bluuebunny/crossref_metadata_2025 huggingface dataset:
Abundances of red fox and pine marten in relation to the composition of boreal forest landscapes
Authors: KURKI SAMI , NIKULA ARI , HELLE PEKKA , LINDÉN HARTO
Published: March 2003

The effects of human‐caused fragmentation of boreal forest on the abundance of red fox Vulpes vulpes L. and pine marten Martes martes L. were studied by combining the Finnish wildlife‐triangle snow‐track data (1990–94) with land‐use and forest resources data employing the GIS. Two study areas (each 45 000 km2) located in northern and southern Finland were selected for the investigation.

The extent of landscape that best explained predator abundance (tracks per 10 km 24 h−1) was the same (about 100 km2) in both species and study areas.

The decreasing proportion of older forest and the increasing proportions of young forest and agricultural land in the landscape positively affected track density of red fox. The relationship between agricultural land and fox abundance, however, was characterized by a convex curve peaking at 20–30% of agricultural land. With the habitat classification used, landscape composition explained 26% and 11% of the spatial variation in fox abundance in the northern and southern study area, respectively.

The relationship between landscape composition and pine marten abundance was not as clear as in that of red fox. Landscape composition explained 10% and 6% of spatial variation in pine marten abundance in the northern and southern study area, respectively. In both areas a positive impact occurred with the increasing proposition of young forest in the landscape, but in the northern area the negative effect of increasing proportion of agricultural land was dominant.

The abundances of red fox and pine marten were not negatively correlated, indicating that competition or intraguild predation by red fox do not determine abundance of pine marten on a landscape scale.

A general increase in predation pressure by generalist predators in fragmented forest landscapes has been an intensively discussed conservation problem during recent years. We conclude that the red fox is a species potentially able to cause elevated predation pressure in boreal landscapes fragmented by human activities, but that the evidence against the pine marten is weaker.
Senescence in a short‐lived migratory bird: age‐dependent morphology, migration, reproduction and parasitism
Authors: Møller A. P. , DE Lope F.
Published: March 2003

1. Senescence reflects age‐dependent changes in residual reproductive value. Annual survival rates of the barn swallowHirundo rusticaL. increased from 1‐ to 2‐year‐old individuals, but decreased among 5 years old or older individuals. Estimates of age‐dependent reproductive value showed a similar pattern.

2.Longitudinal data from two long‐term population studies were used to test whether a number of different measures of performance (condition‐dependent morphological traits, migratory performance, reproductive success, intensity of parasitism) changed among individuals when reaching old age.

3.The length of the outermost tail feathers (a secondary sexual character) decreased among old individuals, while two measures of individual developmental instability increased with age. Migratory performance decreased in old barn swallows as reflected by a delay in spring arrival at the breeding grounds. Reproductive performance measured as seasonal reproductive success decreased with age. The intensity of infestations with an haematophagous mite and a mallophagous ectoparasite increased among old barn swallows.

4.These results suggest that the condition‐dependent secondary sexual character, developmental stability, and measures of migratory and reproductive performance deteriorated, and the frequency of parasitism increased among old individuals. Ageing was thus associated with a general deterioration of performance.
Shaping the body mass distribution of Passeriformes: habitat use and body mass are evolutionarily and ecologically related
Authors: Polo Vicente , Carrascal Luis M.
Published: March 2003

1.The effect of habitat structure on the distribution of the number of species by body size classes was analysed for 277 Passeriformes of the Western Palearctic.

2.The evolutionary history of the group accounted for 68% of the interspecific variation in body mass (estimated with the phylogenetic autoregressive method). The phylogenetic effect decreased from the most recent taxonomic level towards the earlier phases of evolutionary history. In a more fine‐grained study with a subset of 55 passerine species living in central Spain, phylogeny explained significant proportions of the interspecific variation in body mass (62%), habitat use (foraging on the ground vs. foraging in the foliage of scrub/trees; 27%) and structural complexity of preferred habitats (12%).

3.Throughout the evolutionary history there has been a considerable concentration of species around a body mass of 10–40 g (increase in kurtosis), and species with greater body masses have also appeared (increase in skewness).

4.When the effect of evolutionary history on present‐day variation in body mass was removed (specific component of the phylogenetic autoregressive method), the distributions of body masses changed with the structural complexity of preferred habitats: species from woodland habitats were lighter (mainly because of the large frequency of small‐sized species) and their body masses were less concentrated around the modal class than in species from open‐country habitats. Results for the phylogenetic component (attributable to the phylogenetic relatedness of the species) were similar to those of the specific component.

5.Habitat use (i.e. the use of foraging substrata) was strongly correlated with body mass in a subset of 55 species living in central Spain: species foraging on the ground were heavier than those foraging in foliage and small branches of scrub/trees. This result was significant with both specific and phylogenetic components. Habitat use and structural complexity of preferred habitats were significantly correlated using both the specific and the phylogenetic components: species that mainly forage on the ground are mainly open‐country species, while species that forage in pliable and slender substrata have mainly woodland habitats. Structural complexity of preferred habitats was negatively related to body mass, although this correlation was only significant using phylogenetic residuals (specific component).

6.These results show that the evolutionary history of Western Palearctic Passeriformes has not produced neutral variation in body mass with respect to habitat preferences and habitat use.
Rodent post‐dispersal seed predation in deciduous woodland: predator response to absolute and relative abundance of prey
Authors: Hulme Philip. E.. , Hunt Melanie. K..
Published: March 2003

1. The response of post‐dispersal seed predators to changes in the absolute and relative abundance of seeds of two tree species: ash (Fraxinus excelsior) and wych elm (Ulmus glabra) was studied in seminatural woodland in County Durham, UK.

2. Analysis examined two components of seed predation: seed encounter (the probability of at least one seed being removed) and seed exploitation (the proportion of seeds removed once encountered). Exclosure studies identified small mammals, particularly the woodmouse (Apodemus sylvaticus) as the principal post‐dispersal seed predators and revealed a marked preference (almost four‐fold difference in encounter) for seeds of Ulmus over Fraxinus.

3. For both Fraxinus and Ulmus, a linear regression model described the relationship between seed density and the number of seeds removed by rodents more successfully than non‐linear models. These relationships were maintained whether the species were presented singly or together with neither the slopes of Fraxinus or Ulmus changing significantly. These results indicate that, over the range of seed densities used, rodents consumed a constant proportion of seeds irrespective of seed density or frequency. The high rates of exploitation for Ulmus seeds suggests the slope of the relationship primarily reflects rates of encounter, whereas for Fraxinus it is a result of both low encounter and exploitation.

4. Linear regression identified seed removal by rodents to be frequency‐independent both over the woodland as a whole and within each of six micro‐habitats. This appeared to be a result of the marked preference for Ulmus over Fraxinus which was not reversed even when Ulmus was rare. Frequency‐dependent seed predation by rodents is predicted to be most likely when both prey have similar low palatabilities.

5. When encountered by rodents, patches of Ulmus seeds were exploited almost completely, irrespective of seed density or frequency which suggests rodents have the potential to cause local extinction of Ulmus seed populations. In contrast, the lower rates of encounter and exploitation of Fraxinus seeds implies ample opportunities for prey escape.
Numerical and functional responses in generalist predators: hen harriers and peregrines on Scottish grouse moors
Authors: Redpath Stephen M. , Thirgood Simon J.
Published: March 2003

1. The functional and numerical responses of two generalist raptors (hen harrier and peregrine) were studied on one moor for 6 years and on five other moors for 5 years.

2. Neither species showed numerical responses to grouse abundance. Harrier densities were highest in areas and years where their small prey (meadow pipits and small mammals) were most abundant. Peregrine densities were highest on southern study moors, probably in association with high abundance of racing pigeons.

3. For harriers preying on grouse chicks, the available data fitted a sigmoidal or type III functional response. Peregrines showed a type II response to adult grouse densities around eyries.

4. The proportion of grouse chicks taken by harriers was estimated to have been highest at densities of 67 chicks km–2 (equivalent to a mean of about 12 broods km–2). The proportion of adult grouse taken by peregrines appeared to be inversely density dependent, such that an increasing proportion of grouse was taken at grouse densities below 20 km–2.

5. In the absence of persecution, the impact of harriers on grouse populations is most likely to be greatest on moors where alternative prey and thus harriers are abundant. The question of whether harriers may dampen grouse population cycles at low grouse density is discussed.
A fixed energetic ceiling to parental effort in the great tit?
Authors: Tinbergen J. M. , Verhulst S.
Published: March 2003

1. To elucidate the links between avian brood size, parental effort and parental investment, we measured daily energy expenditure (DEEfem), condition (residuals of mass on tarsus) and feeding rate in female great tits Parus major L. rearing broods in which the number of young was either reduced, unmanipulated or enlarged.

2. Female condition was negatively correlated with manipulation when measured at the nestling age of 8 days (measured during the day), which suggests a shift in allocation from self‐feeding to chick‐feeding. However, there was no detectable manipulation effect on condition measured at the nestling age of 12 days (measured during the night). Either female condition was only affected by manipulation in the early nestling phase or the females adjusted their diurnal mass trajectory in response to brood size manipulation. More detailed data are required to verify this point. There were no indications of a fitness cost associated with the condition during the day, but condition at night was positively related to winter survival. Since manipulation only affected condition during the day, there was no link between manipulation and winter survival.

3. The duration of the working day was not affected by manipulation and female feeding rate tended to flatten off with manipulated brood size. Similarly, brood reduction resulted in a lower DEEfem, whilst brood enlargement had no effect. This suggests that females worked at an energetic ceiling when rearing an unmanipulated brood. However, the level of this ‘ceiling’ in DEEfem was not fixed: it differed between years. This leads us to conclude that the observed ceiling was imposed by extrinsic factors (e.g. available foraging time) and not by an intrinsic factor such as maximum energy assimilation rate. We hypothesize that time limitation was the cause for the observed ceiling in energy expenditure and that the annual variation in the level of this ceiling was due to annual variation in ambient temperature.

4. A cost of reproduction was previously demonstrated in this population: brood enlargement caused a reduction in the incidence of second clutches. However, since DEEfem did not differ between control and enlarged broods, we judge it unlikely that daily energy expenditure is a general predictor for parental investment.
Factors affecting maternal care in an income breeder, the European roe deer
Authors: Andersen Reidar , Gaillard Jean‐Michel , Linnell John D. C. , Duncan Patrick
Published: March 2003

1. Maternal care is a major component of demographic tactics in mammals. In ungulates most work has been done on capital breeders (e.g. bighorn sheep), which rely heavily on body reserves to raise their young. Roe deer, in contrast, are close to the income breeder end of the capital–income breeder continuum, and show high levels of maternal care.

2. The aim of this study was to explore the factors determining the level of maternal care in roe deer, in particular the effects of maternal body weight, mother's parity, litter size and year of birth on the amount of prenatal care (i.e. the average mass of an offspring multiplied by the number of offspring) and postnatal care (i.e. the average growth rate of the offspring multiplied by their number). The study was carried out on a captive population of roe deer fedad libitum, and in a wild population.

3. In both populations prenatal care increased with increasing maternal body weight. In the population fedad libitumthis effect was found in light females only (< 22 kg); in the wild population the positive relationship between maternal body weight and prenatal care was entirely accounted for by variation in litter size (i.e. heaviest females produced larger litters) and density (i.e. females were lightest in years with high population density). Parity did not affect prenatal care.

4. In 14 females fedad libitumthere was no relationship between postnatal care and maternal body weight. Multiparous females had higher levels of postnatal care. In contrast, 20 wild females showed a positive relationship between postnatal care and maternal body weight, and only litter size affected the level of postnatal care.

5. Even after accounting for the confounding effects of maternal body weight, parity, litter size and population density, we found no trade‐off between pre‐ and postnatal care in any of the two populations. The conditions under which the pattern of maternal care could impose trade‐offs that affect the individual offspring are discussed.
Mechanisms of population regulation in the fire antSolenopsis invicta: an experimental study
Authors: Adams Eldridge S. , Tschinkel Walter R.
Published: March 2003

We tested for density‐dependent regulation of biomass in a population of the fire antSolenopsis invictaand examined the mechanisms of population recovery following replicated colony removals.

 All colonies were killed within the core area (1018 m2) of six plots, while six additional plots served as undisturbed controls. Over the next 5 years, colonies were mapped several times per year and the biomass of each colony was estimated from the volume of the nest‐mound.

 The average biomass and density of colonies within the removal areas gradually converged on those of control plots and were no longer detectably different after two years. Thereafter, ant biomass on experimental and control plots showed nearly identical seasonal and yearly fluctuations.

Territories of colonies surrounding the removal areas rapidly expanded following the deaths of neighbours, while average territory size on control plots showed little short‐term change.

 Significantly more new colonies were established within core areas of experimental plots than within core areas of control plots during the first year following removals.

 The per‐colony probability of movement and the net influx of colony biomass were significantly higher in central regions of the experimental plots than in control plots during the first year. The directions of colony movements were clustered towards the centres of experimental plots in the first 2 years, but did not show significant directional trends on control plots.

 In all 5 years of the study, annual mortality rates were lower for larger colonies, but the size‐specific risk of mortality was not significantly affected by the experimental removal of competitors.

 The growth rates of colonies, adjusted for initial size, were significantly higher in central regions of experimental plots than in control plots during the first two years of the study. In all years, colony growth rates declined with increasing colony size.

 These results indicate that populations ofS. invictaare regulated by competition among neighbouring colonies. Due to large intraspecific variation in colony size, the dynamics of ant populations are described more accurately by measures of total ant biomass than by colony density alone.
Post‐fledging care, philopatry and recruitment in brown thornbills
Authors: Green David J. , Cockburn Andrew
Published: March 2003

We describe patterns of post‐fledging care, dispersal and recruitment in four cohorts of brown thornbillsAcanthiza pusilla. We examine what factors influence post‐fledging survival and determine how post‐fledging care and the timing of dispersal influence the probability of recruitment in this small, pair breeding, Australian passerine.

 Fledgling thornbills were dependent on their parents for approximately 6 weeks. Male fledglings were more likely than female fledglings to survive until independence. For both sexes, the probability of reaching independence increased as nestling weight increased and was higher for nestlings that fledged later in the season.

 The timing of dispersal by juvenile thornbills was bimodal. Juveniles either dispersed by the end of the breeding season or remained on their natal territory into the autumn and winter. Juveniles that delayed dispersal were four times more likely to recruit into the local breeding population than juveniles that dispersed early.

 Delayed dispersal was advantageous because individuals that remained on their natal territory suffered little mortality and tended to disperse only when a local vacancy was available. Consequently, the risk of mortality associated with obtaining a breeding vacancy using this dispersal strategy was low.

 Males, the more philopatric sex, were far more likely than females to delay dispersal. Despite the apparent advantages of prolonged natal philopatry, however, only 54% of pairs that raised male fledglings to independence had sons that postponed dispersal, and most of these philopatric sons gained vacancies before their parents bred again. Consequently, few sons have the opportunity to help their parents. Constraints on delayed dispersal therefore appear to play a major role in the evolution of pair‐breeding in the brown thornbill.
Life‐history strategies in parasitoid wasps: a comparative analysis of ‘ovigeny’
Authors: Jervis Mark A. , Heimpel George E. , Ferns Peter N. , Harvey Jeffrey A. , Kidd Neil A. C.
Published: March 2003

Ecologists concerned with life‐history strategies of parasitoid wasps have recently focused on interspecific variation in the fraction of the maximum potential lifetime egg complement that is mature when the female emerges into the environment. Species that have all of this complement mature upon emergence are termed ‘pro‐ovigenic’, while those that do not are termed ‘synovigenic’. We document and quantify the diversity of egg maturation patterns among 638 species of parasitoid wasps from 28 families.

 We test a series of hypotheses concerning variation in ‘ovigeny’ and likely life‐history correlates by devising a quantitative index – the proportion of the maximum potential lifetime complement that is mature upon female emergence.

 Synovigeny, which we define as emerging with at least some immature eggs, was found to be by far the predominant egg maturation pattern (98·12% of species). Even allowing for some taxonomic bias in our sample of species, pro‐ovigeny is rare among parasitoid wasps.

 There is strong evidence for a predicted continuum in ovigeny index among parasitoid wasps, from pro‐ovigenic (ovigeny index = 1) to extremely synovigenic species (ovigeny index = 0).

 As predicted, synovigenic species are longer‐lived than pro‐ovigenic ones, and ovigeny index and life span are negatively correlated across parasitoid taxa, suggesting a life span cost of concentrating reproductive effort early in adult life.

 There is equivocal evidence that host feeding (i.e. consumption of host haemolymph and/or tissues by adult wasps) is confined to synovigenic parasitoid wasps. It is also not certain from our analyses whether host feeding is associated with a relatively low ovigeny index.

 As predicted, egg resorption capability is concentrated among producers of yolk‐rich eggs. Also, the hypothesis that it is associated with a tendency towards a low ovigeny index is supported. Parasitoid species that produce yolk‐rich eggs also exhibit a lower ovigeny index than species that produce yolk‐deficient eggs.

 Ovigeny index appears to be linked to parasitoid development mode (koinobiosis–idiobiosis).

 We conclude that ‘ovigeny’ is a concept applicable to insects generally.
The effects of dispersal mode on the spatial distribution patterns of intertidal molluscs
Authors: Johnson M. P. , Allcock A. L. , Pye S. E. , Chambers S. J. , Fitton D. M.
Published: March 2003

As many species of marine benthic invertebrates have a limited capacity for movement as adults, dispersal mode is often considered as a determinant of geographical ranges, genetic structure and evolutionary history. Species that reproduce without a larval stage can only disperse by floating or rafting. It is proposed that the colonization processes associated with such direct developing species result in spatial distributions that show relatively greater fine scale patchiness than the distributions of species with a larval dispersal stage. This hypothesis was tested by collecting molluscs at different spatial scales in the Isle of Man.

Spatial distribution patterns supported the predictions based on dispersal mode. Estimated variance components for species with larval dispersal suggested that the majority of the spatial variation was associated with variation between shores. In comparison, there was relatively more variability within shores for abundance counts of species with direct development.

Multivariate analyses reflected the univariate results. An assemblage of direct developers provided a better discrimination between sites (100 m separation) but the group of species with larval dispersal gave a clearer separation of shores (separated by several km).

The fine scale spatial structure of direct developing species was reflected in higher average species diversity within quadrats. Species richness also reflected dispersal mode, with a higher fraction of the regional species pool present for direct developers in comparison to species with larval dispersal. This may reflect the improved local persistence of taxa that avoid the larval dispersal stage.
Mechanisms of functional response and resource exploitation in browsing roe deer
Authors: Illius Andrew W. , Duncan Patrick , Richard Caroline , Mesochina Pascal
Published: March 2003

The functional responses of roe deer were examined using 11 plant species. A technique to discriminate between encounter‐ and handling‐limited processes was used, and it can be concluded that the functional response applicable to patch browsing by roe deer is governed not by the rate of encounter but by the rate of oral processing.

The large differences between plant species were due to variations in both parameters of the functional response: h
, the time lost in biting, and
R
max , the maximum processing rate. Removing the thorns from three of the species affected these parameters differently, according to the size and density of thorns.

Animals took larger bites from larger patches (branches), and bite mass declined as patch exploitation progressed, implying that animals were selecting the larger items to eat first. It was demonstrated experimentally that depletion of the larger bites does occur first, and it was concluded that prey selection is an important component of herbivore foraging behaviour.

The gain curves for deer feeding on the different plant species are calculated as being virtually linear. Patch depression did not, in general, occur because increasing bite rate compensated for declining bite mass. Our mechanistic approach is contrasted with other approaches to describing the gain curve in the literature.

A priori and empirical grounds are presented for rejecting the hypothesis that resource exploitation by browsing mammals is governed by optimal patch use. Diet optimization, involving a trade‐off between diet quality and quantity, offers a better explanation of herbivore foraging behaviour.
Predator–prey cycles in an aquatic microcosm: testing hypotheses of mechanism
Authors: Shertzer Kyle W. , Ellner Stephen P. , Fussmann Gregor F. , Hairston Nelson G.
Published: March 2003

Fussmann et al. (2000
) presented a simple mechanistic model to explore predator–prey dynamics of a rotifer species feeding on green algae. Predictions were tested against experimental data from a chemostat system housing the planktonic rotifer
Brachionus calyciflorus
and the green alga
Chlorella vulgaris .

The model accurately predicted qualitative behaviour of the system (extinction, equilibria and limit cycles), but poorly described features of population cycles such as the period and predator–prey phase relationship. These discrepancies indicate that the model lacked some biological mechanism(s) crucial to population cycles.

Here candidate hypotheses for the ‘missing biology’ are quantified as modifications to the existing model and are evaluated for consistency with the chemostat data. The hypotheses are: (1) viability of eggs produced by rotifers increases with food concentration, (2) nutritional value of algae increases with nitrogen availability, (3) algal physiological state varies with the accumulation of toxins in the chemostat and (4) algae evolve in response to predation.

Only Hypothesis 4 is compatible with empirical observations and thus may provide important insight into how prey evolution affects predator–prey dynamics.
Interactions between weaver ants Oecophylla smaragdina, homopterans, trees and lianas in an Australian rain forest canopy
Authors: Blüthgen Nico , Fiedler Konrad
Published: March 2003

Tritrophic interactions between the weaver ant Oecophylla smaragdina (Fabricius) (Hymenoptera: Formicidae), plants and honeydew‐producing trophobionts (Hemiptera: Sternorrhyncha and Auchenorrhyncha, Lepidoptera: Lycaenidae) were studied in a rain forest canopy in Northern Queensland, Australia.

Most commonly attended trophobionts by O. smaragdina
at this study site were Coccidae (
Coccus
sp.,
Milviscutulus
sp.) and Membracidae (
Sextius
sp.), followed by
Toxoptera aurantii
(Aphidae),
Planococcus citri
(Pseudococcidae),
Icerya
sp. (Margarodidae), an unidentified species of Eriococcidae,
Austrotartessus
sp. (Cicadellidae), and lycaenid butterfly larvae (
Anthene seltuttus
,
Arhopala centaurus group).

Most trophobionts were highly polyphagous, and trees and lianas from many plant species and families acted as homopteran hosts. However, lianas were found to play a key role. First, the majority (68%) of aggregation sites was found on lianas, especially on the legumes Entada phaseoloides
and
Caesalpinia traceyi
, and secondly, per capita ant visitation rate (
VR
) at coccoids was significantly higher on lianas compared to trees. In total,
VR to homopterans was 64% higher on lianas.

Sites of ant–homopteran aggregations were regularly replaced by new locations on fresh plant growth. The mean longevity of nests of this polydomous ant species was 131 days, of individual aggregation sites with membracids 54 days and with coccoids 130 days.

Our results suggest that plant‐specific differences in suitability for honeydew production (especially the availability of lianas) and the availability of preferred trophobionts have a strong influence on the vigour of Oecophylla colonies.
Predation by Eurasian sparrowhawks produces density‐dependent mortality of wintering redshanks
Authors: Whitfield D. Philip
Published: March 2003

This study examined annual differences in redshank Tringa totanus winter mortality caused by predation by Eurasian sparrowhawks Accipiter nisus over an 11‐year period at a rocky shore in south‐east Scotland.

Redshank numbers at the beginning of a winter showed no trend over the study period and winter mortality rates also showed no temporal trend. Mean winter mortality through predation by sparrowhawks was 30·6% for juveniles and 5·6% for adults.

The study demonstrated density‐dependent winter mortality in both juvenile and adult redshanks due to predation by sparrowhawks. Wind speed was also positively associated with juvenile winter mortality but had a weaker influence on adult mortality. This apparent influence of wind speed on juvenile mortality was not confirmed by correlations between monthly juvenile mortality and weather variables (minimum temperature, rainfall and wind speed).

Density‐dependent functions differed between adult and juvenile redshanks, consistent with differences in the competitiveness of the two age classes. It is suggested that individual differences in vulnerability to predation arose through differences in individual susceptibility to density‐dependent competition during foraging. Companion studies indicated that as bird density increased more birds were forced to spend more time feeding in an area where risk of predation was high.
Ecological and social constraints on conspecific brood parasitism by nesting female American coots (Fulica americana)
Authors: Lyon Bruce E.
Published: March 2003

In 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

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

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

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

1. 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

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.