Romain Julliard

Worldwide decline of specialist species: toward a global functional homogenization?

Specialization is a concept based on a broad theoretical framework developed by evolutionary biologists and ecologists. In the past 10 years, numerous studies have reported that – in many contexts – generalist species are “replacing” specialist species. We review recent research on the concept of the ecological niche and species specialization, and conclude that (1) the observed worldwide decline in specialist species is predicted by niche theory, (2) specialist declines cause “functional homogenization” of biodiversity, and (3) such homogenization may be used to measure the impact of disturbance on communities. Homogenization at the community level could alter ecosystem functioning and productivity, as well as result in the deterioration of ecosystem goods and services. We propose community-level specialization as an indicator of the impact of global changes (habitat and climate disturbances) on biodiversity.

Differences in the climatic debts of birds and butterflies at a continental scale

Climate changes have profound effects on the distribution of numerous plant and animal species(1-3). However, whether and how different taxonomic groups are able to track climate changes at large spatial scales is still unclear. Here, we measure and compare the climatic debt accumulated by bird and butterfly communities at a European scale over two decades (1990-2008). We quantified the yearly change in community composition in response to climate change for 9,490 bird and 2,130 butterfly communities distributed across Europe(4). We show that changes in community composition are rapid but different between birds and butterflies and equivalent to a 37 and 114 km northward shift in bird and butterfly communities, respectively. We further found that, during the same period, the northward shift in temperature in Europe was even faster, so that the climatic debts of birds and butterflies correspond to a 212 and 135 km lag behind climate. Our results indicate both that birds and butterflies do not keep up with temperature increase and the accumulation of different climatic debts for these groups at national and continental scales.

Birds are tracking climate warming, but not fast enough.

Range shifts of many species are now documented as a response to global warming. But whether these observed changes are occurring fast enough remains uncertain and hardly quantifiable. Here, we developed a simple framework to measure change in community composition in response to climate warming. This framework is based on a community temperature index (CTI) that directly reflects, for a given species assemblage, the balance between low- and high-temperature dwelling species. Using data from the French breeding bird survey, we first found a strong increase in CTI over the last two decades revealing that birds are rapidly tracking climate warming. This increase corresponds to a 91 km northward shift in bird community composition, which is much higher than previous estimates based on changes in species range edges. During the same period, temperature increase corresponds to a 273 km northward shift in temperature. Change in community composition was thus insufficient to keep up with temperature increase: birds are lagging approximately 182 km behind climate warming. Our method is applicable to any taxa with large-scale survey data, using either abundance or occurrence data. This approach can be further used to test whether different delays are found across groups or in different land-use contexts.

Advantages of Volunteer-Based Biodiversity Monitoring in Europe

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 in Europe through an on-line questionnaire and is reporting on the results of this survey. In September 2007 the EuMon project had documented 395 monitoring schemes for species, which represents a total annual cost of about 4 million euro, 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, with state-of-the-art survey designs or data-analysis methods, and consequently can yield unbiased results. Quality of data collected by volunteers is more likely determined by survey design, analytical methodology, and communication skills within the schemes rather than by volunteer involvement per se.

Integrating ongoing biodiversity monitoring: potential benefits and methods

Halting the loss of biodiversity comes along with the need to quantify biodiversity composition and dynamics at large spatial and temporal scales. Highly standardized, international monitoring networks would be ideal, but they do not exist yet. If we are to assess changes in biodiversity now, combining output available from ongoing monitoring initiatives is the only option. However, integration of biodiversity information across schemes is still very poorly developed. In this paper, we outline practical issues to be considered when planning to combine existing monitoring information. First, we provide an overview of avenues for integration along the four dimensions that characterize a monitoring design: sample size, biological coverage, spatial coverage and temporal coverage. We also emphasize that complementarity in monitoring targets across schemes enables to describe complex processes of biodiversity dynamics, e.g. through relating species traits to the impacts of environmental changes. Second, we review some methods to overcome differences in designs among monitoring schemes, such as site selection, post-stratification and measurement error. Finally, we point out some commonly used statistical methods that are at hand for combining data or parameter estimates. We especially emphasize the possible levels of data integration (raw data, parameter estimates, or effect size estimates), and the largely under-exploited potential of meta-analysis methods and weighted analyses. This contribution aims to bolster the practice and use of integration of ongoing monitoring initiatives for biodiversity assessment.

Diversifying selection on MHC class I in the house sparrow (Passer domesticus)

Genes of the major histocompatibility complex (MHC) are the most polymorphic loci known in vertebrates. Two main hypotheses have been put forward to explain the maintenance of MHC diversity: pathogen‐mediated selection and MHC‐based mate choice. Host–parasite interactions can maintain MHC diversity via frequency‐dependent selection, heterozygote advantage, and diversifying selection (spatially and/or temporally heterogeneous selection). In this study, we wished to investigate the nature of selection acting on the MHC class I across spatially structured populations of house sparrows (Passer domesticus) in France. To infer the nature of the selection, we compared patterns of population differentiation based on two types of molecular markers: MHC class I and microsatellites. This allowed us to test whether the observed differentiation at MHC genes merely reflects demographic and/or stochastic processes. At the global scale, diversifying selection seems to be the main factor maintaining MHC diversity in the house sparrow. We found that (i) overall population differentiation at MHC was stronger than for microsatellites, (ii) MHC marker showed significant isolation by distance. In addition, the slope of the regression of FST on geographical distance was significantly steeper for MHC than for microsatellites due to a stronger pairwise differentiation between populations located at large geographical distances. These results are in agreement with the hypothesis that spatially heterogeneous selective pressures maintain different MHC alleles at local scales, possibly resulting in local adaptation.

REVIEW: Predictive ecology in a changing world

1. In a rapidly changing world, ecology has the potential to move from empirical and conceptual stages to application and management issues. It is now possible to make large-scale predictions up to continental or global scales, ranging from the future distribution of biological diversity to changes in ecosystem functioning and services. With these recent developments, ecology has a historical opportunity to become a major actor in the development of a sustainable human society. With this opportunity, however, also comes an important responsibility in developing appropriate predictive models, correctly interpreting their outcomes and communicating their limitations. There is also a danger that predictions grow faster than our understanding of ecological systems, resulting in a gap between the scientists generating the predictions and stakeholders using them (conservation biologists, environmental managers, journalists, policymakers). 2. Here, we use the context provided by the current surge of ecological predictions on the future of biodiversity to clarify what prediction means, and to pinpoint the challenges that should be addressed in order to improve predictive ecological models and the way they are understood and used. 3. Synthesis and applications. Ecologists face several challenges to ensure the healthy development of an operational predictive ecological science: (i) clarity on the distinction between explanatory and anticipatory predictions; (ii) developing new theories at the interface between explanatory and anticipatory predictions; (iii) open data to test and validate predictions; (iv) making predictions operational; and (v) developing a genuine ethics of prediction.

PHENOTYPIC ADJUSTMENT OF CLUTCH SIZE DUE TO NEST PREDATION IN THE GREAT TIT

Nest predation may decrease the optimal clutch size for many reasons. In particular, a smaller clutch size may permit more investment in re-laying or in survival to the next reproductive event. The response to nest predation may be either genetic, as shown by comparative studies on birds, or phenotypic, as found in several aquatic species (in- vertebrates and fish). We have studied the effects of several years of high nest predation on clutch size variation in a Great Tit (Parus major) population. We tested whether nest predation was associated with selection on clutch size or with any phenotypic changes. In the year following peak nest predation, mean clutch size was reduced by about one egg. For nest predation, adult survival, and local recruitment, we failed to detect any dependence on clutch size; the reduction in clutch size was mostly phenotypic. Similarly, the return of clutch size to pre-predation values was explained as a phenotypic change. Surprisingly, individuals that did not experience nest predation themselves also modified their clutch size. This suggests that information on past predation persisted in the population for several years. In years with reduced clutch size, adult survival at the population level was higher, suggesting that a reduction in clutch size would be adaptive in case of nest predation, and that females adjusted their clutch size toward the optimum.

Plasmodium relictum infection and MHC diversity in the house sparrow (Passer domesticus)

Antagonistic coevolution between hosts and parasites has been proposed as a mechanism maintaining genetic diversity in both host and parasite populations. In particular, the high level of genetic diversity usually observed at the major histocompatibility complex (MHC) is generally thought to be maintained by parasite-driven selection. Among the possible ways through which parasites can maintain MHC diversity, diversifying selection has received relatively less attention. This hypothesis is based on the idea that parasites exert spatially variable selection pressures because of heterogeneity in parasite genetic structure, abundance or virulence. Variable selection pressures should select for different host allelic lineages resulting in population-specific associations between MHC alleles and risk of infection. In this study, we took advantage of a large survey of avian malaria in 13 populations of the house sparrow (Passer domesticus) to test this hypothesis. We found that (i) several MHC alleles were either associated with increased or decreased risk to be infected with Plasmodium relictum, (ii) the effects were population specific, and (iii) some alleles had antagonistic effects across populations. Overall, these results support the hypothesis that diversifying selection in space can maintain MHC variation and suggest a pattern of local adaptation where MHC alleles are selected at the local host population level.

Evidence for the impact of global warming on the long–term population dynamics of common birds

Taking the opportunity in 2003 of the exceptionally warm spring in France as a natural simulation of possible future climate, we analysed common bird productivity using the French long–term capture–recapture national monitoring scheme. Two–thirds of the 32 species studied had an above–average productivity in 2003. However, this gain in productivity was not consistent among species, with a relatively low productivity for species exhibiting a long–term decline and relatively high productivity for stable or increasing species. Such links between long-term and short–term dynamics suggest that the impact of increasingly warm springs on productivity is a major component of the recent population dynamics of a variety of common bird species.