Showing papers by "Jean Clobert published in 2009"

Informed dispersal, heterogeneity in animal dispersal syndromes and the dynamics of spatially structured populations

Abstract: There is accumulating evidence that individuals leave their natal area and select a breeding habitat non-randomly by relying upon information about their natal and future breeding environments. This variation in dispersal is not only based on external information (condition dependence) but also depends upon the internal state of individuals (phenotype dependence). As a consequence, not all dispersers are of the same quality or search for the same habitats. In addition, the individual's state is characterized by morphological, physiological or behavioural attributes that might themselves serve as a cue altering the habitat choice of conspecifics. These combined effects of internal and external information have the potential to generate complex movement patterns and could influence population dynamics and colonization processes. Here, we highlight three particular processes that link condition-dependent dispersal, phenotype-dependent dispersal and habitat choice strategies: (1) the relationship between the cause of departure and the dispersers' phenotype; (2) the relationship between the cause of departure and the settlement behaviour and (3) the concept of informed dispersal, where individuals gather and transfer information before and during their movements through the landscape. We review the empirical evidence for these processes with a special emphasis on vertebrate and arthropod model systems, and present case studies that have quantified the impacts of these processes on spatially structured population dynamics. We also discuss recent literature providing strong evidence that individual variation in dispersal has an important impact on both reinforcement and colonization success and therefore must be taken into account when predicting ecological responses to global warming and habitat fragmentation.

Advantages of Volunteer-Based Biodiversity Monitoring in Europe

Abstract: Without robust and unbiased systems for monitoring, changes in natural systems will remain enigmatic for policy makers, leaving them without a clear idea of the consequences of any environmental policies they might adopt. Generally, biodiversity-monitoring activities are not integrated or evaluated across any large geographic region. The EuMon project conducted the first large-scale evaluation of monitoring practices inEuropethroughanon-linequestionnaireandisreportingontheresultsofthissurvey.InSeptember 2007 the EuMon project had documented 395 monitoring schemes for species, which represents a total annual cost of about €4 million, involving more than 46,000 persons devoting over 148,000 person-days/year to biodiversity-monitoring activities. Here we focused on the analysis of variations of monitoring practices across a set of taxonomic groups (birds, amphibians and reptiles, mammals, butterflies, plants, and other insects) and across 5 European countries (France, Germany, Hungary, Lithuania, and Poland). Our results suggest that the overall sampling effort of a scheme is linked with the proportion of volunteers involved in that scheme. Because precision is a function of the number of monitored sites and the number of sites is maximized by volunteer involvement, our results do not support the common belief that volunteer-based schemes are too noisy to be informative. Just the opposite, we believe volunteer-based schemes provide relatively reliable data,

Carotenoid-Based Colours Reflect the Stress Response in the Common Lizard

Abstract: Under chronic stress, carotenoid-based colouration has often been shown to fade. However, the ecological and physiological mechanisms that govern colouration still remain largely unknown. Colour changes may be directly induced by the stressor (for example through reduced carotenoid intake) or due to the activation of the physiological stress response (PSR, e.g. due to increased blood corticosterone concentrations). Here, we tested whether blood corticosterone concentration affected carotenoid-based colouration, and whether a trade-off between colouration and PSR existed. Using the common lizard (Lacerta vivipara), we correlatively and experimentally showed that elevated blood corticosterone levels are associated with increased redness of the lizard's belly. In this study, the effects of corticosterone did not depend on carotenoid ingestion, indicating the absence of a trade-off between colouration and PSR for carotenoids. While carotenoid ingestion increased blood carotenoid concentration, colouration was not modified. This suggests that carotenoid-based colouration of common lizards is not severely limited by dietary carotenoid intake. Together with earlier studies, these findings suggest that the common lizard's carotenoid-based colouration may be a composite trait, consisting of fixed (e.g. genetic) and environmentally elements, the latter reflecting the lizard's PSR.

Biodiversity monitoring: some proposals to adequately study species’ responses to climate change

Abstract: Climate change affects all levels of biology and is a major threat for biodiversity. Hence, it is fundamental to run biodiversity monitoring programs to understand the effects of climate change on the biota and to be able to adjust management and conservation accordingly. So far, however, very few existing monitoring programs allow for the detection of climate change effects, as shown by a survey undertaken by the European project EuMon. Despite this shortcoming, several methods exist which allow to make inferences from existing data by integrating data across different monitoring programs: correlative analyses, meta-analyses and models. In addition, experiments are thought to be useful tools to understand the effects of climate change on plants and animals. Here, we evaluate the utility of these four main approaches. All these methods allow to evaluate long term effects of climate change and make predictions of species’ future development, but they are arguable. We list and compare their benefits and inconveniences, which can lead to uncertainties in the extrapolation of species responses to global climate change. Individual characteristics and population parameters have to be more frequently monitored. The potential evolution of a species should be also modelled, to extrapolate results across spatial and temporal scales as well as to analyse the combined effects of different climatic and biotic factors, including intra but also interspecific relationships. We conclude that a combination of methodologies would be the most promising tool for the assessment of biological responses to climate change, and we provide some thoughts about how to do so. Particularly, we encourage long-term studies along natural gradients (altitudinal or latitudinal) on the same species/habitats to be able to extrapolate to large geographic scales, and to have more complete data sets, necessary to understand the mechanisms of responses. Such data may provide a more accurate base for simulations across spatial and temporal scales, especially if they are publicly available in a common database. These recommendations could allow the adaptation of species management and the development of conservation tools to climate change which threatens species.

Climate warming and the evolution of morphotypes in a reptile

Abstract: Climate warming is known to have effects on population dynamics through variations in survival, fecundity and density. However, the impacts of climate change on population composition are still poorly documented. Morphotypes are powerful markers to track changes in population composition. In the common lizard, Lacerta vivipara, individuals display two types of dorsal patterns: reticulated (R individuals) and linear (L individuals). We examined how local warming affected intrapopulation frequencies of these morphotypes across 11 years. We observed changes in morph frequency of dorsal patterns across years, paralleling the rise of spring temperatures. The proportion of R individuals increased with June temperatures in juveniles, yearlings, and adult males and females. Three mechanisms could explain these changes: phenotypic plasticity, microevolution and/or dispersal between populations. We investigated the ontogenetic determinism, fitness and recruitment rates associated with dorsal morphotypes. Dorsal pattern ontogeny showed temperature dependence but this relationship was not associated with the warming trend during this study. We found variation by morphotype in survival and clutch size, but these factors did not explain R frequency increases. Among all the parameters considered in this study, only a decrease of immigration, which was more pronounced in the L morphotype, could explain the change in population composition. To our knowledge, this provides the first evidence of the impact of climate warming on population composition due to its effects on immigration.

High anoxia tolerance in the subterranean salamander Proteus anguinus without oxidative stress nor activation of antioxidant defenses during reoxygenation

Abstract: The present study describes a high anoxia tolerance in an amphibian at high temperature Indeed, the subterranean salamander Proteus anguinus survived 12 h under anoxia at 12°C Surprisingly, such experimental conditions did not affect P anguinus oxidative status while muscles and liver antioxidant enzymes activities decreased under 8 h anoxia and only return to basal level during reoxygenation To test if such adaptation is common in Urodels, equivalent experimentations have been conducted on another newt: the stream-dwelling Calotriton asper This latter species exhibited only 15 h survival under anoxia in spite of higher antioxidant enzymes activities than P anguinus Furthermore, aerobic recovery after 1 h anoxia induced a 30% increase of oxidative damage partly explained by SOD and CAT activities that did not return to control values during reoxygenation, demonstrating a lower capacity to counteract ROS overproduction than P anguinus In addition, uncoupling protein (UCP) transcript was for the first time detected, partly sequenced and quantified in amphibian muscles and liver UCP may be considered as a ROS production attenuator by mediating a discharge of the proton gradient generated by the respiratory chain The putative role of UCP in post-anoxic oxidative status of both species is discussed

Kin‐based recognition and social aggregation in a ciliate

Abstract: Aggregative groups entail costs that must be overcome for the evolution of complex social interactions Understanding the mechanisms that allow aggregations to form and restrict costs of cheating can provide a resolution to the instability of social evolution Aggregation in Tetrahymena thermophila is associated with costs of reduced growth and benefits of improved survival through "growth factor" exchange. We investigated what mechanisms contribute to stable cooperative aggregation in the face of potential exploitation by less-cooperative lines using experimental microcosms We found that kin recognition modulates aggregative behavior to exclude cheaters from social interactions Long-distance kin recognition across patches modulates social structure by allowing recruitment of kin in aggregative lines and repulsion in asocial lines. Although previous studies have shown a clear benefit to social aggregation at low population densities, we found that social aggregation has very different effects at higher densities. Lower growth rates are a cost of aggregation, but also present potential benefits when restricted to kin aggregations: slow growth and crowd tolerance allow aggregations to form and permit longer persistence on ephemeral resources. Thus in highly dynamic metapopulations, kin recognition plays an important role in the formation and stability of social groups that increase persistence through cooperative consumptive restraint.

Cooperative social clusters are not destroyed by dispersal in a ciliate.

Abstract: The evolution of social cooperation is favored by aggregative behavior to facilitate stable social structure and proximity among kin. High dispersal rates reduce group stability and kin cohesion, so it is generally assumed that there is a fundamental trade-off between cooperation and dispersal. However, empirical tests of this relationship are rare. We tested this assumption experimentally using ten genetically isolated strains of a ciliate, Tetrahymena thermophila. The propensity for social aggregation was greater in strains with reduced cell quality and lower growth performance. While we found a trade-off between costly aggregation and local dispersal in phenotypic analyses, aggregative strains showed a dispersal polymorphism by producing either highly sedentary or long-distance dispersive cells, in contrast to less aggregative strains whose cells were monomorphic local dispersers. High dispersal among aggregative strains may not destroy group stability in T. thermophila because the dispersal polymorphism allows social strains to more readily escape kin groups than less aggregative strains, yet still benefit from stable group membership among sedentary morphs. Such dispersal polymorphisms should be common in other social organisms, serving to alter the nature of the negative impact of dispersal on social evolution.

Optimal level of inbreeding in the common lizard.

Abstract: Mate choice with regard to genetic similarity has been rarely considered as a dynamic process. We examined this possibility in breeding populations of the common lizard (Lacerta vivipara) kept for several years in semi-natural conditions. We investigated whether they displayed a pattern of mate choice according to the genetic similarity and whether it was context-dependent. Mate choice depended on genetic similarity with the partner and also on age and condition. There was no systematic avoidance of inbreeding. Females of intermediate ages, more monogamous, did not mate with genetically similar partners, whereas younger and older females, more polyandrous, did but highest clutch proportions were associated with intermediate values of pair-relatedness. These results indicate dynamic mate choice, suggesting that individuals of different phenotypes select their partners in different ways according to their genetic similarity. We consider our results in the light of diverse and apparently contradictory theories concerning genetic compatibility, and particularly, optimal inbreeding and inclusive fitness.

Are dispersal-dependent behavioral traits produced by phenotypic plasticity?

Abstract: Dispersal is a common response to deteriorating conditions such as intense competition, food limitation, predation or parasitism. Although it provides obvious advantages, dispersal is often assumed to be costly. Selection is therefore likely to have acted to decrease these costs, and indeed several studies demonstrated that dispersers and philopatric individuals differ in their morphology, physiology and/or behavior. Using the common lizard (Lacerta vivipara) as our model system, we examined the contribution of phenotypic plasticity to the establishment of dispersal-dependent behavioral traits. We used a reciprocal transplant experiment in which conditions at the maternal site of origin, during offspring development in utero, and at the release site were manipulated. We then compared activity, social interactions and foraging behavior between individuals that stayed philopatric and those that dispersed. Most behavioral traits were also measured at birth and after the dispersal phase.This study demonstrates that (a) 10 months after the dispersal phase, there were still marked behavioral differences between dispersing and philopatric individuals, (b) the reaction when confronted to another individual was also dispersal-status dependent, a result which strongly suggests that individuals are able to recognize the dispersal status of same-age conspecifics and (c) none of the behavioral characteristics were found to be dependent on the environmental conditions (maternal and natal environment) indicating a lack of phenotypic plasticity in the building of the dispersal-dependent behavioral traits examined.

Urbanisation effects on the functional diversity of avian agricultural communities

Abstract: Urbanisation is affecting ecological communities worldwide. Despite the disproportionate impact on farmland over other habitats, the effect on farmland bird communities has been poorly studied. Considering the still-alarming conservation status of farmland birds, investigations into the effects of pressures such as urbanisation on those communities could be of great interest for their conservation. We studied the urbanisation effects on functional diversity using existing indices designed for the purpose of standardisation. This study uses a functional character measuring species habitat specialisation for indices calculation. A bird survey was conducted on 92 plots of 1 × 1 km chosen after stratification on the proportion of urban area and farmland habitat (either 0, 25, 50, 75%), with the focus on farmland habitat. Two aspects of urbanisation were studied: the intensity and the age of the urbanisation. Functional richness was found to decrease with urbanisation, while functional evenness and divergence increased in a nonlinear way. No significant difference was observed in functional richness and evenness with urbanisation age, however extreme ages of urbanisation (young and old) showed higher niche differentiation concerning specialisation. This implies less important resource competition for species and a more vulnerable state for the ecosystem. Using functional diversity indices based on specialisation allows a better insight in the consequences of urbanisation on diversity/ecosystem–community functioning, which is of crucial importance in the face of global changes.

Relationship between female mating strategy, litter success and offspring dispersal

Abstract: The relationship between mating systems and dispersal has generally been studied at the population and species levels. It has hardly ever been investigated at the individual level, by studying the variations of mating and dispersal strategies between individuals. We investigated this relationship in a natural population of the common lizard (Lacerta vivipara). Assuming that dispersal has a genetic basis, juvenile dispersal would be expected to be more family-dependent in monoandrous litters than in polyandrous litters. The opposite pattern was observed. Thus, maternal effects and/or litter effects play a greater role than genetic determinism in shaping the dispersal phenotype of juveniles. Moreover, the relationship between female mating strategy and offspring dispersal depended on litter success, in a way consistent with an influence of mother-offspring competition. Such a link between mating and dispersal strategies of individuals may have major repercussions for the way we consider the roles of these processes in population functioning.

Diverging Cave- and River-Dwelling Newts Exert the Same Mate Preference in their Native Light Conditions

Abstract: When colonizing a new habitat, populations must adapt their sexual behaviour to new ecological constraints. Because caves display drastically different conditions from surface habitats and cave animals are deprived from visual information, hypogean populations are expected to have modified their mate preference and signalling behaviour after cave colonization. Here, we experimentally examined the female preference and the sexual behaviour of brook newts Calotriton asper from different cave and river populations, either in light or in darkness. Our results suggest that females prefer large individuals in both hypogean and epigean populations, but that this preference is only expressed in the light conditions of their native habitat. Hence, some mate choice criteria would be maintained across genetically divergent populations and throughout dissimilar habitats. However, this sexual behaviour is likely to be expressed via a different sensory pathway in the different habitats, suggesting that a sensory shift has occurred in cave populations, enabling animals to communicate through a non-visual channel.