bluuebunny/crossref_metadata_2025_split huggingface dataset:
Climate change causes contrasting trends in reproductive performance of planktivorous and piscivorous alcids
Authors: Kitaysky Alexander S. , Golubova Elena G. 
Published: March 2003

Summary 1. Eight years of observations on seabird reproductive success and oceanographic change in Tauyskaya Bay (Okhotsk Sea, north‐western Pacific) were used to evaluate the hypothesis that interannual climate change causes opposite trends in reproductive performances of planktivorous auklets (Aethia cristatella and Cyclorhinchus psittacula) vs. piscivorous puffins (Lunda cirrhata and Fratercula corniculata). 2. The climate change was assessed by examining changes in sea‐surface temperature (SST), time of permanent ice disappearance (ID), wind (WV) and current vectors (CV). Changes in the distribution of zooplankton biomass in the study region were used to assess changes in prey communities. Bird reproductive success was determined as the number of chicks fledged per nest occupied. 3. There were two distinct sets of oceanographic conditions in the study region, as reflected in the SST, ID, WV and CV. Strong northerly winds in the spring produced a late ice disappearance in the study region, whereas easterly winds determined an early ice disappearance. The patterns in ice disappearance were significantly correlated with SST anomalies during the summer. A negative SST anomaly (– 1·2 °C) defined a ‘cold’ regime, whereas a positive SST anomaly ( +  1·2 °C) defined a ‘warm’ regime. 4. Reproductive success of planktivorous auklets was negatively correlated with the SST in the western part of Tauyskaya Bay, whereas reproductive success of piscivorous puffins was positively correlated with the SST. The ‘cold’ season in 1988 was characterized by a strong in‐flow of water masses into the bay area. The ‘warm’ season in 1989 was characterized by well‐mixed warm water inside the bay that were separated from colder water masses outside the bay. Macro‐zooplankton, which were the main prey of planktivorous auklets, were more abundant during the ‘cold’ regime of the ecosystem. Meso‐zooplankton, a potential prey of juvenile pelagic fish, were more abundant during the ‘warm’ regime of the ecosystem. 5. Interannual oceanographic change probably impacts alcid reproductive performances by affecting food accessibility to planktivorous auklets and piscivorous puffins in opposite ways.
Comparative study on the consequences of culling badgers (Meles meles) on biometrics, population dynamics and movement
Authors: Tuyttens F. A. M. , Macdonald D. W. , Rogers L. M. , Cheeseman C. L. , Roddam A. W. 
Published: March 2003

1. Capture–mark–recapture data were used to describe the process of recovery from a typical badger removal operation (BRO) at North Nibley, Gloucestershire, UK, which was carried out as part of the government's strategy to control bovine tuberculosis. Data on biometrics, demographics and movement from this low‐density disturbed population were compared with those of two nearby high‐density undisturbed populations (Wytham Woods and Woodchester Park, UK) in order to study fundamental principles of population dynamics and density‐dependence. 2. Badgers moved more between social groups at North Nibley than in the other study areas, particularly in the immediate aftermath of the removal operation. 3. Recolonization of the vacated habitat occurred in the first instance by young females. 4. Although in the first year after the BRO no cubs had been reared in any of the culled groups, and although the shortage of sexually mature boars may have limited the reproductive output of sows in the following year, the population took only 3 years to recover to its (already lowered) preremoval density. 5. Losses from the adult (and cub) population due to mortality or emigration were smaller at North Nibley than at the other sites. 6. There was much evidence that during 1995 and 1996 density‐dependent effects constrained the reproductive output of the high‐density populations, and some support for the hypothesis that badgers exhibit the non‐linear ‘large mammal’ type of functional response to density. 7. Badgers at North Nibley were younger, heavier and in better condition than badgers at Wytham Woods and Woodchester Park. 8. We argue that the disease dynamics are likely to be different in disturbed compared with undisturbed badger populations, and that this could affect the effectiveness of BROs.
The cost of interspecific competition in two gerbil species
Authors: Abramsky Zvika , Rosenzweig Michael L. , Subach Aziz 
Published: March 2003

Summary

It has been shown that the two common granivorous gerbil species Gerbillus allenbyi and G. pyramidum that coexist in the sand dunes of the Israeli Negev show temporal partitioning in their time of activity. The bigger species, G. pyramidum, aggressively displaces the smaller species from early night‐time. We examined the change in the activity pattern of G. allenbyi in pure and mixed populations in two 1‐ha field enclosures.
We confirmed the temporal pattern reported by Ziv et al. (1993) and Kotler et al. (1993).
We also measured how much energy it takes (in g of millet seeds) to compensate for the costs, associated with interference and exploitation competition, by adding millet seeds to 18 seed trays/enclosure. We added 1, 3, 5, 7 or 9 g of seeds/seed‐tray. In each seed‐tray we mixed the seeds in 2 L of sand.
It took 3–5 g of seeds/seed‐tray (1·8–3 g seeds/day/ha/individual) to completely overcome the competition by G. pyramidum. This is the cost of the interference and exploitation competition from G. pyramidum (in the currency of millet seeds).
The result suggests that there is a trade‐off between interference competition and food to which gerbils respond behaviourally.
A testable linear model for diversity trends in estuaries
Authors: Attrill Martin J. 
Published: March 2003

Summary

In 1934, Adolf Remane constructed a diagram to describe changes in the number of species along a full salinity gradient within the Baltic. Despite fundamental differences in tidal regimes, the Baltic model has been applied directly to estuaries, becoming subsequently the textbook model for estuarine diversity trends.
Despite its ubiquity, the Remane diagram has many inconsistent features, making it unsuitable as a quantitative tool for comparing diversity trends between estuaries, including poor definition of x‐axis (salinity), y‐axis (number of species) and variations in sample location (subtidal/intertidal) than can greatly influence the resulting diversity/salinity relationship. Consequently, diversity trends within and between estuaries remain to be tested robustly.
The major environmental factor influencing the distribution of organisms in estuaries is salinity variation, rather than absolute salinity tolerance as in the Baltic. As salinity range demonstrates a quadratic relationship with mean salinity, an alternative linear model is therefore suggested utilizing mean salinity range at any one point in the estuary (x‐axis) and mean α‐diversity of macroinvertebrates (y‐axis) obtained from subtidal samples to allow comparison with river systems and to minimize salinity variability between interstitial and overlying water.
The model was tested on an extensive subtidal data set from the Thames estuary (salinity 0–35), significant negative linear relationships between salinity range and α‐diversity being apparent for annual and seasonal data sets. Significant models were also possible for both ‘marine’ and ‘freshwater’ halves of the estuary and for meiofauna α‐diversity.
The linear model allows formal, statistical investigation of the differences in diversity trends between estuaries and the development of testable hypotheses on aspects of estuarine diversity, including the causes of the species minimum in estuaries. It also has potential as a management tool enabling the definition of sites of concern that fall below their predicted diversity.
The new model of diversity now requires testing in systems additional to the Thames in order to determine whether this relationship is a macroecological phenomenon or restricted to the test system.
Large‐scale habitat variability, delayed density effects and red deer populations in Norway
Authors: Mysterud Atle , Langvatn Rolf , Yoccoz Nigel G. , Stenseth Nils CHR. 
Published: March 2003

SummaryParallel to the large‐scale changes in land‐use patterns over the last century in Europe, many deer species have expanded their range and increased in density, but the role of habitat changes for their population ecology remains poorly documented.We tested for effects of variability in agricultural (proportion of meadow and density of sheep) and forestry practices (proportion of coniferous and deciduous forest) in 106 municipalities in Norway on body weight of 10 206 female and 15 499 male adult red deer collected over the period 1965–2000.Long‐term temporal changes in body weights may also be due to delayed density effects, either due to that persistent high density of red deer through grazing and browsing may affect vegetation composition (i.e. an effect of cumulative density after present‐day density is controlled for), or that individuals born at high density start to penetrate the population (cohort‐effects). As these effects may be confounding to variability in forestry or agricultural practice, we also test whether cohort and/or cumulative density may affect body weight of red deer.There was a strong negative effect of cohort density, but no effect of cumulative density in the previous 10 years once the cohort effect was accounted for.There was a clear positive effect of proportion of meadow on red deer body weight, while there was no effect of sheep density once the effect of proportion of meadow was adjusted for. Proportion of meadow increased during the study, but most of the variation was between municipalities (i.e. in space).Neither proportional area of coniferous or deciduous forest consistently affected body weight of red deer in Norway.Our study emphasizes the multitude of factors over time and space that affects body weight, and hence demography and population dynamics, of large herbivores.
Heterotroph species extinction, abundance and biomass dynamics in an experimentally fragmented microecosystem
Authors: Gonzalez Andrew , Chaneton Enrique J. 
Published: March 2003

SummarySpecies extinction in fragmented habitats is a non‐random process described by transient, rather than equilibrium dynamics. Therefore, ‘static’ approaches focusing on experimentally established spatial gradients of diversity may fail to capture essential aspects of ecosystem responses to species loss.Here we document temporal changes in microarthropod species abundance, biomass and richness during a community disassembly trajectory following experimental habitat fragmentation of a moss‐based microecosystem.Habitat fragmentation reduced heterotrophic species richness and community biomass in remnant moss fragments. Extinction was biased towards rare species, and thus occurred initially without significant changes in total community abundance and biomass. Eventual reductions in abundance and biomass were found to lag behind observed declines in species richness.The presence of moss‐habitat corridors connecting fragments to a large ‘mainland’ area coupled with an immigration rescue effect maintained microarthropod richness, abundance and biomass within remnant fragments.Our results indicate that both the order of species loss and the dynamics of remnant populations influence the magnitude and timing of ecosystem‐level responses to habitat destruction and isolation.
Larval anurans with synchronous and asynchronous development periods: contrasting responses to water reduction and predator presence
Authors: Lane Simon J. , Mahony Michael J. 
Published: March 2003

Summary

The larvae of pond breeding frogs experience high rates of mortality, predominantly through predation and pond desiccation. We investigated how the tadpoles of two common species of frog respond to these hazards using factorial experiments conducted in a laboratory.
The eastern brown froglet Crinia signifera
Girard spawns in small, highly ephemeral ponds, while the spotted marsh frog
Limnodynastes tasmaniensis
Günther breeds in more permanent water bodies. Prior to our experiments it was known that
C. signifera
siblings develop quickly and reach metamorphosis comparatively synchronously (
c
. 25–35 days), while
L. tasmaniensis
grow and develop more slowly and time to metamorphosis is highly asynchronous (
c . 60–300 days). It was anticipated that these species would have different strategies for coping with declining water and predators.
A separate experiment was conducted for each species. The factors were Hydroperiod (either constant or gradually declining water volume) and Predator (either the presence or absence of a restrained mosquitofish Gambusia holbrookii
Girard). A random block design was used with six replicates for each possible combination of the factors (
N = 24). Each replicate consisted of a 13‐l tub of water containing 20 tadpoles. Newly emerged frogs were transferred to one of 24 vivaria. In the arrangement of the vivaria, we maintained the block design of the experiment.
Crinia signifera tadpoles responded to declining water by accelerating development and so reduced time to metamorphosis. However, the resulting metamorphs were smaller and survival rate in the terrestrial stage was significantly lower. This is a clear demonstration of the benefit and cost of phenotypic plasticity in metamorphic traits.
Limnodynastes tasmaniensis tadpoles experiencing declining water were also smaller at metamorphosis, but there was no evidence that they had reduced the time to metamorphosis compared with those in constant water. Moreover the survival rates of the resulting frogs did not differ. Consequently no adaptive plasticity can be inferred.
The data suggest that L. tasmaniensis has a bet‐hedging strategy in which some siblings develop more quickly at the expense of size, while others take much longer but are bigger at metamorphosis as a result.
Tadpoles of both species showed clear behavioural responses to the presence of the predator. They tended to occupy the non‐predator halves of the tubs in replicates where a mosquitofish was present. Neither species altered development rate in the presence of the predator and there was no detectable impact on survivorship in the terrestrial stage.
Connectance in stream food webs
Authors: Schmid‐Araya Jenny M. , Schmid Peter E. , Robertson Anne , Winterbottom Julie , Gjerløv Charlotte , Hildrew Alan G. 
Published: March 2003

Summary

The properties of food webs are important both in theoretical ecology and environmental management, yet remain elusive. Here, we examined 12 new stream food webs of higher taxonomic resolution and completeness than any previously published data set and combined them with other 10 published stream webs.
Compared with most previously published food webs, these stream communities (containing between 22 and 212 species) had more feeding links per species, a higher fraction of intermediate species (0·78–0·88) and lower fractions of top (0·04–0·09) and ‘basal’ species (0·07–0·15).
The exponent of the log link‐log species relationship (S1·3) differed significantly (ancova: P < 0·001) from the link‐species ‘law’ (S1) and the constant connectance hypothesis (S2). Based on these results, the link scaling law and the constant connectance hypothesis must be rejected for food webs in stream systems.
Connectance was markedly lower than previously reported and decreased with web size. We attribute this to the body‐size disparity of organisms at the top and the bottom of the web, flow disturbance and to the high physical heterogeneity and complexity of the sedimentary habitat. All these may reduce the fraction of possible feeding links that are realized.
Environmental variability, life‐history covariation and cohort effects in the red‐billed choughPyrrhocorax pyrrhocorax
Authors: Reid J. M. , Bignal E. M. , Bignal S. , McCracken D. I. , Monaghan P. 
Published: March 2003

SummaryThe consequences of environmental variability for life‐history evolution are predicted to depend on the pattern of covariation amongst life‐history traits. Using data from a 20‐year study of individually marked red‐billed choughs, we investigate the short‐ and long‐term life‐history consequences of population‐wide variation in reproductive conditions, and demonstrate clear among‐cohort variation and covariation in life‐history parameters.The mean number of offspring fledging per breeding event varied among years, and was correlated with environmental conditions (temperature and rainfall) during the months preceding breeding. As the variance in breeding performance did not differ among years and choughs did not miss breeding seasons, variation in environmental conditions affected the whole breeding population. Thus the quality of the chough's breeding environment varied amongst years.Juvenile survival, the probability of recruitment to the breeding population and breeding longevity varied amongst cohorts, and these were positively correlated with the quality of the cohort's natal environment. Offspring fledging under good conditions were more likely to survive to breeding age and recruit, and had longer breeding lives than offspring fledging under poor conditions.Age at first breeding varied amongst cohorts, and increased with population size at maturity rather than natal conditions.The total number of offspring that recruits ultimately fledged varied primarily with breeding longevity rather than recruitment age. Thus, the consistent positive covariation amongst life‐history traits meant that the total number of offspring fledged by recruits during their breeding life varied amongst cohorts, and was correlated with the quality of a cohort's natal conditions. Choughs fledging under good conditions themselves ultimately fledged more offspring.Such environmentally determined variation in offspring fitness is expected to influence optimal patterns of parental investment. We discuss the predictions that environmental variability should select for investment in adult survival and for reduced reproductive effort in poor years.
Which chick is tasty to parasites? The importance of host immunology vs. parasite life history
Authors: Roulin Alexandre , Brinkhof Martin W. G. , Bize Pierre , Richner Heinz , Jungi Thomas W. , Bavoux Christian , Boileau Nicolas , Burneleau Guy 
Published: March 2003

SummaryThe Tasty Chick Hypothesis (TCH) proposes that hatching asynchrony evolved as an antiparasite strategy. Hosts would benefit if ectoparasites aggregate more on the offspring that are of lowest reproductive value within a brood, i.e. on the last‐hatched chicks, because offspring reproductive value generally decreases with hatching rank. The poor body condition of the later‐hatched chicks would impair parasite resistance and render them especially attractive to ectoparasites. Thus, the TCH predicts a decline in chick parasite load with hatching order in avian broods.We investigated the main assumption of the TCH that junior chicks are less immunocompetent than their senior siblings. We also examine the prediction of the TCH that junior chicks bear more ectoparasites than their senior siblings.Conform to the assumption of the TCH for hosts, junior chicks in broods of the barn owl (Tyto albaL.) showed a lower humoral immune response than their senior siblings. In contrast, the cell‐mediated immune response of senior chicks in broods of the great tit (Parus majorL.) was not significantly greater than that of their junior siblings.In line with the prediction of the TCH for the distribution of parasites among hosts, the flyCarnus haemapterusNitzsch infested junior chicks in larger numbers than senior chicks in both barn owl and kestrel (Falco tinnunculusL.) broods.In conflict with the TCH, ticks (Ixodes ricinusL.) were distributed randomly with respect to hatching rank in broods of the barn owl and the great tit. Moreover, louse‐fliesCrataerina melbaeRondani infested mainly senior chicks instead of junior chicks in the Alpine swift (Apus melbaL.).Summarizing, the present descriptive study indicates that the distribution of ectoparasites within‐broods is not generally governed by rank‐related variation in host defence of chicks as initially suggested by the TCH. We argue that specific aspects of the morphology, life history and ecological requirements of various ectoparasite species need more consideration as to explain the dynamics and evolution of host–parasite interactions.
Taxonomic distinctness and environmental assessment
Authors: WARWICK R. M. , CLARKE K R. 
Published: March 2003

Summary

The objectives of this paper are to test the performance of the taxonomic distinctness index, δ+, in a number of environmental impact scenarios, to examine its relationship with functional diversity and to examine the influence of habitat type and diversity on the index.
The index was applied to data on free‐living marine nematodes from the coasts of Britain and Chile.
The taxonomic distinctness of nematodes from environmentally degraded locations was generally reduced in comparison with that of more pristine locations, often significantly so.
Some habitat types may have naturally lower values of taxonomic distinctness than others. However, unless the habitats are degraded in some way the δ+ values do not generally fall below the lower 95% confidence limit of the simulated distribution under a null hypothesis that the assemblages behave as if they are a random selection from the regional species pool. This ameliorates the problem encountered with species richness measures of biodiversity, which are much more strongly affected by habitat type and complexity, thus making comparisons difficult between data sets from different habitats or where habitat type is uncontrolled.
Taxonomic distinctness in marine nematodes is shown to be related to trophic diversity: a reduction in trophic diversity will lead to a reduction in taxonomic distinctness, although not necessarily to a reduction in species richness. Trophic composition itself is clearly affected by pollution, but is also strongly responsive to the major influence of habitat type.
These features of the taxonomic distinctness index, coupled with its lack of dependence on sampling effort or differences in taxonomic rigour between workers and a statistical framework for the assessment of the significance of departure from expectation, suggest that it may prove to be a biologically and ecologically relevant measure of biodiversity.
This paper demonstrates that the taxonomic distinctness index has a number of theoretical and logistical advantages over measures of species richness for the purposes of environmental assessment.
Raptor distribution in relation to landscape composition in semi‐arid Mediterranean habitats
Authors: Sánchez‐Zapata José. A. , Calvo José F. 
Published: March 2003

1. Breeding sites of raptors were studied in relation to land‐use and edge habitat using two different scales in semi‐arid Mediterranean landscapes in south‐eastern Spain. Habitat relationships were analysed using Generalized Linear Models. 2. The proportion of forest cover at a small scale was the best predictor for all species. At a larger scale, the proportion of forest cover was also a good predictor, and the amount of edge habitat between forest and extensive agriculture was a very good predictor of booted and short‐toed eagle densities. 3. Models for sedentary species of raptor were similar using both scales whereas trans‐Saharan migrant raptors seemed to be more sensitive to larger landscape features that included longer edges between forest and extensive agriculture. 4. Habitat mosaics created by forestry and traditional farming were especially important for Mediterranean raptors. Strengthening of the Agri‐environmental Regulation (2078/92) will be necessary to compensate for agricultural intensification proposals promoted under the Common Agricultural Policy (CAP).