bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of breeding pond isolation on the spatial and temporal dynamics of pond use by the tungara frog,Physalaemus pustulosus
Authors: Marsh David M. , Fegraus EriC. H. , Harrison Susan 
Published: March 2003

1.Recent theoretical and empirical research has shown that habitat isolation can have strong effects on patterns of abundance and population dynamics of animals. Effects of habitat patch isolation may be particularly strong in taxa such as amphibians, which may have limited dispersal abilities and yet rely on breeding habitats that are variable in space and time.2.We manipulated the distribution of replicated artificial ponds in order to determine the effects of breeding pond isolation on the spatial and temporal dynamics of pond use by the tungara frog (Physalaemus pustulosusLynch), on Barro Colorado Island (BCI), Panama. Our principal objectives were to determine whether pond isolation affects if, when, and how much a pond will be used, and to determine the spatial scale over which isolation effects are likely to be important.3.We used three sets of experimental ponds: ponds placed at distances from 1 to 200 m from active natural breeding sites; ponds placed at these same distances from recently abandoned breeding sites; and ponds placed among different terrestrial habitat types and at least 200 m from any known breeding sites (‘sampling ponds’).4.We found that time to pond use increased with pond isolation, and that ponds near active sites were used more quickly than ponds near abandoned sites. The number of egg masses per pond decreased with pond isolation and was significantly lower near abandoned sites. Ponds near active breeding sites were more likely to be used by tungara frogs than both ponds near abandoned sites and sampling ponds.5.Used sampling ponds were clumped at spatial scales less than 200 m, and mark–recapture data suggest that tungara frogs routinely move between ponds over these distances.6.We conclude that breeding pond isolation is a primary determinant of the temporal and spatial dynamics of pond use by tungara frogs, and can result in spatial patterns in pond use that are independent of pond quality. These isolation effects are, however, unrelated to metapopulation processes, as most turnover in pond use is probably a result of dispersal and breeding site selection by individuals, and not resulting from the extinction of local populations.
Seasonal declines in replacement egg‐layings in a long‐lived, Arctic seabird: costs of late breeding or variation in female quality?
Authors: Hipfner J. Mark , Gaston Anthony J. , Martin Debbie L. , Jones Ian L. 
Published: March 2003

Summary 1. In many species of birds, the proportion of females that relays after losing their first clutch varies. Replacement clutches can make important contributions to an individual's lifetime reproductive success, so the decision on whether or not to relay may have significant consequences for fitness. 2. Many studies report that female birds of ‘high quality’ (e.g. older and more experienced) were more likely to relay following clutch loss, and that the proportion of females that relaid declined as the breeding season progressed. High quality females tend to nest early, and may be less likely to lose their clutches. As a result, it is unclear whether few females relay late in the season because there are prohibitive costs associated with late breeding, or because those females that lay and lose their eggs late are of low quality, and therefore incapable of relaying. 3. We examined the roles of date and quality in causing seasonal declines in replacement layings in Brünnich's guillemot [Uria lomvia (Linnaeus)], a long‐lived, Arctic marine bird that lays a one‐egg clutch. At two low‐Arctic colonies in eastern Canada in 1996 and 1997, the single egg was experimentally removed from samples of early‐laying pairs (presumably those of high quality) at 3‐day intervals beginning on the median laying date and ending 12 days later. 4. In the general population, the proportion of pairs that relaid following natural egg loss declined with the date of loss. In contrast, the proportion of experimental pairs that relaid remained high irrespective of the date their egg was removed. These results support the quality hypothesis, but not the date hypothesis. We conclude that seasonal declines in replacement layings occurred primarily because increasing proportions of low quality females lost eggs as the season advanced. 5. The experimental pairs also suffered no overt reduction in reproductive success as a result of the delay, at least up to the time that their chicks departed to sea. This suggests that timing of breeding had little effect on the immediate success of more capable pairs. 6. Our results may have important implications about the seasonality of low‐Arctic marine environments, and the life histories of birds that inhabit them.
Differential response by males and females to manipulation of partner contribution in the great tit (Parus major)
Authors: Sanz Juan J. , Kranenbarg Sander , Tinbergen Joost M. 
Published: March 2003

1. In birds with bi‐parental care, handicapping is often assumed to decrease the amount of parental care of the handicapped partner. We discuss how handicapping could alter the shape of the handicapped bird's survival–effort curve (theoretical curve relating the survival of a parent to its effort) and show that the optimal response could yield a decrease, no response or even an increase in effort of the handicapped bird. 2. Male or female great tits Parus major (L.) were handicapped during the nestling period by clipping a number of feathers in order to study the effects on parental care and body condition. 3. Handicapped males significantly decreased their feeding rates, while handicapped females did not. Condition of handicapped females significantly deteriorated, while condition of handicapped males did not change during the experiment. Females with a handicapped partner fully compensated for their partner's decrease in work rate, while males with a handicapped partner did not show any compensation and even tended to decrease their feeding rates. 4. Using an inverse optimality approach, we reconstructed the theoretical curve relating the survival of a parent to its effort on the basis of the experimental effects. The handicapped male's survival–effort curve appeared to be slightly steeper than that of handicapped females. This suggests that handicapped males suffer more from an increase in effort than handicapped females.
Reproductive consequences of egg‐laying decisions in snow geese
Authors: Lepage Denis , Gauthier Gilles , Menu Stéphane 
Published: March 2003

Summary1. Even though feeding conditions typically improve over time during the laying period, clutch size decreases over the course of the nesting period in most bird species. We examined whether seasonal decrease in offspring value could explain the seasonal decline in clutch size in arctic‐nesting greater snow geese (Anser caerulescens atlanticusL.).2. Nesting was synchronized within a year, with more than 90% of the nests being initiated within about 8 days. Despite this high synchrony, there was a steep seasonal decline in clutch size in each of the 7 years of the study, from about five eggs in early clutches to three in late ones (−0·20 egg day−1).3. Late parents performed more poorly than early parents in most components of reproductive success. The relationship between laying date and nesting success was curvilinear, early and late nests having a higher failure rate than those initiated near the median. Prefledging survival decreased by about 50% over the season, although the earliest hatched goslings also tended to have a reduced survival. The postfledging survival showed the strongest seasonal decline, as survival probability of late‐hatched birds was about five times lower than in early‐hatched ones.4. Overall reproductive success showed a very steep seasonal decline as the number of young surviving to the first winter was about eight times lower in late‐nesting birds than in early‐nesting ones. Reproductive success declined slightly in the earliest‐nesting birds, suggesting a cost to nesting too early.5. The observed clutch size generally matched the clutch size that yielded the highest reproductive success for each laying date, except in earliest‐nesting birds which should have done better by slightly delaying nesting. Our data suggest that trading off additional eggs for earlier nesting to increase reproductive success is an option in geese. Consequently, the seasonal decline in clutch size may be an adaptive response to seasonally declining survival prospects of offspring.
Food‐supplementation does not override the effect of egg mass on fitness‐related traits of nestling house wrens
Authors: Styrsky John D. , Dobbs Robert C. , Thompson Charles F. 
Published: March 2003

1. Cross‐fostering experiments have shown that egg massper sepositively affects post‐hatching growth and development in passerine birds. In most studies, however, the initial influence of egg mass was not sustained, leading to questions about the importance of egg mass relative to the cumulative effects of environmental factors during the period of post‐hatching care.2. In house wrens,Troglodytes aedonVieillot, evidence from cross‐fostering experiments suggests that food availability mitigates the influence of egg mass on posthatching growth: early in the season, when food was putatively abundant, the initial effect of egg mass was lost as nestlings aged; however, later, when food was putatively scarcer, the effect of egg mass persisted until nestlings left the nest.3. We tested the hypothesis that abundant food for provisioning nestlings can decouple the relationship between fitness‐related traits of nestlings and the mass of the eggs from which they hatch (‘egg‐mass override hypothesis’) by providing daily mealworm supplements to broods of house wrens.4. The food supplements did not increase final nestling mass, final nestling tarsus length, growth rate, or survival until nest‐leaving in late‐season broods, when the hypothesis of food limitation predicts that there should be such an effect. Instead, the food supplements significantly, but only slightly, increased final nestling mass in early‐season broods, when food is putatively abundant.5. The effect of the food supplements on final nestling mass was independent of egg mass. Nestling survival in early‐season broods, and final nestling mass and tarsus length in both early and late‐season broods significantly increased with increasing egg mass in both experimental and control broods.6. We propose that food was not limiting during the course of the experiments and that final nestling mass and tarsus length remained positively related to egg mass because nestling growth and development in house wrens is ‘predetermined’ by some component or property of eggs that covaries with egg mass.
The effect of helpers on reproductive success in the laughing kookaburra
Authors: Legge Sarah 
Published: March 2003

1. In co‐operatively breeding birds and mammals that live in family groups, helpers may gain indirect fitness benefits by increasing the number of breeding attempts in a season, by increasing the success of each nesting attempt, and by increasing the survivorship of related breeders. 2. The effects of helpers were examined in an analysis of reproductive success in the laughing kookaburra (Dacelo novaeguineae), where a monogamously breeding pair is assisted by offspring of both sexes. 3. Helpers could not increase the number of attempts in a season, because kookaburras are single‐brooded. 4. In a paired analysis controlling for pair and territory quality, increases in group size were not matched by increases in the number or weight of fledglings in each breeding attempt, even though brood reduction was the major source of productivity loss. This concurs with previous results showing that group size does not affect overall provisioning levels to broods, because all group members reduced their provisioning effort as group size increased. 5. Because kookaburras prefer to reduce workloads during breeding rather than raise larger broods, the costs of caring for young must be high. Thus breeders with helpers may enjoy energetic savings and enhanced survivorship. 6. Helpers had different effects on nest success depending on their sex. Whereas male helpers had a neutral effect on fledging success and fledgling weight, additional female helpers reduced fledging success. Females are relatively poor helpers, and other group members may not properly compensate for the female's ‘inadequate’ help. 7. High‐quality kookaburra pairs, or pairs on good territories, were more likely to be in larger groups because they produced more potential recruits for their groups than relatively ‘poor’ performers. This was demonstrated by comparing the results of the paired comparisons with those of a correlational analysis that showed that in groups of two to six birds, group size was positively correlated with fledging success and fledgling weight (which affects the probability of juvenile survival). 8. However, unusually large groups of seven or more birds suffered drastically reduced nest success because eggs were damaged during incubation.
A quantitative analysis of fishing impacts on shelf‐sea benthos
Authors: Collie Jeremy S. , Hall Stephen J. , Kaiser Michel J. , Poiner Ian R. 
Published: March 2003

Summary 1. The effects of towed bottom‐fishing gear on benthic communities is the subject of heated debate, but the generality of trawl effects with respect to gear and habitat types is poorly understood. To address this deficiency we undertook a meta‐analysis of 39 published fishing impact studies. 2. Our analysis shows that inter‐tidal dredging and scallop dredging have the greatest initial effects on benthic biota, while trawling has less effect. Fauna in stable gravel, mud and biogenic habitats are more adversely affected than those in less consolidated coarse sediments. 3. Recovery rate appears most rapid in these less physically stable habitats, which are generally inhabited by more opportunistic species. However, defined areas that are fished in excess of three times per year (as occurs in parts of the North Sea and Georges Bank) are likely to be maintained in a permanently altered state. 4. We conclude that intuition about how fishing ought to affect benthic communities is generally supported, but that there are substantial gaps in the available data, which urgently need to be filled. In particular, data on impacts and recovery of epifaunal structure‐forming benthic communities are badly needed.
Size matters: competition between male and female great tit offspring
Authors: Oddie Kate R. 
Published: March 2003

Summary 1. Studies of sex allocation in birds have traditionally centred on Fisher's (1930) theory of equal parental investment in male and female offspring. They concentrate particularly on sexually dimorphic species, where costs of rearing offspring are assumed to vary between male and female young because of body size differences. 2. Higher mortality of the larger sex (males), particularly in poorer conditions, is expected to result in female‐biased sex ratios in the great tit, Parus major. Several studies have found the contrary, reporting male‐biased fledging and recruiting sex ratios when conditions are poor. One reason why this may be the case is that males can gain more food resources than their sisters because of the competitive advantage afforded by their larger size. They may thus suffer less mortality in the nest or fledge in better condition, thereby enhancing their survival prospects. 3. This study investigates the importance of size in competitive interactions between nestlings of different sexes. A cross‐fostering design was employed to create broods of mixed size through swapping half a brood of 2‐day‐old ‘small’ and half a brood of 4‐day‐old ‘large’ nestlings. Nestling morphometrics and mortality were measured during the nestling period. Nestlings were sexed by PCR amplification of sex‐linked genes. To test for a male advantage in competitive environments, size and mortality measures were compared between ‘small’ males and females, and ‘large’ males and females (i.e. the interaction term ‘size treatment’ and ‘sex’). 4. There was greater sexual dimorphism between small nestlings than large nestlings at fledging. This is interpreted as revealing enhanced competitive ability of male offspring under stressful conditions. Offspring from the ‘large’ group suffered lower mortality, but there was no difference in mortality according to sex, and no significant size*sex interaction. Similarly, no difference in recruitment was found, although this may be due to the small overall proportion of birds recruiting (3·1%). 5. The study suggests that male biased fledging/recruitment sex ratios in great tits may be explained by enhanced competitive ability of male nestlings in poor rearing environments.
Trawling disturbance can modify benthic production processes
Authors: Jennings Simon , Dinmore Tracy A. , Duplisea Daniel E. , Warr Karema J. , Lancaster John E. 
Published: March 2003

Summary Trawling disturbance has wide‐ranging impacts on the marine environment and is well known to modify benthic habitat and community structure. This has led to speculation about the positive and negative impacts of trawling on ecosystem processes such as production. Existing theory suggests that frequent trawling disturbance may lead to the proliferation of smaller benthic species, with faster life histories, because they can withstand the mortality imposed by trawling and benefit from reduced competition or predation as populations of larger species are depleted. Since smaller species are more productive, trawling disturbance may ‘farm the sea’, with knock‐on benefits for consumers, including fish populations. We conducted the first large‐scale studies of trawling effects on benthic production across quantified gradients of trawling disturbance on real fishing grounds in two regions (Silver Pit and Hills) of the North Sea. There were 27‐ and 10‐fold differences in levels of beam trawl disturbance among the Silver Pit and Hills sites, respectively. Size structure was described using normalized size‐spectra, and the slopes and intercepts of these spectra were related to levels of trawling disturbance. Production was estimated from the size spectra, using a new allometric relationship between body mass and the production to biomass (P:B) ratio of marine invertebrates. The general validity of the relationship was confirmed using a phylogenetic comparative approach. In the Silver Pit region, trawling led to significant decreases in infaunal biomass and production. The abundance of larger individuals was depleted more than smaller ones, as reflected by the positive relationship between the slope of the normalized size spectra and trawling disturbance. The effects of trawling disturbance were not significant in the epifaunal community. In the Hills region, where the range of trawling disturbance was lower, trawling disturbance did not have significant effects on biomass or production. In the Silver Pit, relative infaunal production (production per unit biomass) rose with increased trawling disturbance. This was attributable largely to the dominance of smaller animals in the disturbed communities. The increase in relative production did not compensate for the loss of total production that resulted from the depletion of large individuals. There was some evidence for the proliferation of small polychaetes at moderate levels of disturbance, but at higher levels of disturbance their biomass and production fell. We conclude that reported increases in the biomass and production of small infaunal invertebrates in the North Sea are attributable largely to recent increases in primary production that were driven by climate change, and not to the effects of trawling disturbance.
Variation in survivorship of a migratory songbird throughout its annual cycle
Authors: Sillett T. Scott , Holmes Richard T. 
Published: March 2003

SummaryDemographic data from both breeding and non‐breeding periods are needed to manage populations of migratory birds, many of which are declining in abundance and are of conservation concern. Although habitat associations, and to a lesser extent, reproductive biology, are known for many migratory species, few studies have measured survival rates of these birds at different parts of their annual cycle.Cormack–Jolly–Seber models and Akaike’s information criterion model selection were used to investigate seasonal variation in survival of a Nearctic – Neotropical migrant songbird, the black‐throated blue warbler,Dendroica caerulescens. Seasonal and annual survival were estimated from resightings of colour‐ringed individuals on breeding grounds in New Hampshire, USA from 1986 to 2000 and on winter quarters in Jamaica, West Indies from 1986 to 1999. Warblers were studied each year during the May–August breeding period in New Hampshire and during the October–March overwinter period in Jamaica.In New Hampshire, males had higher annual survival (0·51 ± 0·03) and recapture probabilities (0·93 ± 0·03) than did females (survival: 0·40 ± 0·04; recapture: 0·87 ± 0·06). In Jamaica, annual survival (0·43 ± 0·03) and recapture (0·95 ± 0·04) probabilities did not differ between sexes. Annual survival and recapture probabilities of young birds (i.e. yearlings in New Hampshire and hatch‐year birds in Jamaica) did not differ from adults, indicating that from the time hatch‐year individuals acquire territories on winter quarters in mid‐October, they survive as well as adults within the same habitat.Monthly survival probabilities during the summer (May–August) and winter (October–March) stationary periods were high: 1·0 for males in New Hampshire, and 0·99 ± 0·01 for males in Jamaica and for females in both locations.These annual and seasonal survival estimates were used to calculate warbler survival for the migratory periods. Monthly survival probability during migration ranged from 0·77 to 0·81 ± 0·02. Thus, apparent mortality rates were at least 15 times higher during migration compared to that in the stationary periods, and more than 85% of apparent annual mortality ofD. caerulescensoccurred during migration.Additional data from multiple species, especially measures of habitat‐specific demography and dispersal, will improve our understanding of the relative impacts of the breeding, migratory, and winter periods on population dynamics of migratory birds and thus enhance future conservation efforts.