bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ecological and social constraints on conspecific brood parasitism by nesting female American coots (Fulica americana)
Authors: Lyon Bruce E. 
Published: March 2003

SummaryIn a population of American coots (Fulica americana) breeding in central British Columbia, Canada, some females pursued a reproductive strategy that combined nesting with laying parasitic eggs in the nests of conspecifics. To understand why only one quarter of the nesting females laid parasitically, I examined social and ecological factors that could potentially constrain nesting females from engaging in brood parasitism.Variation among females in each of three prerequisite conditions essential for adaptive parasitism to occur – host availability, access to host nests and a benefit to allocating eggs to parasitism – helps explain why not all females are parasitic.Due to limited spatiotemporal patterns of parasitism, an estimated 23% to 39% of non‐parasitic females completely lacked potential hosts to parasitize when they began breeding. In theory, females could avoid host limitation by delaying breeding to wait for hosts, but timing of breeding comparisons did not support this idea. Relative to the vegetation density on their territories, parasites and non‐parasites began laying eggs on the same date but, due to the time taken to lay parasitic eggs, parasites initiated their own nests later.Brood parasitism was less likely to occur between dyads of females where the potential host female was substantially larger than the potential parasitic female, which suggests that antagonistic social interactions between hosts and parasites may constrain some females from parasitism.Comparisons of two classes of non‐parasitic females, those with and without hosts, revealed smaller clutch sizes in the former, suggesting that limited fecundity may have constrained some of these females from laying parasitic eggs. Additionally, brood parasites were older and laid more total eggs than non‐parasitic females and, among parasites, older females laid more parasitic eggs. Together, these patterns suggest that variation in egg‐laying capacity may determine whether females benefit from allocating eggs to parasitism.The large number of correlates of parasitism indicates that parasitism by nesting females is a conditional reproductive tactic, not part of a stochastic mixed evolutionary stable strategy.
Effects of palm heart harvesting on avian frugivores in the Atlantic rain forest of Brazil
Authors: Galetti Mauro , Aleixo Alexandre 
Published: March 2003

1.  It has been suggested that palm fruits are keystone resources for frugivores in tropical rain forests, but no study has addressed this hypothesis. The effects of the harvesting of a dominant palm tree Euterpe edulis were studied over 2 years in the Atlantic forest of Brazil. 2.  The abundance of 15 large frugivorous birds from five families (Ramphastidae, Cracidae, Cotingidae, Trogonidae and Psittacidae) was estimated using unlimited distance point counts (IPA) and encounter rate. 3.  Although all species studied are known to eat Euterpe fruits, only one Cotingidae (Carpornis melanocephalus) and one Ramphastidae (Ramphastos vitellinus) were negatively affected by the removal of this palm from the forest. 4.  This result indicates that Euterpe palms in the lowland forests do not fulfil the role of keystone species, because they bear ripe fruits during the period of peak overall fruit availability and because birds may switch their diets to other food sources when palms are removed. 5.  Palm‐heart exploitation is not recommended in small forest areas, nor in areas where E. edulis bears fruit during the period of overall fruit scarcity. Only long‐term monitoring can evaluate the responses of the bird and mammal communities to the harvesting process.
Palm heart harvesting in the Brazilian Atlantic forest: changes in industry structure and the illegal trade
Authors: Galetti Mauro , Fernandez JosÉ Carlos 
Published: March 2003

1.  Until the late 1960s, Euterpe edulis was the most important edible palm species in the Brazilian markets. Since then, overharvesting of natural stands and the limited scope of plantations have caused the industry to shift to the multistemmed E. oleracea from the Amazon river estuary. 2.  As a result of the relocation of the industry, the structure of the palm harvesting industry has changed and illegal trade has continued to exploit the remaining natural stands of E. edulis. 3.  It is suggested that, to avoid the total harvesting of E. edulis and to achieve sustainable management of the palm heart, it will be necessary to diversify the local economy, create incentives for small land owners to improve their management practices, while keeping their competitiveness against the illegal trade, create the incentive of new sources of palm hearts and create a ‘green stamping’ for management palms. 4.  Transformation of the illegal structure of the palm heart industry is probably the only solution to avoid the total depletion of the wild stands of E. edulis.
Reproduction and nest behaviour of Tennessee warblers Vermivora peregrina in forests treated with Lepidoptera‐specific insecticides
Authors: Holmes Stephen B. 
Published: March 2003

1.  This study was designed to test the hypothesis that food reductions caused by forest spraying with Lepidoptera‐specific insecticides would affect Tennessee warbler behaviour and reproduction. 2.  Tennessee warbler nests and parental behaviour were monitored in two spray blocks, one treated with Bacillus thuringiensis (Bt) and the other with tebufenozide (MIMIC), and in an untreated control area. 3.  Nestling survival and growth were unaffected by the insecticide treatments. Nests in the treated blocks had smaller clutches, smaller broods and lower hatch rates than nests in the control block, but these differences were not statistically significant. 4.  Nestling diets were similar in the MIMIC and control blocks. 5.  There were slight differences in the behaviour patterns of female Tennessee warblers in the MIMIC and control blocks. MIMIC females spent less time at the nest and more time foraging. 6.  The results of this study suggest that the indirect effects of forest spraying with Lepidoptera‐specific insecticides pose little risk to forest songbirds.
Testing a non‐equilibrium model of rangeland vegetation dynamics in Mongolia
Authors: Fernandez‐Gimenez Maria E. , Allen‐Diaz Barbara 
Published: March 2003

Summary 1. Few studies have tested the applicability of current non‐equilibrium models of rangeland vegetation dynamics to a particular ecosystem, or across a range of systems that might be expected to respond differently to grazing. This study assessed the extent to which the non‐equilibrium persistent (NEP) model of rangeland vegetation dynamics applies to three distinct Mongolian rangeland ecosystems, the desert‐steppe, steppe and mountain‐steppe. 2. Standing biomass, vegetation cover and composition, and species richness and diversity were examined along grazing pressure gradients in ecological zones of differing productivity and interannual variability in precipitation. 3. In the desert‐steppe, biomass, functional group cover, richness and diversity did not vary along grazing pressure gradients, but all vegetation variables except the cover of weedy annuals and unpalatable forbs varied significantly between years. Vegetation dynamics in this zone largely conformed to the NEP model of rangeland dynamics. 4. In the mountain‐steppe, grass and total biomass, total vegetative cover, the cover of grasses, weedy annuals and unpalatable forbs, and richness and diversity varied along grazing pressure gradients. With increasing grazing pressure, grasses decreased and forbs and weedy annuals increased, as the conventional range condition (RC) model predicts. Interannual variation in precipitation influenced total vegetative cover, species and functional group cover, and richness and diversity. 5. In the steppe, forb biomass, grass, forb, unpalatable forb and weedy annual cover, and diversity varied along grazing pressure gradients. Grass biomass and total vegetative cover responded interactively to rainfall and grazing. Forb biomass, grass, forb and weedy annual cover and richness varied between years. Grasses decreased and forbs and weedy annuals increased with increasing grazing pressure, conforming to the RC model. 6. Ecosystem response to rainfall and grazing is complex, and interpretation of the response depends on the specific variables examined. The recent paradigm shift in rangeland science from the RC model to non‐equilibrium models has been embraced with such enthusiasm by some that the concept of non‐equilibrium rangelands may be as much in danger of being misapplied as equilibrium‐based models have been.
Moth assemblages as indicators of environmental quality in remnants of upland Australian rain forest
Authors: Kitching R.L. , Orr A.G. , Thalib L. , Mitchell H. , Hopkins M.S. , Graham A.W. 
Published: March 2003

Summary 1.  Despite great concern about the effects of fragmentation on biodiversity, quantitative studies are still scarce with respect to many major groups and important environments. Well‐studied natural reference sites are few. 2.  Extensive light trapping surveys for moths were thus carried out in both dry and wet seasons in nine remnants of complex notophyll vine forest on basalt on the Atherton Tablelands in tropical north Queensland, Australia. Three sites had never been cleared, three secondary sites had substantial regrowth, and three sites were newly cleared. 3.  A total of 15 632 moths of 835 species was collected, counted and identified. These represent more than 17% of the named Australian fauna of our target families. 4.  A principal components analysis (PCA) indicated clear discrimination among assemblages based on forest type. This discrimination did not differ qualitatively between seasons (although abundance levels of moths did) but the pattern was most evident in the smaller dry season samples. 5.  Taxa, the relative abundance of which increased significantly with disturbance, were the Arctiinae, Amphipyrinae, Catocalinae, Hadeninae, Heliothinae, Hypeninae, Noctuinae, Plusiinae, Hermeniidae and Phycitinae. In contrast, a number of subfamilies showed a marked decrease in relative abundance with increased disturbance, namely Ennominae, Geometrinae, Larentiinae, Oenochrominae, Epipaschiinae, Lymantriidae and Anthelidae. 6.  A weighted sum with importance values based on the eigenvalues associated with each of these taxa derived from the PCA is a powerful predictor set of forest quality. 7.  These differential responses may be explained on the basis of broad known and expected host‐plant patterns. The results show how moth assemblages are powerful indicators of forest disturbance, and should prompt parallel studies elsewhere in the world.
Effects of air pollution on natural enemies of the leaf beetle Melasoma lapponica
Authors: Zvereva Elena L. , Kozlov Mikhail V. 
Published: March 2003

Summary 1.
Air pollution might have differential effects on herbivores and their natural enemies, thus changing population dynamics. Therefore, from 1993 to 1998 we studied mortality caused by parasitoids and predators to the willow‐feeding leaf beetle Melasoma lapponica in the impact zone of the Severonikel nickel–copper smelter (Kola Peninsula, north‐western Russia). 2.
Densities of M. lapponica were very low at clean forest sites (below five beetles per 10‐min count) but higher in polluted areas (10–340 beetles per count). There were, however, variations between study years. 3.  Egg predation, mainly by syrphid larvae and zoophagous bugs, was higher at relatively clean sites (55·3%) than at polluted sites (22·2%). Similarly, predation on larvae by zoophagous bugs and wood ants was higher at clean sites (68·4%) than at polluted sites (32·9%). 4.
In contrast to predation, mortality caused by the parasitoid flies Megaselia opacicornis (Phoridae) and Cleonice nitidiuscula (Tachinidae) was lower at clean sites (12·3%) than at polluted sites (35·3%). Total parasitism levels increased significantly with pollution load. 5.
Total mortality caused by natural enemies was higher at clean sites (93·7%) than at polluted sites (79·4%) due to higher predation rates, which may partly explain increased leaf beetle density within the smelter's impact zone. The effects of predators in clean forests were confirmed by the extinction of adults of M. lapponica introduced to one of the forest sites. 6.  Although some individual sources of mortality appeared to be density dependent (direct or inverse), the joint effect of all natural enemies was not. 7.  Our data show that a decrease in predation can contribute to increased leaf beetle density at polluted sites. However, the overall effects of natural enemies in this case were not sufficient to account for all density variations between sites. To our knowledge this is the first study to assess how pollution affects the partitioning of mortality in herbivorous insects between predators and parasitoids.
Assisted revegetation trials in degraded salt‐marshes
Authors: Handa I.T. , Jefferies R.L. 
Published: March 2003

Summary1. At coastal sites adjacent to the Hudson Bay lowlands, intensive foraging by increasing numbers of lesser snow geeseAnser caerulescens caerulescenshas converted salt‐marsh swards to hypersaline mudflats largely devoid of vegetation. Assisted revegetation trials were undertaken in order to determine the ability of plants to establish in degraded salt‐marsh sediments.2. Soil plugs of the former dominant graminoids,Puccinellia phryganodesandCarex subspathacea, were transplanted into plots of hypersaline bare soil. Some plots were treated with fertilizer and peat mulch to determine if ameliorations enhance plant growth.3. Transplants ofP. phryganodesestablished in degraded sediments, but those treated with fertilizer and peat showed significantly higher growth than those in bare soil after two growing seasons. The ratio of the mean basal area of plants in treated plots compared with bare plots was between 1·7 and 4·0 : 1 at different sites. Transplants ofC. subspathaceadid not establish readily in degraded sediments and no growth enhancement was observed with soil amendments.4. Growth rate and mortality of plants both varied between sites and years, reflecting variation in the frequency of hot, dry weather from late June to early August of each year, and the salinity and water content of soils during that period. The potential for revegetation of mudflats is discussed in the context of the soil degradation processes. Fine‐grain variation in soil conditions presents a major challenge for the restoration of plant assemblages in these coastal marshes.5. The extent of soil degradation and of vegetation loss makes it unlikely that unassisted revegetation will occur at some sites, even in the absence of goose foraging, without erosion of consolidated sediments and the establishment of plant assemblages in fresh unconsolidated sediments.
A spatial model for the successful biological control of Sitona discoideus by Microctonus aethiopoides
Authors: John M. Kean , Barlow Nigel D. 
Published: March 2003

Summary

Here we describe a new model for the biological control of the pest weevil Sitona discoideus by the parasitoid Microctonus aethiopoides. Based on an earlier empirical model, the new model was expanded to include explicit dispersal in a coupled map lattice metapopulation. Model results were consistent with observed data from New Zealand, mimicking successful biological control with a reduction in host density from 1984 to 1991 and a sustained suppression of around 75% thereafter.
The metapopulation model was locally stable because of strong host density‐dependence and a non‐random parasitoid attack function. Metapopulation structure had little effect on the local dynamics, except in transient behaviour such as initial rates of parasitoid spread or the response to a local perturbation. The survival rate of dispersing weevils was nevertheless important in determining overall weevil abundance.
Assuming that the observed low survival rate of weevils during dispersal (around 0·3%) was related to the relative scarcity of its host‐plant in the landscape, the model suggested that local weevil density could substantially increase with an increase in area of crop planted. Although the extent of biological control would be sustained in relative terms, increasing the crop abundance could allow a substantial increase in absolute pest density.
With appropriate adjustment, the model also simulated the unsuccessful biological control observed in Australia. Advancing weevil oviposition in autumn (reflecting warmer autumn temperatures in Australia) and reducing parasitism rates among aestivating weevils (reflecting a lack of summer development of parasitoids in Australia, compared with the atypical development of a proportion in New Zealand), led to an inability of the parasitoid to significantly reduce weevil populations in the model.
This host–parasitoid system is unique for the quality and duration of monitoring conducted before, during and after parasitoid introduction. It also represents one of the few biological control case studies to be thoroughly evaluated through use of empirical models such as the spatial and non‐spatial versions presented here.
The influence of thermal ecology on the distribution of three nymphalid butterflies
Authors: Bryant Simon R. , Thomas Chris D. , Bale Jeffrey S. 
Published: March 2003

Summary

Studies have shown that many adult and immature insects are able to maintain body temperature well above, and often independently of, ambient temperature in the presence of direct solar radiation. They may do so directly by basking, or indirectly via microhabitat choice. The implications for this are often ignored in development models that serve to predict species’ responses to climate change.
To investigate the difference in development times attributable to solar input, field development of Aglais urticae, Inachis io and Polygonia c‐album larvae (Lepidoptera: Nymphalidae) was followed both in a natural open situation and in an artificially shaded environment. Each species completed development more quickly in the open, equivalent to a 20%, 10% and 15% reduction in development time, respectively.
Observed development times in the artificially shaded environment were used to compare the techniques of rate summation and degree‐day modelling. Rate summation models were found to describe development in the shade best for A. urticae and I. io, although a degree‐day model performed best for P. c‐album, possible reasons for which are discussed. The best‐performing models for each species were modified to include larval thermoregulation data, assuming a linear relationship between body and ambient temperatures during the measured sunshine hours each day, and tested against observed development times in the open situation. Times for 50% adult emergence were predicted exactly for A. urticae, and to an accuracy of 1 day for I. io and 5 days for P. c‐album.
The models were tested further using climate data from 128 UK Meteorological Office weather stations across England, Wales and Scotland. Thermoregulation model predictions matched observed UK distribution and voltinism better than predictions made by the standard unmodified models. It was estimated that larval thermoregulation allows A. urticae and I. io populations to persist approximately 200 km further north than would otherwise be possible, and that the extent of bivoltinism may be shifted northwards by around 300 km.
These results have significant implications for predicting the effects of global warming on insects’ geographical ranges, the potential distributions of invasive species, and the phenology and voltinism of introduced biocontrol agents as one component of their likely success.
Birds and wine grapes: foraging activity causes small‐scale damage patterns in single vineyards
Authors: Somers Christopher M. , Morris Ralph D. 
Published: March 2003

Summary

Crop damage caused by pest bird species is an economic problem in agricultural areas world‐wide. Previous research in North America has focused on estimating regional loss of yield for economic purposes, and largely ignored small‐scale variation in crop damage. If a bird depredation problem is perceived, farmers need to know how to identify areas of their farms that are most susceptible to bird damage so that they may focus their deterrent efforts most efficiently.
We developed sensitive sampling and analysis techniques to allow the identification of spatial and temporal patterns in bird damage to wine grapes at the level of single vineyards.
We used visual estimation techniques and novel data collection and management procedures to detect small‐scale spatiotemporal patterns in bird damage to Baco Noir and Vidal (ice‐wine) grape varieties in the St Catharine’s area of Ontario, Canada, during the 1998 and 1999 ripening seasons. We detected three overall trends in study vineyards: (i) bird damage was greatest on the edges of vineyards and decreased with distance towards the centre; (ii) bird damage was vertically stratified in vineyards, with grape clusters near the top of vines sustaining more damage than those close to the ground; and (iii) bird damage increased at specific times during the ripening season.
An exotic species, the European starling, was responsible for most of the crop damage. Starlings foraged by making short forays into vineyards from perches in adjacent vegetation. This kind of foraging behaviour was reflected in the spatial damage patterns measured in our study plots.
We suggest that the data presented here are more useful than estimates of total loss of yield to the managers of individual farms, because they identify the areas of vineyards most susceptible to bird damage. Future field experiments should evaluate the utility of focusing deterrent measures only in the most highly susceptible areas of crop fields. More detailed knowledge of where birds concentrate their foraging efforts, when crops become susceptible, and which species are responsible will allow farmers to focus their deterrent efforts most effectively, while attenuating conflict with non‐offending species.