bluuebunny/crossref_metadata_2025 huggingface dataset:
An endoscopic approach to biliary complications following orthotopic liver transplantation
Authors: Thuluvath Paul J. , Atassi Tamer , Lee John
Published: December 2004

Abstract: Biliary complications following orthotopic liver transplantation (OLT) may be associated with significant morbidity and mortality. In this report, we reviewed our endoscopic experience of managing post OLT biliary complications in 79 patients over a 12‐year period.

Methods: OLT (n = 423) recipients between 10/86 and 12/98 were obtained from the transplant registry at the Johns Hopkins Hospital. OLT recipient who underwent at least one endoscopic retrograde cholangiography (ERC) were identified through a radiology database. Indications, findings and interventions performed were noted for each ERC report. Outpatient and inpatients medical records were reviewed for outcome and complications.

Results: Seventy‐nine (79/423, 18.7%) patients had at least one ERC for suspected biliary complication. Sixty‐four (15.1%) patients had at least one or more biliary complications. The mean follow‐up for patients with abnormal ERC was 33.9 months. Nineteen patients had bile leaks; 10 of these patients had leak at the exit site of the T‐tube and five patients had at the anastomosis. Biliary stenting with or without endoscopic sphincterotomy led to resolution of bile leak in 16 patients. Three patients failed endoscopic therapy: one underwent surgery and two had percutaneous drainage. Twenty‐five patients presented with biliary strictures. Nineteen strictures were at the anastomotic or just proximal to the anastomosis, one at the hilum (ischemic in nature) and three were at the distal, recipient common bile duct; one had strictures at the anastomosis as well as the distal recipient bile duct and another had diffuse intrahepatic strictures. Seventeen patients in the stricture group improved with endoscopic intervention. One patient was re‐transplanted (diffuse intrahepatic strictures), but no patient underwent percutaneous drainage.

Conclusions: ERC is safe and effective in the diagnosis and management of biliary complications following liver transplantation with choledochocholedochal anastomosis and obviates the need for surgical or percutaneous transhepatic approaches in majority of cases.
Triiodothyronine and interleukin‐6 (IL‐6) induce expression of HGF in an immortalized rat hepatic stellate cell line
Authors: Kariv R. , Enden A. , Zvibel Isab , Rosner G. , Brill S. , Shafritz D. A. , Halpern Z. , Oren R.
Published: December 2004

Abstract: Background/Aims: Despite its being considered a primary mitogen for hepatocytes, triiodothyronine (T3) has no effect on the proliferation of hepatocytes in vitro, and in our studies, induces significant in vivo hepatocyte proliferation only during liver injury. We hypothesized that T3 may affect hepatocytes proliferation indirectly, by inducing other cells in the liver to secrete hepatic mitogens.

Methods: In vivo studies: Lipopolysaccharide, T3 and a combination of the two were injected into rats, and hepatocyte proliferation was determined by PCNA staining and mitotic index. In vitro studies: a rat hepatic stellate cell line (HSC‐6T) was cultured with T3, IL‐6 and a combination of the two, and we assessed the effect of these cytokine/hormone combinations on the cell proliferation and on secretion of IL‐6 and HGF, measured by ELISA. Expression of thyroid hormone receptors was assessed by RT‐PCR.

Results: In vivo: T3, together with lipopolysaccharide, enhances PCNA staining and the mitotic index of hepatocytes in the treated rats. In vitro: the hepatic stellate cell line expresses thyroid hormone receptor α1, but not β1. Proliferation of stellate cells is not affected by T3, with or without IL‐6. T3 has no effect on secreted levels of IL‐6 in the stellate cell line. Hepatic stellate cells cultured with T3 and IL‐6 show significantly increased amounts of secreted HGF after 48 h in culture.

Conclusion: T3 may induce hepatocyte proliferation in vivo during injury by turning on expression of HGF in stellate cells and acting together with IL‐6.
Hepatic stimulator substance administration ameliorates liver regeneration in an animal model of fulminant hepatic failure and encephalopathy
Authors: Margeli Alexandra P. , Papadimitriou Lila , Ninos Sotirios , Manolis Evangelos , Mykoniatis Michael G. , Theocharis Stamatios E.
Published: December 2004

Abstract: Aims/Background: Hepatic stimulator substance (HSS) is a liver‐specific growth factor implicated in hepatocellular proliferation and hepatoprotection in models of acute liver injury. In the present study, we examined the effect of exogenous HSS administration on liver proliferating capacity and survival outcome in an experimental animal model of fulminant hepatic failure (FHF) and encephalopathy, induced by repeated injections of thioacetamide (TAA) in rats.

Methods: Fulminant hepatic failure was induced in adult male Wistar rats by three consecutive intraperitoneal injections of TAA (400 mg/kg of body weight), at 24 h time intervals. The animals received intraperitoneally either a saline solution or HSS (50 mg protein/kg of body weight), 2 h after the second and third TAA injections. The animals were killed at 6, 12 and 18 h post the last injection of TAA.

Results: Levels of liver enzymes and urea in serum, blood ammonia values, liver histology, stage of hepatic encephalopathy and survival were statistically significantly improved in TAA‐intoxicated and HSS‐treated rats compared to TAA‐intoxicated and saline‐treated ones. Furthermore, HSS ameliorated liver regenerative indices – DNA biosynthesis, thymidine kinase activity and hepatocyte mitotic activity – in a statistically significant manner.

Conclusions: Our data suggest the beneficial effect of HSS administration in this animal model of FHF and encephalopathy, supporting evidence for a possible use of HSS as supportive therapy, by increasing hepatocellular proliferation, in management of FHF.
Effects of ants on the reproductive success of Euphorbia cyparissias and associated pathogenic rust fungi
Authors: Schürch S. , Pfunder M. , Roy B. A.
Published: December 2004

Ants are common visitors to the flowers of Euphorbia cyparissias
, and also often forage on E. cyparissias stems that are infected
by rust fungi of the species complex Uromyces pisi. These fungi
sterilise their host, produce nectar and require insects for their sexual
reproduction. Our objective was to determine whether ant visits enhance
the sexual reproduction of either E. cyparissias or the rust
fungi. Uromyces pisi is known to be obligately outcrossing,
whereas a breeding system experiment established that E.
cyparissias can self, but sets more seeds when outcrossed. We used
insect exclusion experiments to test whether ants fertilise the rust
fungi and to determine whether ants are pollinators of E.
cyparissias. These experiments showed that insect pollination is necessary for seed set and that ants can pollinate the flowers. However, ants do not fertilise the rust fungi.
Flight and thermoregulation in moths were shaped by predation from bats
Authors: Rydell Jens , Lancaster Winston C.
Published: December 2004

Most larger nocturnal moths (“macrolepidoptera”) are equipped with ultrasonic tympanic organs (ears), which give them a considerable survival advantage in encounters with echolocating bats. However, 4.2% of the Scandinavian species lack such organs, and are presumably deaf. Our results show that the earless species are larger and have higher wing loadings than the tympanate forms. They also fly with higher body temperatures. They are thus adapted for fast and erratic flight, and may represent an alternative evolutionary pathway to efficient bat defence, but one that is energetically more demanding. We suggest that the tympanic organs in nocturnal moths were key innovations that “released” their bearers from the energetic constraints imposed by a high flight body temperature, necessary to avoid bats, and probably set the stage for subsequent adaptive radiation of slow flying forms.
Community structure, abundance, and morphology
Authors: Stevens Richard D. , Willig Michael R.
Published: December 2004

The role of interspecific competition in structuring communities has been a highly debated issue for the last two decades. The nonrandom nature of morphological patterns within communities has been at the center of this controversy. Null models addressing community‐wide dispersions in morphology have produced equivocal results and may be based on assumptions that are too restrictive (e.g., competitive exclusion or displacement). If morphological distinctiveness allows species to escape competitive pressures and exhibit higher densities, then a positive relationship should exist between morphological dissimilarity and abundance. We develop a suite of models that evaluates patterns in abundance that are associated with the morphological proximity of a species to other competitors. We evaluated the relationship between morphological distance and abundance from a variety of morphological perspectives, from those representing strictly diffuse interactions to those representing only interactions between a species and its nearest neighbor in morphological space. These models were sufficiently powerful to detect positive associations between abundance and morphological differences in a nocturnal desert rodent guild for which the effects of competition on structure are well established. Models such as these may be more useful than traditional models evaluating morphological dispersions for many reasons. They do not require that communities reach equilibrium before competitive interactions give rise to deterministic structure. They do not suffer from limitations of potentially inaccurate faunal pools or from phylogenetic constraints. Lastly, they may be used as a diagnostic tool in comparative studies to determine the degree to which competitive interactions structure communities.
Activity patterns of insectivorous bats and birds in northern Scandinavia (69° N), during continuous midsummer daylight
Authors: Speakman J. R. , Rydell J. , Webb P. I. , Hayes J. P. , Hays G. C. , Hulbert I. A. R. , McDevitt R. M.
Published: December 2004

Previous studies suggest that many species of insectivorous bats are nocturnal, despite the relatively low availability of their insect prey at night, because of the risk of predation by diurnal predatory birds. We hypothesised that if this was the case bats living above the arctic circle would alter their feeding behaviour during midsummer because there would no longer be any benefit to restricting their activity to the period when their prey are least abundant. Alternatively, if bats were more influenced by competition from aerial insectivorous birds they would continue to feed at ‘night’ to avoid such competition. In northern Norway (69° N), during continuous midsummer daylight, insectivorous sand martins (Riparia riparia) concentrated their
aerial feeding activity when aerial insects were most abundant. The birds
stopped feeding between 23:00 and 07:00 when aerial insects were least
abundant. In contrast, northern bats (Eptesicus nilssonii), fed mostly between 22:00 and 02:00, coinciding with the lowest aerial insect availability, and with the period when light levels were lowest (ca 1000 lux). Bat activity patterns were closest to those predicted by the avian competition hypothesis. The low densities of both sand martins and Northern bats in the study area, however, were less consistent with this hypothesis. Possibly populations of both species were higher historically and the observed patterns reflected historical competition. Bat activity was most closely correlated to ambient light levels. This raised two alternative explanations that we could not eliminate. Perhaps there was differential predation risk, between the brightest and darkest parts of the day, because the visual capacities of falcons are strongly dependent on luminance. Alternatively the bats may have been entrained to emerge at given light levels by their behaviour at other times of year.
Trade‐offs in evolutionary immunology: just what is the cost of immunity?
Authors: Lochmiller Robert L. , Deerenberg Charlotte
Published: December 2004

It has become increasingly clear that life‐history patterns among the vertebrates have been shaped by the plethora and variety of immunological risks associated with parasitic faunas in their environments. Immunological competence could very well be the most important determinant of life‐time reproductive success and fitness for many species. It is generally assumed by evolutionary ecologists that providing immunological defences to minimise such risks to the host is costly in terms of necessitating trade‐offs with other nutrient‐demanding processes such as growth, reproduction, and thermoregulation. Studies devoted to providing assessments of such costs and how they may force evolutionary trade‐offs among life‐history characters are few, especially for wild vertebrate species, and their results are widely scattered throughout the literature. In this paper we attempt to review this literature to obtain a better understanding of energetic and nutritional costs for maintaining a normal immune system and examine how costly it might be for a host who is forced to up‐regulate its immunological defence mechanisms. The significance of these various costs to ecology and life history trade‐offs among the vertebrates is explored. It is concluded that sufficient evidence exists to support the primary assumption that immunological defences are costly to the vertebrate host.
Components of additive variance in life‐history traits of Daphnia hyalina: seasonal differences in the response to predator signals
Authors: Stibor Herwig , Lampert Winfried
Published: December 2004

We attempted to separate the additive variance of life‐history parameters (size at first reproduction (SFR), proportion of total production allocated to reproduction) of Daphnia hyalina in a
mesotrophic lake during different seasons into genetic components and
phenotypic plasticity. Every month we randomly isolated juveniles of 20
clones from the lake and measured their life‐history parameters
immediately after isolation, i.e., under the influence of all modifying
factors in the lake. The measurements were repeated after the clones had
been kept in the laboratory for at least six generations without predator
signals (controls) and with the addition of fish and Chaoborus
kairomones. SFR increased monotonously from July to December in fresh
field isolates. Laboratory controls showed always much larger SFR, but
approached field value in December. Most of the size difference was due
to maternal effects. Reproductive allocation showed a different pattern
than SFR with a minimum in September both in field samples and laboratory
controls. Fish kairomone reduced SFR in July and August when fish
predation is high, but not later in the year. On the contrary,
Chaoborus kairomone increased SFR in September and October when
Chaoborus larvae are abundant in the lake, but not in summer. This
indicates a seasonal shift in the clonal composition of D. hyalina
populations towards clones adapted to the specific predation pressure.
Reproductive allocation changed in response to fish kairomone in July and
August, but not in response to Chaoborus kairomone. In this
mesotrophic lake, fish have a stronger direct and indirect impact on
Daphnia life history than Chaoborus larvae.
Morphological and life history responses to predators in larvae of seven anurans
Authors: Lardner Björn
Published: December 2004

Amphibian larvae often face two major sources of mortality: pond desiccation and predation. Tadpoles of seven anuran species with different preferences for type of breeding habitat, on a hydroperiod scale, were tested for responses to the presence of predators by raising them experimentally in the presence and absence of a separately caged invertebrate predator that was fed on conspecific tadpoles.  The species typically breeding in temporary or semi‐permanent ponds (Rana temporaria, Rana arvalis, Rana dalmatina and
Hyla arborea) – where invertebrate predator populations are
predicted to vary considerably spatiotemporally – all showed marked
induced increases in tail fin depth in response to predator presence.
These species also tended to respond by reduced growth rates. 
The representative of the most ephemeral habitats, Bufo calamita,
did not respond in any of these traits. Its congeneric, Bufo bufo,
a toxic inhabitant of permanent ponds and lakes, tended to respond to
predator presence by reducing its growth rate, though not by a tail depth
increase. I argue that the rather poor swimming performance in Bufo
tadpoles may opt for defences other than locomotor ability. 
The palatable, permanent pond species Pelobates fuscus did not alter either its growth rate or tail morphology. Possible explanations for this result are discussed.
Effects of fish chemical cues on the interactions between tadpoles and crayfish
Authors: Nyström Per , Åbjörnsson Kajsa
Published: December 2004

We studied the effects of predatory crayfish (Pacifastacus
leniusculus), the non‐lethal effects of fish chemical cues
(Oncorhynchus mykiss), and the combined effects of crayfish and
fish chemical cues on the performance of tadpoles of two co‐existing
anuran species, Rana temporaria and Bufo bufo, in
experimental pools. We also examined grazing effects on periphyton, the
main food source for the tadpoles. Crayfish significantly reduced tadpole
survival, particularly by feeding on Bufo. Rana benefited
from reduced numbers of competitors, resulting from crayfish predation,
by increased growth rate, whereas the growth rate of Bufo was
unaffected by crayfish. The proportion of Rana in refuges (in
relation to the number of survivors at the end of the experiment) was
unaffected by crayfish, whereas proportionally more Bufo stayed in
refuges in the presence of crayfish, relative to controls. Fish cues had
no effect on tadpole survival of either species. During the entire larval
period, Rana responded to fish cues by increasing the use of
refuges relative to controls, whereas Bufo did not show any
significant behavioural response to fish cues. In accordance with these
observations, the proportion of Rana in refuges at the end of the
experiment was high in the presence of fish cues, whereas the use of
refuges by Bufo was not affected by fish cues. Predatory crayfish
and fish chemical cues had additive effects on tadpole survival, growth
and refuge use. 
Tadpoles in all treatments reduced periphyton biomass. Both crayfish and
fish cues had positive indirect effects on periphyton biomass. The
positive indirect effect of fish cues on periphyton was likely an effect
of reduced grazing from Rana. Thus lethal, as well as non‐lethal, predator effects on prey populations can influence lower trophic levels.
Lack of species‐specific primer effects of odours from female Atlantic salmon, Salmo salar, and brown trout, Salmo trutta
Authors: Olsén K. Håkan , Bjerselius Rickard , Petersson Erik , Järvi Torbjörn , Mayer Ian , Hedenskog Mikael
Published: December 2004

We exposed, in two successive spawning seasons, individually placed precocious male Atlantic salmon (Salmo salar) and brown trout
(Salmo trutta) parr to odour stimuli (ovarian fluid and urine mix) from ovulated conspecific or heterospecific anadromous females. Atlantic salmon parr had significantly higher plasma concentrations of the hormones 17α,20β‐dihydroxy‐4‐pregnen‐3‐one (17,20β‐P), 11‐ketotestosterone (11‐KT) and testosterone (T) after exposure to odours from conspecific females or from brown trout females compared to parr exposed to a control solution (0.9% NaCl). We did not observe any significant differences between the hormone levels in salmon parr exposed to the two female odours. The salmon parr exposed to conspecific odours had significantly higher volumes of strippable milt compared to the controls, but we did not find any significant differences when comparing the effect of the two female odours. Brown trout parr had significantly higher plasma 17,20β‐P levels following exposure to heterospecific female odours compared to control males, but there was no significant difference between males exposed to the different female odours. We did not observe any significant differences in plasma levels of T and 11‐KT and in milt volumes between exposed and control trout. Taken together, the results from both tested species indicate that the potency of heterospecific stimuli in stimulating increased plasma sex steroid hormone levels in male parr was as strong as stimuli from conspecific females. The results are discussed in connection to observed hybridisation between the two sympatric species.
Are plant populations seed‐limited? A review of seed sowing experiments
Authors: Turnbull Lindsay A. , Crawley Michael J. , Rees Mark
Published: December 2004

We define seed limitation to be an increase in population size following seed addition. Here, we briefly consider how theoretical models deal with seed limitation and how seed sowing experiments can be used to unravel the extent of seed limitation in natural systems. We review two types of seed addition experiments: seed augmentation studies where seeds are added to existing populations; and seed introductions where seeds are sown in unoccupied sites. Overall, approximately 50% of seed augmentation experiments show evidence of seed limitation. These studies show that seed limitation tends to occur more commonly in early successional habitats and in early successional species. Most of the studies have concentrated on simply categorising populations as seed‐ or microsite‐limited, but we believe that seed sowing experiments could be used to reveal much more about community structure, and we discuss possible future directions.  In 53% of introduction studies (where seeds were sown at sites from which the species was known to be absent) the introduced species was recorded in at least one of the experimental sites following sowing. However, of the subset of studies where both seedlings and adult plants were recorded, 64% of sites contained seedlings while only 23% contained adults. This implies that, for many species, conditions for establishment are more stringent than conditions for germination. The successful establishment of plants in unoccupied patches indicates the potential for immigration to enhance local diversity (the spatial mass effect). Few studies continued monitoring for long enough to determine whether or not self‐sustaining populations were successfully established, and no study attempted to link introduction sites to a putative natural source of propagules, or considered the dynamics of the metapopulation as a whole.
Confidence intervals for population growth rate of organisms with two‐stage life histories
Authors: Sibly Richard M. , Hansen Flemming T. , Forbes Valery E.
Published: December 2004

Although life histories can be modelled with great generality using projection matrices, for organisms with life histories that can be accurately described by a simplified set of parameters, e.g. when adult fecundity and mortality are independent of age, more accurate estimates of life table parameters and of population growth rate and its standard error can be readily obtained. Here an analytic method for calculating approximate confidence intervals for population growth rate is given for two‐stage life histories that can be described by four variables representing age at first breeding, fecundity per unit time, and juvenile and adult survivorships per unit time. The method is applied to experimental data on Capitella sp. I obtained by Hansen et al., and quite good agreement is found between the analytic and bootstrap estimates of the standard error of Λ. The analytic estimates were a little conservative, probably because of the way the action of mortality was modelled. Alternative life‐history models are briefly discussed, and the desirability of formulating life‐history models so that the variables involved are independent of each other is stressed. Analytic estimates of Λ may be biassed if an inappropriate model is chosen or if variables are not independent and the correlations between them are not measured. To allow for these possibilities, where necessary a conservative approach should be taken to significance testing using the analytic method.
Time‐dependent reproductive decisions in the blue tit
Authors: Nilsson Jan‐Åke
Published: December 2004

Many breeding attempts in birds do not result in any fledged young due to predation on eggs or young. Consequently, the influence of time constraints on reproductive decisions are integrated parts of the reproductive behaviour of birds breeding within short, seasonal climate zones. In this study, I mimicked nest predation by removing blue tit (Parus caeruleus) clutches shortly after completion. Around 75% of the removed clutches were followed by a repeat clutch. Females producing their first clutch early in the season and females with an early onset of incubation in the laying sequence (an indication of high parental or territory quality) were most likely to initiate a repeat clutch. A trade‐off between the benefits of a repeat clutch and survival likely stopped late females in bad condition from investing more in the current reproductive season. Females producing a repeat clutch laid fewer eggs, had an earlier onset of incubation in the laying sequence and produced larger eggs than they did when producing their original first clutch. Eggs produced after the onset of incubation were especially large in the repeat clutches. Since food availability was presumably higher when the female produced her repeat clutch compared with her first clutch, females made a strategical decision when reducing clutch size, whereas onset of incubation and egg size may have been energetically constrained when producing the first clutch. Females that produced a relatively large clutch, had a relatively early onset of incubation, and laid relatively large eggs in their first clutch also did so when producing a repeat clutch, indicating that some of the variation in breeding parameters are due to differences in parental or territory quality. Differences between years in the temperature‐dependent development rate of caterpillars seem to affect the time constraints on breeding. A year with a predicted early seasonal decline in caterpillars resulted in short intervals between removal and relaying, small clutches and an early onset of incubation.
Population biology of the clonal moss Hylocomium splendens in Norwegian boreal spruce forests. 5. Vertical dynamics of individual shoot segments
Authors: Økland Rune Halvorsen
Published: December 2004

Demographic information was obtained for 12 528 mature segments (for which dry weight was estimated and vertical position in the bryophyte carpet recorded) and 3109 regenerated growing points for the perennial clonal moss Hylocomium splendens, recorded in Norwegian
boreal spruce forests during a 6‐year period. Branching frequency varied
with vertical position in the bryophyte carpet. Termination risk
(probability of producing no offspring) was highest (44%) for buried
segments, lowest (12%) for segments at intermediate vertical positions,
and also high (26%) for emergent segments (due to increasing exposure to
external mortality agents). Segment size increased from low levels in the
bryophyte carpet to a maximum ca 2–10 mm below the top of the
bryophyte carpet. This intermediate level was interpreted as the optimal
compromise between incoming radiation (attenuating downwards) and
microclimatic moisture conditions (improving downwards). Size‐corrected
fitness, the number of offspring emerging from a mature segment within
one year after maturation after allowance for differences in size, was
lower for buried and emergent segments than for segments at intermediate
positions. Small emergent segments were apparently liable to suffer from
vitality reductions due to desiccation. The vertical position of a
daughter segment depended on that of its parent segment, but also showed
considerable stochastic variation. Burial acted as a strong sink for
small segments regardless of vertical position. No evidence was found for
species‐specific differences in the way pleurocarpous bryophytes
interact, but reduced vertical mobility of H. splendens when
growing among acrocarps indicated that growth‐form is an important
determinant of bryophyte interactions. Evidence was found for vertical
layering of the bryophyte carpet according to dominant type of
interactions among individuals: none (environmental stress) above and at
top, facilitation [a (+, +) interaction] at intermediate levels
because of favourable water relationships in closed stands, and
amensalism [a (0, −) interaction] from higher‐situated
segments that deprive lower‐situated segments access to light at lower
relative levels. The intensity of amensalism increased downwards in the
bryophyte carpet as indicated by a reinforced size hierarchy. The
tendency for small H. splendens segments to become buried and lost from the population by amensalism is likely to represent a general mechanism for interactions between bryophyte species and succession in bryophyte‐dominated stands. Population effects of climatic and local environmental factors (favourability vs stress), disturbance and apparently random events are discussed with reference to their impact on the relative sizes of subpopulations acting as sources (due to facilitation) and sinks (due to amensalism).
Explanations of commonness and rarity in British breeding birds: separating resource use and resource availability
Authors: Gregory Richard D. , Gaston Kevin J.
Published: December 2004

Two of the most prominent explanations for a positive interspecific relationship between local abundance and regional distribution are the resource breadth and the resource availability hypotheses. Here we test these hypotheses by characterising habitat use of British breeding birds using extensive census and environmental data. A group of 85 bird species was considered for study along with 34 land use or environmental variables, which were used to generate four ordination axes by Canonical Correspondence Analysis. Measures of niche breadth and position were derived from these synthetic environmental axes using standard procedures. Across species, none of five measures of abundance and distribution chosen were correlated with niche breadth, whereas four out of five of these measures were correlated negatively with niche position. Repeating the analyses using a method designed to control for phylogenetic non‐independence confirmed these general patterns. Birds that tended to use resources that were more atypical of the environment tended to be rarer and thinly distributed, while those using typical resources were common and widely distributed. Performing the analyses on subsets of the data based on species sample sizes did not alter the conclusions. On the assumption that our analyses properly capture patterns of niche use by birds, we find little support for the resource breadth hypothesis, but considerable support for the resource availability hypothesis.
Does fecundity drive the evolution of insect diet?
Authors: Agnew Kelly , Singer Michael C.
Published: December 2004

We investigate whether egg load (a surrogate for fecundity) drives host specificity in a herbivorous insect. In many insects, including our study organism (Edith's checkerspot butterfly), both egg load and tendency to accept low‐ranked hosts increase during each search for an oviposition site. Effects on host acceptance of egg load and passage of time are thereby potentially confounded. We conducted two experiments designed to disentangle these effects. In both experiments, we estimated the times of first acceptance of both a high‐ranked and a low‐ranked host, without allowing the insects to oviposit. In the first experiment, we measured egg load at the time of first acceptance of the low‐ranked host. The later the time of first acceptance, the higher was the fecundity. We therefore reject the hypothesis that all insects accepted the low‐ranked host at the same predetermined egg load. In the second experiment, we measured egg load 48 h after the high‐ranked host was first accepted. We found no relationship between egg load and timing of acceptance of the low‐ranked host. Insects with higher rates of egg accumulation did not accept the low‐ranked host sooner. Taken together, these results suggest that acceptance of the low‐ranked host is not driven directly by egg load. Rather, this acceptance results from some other process that is influenced by time since last oviposition. We conclude that there is no evidence to support the assumption that females with high rates of egg accumulation are more likely to accept low‐ranked hosts.
On harvesting a structured ungulate population
Authors: Milner‐Gulland E. J. , Coulson T. N. , Clutton‐Brock T. H.
Published: December 2004

Variation in demographic rates within a spatially structured population could have important consequences for management decisions, harvesting strategies and offtake rates. Although there is a growing body of evidence suggesting that demographic rates vary within populations over a range of spatial scales, there has been little research investigating the consequences of this variation for population management. In this paper, data on the dynamics of two female red deer sub‐populations on Rum are analysed, and evidence is presented for differences between the fecundity and mortality rates of the two sub‐populations. A simple harvesting model is developed to represent the dynamics of the two sub‐populations, including density‐independent migration between sub‐populations and spatially correlated environmental variability. The highest monetary yield in the model is obtained by harvesting the more resilient sub‐population at a higher rate. Surprisingly the losses involved in harvesting both sub‐populations at the same rate are insignificant. However, if migration were density‐dependent, the size of one sub‐population would be more relevant to harvesting policy for the other sub‐population. The results of this empirical study are compared to theoretical work on spatially structured populations; it is shown that when a species has complex age‐ and sex‐structured population dynamics, previous theoretical results may not hold.
Differences in larval feeding behavior correlate with altered developmental strategies in two parasitic wasps: implications for the size‐fitness hypothesis
Authors: Harvey Jeffrey A. , Kadash Kristy , Strand Michael R.
Published: December 2004

Parasitoid wasps have long been favored organisms for fundamental studies on reproductive strategies and life‐history evolution. Progeny allocation models designed with parasitoids in mind assume that offspring develop by consuming most or all of the resources available from a single host, and that size is the most important factor affecting offspring fitness. Many parasitoids exhibit host usage patterns consistent with these assumptions, but our recent observations suggested that endoparasitic wasps in the family Braconidae often do not. To investigate how differences in host usage patterns might affect developmental strategies, we compared two related braconids with contrasting host usage patterns. Apanteles carpatus consumed virtually all host tissues
during immature development, whereas Microplitis demolitor fed
exclusively on host hemolymph and consumed a relatively small proportion
of available host resources. Development time of M. demolitor was
unaffected by host size, whereas development time of A. carpatus
was much longer in small hosts than in large hosts. On the other hand,
offspring size in M. demolitor correlated strongly with host size,
but it correlated only weakly with host size in A. carpatus. Our
results collectively suggest that selection has favored rapid development
at the potential cost of reduced size in M. demolitor, and
increased size at the potential cost of increased development time in
A. carpatus. Tissue feeding appears to be more prevalent among parasitoids overall, but hemolymph feeding is the predominant pattern of host usage in several subfamilies of endoparasitic braconids. We argue that the relative importance of offspring size and development time will be influenced by host ecology and the effects of selected traits on parasitoid survival.
Costs of reproduction in male lizards, Sceloporus virgatus
Authors: Abell Allison J.
Published: December 2004

Models of life history evolution typically assume a balance between the benefits of current reproductive activity and the costs to future reproductive success or survivorship, but empirical studies often find positive correlations between such components of fitness in undisturbed animal populations. I examined possible survivorship costs of reproduction in free‐ranging male lizards, Sceloporus virgatus, and found that males with low levels of mating success were less likely to survive to the following breeding season. I also investigated two possible indicators of reproductive effort, increase in ectoparasite load and decrease in body weight during the breeding season. Levels of parasitism with trombiculid mites at the end of the breeding season were not associated with any measure of fitness or body condition (mating success, survivorship to the following year, relative weight loss). Yearling males (which have low levels of mating success) usually gained weight during the breeding season, while older males generally lost weight during this period. This suggests that young males may have postponed reproduction in favor of body growth and that seasonal weight loss of older males might reflect reproductive effort. Within the group of older males, individuals with the highest levels of mating success did not have high levels of either weight loss or mortality. Mate guarding behavior, an alternative to the aggressive territorial behavior typical of many lizard species, may allow certain males to obtain mates without expending large amounts of energy or exposing themselves to great mortality risks.
A microsatellite analysis of natterjack toad, Bufo calamita, metapopulations
Authors: Rowe G. , Beebee T. J. C. , Burke T.
Published: December 2004

Although it is widely recognised that spatial subdivision of populations is common in nature, there is no consensus as to how metapopulation dynamics affect genetic diversity. We investigated the genetic differentiation of natterjack toads, Bufo calamita, in
three regions of Britain where habitat continuity indicated the likely
occurrence of extensive metapopulations. Our intention was to determine
whether genetic analysis supported the existence of metapopulation
structures, if so of what type, and to identify barriers to migration
between subpopulations. Allele frequencies were determined across eight
polymorphic microsatellite loci for a total of 24 toad subpopulations at
three separate sites. Genetic differentiation was assessed using five
measures of genetic distance, notably FST,
RST, Nei's standard distance Ds,Δμ2 and the Cavalli‐Sforza
chord distance Dc. B. calamita exhibited
small but significant levels of genetic differentiation between
subpopulations in all three study areas, and genetic and geographic
distance correlations indicated isolation‐by‐distance effects in all
three cases. The effects on correlation strengths of compensation for
positive (sea, rivers, urban development) and negative (pond clusters)
barriers to toad migration between the subpopulations in each area were
also determined. Dc, a measure which assumes that differentiation is caused by drift with negligible mutation effect, yielded the most plausible interpretation of metapopulation structures. Overall the patterns of genetic variation suggested the existence of a mixed metapopulation model for this species, with high levels of gene flow compatible with one version of the classical model but often supported by particularly stable subpopulations as in the mainland‐island model.
Risk‐sensitive foraging: the effect of relative variability
Authors: Shafir Sharoni
Published: December 2004

Animals are sometimes sensitive and sometimes indifferent to variability in amount of reward. I analyzed a large set of published studies to test whether these differences in risk‐sensitivity may be influenced by the coefficient of variation (s.d./mean) of the variable reward and by the presence of empty rewards. The coefficient of variation had a strong effect on the strength of risk‐sensitivity among studies with nectarivores, both invertebrates and vertebrates. The effect was not significant for studies with non‐nectarivores, but these studies included only a limited range of coefficients of variation, and risk‐sensitivity in these studies was based on fewer subjects per experimental condition than in studies of nectarivores. The presence of empty rewards had no effect on the strength of risk‐sensitivity. The apparent effect of empty rewards seems to be an artifact of the tendency of distributions that include zero rewards to have larger coefficients of variation than distributions that do not include zero rewards. I introduce the CV model, a simple descriptive model that accounts for a large proportion of the variability in levels of risk‐sensitivity among experiments. My analysis resolves the apparent discrepancies among studies that report risk‐sensitivity and risk‐indifference. It is necessary to control for the magnitude of the coefficient of variation when testing risk‐sensitivity under different conditions (e.g., energy budgets). A successful descriptive model of risk‐sensitive choice behavior is useful for guiding future research both in ecology and in the underlying mechanism of cognitive processes.
Host concealment: a determinant for host acceptance and feeding in an ectoparasitoid wasp
Authors: Ueno Takatoshi
Published: December 2004

In general, ectoparasitoids attack concealed hosts in protected situations whereas endoparasitoids use both concealed and exposed hosts. The difference is assumed to be the consequence of ecological constraints; ectoparasitic larvae are vulnerable both to predation and to climatic factors such as rainfall, and, hence, require some structures to protect themselves. I hypothesized that such ecological constraints should act as a within‐species selection pressure to female ectoparasitoids, and hence that females should recognize the degree of concealment of the host and prefer concealed over exposed hosts for oviposition. To test this hypothesis, I examined 1) whether host concealment could influence host acceptance by the ectoparasitoid wasp
Agrothereutes lanceolatus and 2) whether host concealment could
influence the fitness of the offspring. Female wasps recognized and
attacked (probed) both cocooned and exposed host prepupae in equal
proportions, but discriminated between them after ovipositor insertion,
and preferred the former for oviposition and the latter for host‐feeding.
They also selected to oviposit on hosts concealed in paper tubes. Thus
host concealment was important for host selection in A. lanceolatus
. Offspring fitness (measured as survival and size) was much lower on
exposed hosts than on cocooned and paper‐concealed hosts, even under
laboratory conditions. Thus, host concealment influenced the fitness of
wasp offspring, and, hence, is a good indicator of host quality for
female wasps. Adaptiveness of host selection and host‐feeding in A.
lanceolatus in relation to host concealment is discussed.
Community structure and the habitat templet: ants in the tropical forest canopy and litter
Authors: Yanoviak S. P. , Kaspari M.
Published: December 2004

The tropical forest canopy and litter differ in physical structure, resource availability, and abiotic conditions. We used standardized bait experiments in the canopy and litter of four neotropical tree species to explore how these differences shape the behavior, morphology, and diversity of ant assemblages. Ant activity (biomass at a bait after 32 min) was higher in the canopy, and higher on protein baits than carbohydrate baits. Aggressive bait defense occurred more frequently in the canopy (60%) than in the litter (32%), but was not associated with tree species or bait type in either habitat. The median size of workers of species in the canopy and litter was nearly identical, but body size distribution was unimodal in the canopy and bimodal in the litter. The colony size of the most aggressive species was an order of magnitude larger in the canopy. Species richness at a bait was relatively uniform across tree species and habitats. Litter and canopy shared no species, but overlap among tree species was three times higher in the litter assemblages. Litter assemblages showed less activity, less interference, less differentiation across the landscape, and different size distributions than canopy assemblages. The canopy and litter templets subsume a number of environmental gradients that combine to shape ant community structure.
Dr. Pangloss restrained by the Red Queen – steps towards a unified defence theory
Authors: Jokela Jukka , Schmid‐Hempel Paul , Rigby Mark C.
Published: December 2004

Animals and plants defend themselves against a variable community of biological enemies. We argue that the effectiveness of allocation to defence (the success of defence per unit allocation) may be expected to decrease as the diversity of attack types increases, and asked how the optimal allocation to defence covaries with the effectiveness of defence. Variation in effectiveness links optimal defence to coevolutionary processes; the prime characteristic of coevolutionary interactions is that they promote and maintain genetic variation in both hosts and their enemies, leading to variation in the effectiveness of defence. We present a simple model suggesting that as effectiveness decreases, the fitness benefit of defence disappears. In other words, when effectiveness is low, the optimal strategy is to tolerate damage. As effectiveness increases, the optimal allocation flips rapidly from no‐defence (tolerance) to high allocation to defence, and then decreases at a decelerating pace as effectiveness increases. We conclude that diversifying coevolution, as it covaries with the effectiveness of defence, constrains the evolution of optimal defence strategies and may be a very important component in determining the optimal allocation to defence and variation in the success of defence as it is seen in the wild.