

Several predictions of the theory developed for pelagic food webs of the Northern Hemisphere were tested on water bodies of Eastern Australia. Eleven reservoirs, representing trophic and latitudinal gradients were sampled for nutrients, phytoplankton, zooplankton and pelagic fish. Two models of regression analysis, which analysed possible interactions between trophic levels were based on different sets of data. In one, each reservoir was represented by only one pair of observations – annual mean or single observation (“regional model”). In the other, seasonal means of four frequently sampled reservoirs similar in productivity were used (“temporal model”). Significant variation in total phytoplankton biovolume (TPB) was predicted by total phosphorus concentration (TP), total nitrogen concentration (TN), mean crustacean length and acoustic biomass of planktivorous fish in both models. This suggested that nutrient limitation, zooplankton grazing and positive effects of fish were probably important in controlling the biomass of primary producers at both regional and temporal scales. In the regional model, the biomass of fish was also negatively correlated with Daphnia biomass and mean crustacean length, suggesting that the trophic cascade hypothesis may be applicable to Eastern Australia for the considered range of reservoir productivities.

The biovolume of cyanobacteria was not correlated to any variables tested in the regional model. In contrast, nutrient and food web variables had significant effects on cyanobacterial biovolume in the temporal model. This suggested that factors governing seasonal succession were probably more important for cyanobacteria than variation in reservoir productivity or location.

Contrary to previous views, no negative relationship between total biomass of zooplankton and TPB was found in both models, suggesting that the community structure of zooplankton rather than its total biomass mediates top‐down effects. Many predictions of the food web theory remained robust in spite of substantial differences in animal taxonomy and physical environment of Australian ecosystems.
To grow and defend: lack of tradeoffs for brown algal phlorotannins
Authors: Arnold T. M. , Targett N. M.
Published: December 2004

The concept of cost is an integral element of ecological theories, including optimal defense theory, resource availability theory, and growth‐differentiation balance theory. Indeed most frameworks that attempt to explain within‐plant patterns of secondary metabolites, as well as account for the evolution of induced defenses, presume that defenses are ‘costly’. One way in which investigators have sought to quantify the cost of secondary metabolites is to examine growth/defense tradeoffs, which are predicted to occur wherever resources cannot be simultaneously allocated to both growth and defense. However, emerging evidence suggests that these critical assumptions may not be valid for brown algal phlorotannins, compounds that occur throughout the division Phaeophyta and have served as analogs to vascular plant tannins in numerous tests of terrestrial‐derived ecological theories in the marine environment. Here we present a model of phlorotannins as metabolites with both primary and secondary roles and argue that apparent trade‐offs between algal growth and phlorotannin content are not a reliable indicator for establishing a cost of defense. We suggest the ecological theories which presume that defenses are costly because resources allocated to defense cannot also be allocated to other ‘primary’ functions are unlikely to accurately predict the striking variations in algal phlorotannin concentrations that are observed in nature.
Cold winter microenvironments conserve energy and improve overwintering survival and potential fecundity of the goldenrod gall fly, Eurosta solidaginis
Authors: Irwin Jason T. , Lee, Jr Richard E.
Published: December 2004

We studied the influence of two overwintering microenvironments on survival and potential fecundity of goldenrod gall flies, Eurosta solidaginis (Fitch) (Diptera, Tephritidae). These freeze‐tolerant larvae overwinter above the snow on standing goldenrod stems (elevated) or below the snow on broken stems (ground‐level). When covered by snow, the ground‐level larvae were well insulated and thus protected from the lowest temperatures of the winter, but, because they were warmer, they consumed more energy than their elevated counterparts. The ground‐level group also experienced greater warming from the soil during sunny spring days, and their galls were less prone to drying than their elevated counterparts. By winter's end the ground‐level larvae exhibited significantly lower rates of emergence (83.5% vs 93.0%) and reduced potential fecundity (274±11 eggs/female vs 336±17 eggs/female). Models of seasonal energy use indicate that these differences were due to higher metabolic rates in the ground‐level microenvironment due to insulation by snow and warming from the soil, which reduced the energy available for morphological development and egg production in the spring. We conclude that colder winter microenvironments can have a strong positive effect on overwintering ectotherms, particularly those that rely on energy stores accumulated during the autumn to produce eggs in spring. The enhanced reproductive output of insects overwintering in colder microenvironments may be a selective force promoting the evolution of increased cold‐hardiness.
Effects of seed size of wind‐dispersed pines (Pinus) on secondary seed dispersal and the caching behavior of rodents
Authors: Vander Wall Stephen B.
Published: December 2004

Seeds and nuts dispersed by scatter‐hoarding animals are relatively large compared to propagules dispersed by other means. Possible selective forces in the evolution of large seed size include the selectivity of foraging animals and the ways that food‐storing animals treat seeds and nuts after harvest. Treatment by rodents, primarily yellow pine chipmunks (Tamias amoenus), of four species of pine seeds that vary in size was studied in the Carson Range of western Nevada. The pines, lodgepole pine (Pinus contorta, 8.7 mg), ponderosa pine (P. ponderosa, 55 mg), Jeffrey pine (P. jeffreyi, 157 mg), and sugar pine (P. lambertiana, 213 mg), produce winged seeds that are initially wind‐dispersed but are gathered by rodents and cached in the soil. Radioactive scandium‐46 was used to follow the fates of seeds of all fours species placed around three source trees during autumn 1998 to 2000. Rodents gathered the seeds of all four species, but they took fewer of the lodgepole pine seeds and only six lodgepole seed caches (n=2106 total caches) were found during the three years. Among the other three species, number of seeds per cache decreased with increasing seed mass. However, the product of number of seeds per cache and seed mass was similar for all species. Sugar pine seeds were cached slightly deeper than ponderosa and Jeffrey pine seeds. For the species examined, seed size appeared to have had little effect on several other attributes, including mean dispersal distance, substrate choice, and microhabitat choice. Large size decreases wind dispersibility of pine seeds, but secondary dispersal by scatter‐hoarding rodents compensates for poor wind dispersal so that total dispersibility of large‐seeded pines is not compromised.
Determinants of lepidopteran community composition and species diversity in eastern deciduous forests: roles of season, eco‐region and patch size
Authors: Summerville Keith S. , Crist Thomas O.
Published: December 2004

Ecologists have long recognized that factors operating at both local and regional scales influence whether a given species occurs in an ecological community. The relative roles of variables manifested at local and regional scales on community structure, however, remain an unexplored issue for many faunas. To address this question, we compared the community composition and species diversity of forest Lepidoptera between (i) large forest tracts in historically glaciated and unglaciated regions of the eastern deciduous forest in North America, and (ii) large and small forest patches within a highly fragmented forest landscape. Specifically, we used seasonally stratified sampling to test whether regional and local differences in moth communities were related to variation in stand structure and floristic composition. At the local scale, we tested three alternative hypotheses describing the effects of patch size on moth species richness: species impoverishment, species replacement, or species supplementation.

Cluster analysis revealed significant compositional differences in moth communities sampled between (i) early and late seasons, (ii) glaciated and unglaciated forest eco‐regions, and (iii) large and small forest patches. Canonical correspondence analysis suggested that floristic variation at regional scales had a greater role in determining moth community composition than local vegetation or patch‐size effects. Species richness was higher in the glaciated North Central Tillplain, and was attributable to a more diverse herbaceous feeding moth assemblage. Finally, we found evidence that both species impoverishment and species replacement processes structure the moth fauna of small woodlots; the richness of moths with larvae that feed on woody plants decreased with patch area, but herbaceous feeding species increased in diversity in smaller patches. Thus, our results suggest that local and regional differences in moth community structure are mediated by differences in host‐plant resources attributable to regional biogeographic history and local differences in patch size. Because community composition appeared to be more sensitive to environmental variation than species richness, we suggest that monitoring lepidopteran species diversity in forests will not detect significant changes in species composition due to environmental change.
Searching behaviour of the sevenspotted ladybird, Coccinella septempunctata– effects of plant‐plant odour interaction
Authors: Ninkovic Velemir , Pettersson Jan
Published: December 2004

In the present study the main aim was to investigate the odour mechanisms affecting habitat preferences of Coccinella septempunctata (L.). In a field study, the frequency of adult C. septempunctata was higher in barley plots containing high densities of the common weeds Cirsium arvense (L.) Scop. and Elytrigia repens (L.) Nevski. than in control plots with only barley. In olfactometer experiments in the laboratory, adult C. septempunctata showed a significantly more positive response to mixed odours of barley and each of the two weeds than to barley alone. Ladybirds responded differently to barley plants that were previously exposed to volatiles from the two weeds. The E. repens‐exposed barley plant lost its attractivity while the C. arvense‐exposed barley plants maintained attractivity. As no aphids or pollen resources were present in the plots during the experiment, the results show that C. septempunctata responds to the botanical characteristics of the habitat even if no food resources are available. These results strongly suggest that olfactory cues and plant‐plant communication from diversified plant stands can be important mechanisms in predator attraction to sites with a complex botanical diversity.
Using pattern‐oriented modeling for revealing hidden information: a key for reconciling ecological theory and application
Authors: Wiegand Thorsten , Jeltsch Florian , Hanski Ilkka , Grimm Volker
Published: December 2004

We suggest that the conscious use of information that is “hidden” in distinct structures in nature itself and in data extracted from nature (=pattern) during the process of modeling (=pattern‐oriented modeling) can substantially improve models in ecological application and conservation. Observed patterns, such as time‐series patterns and spatial patterns of presence/absence in habitat patches, contain a great deal of data on scales, site‐history, parameters and processes. Use of these data provides criteria for aggregating the biological information in the model, relates the model explicitly to the relevant scales of the system, facilitates the use of helpful techniques of indirect parameter estimation with independent data, and helps detect underlying ecological processes. Additionally, pattern‐oriented models produce comparative predictions that can be tested in the field.  We developed a step‐by‐step protocol for pattern‐oriented modeling and illustrate the potential of this protocol by discussing three pattern‐oriented population models: (1) a population viability analysis for brown bears (Ursusarctos) in northern Spain using time‐series data on females with cubs of the year to adjust unknown model parameters; (2) a savanna model for detecting underlying ecological processes from spatial patterns of tree distribution; and (3) the incidence function model of metapopulation dynamics as an example of process integration and model generalization.  We conclude that using the pattern‐oriented approach to its full potential will require a major paradigm shift in the strategies of modeling and data collection, and we argue that more emphasis must be placed on observing and documenting relevant patterns in addition to attempts to obtain direct estimates of model parameters.
Implication of climate change for the persistence of raptors in arid savanna
Authors: Wichmann Matthias C. , Jeltsch Florian , Dean W. Richard J. , Moloney Kirk A. , Wissel Christian
Published: December 2004

Arid savannas are regarded as one of the ecosystems most likely to be affected by climate change. In these dry conditions, even top predators like raptors are affected by water availability and precipitation. However, few research initiatives have addressed the question of how climate change will affect population dynamics and extinction risk of particular species in arid ecosystems. Here, we use an individual‐oriented modeling approach to conduct experiments on the population dynamics of long lived raptors. We investigate the potential impact of precipitation variation caused by climate change on raptors in arid savanna using the tawny eagle (Aquila rapax) in the southern Kalahari as a case study.

We simulated various modifications of precipitation scenarios predicted for climate change, such as lowered annual precipitation mean, increased inter‐annual variation and increased auto‐correlation in precipitation. We found a high impact of these modifications on extinction risk of tawny eagles, with reduced population persistence in most cases. Decreased mean annual precipitation and increased inter‐annual variation both caused dramatic decreases in population persistence. Increased auto‐correlation in precipitation led only to slightly accelerated extinction of simulated populations. Finally, for various patterns of periodically fluctuating precipitation, we found both increased and decreased population persistence. In summary, our results suggest that the impacts on raptor population dynamics and survival caused by climate change in arid savannas will be great. We emphasize that even if under climate change the mean annual precipitation remains constant but the inter‐annual variation increases the persistence of raptor populations in arid savannas will decrease considerably. This suggests a new dimension of climate change driven impacts on population persistence and consequently on biodiversity. However, more investigations on particular species and/or species groups are needed to increase our understanding of how climate change will impact population dynamics and how this will influence species diversity and biodiversity.
Causes of sex‐biased adult survival in ungulates: sexual size dimorphism, mating tactic or environment harshness?
Authors: Toïgo Carole , Gaillard Jean‐Michel
Published: December 2004

Using both a conventional and a phylogenetic approach, we tested whether sexual size dimorphism, mating tactic and environmental conditions influenced the between‐sex differences in adult survival among 26 populations of polygynous ungulates. As a general rule, male survival was both lower and more variable among species than female survival. Whatever the method we used, sexual size dimorphism had no direct influence on male‐biased mortality. In food‐limited environments, the survival of males relative to that of females was lower than in good environments, suggesting a cost of large size for males facing harsh conditions. On the other hand, the survival of males relative to that of females tended to increase with sexual size dimorphism in good environments, indicating that large size may be profitable for males facing favourable conditions. Lastly, we found that the between‐sex differences in adult survival did not vary with sexual size dimorphism in harem‐holding or tending species, but tended to increase with sexual size dimorphism in territorial species. Our analyses indicate that sexual size dimorphism does not lead directly to a decrease in male survival compared to that of females. Thus, environmental conditions rather than the species considered could shape between‐sex differences in adult survival observed in ungulate populations.
Estimating plant migration rates under habitat loss and fragmentation
Authors: Higgins Steven I. , Lavorel Sandra , Revilla Eloy
Published: December 2004

Changes in the global environment are modifying the geographical locations of habitats suitable for plant growth. The capacity of plants to migrate to sites of suitable environmental quality will strongly influence future distributions of plant diversity. However, it is not well understood how rates of plant migration are influenced by the habitat loss and habitat fragmentation that characterise contemporary landscapes. In this study we develop a model that can predict migration rates in both intact landscapes (potential migration rate) and in fragmented landscapes (realised migration rates). Migration rates in fragmented landscapes might be slower for many reasons. In this study we focus on two, non‐exclusive reasons. First, the processes that move seeds may break down in fragmented landscapes causing seeds to be dispersed shorter distances. Second, in fragmented landscapes some proportion of seeds will not be deposited in habitats suitable for recruitment. We describe the breakdown of dispersal processes as a competing risk between the factors influencing dispersal in intact landscapes and the factors that may disrupt dispersal processes in fragmented landscapes. We show how the parameters that influence dispersal in fragmented landscapes can be estimated, and how these estimates can be used to forecast migration rates using an integrodifference equation (IDE). The forecasts of the IDE described the effects of reduced dispersal distances adequately. However, the IDE produced biased estimates of the effects of a reduction in plant habitat on migration rates. Model analyses showed that, although we can expect realised migration rates to be lower than potential migration rates, we can also expect the sensitivity of migration rate to habitat loss to vary. In addition, simulations showed that the qualitative nature of the responses of migration rate to habitat loss were variable – some model species responded non‐linearly to habitat loss, others responded linearly. While our method provides guidelines for empirical data collection and model parameterisation, we recognise that obtaining these data will be challenging.
Guilds or functional groups: does it matter?
Authors: Blondel Jacques
Published: December 2004

Although most researchers use the terms “guild” and “functional group” more or less synonymously, these two concepts bear different meanings. The guild concept refers primarily to the mechanisms of resource sharing by species in a competitive context whereas the functional groups concept is concerned with how a resource or any other ecological component is processed by different species to provide a specific ecosystem service or function. In many cases but not necessarily all, the two concepts are the two “faces” or “sides” of the same coin: the sharing by species of a similar resource is the guild facet (structural), while the ecosystem processes these species eventually perform through resource exploitation is the functional group facet. The two concepts differ in that competitive relationships within groups of species are not the focus of the functional group approach, exactly as processes or functions are not the focus of the guild approach. A group of species can be considered either as a guild or a functional group depending on the question addressed. Guild and functional group membership is independent of phylogenetic relationships but because species tend to share similar life history traits and adaptations through common evolutionary history, guild and functional group associates are often closely related. The concept of guild has had broader application in animal studies than in plant studies, whereas the reverse is true for the concept of functional group. Recent methodological advances to objectively partition species into guilds and functional groups, taking into consideration the most relevant characters or traits for delineating them, provide the means to construct an operational framework for making in situ and ex situ experiments that are urgently needed for a better understanding of the role of species in ecosystem functioning, especially in relation to global change concerns.
Light dependent shift in the anti‐predator response of a pyralid moth
Authors: Svensson A. Monica , Eklöf Johan , Skals Niels , Rydell Jens
Published: December 2004

Male small china‐mark moth Cataclysta lemnata (Pyralidae) swarming over shallow water show a flight activity that peaks during the afternoon but which sometimes is extended into the night. We exposed wild, naturally flying C. lemnata to simulated predator attacks consisting of a) bursts of ultrasound (26 kHz, simulating a bat) and b) a thrown stick (rapid movement, simulating a small bird), during day and night, respectively. We thus investigated the possibility that these moths are able to switch between defensive strategies as the predator regime shifts from insectivorous birds to bats in the evening. The defensive response differed qualitatively between day and night, as expected, but it was independent of the kind of stimulus. We thus demonstrate a previously unknown flexibility in the defensive strategy of moths.
Growing tall vs growing wide: tree architecture and allometry ofAcacia karrooin forest, savanna, and arid environments
Authors: Archibald Sally , Bond William J.
Published: December 2004

In order to investigate how environmental factors other than light availability affect tree architecture, differences in branching architecture and allometry were analysed in populations ofAcacia karrooHein. from three different environments in South Africa: forests, savannas and arid‐shrublands. Factors such as fire and herbivory have a large effect on tree life history in certain environments and are likely to have selected for trees that have different architectures from those of forest trees, whose major limitation is light assimilation.

Significant differences were found in stem architecture and branching architecture between trees in each environment. Compared with forest trees, trees in savannas had an elongated growth form with small canopy and leaf areas, and tall, thin, unbranched trunks. Trees in arid areas showed opposite trends with wider canopies, and increased lateral branching. Savanna trees had significantly smaller spines than trees in other environments, and both forest and savanna trees showed delayed reproduction.

These differences are probably related to a trade‐off between an architecture geared towards rapid height‐gain and one promoting lateral spread, and can be explained with reference to the different selective pressures in each environment. In forests, vertical and horizontal growth are both important. However, in savannas there is a great pressure for rapid vertical growth to escape fires, while in arid areas a defensive, lateral growth form is selected for.

Savanna trees and arid karoo trees have evolved architectures that are more extreme vertically and laterally than the range of architectures displayed in a forest community.
Nutrient enrichment overwhelms diversity effects in leaf decomposition by stream fungi
Authors: Bärlocher Felix , Corkum Miranda
Published: December 2004

Mass losses of oak leaves were studied in microcosms, where numbers of aquatic hyphomycete species (1–5) and nutrient concentrations (2 levels each of N, P, and Ca) were varied. Species numbers, species identities, N, P and N×P interactions all had significant effects on leaf mass loss, but the magnitude of the effect was greater for N and P than for species numbers. Mass loss in multicultures was greater than predicted from average contributions of the component species in single cultures. This may have been due to sampling effects or niche complementarity.