bluuebunny/crossref_metadata_2025_split huggingface dataset:
From peripheral to full participation in a blended trade bargaining simulation
Authors: Carr Tony , Cox Lenda , Eden Ndrea , Hanslo Monique 
Published: March 2004

AbstractThis article considers the extent and nature of student participation in a trade bargaining simulation from a community of practice perspective. This third‐year economics module included a blend of online communication (through email, online chats and online discussions) and face‐to‐face meetings, both in smaller bargaining groups and in whole class plenary meetings. Our method of analysis includes the use of Exchange Structure Analysis of text chats and face‐to‐face learning conversations, triangulated by observation, survey and interview data. The focus on community of practice enables us to offer a nuanced interpretation of differences in crude participation data derived from the online chats. Superficially, the data may suggest marginalisation of participants, but Wenger's (1988) notion of peripheral participation with a trajectory towards full participation reframes the disparities in terms of an active community of practice. Some members are fully engaged with the practices of trade bargaining from the early stages of the simulation, while others move towards full participation over the duration of the simulation. Our results suggest that the laboratory‐based online text chats did provide opportunities for student participation in the simulation, and that male and female students exhibited different patterns of participation in the chats.
Demography of fluctuating populations: temporal and phase‐related changes in vital rates of Microtus ochrogaster
Authors: Ozgul Arpat , Getz Lowell L. , Oli Madan K. 
Published: March 2004

Summary

Small mammal population fluctuations, cyclic or not, have been an ecological puzzle and a source of heated debate among ecologists. Identifying the demographic parameters that covary closely with density changes can help elucidate the underlying causes of population fluctuations, but few studies have reported rigorous estimates of these parameters.
We applied capture–mark–recapture analysis to twice‐weekly trapping data from a long‐term study of a fluctuating Microtus ochrogaster (prairie vole) population in Illinois, USA to estimate stage‐specific apparent survival and maturation rates. We also estimated population density, fecundity rate, age at maturity and life span on a weekly basis.
Survival, maturation and fecundity rates exhibited phase‐related changes during major density fluctuations, but they showed density‐independent temporal variations during the prolonged low‐density phases. Among these variables, maturation and juvenile survival rates covaried most closely with population density.
These results suggest that phase‐related changes in maturation and juvenile survival rates are likely to be the main demographic factors driving the dynamics of our study population.
Phase‐related changes in maturation rates provide a plausible demographic explanation of density fluctuations in our study population. Our results suggest that direct predation may not be necessary for large‐scale fluctuations in M. ochrogaster abundance.
Life history and fitness consequences of ectoparasites
Authors: Fitze Patrick S. , Tschirren Barbara , Richner Heinz 
Published: March 2004

SummaryFor iteroparous organisms life‐history theory predicts a trade‐off between current and future reproduction, and therefore the evolution of host responses to current parasite infestation that will maximize lifetime reproductive success. The parasite‐induced variation in reproductive success is thus not the net result of parasite infestation alone, but the parasite‐mediated outcome of optimal resource allocation among current and future reproductive events. Understanding the importance of parasites for the evolution of host life history therefore requires an experimental investigation of the effects of parasites over the host's life span. Such studies are currently scant.We manipulated the load of an ectoparasite, the hen flea (Ceratophyllus gallinae), in the nests of its most common host, the great tit (Parus major), over a period of 4 years and recorded, the components of current and future reproductive success including survival, divorce, breeding dispersal and various reproductive parameters. Finally we assessed, for females only as paternity of males was unknown, the lifetime reproductive success as a close correlate of Darwinian fitness.For current reproduction, our experiment demonstrates that parasites reduce current reproductive success via an increase in the probability of nest failure during incubation and the nestling period. In the presence of fleas, clutch size and the number of fledglings were reduced while the incubation and the nestling period were prolonged. Thus parasitism led to an increase in parental effort but nevertheless reduced current reproductive success.For future reproduction, the experiment shows that females breeding in infested nests dispersed over longer distances between breeding attempts. The divorce rate following infestation, the probability of breeding locally in the future and residual reproductive success were not affected significantly by ectoparasites. The study thus suggests that hen fleas play a minor role in shaping the trade‐off between current and future reproduction.Lifetime reproductive success of females, measured as the total number of locally recruiting offspring over the 4 experimental years, was reduced significantly by ectoparasites. The negative effect of parasites arose by a reduction of the number of fledglings per breeding attempt rather than by a reduction of the number of breeding attempts.
Altitudinal variation in the relationship between growth and maturation rate in salmon parr
Authors: Baum Diane , Laughton Robert , Armstrong John D. , Metcalfe Neil B. 
Published: March 2004

Summary

It is well established that the likelihood of an individual animal becoming mature is influenced strongly by its previous growth. However, with few exceptions, it is not known whether common relationships between the two parameters apply within and among populations.
Using data collected from tributaries of a single river, we investigate the relationship between size and maturation in Atlantic salmon parr, and whether spatial variation in the incidence of parr maturation can be explained by variation in growth rates.
There was spatial variation in the size of parr, a large proportion of which was attributable to altitude. However, this did not explain the variation between sites in the maturation rate of parr. In contrast to earlier findings, there was no relationship between the mean size of parr at a site and the percentage of males that matured there for the age class in which most mature males were found.
Within a site size at age was a good predictor of maturation, but across sites this relationship was modified by altitude. For a given age and size a parr was more likely to become sexually mature if it came from a high‐altitude site.
Spatial variation in the incidence of male parr maturity is not simply the result of variation in growth rates. The size threshold above which parr male parr matured depended on altitude, which could serve as a proxy for growth opportunity.
We suggest adaptive explanations for variation in the relationship between growth and maturation, particularly the importance of relative, as opposed to absolute body size.
Our study suggests a high level of complexity in the proximate mechanisms governing life‐history strategies in order to bring about adaptive strategy choice.
Generalized linear models for means and variances applied to movement of tiger beetles along corridor roads
Authors: Van Dooren Tom J. M. , Matthysen E. 
Published: March 2004

SummaryMovement is often conditional on environmental parameters and behavioural phenotype. A reasonable assumption is that individuals behave as random walkers, when environment and behaviour are fixed.Based on this assumption, observations of movements can be analysed with a set of generalized linear models. Such models can predict the occurrence of behaviour and movement distance distributions resulting from different behavioural or environmental parameters.This method was applied to study short‐range movement of tiger beetles (Cicindela hybrida) along corridor roads.Logistic regression was used to estimate probabilities of behaviour types occurring during 5‐min observation intervals.Movement distances were investigated with a pair of generalized regression models for both the mean and the variance of the distances covered during observations. The models estimate mean and variance of a normal distribution per set of environmental conditions and per combination of behaviour types observed in the observation interval.Flying behaviour, the number of interactions with other beetles and the amount of food items handled differed between spring and summer season.Advective movement was demonstrated, and it occurred in the direction of the sun. The advection effect is more pronounced when beetles fly. We propose that this advection occurs as a side effect of thermoregulatory behaviour.Diffusion or spread of displacements increased with the occurrence of flying and decreased when beetles spent time sheltering in shade or handling food.Simulations were used to generate movement distributions over longer time spans, assuming that the selected model applies per time step. Such distributions can be used to generate null hypotheses for different types of experiments, and for extrapolation.The simulations show that only when there is little advection do distance distributions remain normal. Mean predicted displacement distances reach up to around 100 meter after 2 h.
Contrasting dynamics in two subpopulations of a leech metapopulation over 25 year‐classes in a small stream
Authors: Elliott J. M. 
Published: March 2004

SummaryThe leech,Erpobdella octoculata(L.), occurred as two local populations at sites A (deep section with macrophytes) and B (shallow stony section) in a small stream. A June census estimated densities of young leeches (R1 m−2) and mature leeches (R2 m−2) towards the end of the first and second years of the life cycle, respectively. An August census estimated the density of cocoons laid by the mature leeches before they died in autumn. Cocoon density multiplied by the mean number of young per cocoon estimated the density of young produced at the end of each year‐class (R3 m−2) and also the density at the start of the next year‐class (Sm−2). Information was obtained for 25 year‐classes (1966–90).The spatial distribution of the leeches and their cocoons was aggregated and similar at both sites in spite of the marked differences in habitat. Survivor density at three life stages (R1,R2,R3) was related to the density of young at the start of each year‐class (S), the density‐dependent relationship being described by a dome‐shaped Ricker curve that differed markedly between sites. A few year‐classes were excluded from the analyses because their density was reduced by a severe spate and three summer droughts. A stability analysis showed that the subpopulation at site A was essentially stable around the equilibrium density, whereas that at site B was strongly cyclic and was approaching chaotic behaviour.Loss‐rates were fairly constant in the second year of the life cycle, but those in the first year were very variable and related positively to the density of mature leeches. The latter ate newly hatched leeches, even those still in cocoons. Cannibalism appeared to be the most obvious mechanism responsible for the density‐dependent relationships, its impact being greatest at site B. Loss‐rates were not dependent on the density of the young leeches themselves (i.e. direct density dependence) but on the density of mature leeches that ate them (i.e. delayed density dependence). This case study illustrates how subpopulations in a metapopulation can have both similar (spatial distribution) and contrasting (density fluctuations) dynamics.
Seasonal dynamics of mycoplasmal conjunctivitis in eastern North American house finches
Authors: Altizer Sonia , Hochachka Wesley M. , Dhondt André A. 
Published: March 2004

SummaryMycoplasma gallisepticumis an emerging eye disease that spread rapidly among wild house finches (Carpodacus mexicanus) in the eastern United States following initial reports of infected birds in 1994. The hallmark signs of infection have allowed systematic monitoring of disease at both local and continent‐wide scales for more than 7 years since the onset of the epidemic.Using data collected by a network of citizen science volunteers, we examined both long‐term trends and seasonal dynamics of mycoplasmal conjunctivitis in three different climatic regions in eastern North America over a 77‐month period (November 1994–March 2001).Time‐series prevalence data from all three regions suggest that following establishment, marked seasonal fluctuations in prevalence each year were characterized by autumn–winter epidemics (in October and February) and consistent summer declines (with prevalence falling close to zero from May to July).The maximum peak, annual rates of increase and timing of epidemics varied among three geographical locations that were delineated by minimum winter temperatures. Annual autumn prevalence in the South increased more rapidly, and maximum prevalence was nearly three times greater in the South than in the colder North and Central regions.Longer‐term trends showed evidence for multiyear fluctuations in prevalence that were characterized by greater amplitude in the southern region.Finally, monthly estimates of house finch flock sizes derived from a similar citizen science data set showed that winter flock sizes were associated positively with average monthly prevalence in the northern and central regions, although regional differences in flock sizes did not correspond to regional differences in maximum prevalence.This study represents the first evidence of multiyear fluctuations, regional differences and highly predictable annual outbreaks of this recently emerged wildlife pathogen. Several factors associated with house finch life history and behaviour are likely to contribute to temporal and spatial variation in prevalence, including annual changes in host reproduction, social behaviour and environmental effects on host stress or immunocompetence.
Emerging associations on marine rocky shores: specialist herbivores on introduced macroalgae
Authors: Trowbridge Cynthia D. 
Published: March 2004

Summary

Sacoglossan sea slugs (Gastropoda: Opisthobranchia) can change their highly specialized algal host associations in response to introduced hosts.
Adult sacoglossans (Placida dendritica) collected from the introduced green macroalga Codium fragile ssp. tomentosoides in west‐coast Scottish sea lochs tended to associate with and consume introduced hosts over the native C. tomentosum in pairwise‐choice feeding trials.
On west‐coast Irish shores, where native congeneric hosts were more common, significantly more P. dendritica attacked C. tomentosum on the shore whereas Elysia viridis disproportionately attacked the exotics. In Lough Hyne, Co. Cork, Ireland, juvenile E. viridis attacked both C. fragile ssp. tomentosoides and the native, sympatric C. vermilara; in pairwise‐choice feeding trials, sacoglossans preferred the host species from which they were collected.
In the Channel Islands, adult E. viridis were common on C. tomentosum on Guernsey shores. In pairwise‐choice feeding trials adults exhibited no preference between native and introduced hosts, indicating that the stenophagous herbivores could change their associations.
On temperate Australian shores, the native sacoglossan Placida aoteana attacked the recently introduced C. fragile ssp. tomentosoides as well as native congeners and conspecifics. P. aoteana was common and its herbivory evident in Victoria and Tasmania. Slugs collected from native C. fragile exhibited no preference between algal subspecies in Victoria but a strong preference for the introduced subspecies in Tasmania.
Flexibility in host use enables stenophagous marine herbivores to respond within years to the presence of recently introduced hosts. The implicit peril of the host‐specificity paradigm − that specialists could change their associations − does occur in stenophagous sacoglossans, and there is considerable intra‐ and interspecific variation in response.
Biological control of invasive green algae using sacoglossan herbivores is fraught with several risks, including taxonomic uncertainty of species’ boundaries, ecological flexibility of feeding, unexplored role of host susceptibility and insufficient evolutionary–developmental information to establish coevolutionary associations.
Low‐temperature‐driven early spawning migration of a temperate marine fish
Authors: Sims David W. , Wearmouth Victoria J. , Genner Martin J. , Southward Alan J. , Hawkins Stephen J. 
Published: March 2004

Summary

It is often assumed that the timing of annual migrations of marine fish to spawning grounds occurs with very little change over time. However, it is unclear how much migration is influenced by climate change in marine species that spawn at sea but spend most time in estuarine conditions, especially as thermal regimes in estuaries may differ significantly from those in the open sea.
Migration phenology was studied in a population of flounder, Platichthys flesus (L.) off south‐west England using high‐temporal resolution trawling data over a 13‐year period.
Flounder migrated from their estuarine habitat to spawning grounds at sea some 1–2 months earlier in years that were up to 2 °C cooler. Flounder arrived on the spawning grounds over a shorter time period (2–6 days) when colder than normal conditions prevailed in the estuary, compared to warmer years (12–15 days). This suggests that they were responding to low temperatures by exhibiting a more synchronous, population‐level early migration.
The timing of migration was earlier when the largest differences in temperatures between near‐estuary and offshore environments occurred, differences that were related significantly to cold, negative phases of the North Atlantic Oscillation (NAO).
Flounder migration phenology appears to be driven to a large extent by short‐term, climate‐induced changes in the thermal resources of their overwintering habitat. This suggests that climate fluctuations characterizing the NAO may have significant effects on the timing of the peak abundance of fish populations generally, which, in turn, may have implications for fisheries management.
Year‐ and sex‐dependent effects of experimental brood sex ratio manipulation on fledging condition of Eurasian kestrels
Authors: Laaksonen Toni , Fargallo Juan A. , Korpimäki Erkki , Lyytinen Sami , Valkama Jari , Pöyri Ville 
Published: March 2004

SummaryOffspring sex ratio may be an unpredictable component of life history that might select for behavioural plasticity in parental care. If the parents do not have such plasticity and the two sexes of offspring differ in size, individuals in a brood or litter biased towards the larger sex offspring may suffer from food shortage. Sibling sex ratio could also affect the young through asymmetric sex‐related sibling competition.We created single‐sex broods of sexually size‐dimorphic Eurasian kestrels (Falco tinnunculusL.) with mixed‐sex control broods in order to test whether parents have behavioural plasticity to respond to the sex ratio of their brood and whether smaller male chicks suffer from reduced health status because their larger female siblings outrival them in sibling competition. The experiment was conducted during two years (2000 and 2001) that differed in the abundance of voles, the main natural prey of kestrels.No obvious effects of the brood sex ratio manipulation on parental effort were detected, as there were no differences in prey delivery rate, biomass of prey brought to the nest, body mass or heterophile/lymphocyte ratio of the parents.Female chicks in all‐female broods had lower haematocrit levels than those in mixed‐sex broods in a year of low vole abundance. As haematocrit is an index of nutritional condition and health state, this result indicates that in the year of low vole abundance the female chicks in all‐female broods fledged in poorer condition than those in mixed‐sex broods.These results indicate that when the parents do not alter their level of parental effort in response to the sex ratio of their brood, the young in a brood biased towards the larger sex offspring can be reared successfully when food is abundant, while they may suffer under food shortage situations.Kestrel chicks of both sexes had low haematocrit levels and T cell‐mediated immune responses in the year of low vole abundance. This result indicates that poor health state at fledging may provide a causal link for low recruitment of kestrels hatched in years of low vole abundance.
Competition for breeding sites and site‐dependent population regulation in a highly colonial seabird, the common guillemot Uria aalge
Authors: Kokko Hanna , Harris Michael P. , Wanless Sarah 
Published: March 2004

Summary

The hypothesis of site‐dependent population regulation predicts that birds utilize available nesting sites in a pre‐emptive (ideal despotic) manner, leading to density dependence in heterogeneous habitats as poorer sites are used at higher population densities. At small population sizes adaptive site choice protects populations against fluctuations (the buffer effect).
Common guillemots Uria aalge (Pontoppidan) breed at high density on sea‐cliffs. The population breeding on the Isle of May, Scotland increased by 60% between 1981 and 2000. A good nest‐site is a prerequisite for successful breeding and there is much competition for the best sites. Throughout this period, site use correlated with two measures of site quality, and photographs taken in 1936 show that this pattern has been extremely stable.
The data indicate declining quality of sites that remain available as the population has increased. Site‐dependent regulation was evident in that average breeding success declined over the years, but no declining trend was detected in the best (and most preferred) sites.
An individual guillemot generally uses the same nest‐site from year to year, but a minority move, usually less than 2 m, between breeding seasons. These movements can be involuntary or voluntary. Involuntarily moving birds that had occupied very good sites before moving often spent several years as non‐breeders (floaters) close to their previous site before breeding again, and then occupied poorer sites. Voluntarily moving birds significantly improved their site quality by moving.
Birds responded both to the physical site characteristics and to their own experience (breeding failure) when abandoning a site. Their behaviour thus combined aspects of the ‘win‐stay, lose‐switch’ strategy with direct assessment of site quality. Our data set is inconclusive with respect to the public information hypothesis, i.e. whether birds use conspecific cues of breeding success when settling in a new site.