bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mycoplasma gallisepticuminfection dynamics in a house finch population: seasonal variation in survival, encounter and transmission rate
Authors: Faustino Cristina R. , Jennelle Christopher S. , Connolly Véronique , Davis Andrew K. , Swarthout Elliott C. , Dhondt André A. , Cooch Evan G. 
Published: June 2004

SummaryWe considered the impact of an emerging pathogen (Mycoplasma gallisepticumEdward and Kanarek) on apparent survival, encounter and transition rates in a population of a novel host (the house finch,Carpodacus mexicanusMüller). We used a multistate analysis of mark–encounter data from individually marked birds. Individual birds were categorized to a particular disease ‘state’; transition rates among states, conditional on apparent survival, were analogous to rates of new infection and recovery from infection. We hypothesized thatM. gallisepticuminfection would reduce the apparent survival of infected individuals, and that the magnitude of this reduction would vary as a function of the physiological condition of the host (which was characterized in our analyses by including a demographic and an environmental surrogate as covariates).We found consistent support for the hypothesis thatM. gallisepticuminfection resulted in lower apparent survival among infected individuals, and that recovery rates (from infected to non‐infected) were greater than infection rates in this population. We also found strong evidence indicating that infected individuals were less likely to be encountered than were non‐infected individuals. Although we predicted that both sex and temperature (proxies for physiological condition) would explain a significant proportion of the variation in our data, only marginal influences of both factors on apparent survival, encounter and state transition rates were detected.Our analyses identified several factors that may be important to studies of disease in the wild. First, disease state assignment may be uncertain, which can complicate parameter estimation. Secondly, encounter rate for infected individuals in our study was low relative to that for non‐infected individuals, reflecting possible behavioural changes in infected individuals. Low encounter rates reduces precision of estimated parameters, especially for multistate models. Finally, our results (and mark–recapture models in general) assume independence among individual birds. However, we are aware that there is a social structuring in house finches (and in general for many bird species). Accounting for such non‐independence may be especially important for situations where the state transitions are directly related to the pattern of social contact.
Demographic mechanisms of the population decline of the song thrush Turdus philomelos in Britain
Authors: Robinson Robert A. , Green Rhys E. , Baillie Stephen R. , Peach Will J. , Thomson David L. 
Published: June 2004

Summary

In Britain, the song thrush Turdus philomelos is categorized as a species of high national conservation concern because of a large population decline during the last three decades. We calculated a series of annual national population estimates for woodland and farmland habitats combined for the period 1964–2000. We then used turning points analysis to identify seven blocks of years within the period of decline (1968–2000) with uniform rates of population change in the smoothed trend.
We used recoveries of song thrushes ringed as nestlings, juveniles and adults during April–September to estimate survival rates separately for the post‐fledging period, the remainder of the first year and for adults. Daily survival probability was lower during the post‐fledging period than during the remainder of the first year or for older birds.
There was evidence for variation in survival rates among blocks of years with different rates of population change, particularly for first‐year survival. There were significant positive correlations across blocks between mean population multiplication rate (PMR) and both post‐fledging and first‐year survival.
Survival of first‐year birds was correlated negatively with the duration of the longest run of frost days and the survival of adults was correlated negatively with the duration of the longest summer drought. Variation among blocks in mean PMR was correlated with block means of the duration of runs of frost days and drought days, but significant correlations between PMR and both post‐fledging and first‐year survival remained after allowing for the influence of weather on survival.
Changes in survival in the first winter, and perhaps also the post‐fledging period, are sufficient to have caused the song thrush population decline. The environmental causes of these changes are not known, but changes in farming practices, land drainage, pesticides and predators are all candidates. Adverse weather conditions contributed to the decline, but were not the primary driver.
Spatial synchrony in population dynamics of West African fishes: a demonstration of an intraspecific and interspecific Moran effect
Authors: Tedesco Pablo A. , Hugueny Bernard , Paugy Didier , Fermon Yves 
Published: June 2004

Summary

Synchronous fluctuations of the abundance of several populations at a regional scale can be a sign of a climatic effect on their dynamics (Moran effect). However, the interpretation of spatial synchrony is often complicated by the interaction between climatic disturbances and migrations between the studied populations.
We addressed this question by studying 24‐year time‐series of abundance estimates for four populations of four fish species in three different catchment basins in Côte d’Ivoire (West Africa). As localities from two different basins cannot exchange individuals, dispersal cannot be considered a synchronizing factor in this system.
A sign test performed on the four site × site correlation matrices rejected the null hypothesis of no spatial synchrony. No relation was detected in relating the level of synchrony in species dynamics (r = 0·58 on average) to the geographical distances between the four sites (176–367 km). A more detailed analysis taking account of sampling error was carried out between two sites, and confirmed the above results. When corrected for sampling noise, high values of spatial synchrony were obtained (r = 0·88 on average).
Interspecific spatial synchronies (r = 0·57 on average) were almost as high as intraspecific values, suggesting that the four species are reacting in the same way to the same Moran effect.
A good correlation (r = 0·54) between a regional river discharge index and the total catch of the four species 1 year later was observed, suggesting that hydrological variability is one of the main synchronizing factors. Moreover, as expected on theoretical grounds, spatial synchrony in river discharge (r = 0·84 and 0·88 on a log scale) is similar to spatial synchrony in population dynamics (r = 0·88 on average and corrected for sampling error).
Parasitoids flip a coin before deciding to superparasitize
Authors: Plantegenest Manuel , Outreman Yannick , Goubault Marlene , Wajnberg Eric 
Published: June 2004

Summary

Host acceptance decision in parasitic wasps depends strongly on the parasitism status of the encountered host. In solitary species, a host allows the development of only a single parasitic larva, and then any oviposition in an already parasitized host leads to larval competition and to potential loss of offspring. The ability of parasitoids to discriminate between parasitized and healthy hosts is well documented. Despite this, parasitized hosts are still accepted by the foraging wasps, an occurrence termed superparasitism.
In the last decades, theoretical studies have suggested that under certain circumstances superparasitism can be optimal. Generally, the superparasitism theory predicts that the optimal host acceptance decision should follow a zero‐one rule: in response to both environmental and physiological state characteristics, a given female should switch from acceptance to rejection of parasitized hosts.
However, some experiments have shown that parasitoids may decide to accept parasitized hosts with an intermediate probability.
A model was developed in order to explain this partial preference in parasitoids.
More generally, the present study demonstrates that when the consequences of one decision cannot be predicted perfectly, the optimal decision rules could be stochastic rather than deterministic. Accordingly, behavioural stochasticity need not necessarily result from errors in decision‐making or from an incapacity to assess the actual environmental state but could instead have evolved as the optimal response to the uncertainty of future environmental state.
Migration supports uneven consumer control in a sewage‐enriched river food web
Authors: DeBruyn Adrian M. H. , McCann Kevin S. , Rasmussen Joseph B. 
Published: June 2004

Summary

We studied the response of the St Lawrence River food web to enrichment by primary‐treated sewage from the city of Montreal, Canada.
Despite the richness and complexity of this food web, the openness of the system and the limited production possible in this temperate river's short growing season, we found that biomass densities of consumers responded to enrichment according to the qualitative predictions of a simple bioenergetic model.
All consumer trophic levels responded to sewage enrichment, but not all members of each trophic level: top piscivores seemed to control small, benthivorous fish but were unable to control larger fish, so the intermediate consumer level became dominated by Catastomidae (suckers). Consequently, the epiphytic prey of small fish were free to respond to sewage enrichment, but the benthic prey of suckers were not.
The important elements of complexity seemed to be the factors that determine the realized pattern of feeding linkages: heterogeneity in prey vulnerability (predator–prey size ratios) and predator efficiency (vegetation cover for ambush predators, inaccessibility of epiphytic prey to bottom‐feeding suckers).
Because of the openness of the system, the community was able to respond to enrichment by a combination of demographic (production) and behavioural (migration) mechanisms. We argue that the food web model described an energetically favourable state, and that migration provided a ‘shortcut’ for the system to approach this state within a short growing season.
Stage‐structured competition and the cyclic dynamics of host–parasitoid populations
Authors: Wearing Helen J. , Sait Steven M. , Cameron Tom C. , Rohani Pejman 
Published: June 2004

SummaryCyclic dynamics of various periods are pervasive in many insect populations where interactions with natural enemies are known to be important. How stage‐structured processes within the host population, such as competition and cannibalism, affect these interactions has received little attention so far.Using the well‐studied laboratory host–parasitoid system ofPlodia interpunctellaandVenturia canescens, we explore a series of host–parasitoid models of increasing complexity. Specifically, we identify the circumstances under which stage‐structured processes both within the host and parasitoid populations generate dynamical behaviour ranging from generation to true consumer–resource (multi‐generation) cycles.We find that both within‐host interactions (strong competition and egg cannibalism by late instar larvae) and parasitoid recruitment structure (a developmental lag in the parasitism of larvae) can suppress long period cycles and promote host generation cycles. In short, we show that simple stage‐structured processes in both host and parasitoid can modulate the strength of the consumer–resource interaction.For some parameters we find more than one stable cyclic attractor. The presence of multiple attractors means that the same mechanism can give rise to cycles of different periods depending on initial population numbers. Because the host‐alone system may exhibit transient dynamics for a substantial period, the timing of a parasitoid invasion can be crucial to the dynamical outcome.We discuss the consequences of using a single descriptor of an ecological time series, the cycle period, to infer properties about the underlying system and its food web interactions.
Food patch use by parent birds: to gather food for themselves or for their chicks?
Authors: Markman Shai , Pinshow Berry , Wright Jonathan , Kotler Burt P. 
Published: June 2004

Summary

Despite its importance in the evolution of central‐place foraging strategies, few studies have distinguished between patch use by parent birds for their own consumption vs. patch use for the purpose of provisioning young in the nest.
Adult Palestine sunbirds (Nectarinia osea) consume nectar and arthropods, but feed only arthropods to their nestlings. This partial separation of food types allowed us to experimentally test sex‐specific trade‐offs in parental foraging effort between two patches.
A ‘variable’ patch on one side of a pair's territory contained only artificial nectar for parental self‐feeding (in varying sucrose concentrations between 0·25 and 0·75 mol kg−1 H2O). A ‘constant’ patch on the other side of the territory contained artificial nectar for parental self‐feeding (sucrose concentration = 0·25 mol kg−1 H2O), plus a dish of flightless houseflies for provisioning young.
Experimental increases in sucrose concentration in the variable patch led the parents to: (a) consume greater amounts of sucrose solution from this patch; (b) collect more flies from the constant patch to feed their young; and (c) persistently use the 0·25 mol kg−1 H2O feeder near the dish of flies. By titration (gradually changing the sucrose concentration in the variable patch), we demonstrate that at concentrations of 0·47 mol kg−1 H2O for males and 0·55 mol kg−1 H2O for females, the birds spent an equal amount of time foraging in both patches. Therefore, sucrose concentration in the variable patch (for self‐feeding only), had to be higher for the females than for the males, in order to balance the additional value females placed upon the flies provided for chick‐feeding in the constant patch.
These results reflect previously described sex‐specific parental roles in this species, with females provisioning young mainly in the nest and males patrolling more and guarding against nest predators. Furthermore, we demonstrate for the first time the fine details of alternative adaptive trade‐offs in foraging effort by parent birds when using patches for self‐feeding or for delivery of food to the young.
Assessment of hypotheses about dispersal in a long‐lived seabird using multistate capture–recapture models
Authors: Cam Emmanuelle , Oro Daniel , Pradel Roger , Jimenez Juan 
Published: June 2004

SummaryDispersal contributes to spatio‐temporal variation in population size and is a key process in studies of life history evolution and studies with conservation implications. However, dispersal is still one of the major gaps in our knowledge of ecological dynamics. The very large literature on metapopulation dynamics lacks empirical bases on dispersal and relevant behavioural parameters. We used multistate capture–recapture models (data from 1988 to 2001) to address hypotheses about movement probability and habitat selection within a system of two breeding colonies in Audouin's gulls (Larus audouinii), an endemic species breeding in the Mediterranean and considered as threatened.Movement probability varied over time, and differed greatly between the colonies.We did not find evidence of an influence of colony size or density of predators on movement probability.In dispersers, our results did not support the hypotheses that movement probability between yeartandt+ 1 was influenced by mean breeding success in the colony of origin (i.e. an indicator of habitat quality) or the destination colony in yeartort+ 1, or by the ratio of breeding success in these colonies in yeartort +1 (i.e. quality gradient).Overall, movement probability was higher from the smaller colony to the larger, and from the colony with lower breeding success in yeartto the more productive one. This provides slight support for two nonexclusive hypotheses about habitat selection (conspecific attraction and conspecific success attraction).Movement probability from the smaller, less productive colony was very high in some years, suggesting that the dynamics of both colonies were strongly influenced by adult dispersal. However, in absolute numbers, more individuals moved from the larger, more productive colony to the smaller one. This suggests that the system may function as a source–sink system.Use of multistate models to re‐assess local survival showed that survival was lower in the less productive colony with higher emigration probability. This may reflect genuine differences in mortality between colonies, or more probably differences in permanent emigration from the study area.
Detritus processing, ecosystem engineering and benthic diversity: a test of predator–omnivore interference
Authors: Zhang Yixin , Richardson John S. , Negishi Junjiro N. 
Published: June 2004

Summary

Interference between species from different functional groups may influence ecosystem functioning and biological diversity. This study tested whether interactions between predacious cutthroat trout and an omnivorous signal crayfish modified the crayfish's trophic and engineering effects within a detrital‐based, stream benthic community.
We show in a trough experiment that omnivorous crayfish through their trophic and engineering roles enhance detritus decomposition, reduce particulate organic matter (POM) accumulation, and diminish diversity in leaf packs.
In crayfish troughs by day 30, leaf dry weight loss was 1·8‐fold greater, whereas POM trapped in leaf packs was 80% less, than of those in controls, and the abundance, biomass and taxon richness of benthos in leaf packs were lower than those in controls. Predatory cutthroat trout did not affect those variables and did not interfere with the crayfish.
Crayfish and cutthroat trout both decreased fine material sedimentation in the troughs.
Thus, with no interference from cutthroat trout, the signal crayfish acted as ecosystem processors and engineers, and strongly influenced detrital processing, benthic diversity, and the accumulation of POM and fine sediments.
High trophic overlap within the seabird community of Argentinean Patagonia: a multiscale approach
Authors: Forero Manuela G. , Bortolotti Gary R. , Hobson Keith A. , Donazar Jose A. , Bertelloti Marcelo , Blanco Guillermo 
Published: June 2004

Summary

Food web interactions in animal communities can be investigated through the measurement of stable isotopes (e.g. δ15N, δ13C). We used this approach in a community of 14 species of seabirds breeding on the Argentinean Patagonian coast. Tissue samples were collected from nestling and adult seabirds, as well as prey, during three consecutive breeding seasons in 28 breeding colonies.
Relative to those in other temperate and polar regions, this seabird community showed a high degree of overlap in trophic level (TL) among species (93% of species within a TL range of 0·7) and also a comparatively high mean trophic level (4·1).
Relative positions of seabirds in relation to prey suggest that most species feed on pelagic fish and to a lesser extent on invertebrates. Stable isotope values of specialist feeders, Olrolg's (Larus atlanticus) and dolphin gulls (Leucophaeus scoresbii), which were previously assumed to feed mainly on crabs and sea lion excrement, respectively, suggested a broader diet than expected.
Based on stable isotope values of individuals, groups of phylogenetically related species generally showed a high degree of overlap within each group.
Given the degree of isotope overlap in this species‐rich community, coexistence could be interpreted as a consequence of superabundance of food or species diversification in morphology and foraging strategies. The short range of trophic level makes these seabirds vulnerable to the reduction of fish stocks due either to commercial fishing or stochastic fluctuations.
The shape of red grouse cycles
Authors: Shaw Darren J. , Haydon Daniel T. , Cattadori Isabella M. , Hudson Peter J. , Thirgood Simon J. 
Published: June 2004

Summary

We examined 223 time‐series of red grouse (Lagopus lagopus scoticus) numbers compiled from shooting bag‐records from grouse moors located across England, Scotland and Wales for evidence of non‐time‐reversibility, asymmetry in cycle shape and non‐linearity.
We found 44% of time‐series to be non‐time‐reversible. Over 80% of time‐series spent more time increasing than decreasing (but only 32% did so significantly).
Non‐linearity was detected in 44% of time‐series examined, and these non‐linear time‐series were 1·7 times more likely to be non‐time‐reversible compared to the linear time‐series.
The occurrence of non‐linear and non‐time‐reversible series was not related to location, number of days with rain, temperature, moor area or population growth rate. The predominance of symmetrical peaks increased with easting but was not related to number of days with rain, temperature, northing or moor area.
There were no significant relationships between time‐reversibility or non‐linearity status and either tendency to cycle or cycle periodicity. However, populations that cycled with longer periods exhibited slower rates of increase and more equal lengths of time increasing and decreasing in numbers.
Our results provide little evidence that grouse cycles observed in different parts of the species range in the United Kingdom arise from fundamentally different processes.