The trade-off between current and future reproduction plays an important role in demographic analyses. This can be revealed by the relationship between the number of years without reproduction and reproductive investment within a reproductive year. However, estimating both the duration between two successive breeding season and reproductive effort is often limited by variable recapture or resighting effort. Moreover, a supplementary difficulty is raised when nonbreeder individuals are not present sampling breeding grounds, and are therefore unobservable. We used capture-recapture (CR) models to investigate intermittent breeding and reproductive effort to test a putative physiological trade-off in a long-lived species with intermittent breeding, the leatherback sea turtle. We used CR data collected on breeding females on Awa:la-Ya:lima:po beach (French Guiana, South America) from 1995 to 2002. By adding specific constraints in multistate (MS) CR models incorporating several nonobservable states, we modelled the breeding cycle in leatherbacks and then estimated the reproductive effort according to the number of years elapsed since the last nesting season. Using this MS CR framework, the mean survival rate was estimated to 0.91 and the average resighting probability to 0.58 (ranged from 0.30 to 0.99). The breeding cycle was found to be limited to 3 years. These results therefore suggested that animals whose observed breeding intervals are greater than 3 years were most likely animals that escaped detection during their previous nesting season(s). CR data collected in 2001 and 2002 allowed us to compare the individual reproductive effort between females that skipped one breeding season and females that skipped two breeding seasons. These inferences led us to conclude that a trade-off between current and future reproduction exists in leatherbacks nesting in French Guiana, likely linked to the resource provisioning required to invest in reproduction.

Summary 0[ Density\ maturation and survival of female bank vole "Clethrionomys glareolus# in the northern taiga of Finnish Lapland were studied using long!term captureÐmarkÐ recapture data from two large grids\ one food!addition grid and one control grid\ in 0871Ð83[ 1[ The density on the food grid was consistently higher than the density on the control grid[ 2[ Females born early in the breeding season usually matured\ except at very high densities[ Those born later in the summer season commonly delayed maturation to the following spring[ 3[ Winter survival of sub!adult "having delayed maturation# females was signi_cantly higher than survival of adult "breeding# females[ However\ empirical values of sub! adult and adult survival\ as well as di}erence between them\ were not consistent with survival values assumed in theoretical models on optimal deferred breeding[ 4[ There was a density!dependent relationship between the maturation rate of young voles and the density of already established breeding females "both bank voles and all Clethrionomys together^C[ rutilus and C[ rufocanus occasionally occurred on the study grids#[ This density dependence was di}erent for the two grids "weaker on the food!addition grid#[ 5[ These _ndings are discussed within an evolutionary context] we have\ on the basis of these _ndings\ no evidence suggesting that the observed delayed maturation represents an evolutionary optimal strategy[ Rather\ there is evidence suggesting that the delay is due to social constraints[ Key!words] captureÐmarkÐrecapture "CMR# statistical modelling\ Clethrionomys\ food addition experiment\ population cycles\ survival[ Journal of Animal Ecology "0887# 57\ 573Ð586

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Summary 0[ By identifying ecological factors speci_c to functional categories of individuals\ it may be possible to understand the mechanisms underlying life!history evolution and population dynamics[ While empirical analyses within the _eld of population biology have focused on changes in population size\ theoretical models assuming di}erential sensitivities of population growth rate or _tness to demographic parameters have mostly been untested\ particularly against data on small mammals[ 1[ Statistical modelling of captureÐmarkÐrecapture data on the multimammate rat "Mastomys natalensis# from Tanzania shows that] "i# females survive slightly better than males and subadults survive much better than adults^"ii# temporal variation of survival of all individuals is similarly related to the rainfall of the month^"iii# subadults exhibit a strongly density!dependent low persistence rate in the population immedi! ately after their _rst capture^"iv# subadults survival in later months is\ however\ positively related to density^and "v# adult survival shows negative density!dependence[ 2[ Both density!dependent and density!independent factors simultaneously determine stage!dependent survival variation of the multimammate rat[ Whereas environmental factors in this population seem to a}ect survival rates of all individuals in a similar manner\ density!dependent relationships are more complex[ 3[ The patterns of survival variation in small mammals may be di}erent from those observed in large mammals[ 4[ Further studies of demography in small mammals should aim at understanding how much of the variability in population growth rate is accounted for by the variability of the demographic rates resulting from limiting "density!independent# and regulating "density!dependent# factors\ respectively[ This study emphasizes the use of robust and accurate statistical methods as well as stage! or age!structured population modelling[ Key!words] captureÐmarkÐrecapture statistical modelling\ density dependence\ Mas! tomys natalensis\ state!dependent life history\ tropical rodent demography[ Journal of Animal Ecology "0888#\ 57\ 449Ð450Correspondence] Nils

Theoretical evolutionary ecology assumes the existence of fitness variability in natural populations. As realistic measures of fitness are usually difficult to perform directly, integrating fitness indices are proposed in all taxa. In sauropsids, locomotor performances have been proposed as a good integrating index of fitness in natural populations. Concerning aquatic turtles, a performance trait that may be important for the survival of juveniles is the righting response of individuals when they are placed on their carapace. In the present study, we examined the righting response in juveniles of the red-eared slider turtle, Trachemys scripta elegans . We tested two different measures of the righting response for 170 juveniles from constant incubation temperature and for 86 juveniles from three sinusoidal fluctuating incubation temperatures that are considered as more representative of natural conditions in the nest. We compared the effects of offspring sex, maternal identity, juvenile growth rate, and juvenile survival (i.e. individual characteristics), as well as the nutritional status of juveniles (i.e. experimental conditions), on the two different measures of righting response and for each thermal incubation treatments of the eggs (i.e. experimental treatments). We observed that the effects of the individual characteristics were markedly different between the two measures of the righting response and between experimental treatments. These results highlight the importance of the choice of the measure and of the experimental conditions and treatments in the study of a phenotypic trait. Results obtained for only one performance measure under constant laboratory conditions must therefore be extrapolated to the field with caution. Our results also show that the righting response presents individual variability that is probably heritable and is indirectly correlated with survival. These findings support the validity of the righting response as a good candidate for a fitness index in aquatic turtles.

ABSTRACT1. Massive importation of slider turtles (Trachemys scripta elegans) as a pet in France over the past few decades has been followed by the release of many of these turtles into natural environments. T. scripta elegans is now widely distributed in France.2. This paper reports on the successful reproduction of this species in France, with confirmed production of both sexes from nests incubated in the wild. These results indicate that the turtle T. scripta elegans can reproduce in the wild and that its long-term persistence is possible in France.3. The potential impact of this invasive species in natural ecosystems warrants future study. Meanwhile, authorities are strongly encouraged to educate the public to the potential danger of exotic species introduction for local ecosystems and to capture and remove this species from wetlands in southern Europe.

For most organisms, both within‐year (i.e. seasonal) and between‐year variations in demography are important components in shaping the population dynamic patterns observed on a multiannual scale. These two sources of variation have, however, rarely been studied simultaneously. Most of the recent work on small rodent population dynamics, for example, has focused on between‐year variation. Densities of seed‐ and fruit‐eating rodents, such as the bank vole (Clethrionomys glareolus), are in particular known to have between‐year variation related to seed crop production. Here we report on the analysis of a long‐term (1976–1982) capture‐mark‐recapture (CMR) study of the bank vole in Belgium. The study was done on two grids, an open and a fenced grid. As part of the CMR statistical analysis, we propose a general modelling approach which allows for a detailed understanding of the relative importance of seasonal and between‐year variation in survival. We demonstrate that most of the seasonal variation corresponds to a lower apparent survival in spring compared to the rest of the year. During winter, apparent survival was lower on the open grid than on the fenced grid. Dispersal is therefore concluded to be an important determinant of the seasonal pattern. The between‐year variation in survival is largely attributable to variation in seed crops, and is comparable in magnitude to the seasonal variation.

Urbanization is a major challenge for biodiversity conservation, yet the evolutionary processes taking place in urbanized areas remain poorly known. Human activities in cities set new selective forces in motion which need to be investigated to predict the evolutionary responses of animal species living in urban areas. In this study, we investigated the role of urbanization and parasites in the maintenance of melanin-based color polymorphism in the feral pigeon Columba livia. Using a correlative approach, we tested whether differently colored genotypes displayed alternative phenotypic responses to urbanization, by comparing body condition, blood parasite prevalence and parasite load between colored morphs along an urbanization gradient. Body condition did not vary with urbanization, but paler individuals had a higher body condition than darker individuals. Moreover, paler morphs were less often parasitized than darker morphs in moderately urbanized habitats, but their parasite prevalence increased with urbanization. In contrast, darker morphs had similar parasite prevalence along the urbanization gradient. This suggests that paler morphs did better than darker morphs in moderately urbanized environments but were negatively affected by increasing urbanization, while darker morphs performed equally in all environments. Thus, differently colored individuals were distributed non-randomly across the urban habitat and suffered different parasite risk according to their location (a gene-by-environment interaction). This suggests that melanin-based coloration might reflect alternative strategies to cope with urbanization via different exposure or susceptibility to parasites. Spatial variability of parasite pressures linked with urbanization may, thus, play a central role in the maintenance of plumage color polymorphism in this urban species.