Jiří Reif

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.

More and more generalists: two decades of changes in the European avifauna.

Biotic homogenization (BH) is a process whereby some species (losers) are systematically replaced by others (winners). While this process has been related to the effects of anthropogenic activities, whether and how BH is occurring across regions and the role of native species as a driver of BH has hardly been investigated. Here, we examine the trend in the community specialization index (CSI) for 234 native species of breeding birds at 10 111 sites in six European countries from 1990 to 2008. Unlike many BH studies, CSI uses abundance information to estimate the balance between generalist and specialist species in local assemblages. We show that bird communities are more and more composed of native generalist species across regions, revealing a strong, ongoing BH process. Our result suggests a rapid and non-random change in community composition at a continental scale is occurring, most likely driven by anthropogenic activities.

FEMALE HETEROGAMETY AND SPECIATION: REDUCED INTROGRESSION OF THE Z CHROMOSOME BETWEEN TWO SPECIES OF NIGHTINGALES

Several lines of evidence suggest that the X chromosome plays a large role in intrinsic postzygotic isolation. The role of the Z chromosome in speciation is much less understood. To explore the role of the Z chromosome in reproductive isolation, we studied nucleotide variation in two closely related bird species, the Thrush Nightingale (Luscinia luscinia) and the Common Nightingale (L. megarhynchos). These species are isolated by incomplete prezygotic isolation and female hybrid sterility. We sequenced introns of four Z‐linked and eight autosomal loci and analyzed patterns of polymorphism and divergence using a divergence‐with‐gene flow framework. Our results suggest that the nightingale species diverged approximately 1.8 Mya. We found strong evidence of gene flow after divergence in both directions, although more introgression occurred from L. megarhynchos into L. luscinia. Gene flow was significantly higher on the autosomes than on the Z chromosome. Our results support the idea that the Z chromosome plays an important role in intrinsic postzygotic isolation in birds, although it may also contribute to the evolution of prezygotic isolation through sexual selection. This highlights the similarities in the genetic basis of reproductive isolation between organisms with heterogametic males and organisms with heterogametic females during the early stages of speciation.

Between Geometry and Biology: The Problem of Universality of the Species-Area Relationship

The species-area relationship (SAR) is considered to be one of a few generalities in ecology, yet a universal model of its shape and slope has remained elusive. Recently, Harte et al. argued that the slope of the SAR for a given area is driven by a single parameter, the ratio between total number of individuals and number of species (i.e., the mean population size across species at a given scale). We provide a geometric interpretation of this dependence. At the same time, however, we show that this dependence cannot be universal across taxa: if it holds for a taxon composed from two subsets of species and also for one of its subsets, it cannot simultaneously hold for the other subset. Using three data sets, we show that the slope of the SAR considerably varies around the prediction. We estimate the limits of this variation by using geometric considerations, providing a theory based on species spatial turnover at different scales. We argue that the SAR cannot be strictly universal, but its slope at each particular scale varies within the constraints given by species’ spatial turnover at finer spatial scales, and this variation is biologically informative.

Long-term trends in bird populations: a review of patterns and potential drivers in North America and Europe

Abstract Data from breeding bird monitoring schemes provided material for numerous studies to relate the trends of particular species to their ecological and life history traits. This review contains a comprehensive comparison of results of these studies, describes the patterns in bird population trends in North America and Europe in last forty years and discusses potential drivers. I omitted other sources of bird population trend estimates to reduce methodological bias and because bird monitoring studies are rarely represented in other parts of the world. The most intensively studied driver is habitat alteration on breeding grounds represented by agricultural intensification in Western Europe and North American grasslands, forest expansion and land abandonment in Northern, Southern and Eastern Europe and parts of North America, and more localized urbanization and forest habitat fragmentation. Evidence for climate change impacts is robust and includes almost all European regions covered by the reviewed studies but the causal mechanisms of its influence on bird abundance are not sufficiently known. Population limitation by environmental changes in wintering quarters is well supported by the studies covering 1970s and 1980s, whereas the effects of migration strategy became less important from 1990s onwards. Support for other potential drivers, such as direct disturbance by humans, is rather limited and further studies are needed to confirm their effects.

Rarity, Commonness, and the Contribution of Individual Species to Species Richness Patterns

Common species have a greater effect on observed geographical patterns of species richness than do rare ones. Here we present a theory of the relationship between individual species occurrence patterns and patterns in species richness, which allows purely geometrical and statistical causes to be distinguished from biological ones. Relationships between species occupancy and the correlation of species occurrence with overall species richness are driven by the frequency distribution of species richness among sites. Moreover, generally positive relationships are promoted by the fact that species occupancy distributions are mostly right skewed. However, biological processes can lead to deviations from the predicted pattern by changing the nestedness of a species’ spatial distribution with regard to the distributions of other species in an assemblage. We have applied our theory to data for European birds at several spatial scales and have identified the species with significantly stronger or weaker correspondence with the overall richness pattern than that predicted by the null model. In sum, whereas the general macroecological pattern of a stronger influence of common species than of rare species on species richness is predicted by mathematical considerations, the theory can reveal biologically important deviations at the level of individual species.

Habitat specialization of birds in the Czech Republic: comparison of objective measures with expert opinion

Capsule Expert‐based classification of bird species as habitat specialists and as generalists agrees with objective measures of species’ habitat requirements based on large‐scale monitoring data. Aims To compare habitat specialization of 137 common bird species breeding in the Czech Republic using three different measures and to test their relationships to species’ abundance and habitat associations. Methods Data on bird abundance and surveyed habitats were collected through a standardized monitoring scheme of common breeding species in the Czech Republic. From these data we calculated a quantitative species specialization index (SSI). Canonical correspondence analysis (CCA) was applied to calculate species’ habitat niche breadth and the level of association of each species to the main habitats. A panel of 11 local bird experts classified each species as habitat generalist or habitat specialist. Results Species classified as habitat specialists by expert opinion showed higher habitat specialization according to the SSI, as well as according to CCA‐based habitat niche breadth. These species were also more closely associated with one of the main habitat types. These relationships were significant even after controlling for abundance. Conclusions As expert opinion accords with the level of species’ habitat specialization expressed using two quantitative objective measures, we suggest that these characteristics reflect real interspecific variation in the breadth of habitat requirements in birds. Interspecific differences in habitat specialization are not caused solely by the variability in abundance among species.

Ecological character displacement in the face of gene flow: evidence from two species of nightingales.

BackgroundEcological character displacement is a process of phenotypic differentiation of sympatric populations caused by interspecific competition. Such differentiation could facilitate speciation by enhancing reproductive isolation between incipient species, although empirical evidence for it at early stages of divergence when gene flow still occurs between the species is relatively scarce. Here we studied patterns of morphological variation in sympatric and allopatric populations of two hybridizing species of birds, the Common Nightingale (Luscinia megarhynchos) and the Thrush Nightingale (L. luscinia).ResultsWe conducted principal component (PC) analysis of morphological traits and found that nightingale species converged in overall body size (PC1) and diverged in relative bill size (PC3) in sympatry. Closer analysis of morphological variation along geographical gradients revealed that the convergence in body size can be attributed largely to increasing body size with increasing latitude, a phenomenon known as Bergmanns rule. In contrast, interspecific interactions contributed significantly to the observed divergence in relative bill size, even after controlling for the effects of geographical gradients. We suggest that the divergence in bill size most likely reflects segregation of feeding niches between the species in sympatry.ConclusionsOur results suggest that interspecific competition for food resources can drive species divergence even in the face of ongoing hybridization. Such divergence may enhance reproductive isolation between the species and thus contribute to speciation.

Changes in bird community composition in the Czech Republic from 1982 to 2004: increasing biotic homogenization, impacts of warming climate, but no trend in species richness

AbstractRecent major environmental changes could lead to homogenization in the composition of plant and animal communities, with generalist species replacing more specialized species, as well as to the increased domination of species adapted to warmer climatic conditions. Using common bird monitoring data, we have tested whether these patterns can be observed in the long-term changes in the structure and species richness of bird communities in the Czech Republic. We focused on a comparison of two time periods (1982–1990 and 1991–2004) that differ in land use (high agricultural intensity in the former, and a drop in agricultural intensity accompanied by forest expansion in the latter). We found that bird communities became less specialized and that this decline in specialization did not change after 1990. In contrast, taxonomic homogenization increased during the first time period but declined at the beginning of the second one. Moreover, the community composition developed towards a dominance of species breeding in warmer climates, and this change coincided with an increase in spring temperatures. Therefore, it would appear that both functional and taxonomic homogenization took place in the 1980s but the latter did not continue in subsequent decades. Species richness of local bird communities did not show any trend over time. We suggest that climate warming might be an important driving force of changes in the bird community composition in the Czech Republic, but the role of land-use changes is less clear, although it is probable that habitat specialists probably did not benefit from lower intensity of agricultural activities and increased forest cover.ZusammenfassungÄnderungen in der Zusammensetzung von Vogelgemeinschaften in der Tschechischen Republik zwischen 1982 und 2004: zunehmende biotische Vereinheitlichung, Einfluss von Klimaerwärmung, aber kein Trend im Artenreichtum Aktuelle große Veränderungen in der Umwelt könnten zu einer Vereinheitlichung der Zusammensetzung von Tier- und Pflanzengemeinschaften führen, wobei Generalisten die spezialisierteren Arten ersetzen und Arten dominieren, die an wärmere Klimate angepasst sind. Anhand normaler Vogel-Monitoring Daten testen wir in dieser Studie, ob sich diese Muster in langfristigen Veränderungen in der Struktur und dem Artenreichtum der Vogelgemeinschaften in der Tschechischen Republik beobachten lassen. Wir konzentrieren uns auf einen Vergleich zwischen zwei Zeiträumen (1982–1990 und 1991–2004), die sich in der Landnutzung unterscheiden (intensive Landwirtschaft im früheren und ein Absinken der Intensität der Landnutzung begleitet von einer Ausbreitung von Waldgebieten im letzteren). Wir fanden, dass die Vogelgemeinschaften weniger spezialisiert wurden, und diese Abnahme der Spezialisierung änderte sich nicht nach 1990. Dagegen stieg die taxonomische Vereinheitlichung während des ersten Zeitraums an, nahm aber am Beginn des zweiten wieder ab. Darüber hinaus entwickelte sich die Zusammensetzung der Gemeinschaft hin zu einer Dominanz von Arten, die ihre Brutgebiete in wärmeren Klimaten haben, und diese Änderung fiel zusammen mit einem Ansteigen der Frühlingstemperaturen. Daher scheint es, als hätten sowohl die funktionale als auch die taxonomische Vereinheitlichung in den 1980er Jahren stattgefunden, aber die erstere schritt später nicht fort. Der Artenreichtum lokaler Vogelgemeinschaften zeigte keinerlei Trend über die Zeit. Wir stellen zur Diskussion, dass die Klimaerwärmung eine treibende Kraft sein könnte für Änderungen in der Zusammenstellung der Vogelgemeinschaft in der Tschechischen Republik, jedoch ist die Rolle der Landnutzung weniger klar. Arten, die auf ein bestimmtes Habitat spezialisiert sind, konnten wahrscheinlich nicht profitieren von der weniger intensiven Landnutzung und der Zunahme der Wälder.

Changes in bird distribution in a Central European country between 1985–1989 and 2001–2003

European birds have been significantly affected by dramatic environmental changes during the last decades. The effects of these changes on species richness and distribution in particular countries are still poorly understood because of a lack of high-quality, large-scale data standardized over time. This is especially true in Central and Eastern Europe. On a model group of birds in the Czech Republic (countrywide atlas mapping data), we examined whether long-term changes of species richness and distribution between 1985–1989 and 2001–2003 differed among groups of species defined by their habitat requirements, type of distribution in Europe, migratory strategy and the degree of national legal protection. Further, we investigated the effects of colonizers and local extinctions on these changes. Whereas the number of species in the whole country remained the same in both periods (208 species), species composition had changed. Increasing occupancy (i.e., number of occupied mapping squares) was observed in species of forest and wetland habitats, in short-distance migrants and in non-protected species. Southern species also positively changed their occupancy, but this pattern disappeared after the inclusion of six species dependent on extensively cultivated farmland that went extinct between mappings. The overall occupancy of all species together showed positive changes after excluding colonizers and extinct species. We suggest that the improvement of environmental conditions after 1990 caused the stability of or increased the distribution of common birds in the Czech Republic, and it was the disappearance of specific farmland practices that might have caused the loss of several species.