Seasonal climatic niches diverge in migratory birds

Migratory birds occupy different geographical areas during breeding and non-breeding periods, and thus different factors may determine their range limits depending on each season. One such factor is the spatial climatic component of the niche, which is widely used to model species distributions, yet the temporal component is often neglected and is generally assumed to be constant. We tested the hypothesis that the climatic niche is conserved between breeding and non-breeding areas in 355 bird species migrating through Eurasian–African flyways. For this, we performed niche overlap analyses and compared niche differences between sister or phylogenetically closely related species, as well as linking the differences to migratory distances. For more than 80% of the species, there was no or very little overlap between their breeding and non-breeding climatic niches. For most closely related species, the degree of overlap of their breeding climatic niches was larger than the overlap observed within each species, but not for their wintering climatic niches, suggesting a phylogenetic conservation of breeding climatic niches. Finally, there was a clear negative relationship between migratory distances and climatic niche overlap within each species. Our results confirmed that the climatic niche of most Eurasian–African migratory species differs between both breeding and non-breeding ranges, suggesting distinctive seasonal climatic requirements. Given these results and the geographically uneven effects of climate change, the impact of global change is likely to have different effects in each seasonal range. Hence, both breeding and non-breeding climatic data need to be considered when using species distribution models.     

Relating habitat and climatic niches in birds

Predicting species' responses to the combined effects of habitat and climate changes has become a major challenge in ecology and conservation biology. However, the effects of climatic and habitat gradients on species distributions have generally been considered separately. Here, we explore the relationships between the habitat and thermal dimensions of the ecological niche in European common birds. Using data from the French Breeding Bird Survey, a large-scale bird monitoring program, we correlated the habitat and thermal positions and breadths of 74 bird species, controlling for life history traits and phylogeny. We found that cold climate species tend to have niche positions in closed habitats, as expected by the conjunction of the biogeographic history of birds' habitats, and their current continent-scale gradients. We also report a positive correlation between thermal and habitat niche breadths, a pattern consistent with macroecological predictions concerning the processes shaping species' distributions. Our results suggest that the relationships between the climatic and habitat components of the niche have to be taken into account to understand and predict changes in species' distributions.     

Predicting the past distribution of species climatic niches

Predicting past distributions of species climatic niches, hindcasting, by using climate envelope models (CEMs) is emerging as an exciting research area. CEMs are used to examine veiled evolutionary questions about extinctions, locations of past refugia and migration pathways, or to propose hypotheses concerning the past population structure of species in phylogeographical studies. CEMs are sensitive to theoretical assumptions, to model classes and to projections in non-analogous climates, among other issues. Studies hindcasting the climatic niches of species often make reference to these limitations. However, to obtain strong scientific inferences, we must not only be aware of these potential limitations but we must also overcome them. Here, I review the literature on hindcasting CEMs. I discuss the theoretical assumptions behind niche modelling, i.e. the stability of climatic niches through time and the equilibrium of species with climate. I also summarize a set of 'recommended practices' to improve hindcasting. The studies reviewed: (1) rarely test the theoretical assumptions behind niche modelling such as the stability of species climatic niches through time and the equilibrium of species with climate; (2) they only use one model class (72% of the studies) and one palaeoclimatic reconstruction (62.5%) to calibrate their models; (3) they do not check for the occurrence of non-analogous climates (97%); and (4) they do not use independent data to validate the models (72%). Ignoring the theoretical assumptions behind niche modelling and using inadequate methods for hindcasting CEMs may well entail a cascade of errors and naïve ecological and evolutionary inferences. We should also push integrative research lines linking macroecology, physiology, population biology, palaeontology, evolutionary biology and CEMs for a better understanding of niche dynamics across space and time.     

Phylogenetic signals in the climatic niches of the world's amphibians

The question of whether closely related species share similar ecological requirements has attracted increasing attention, because of its importance for understanding global diversity gradients and the impacts of climate change on species distributions. In fact, the assumption that related species are also ecologically similar has often been made, although the prevalence of such a phylogenetic signal in ecological niches remains heavily debated. Here, we provide a global analysis of phylogenetic niche relatedness for the world's amphibians. In particular, we assess which proportion of the variance in the realised climatic niches is explained on higher taxonomic levels, and whether the climatic niches of species within a given taxonomic group are more similar than between taxonomic groups. We found evidence for phylogenetic signals in realised climatic niches although the strength of the signal varied among amphibian orders and across biogeographical regions. To our knowledge, this is the first study providing a comprehensive analysis of the phylogenetic signal in species climatic niches for an entire clade across the world. Even though our results do not provide a strong test of the niche conservatism hypothesis, they question the alternative hypothesis that niches evolve independently of phylogenetic influences.     

The diversity of temporal niches in mammals

The division of animals into those that are diurnal (day-active) and those that are nocturnal (night-active) is widely recognized. However, closer examination of the selection of temporal niches by mammalian species reveals the existence of a gradient of diurnality between and within species, wherein “diurnal” and “nocturnal” are merely the opposite ends of a continuum. Evidence against a simple diurnal - nocturnal dichotomy includes the existence of species without any preference for time of day, species with a crepuscular pattern of activity, species containing both diurnal and nocturnal individuals, species containing individuals that spontaneously shift from a nocturnal to a diurnal activity pattern, species showing degrees of diurnality greater or smaller than those of other species, organismal variables exhibiting degrees of diurnality greater or smaller than those of other variables, and species having different temporal patterns under the effects of different environmental variables. Research on the neural processes responsible for temporal niche selection has revealed no fundamental difference between the circadian clocks of diurnal and nocturnal animals, but recent findings suggest that different output pathways from the clock in a given species may operate with different circadian phases, thus providing an explanation for why different body functions in the same individual are subjected to different temporal niche selections.     

The macroevolution of climatic niches and its role in ant diversification

1. Investigating how climatic niches change over evolutionary timescales is a necessary step to understanding the current distribution of lineages, yet few studies have addressed this issue using comprehensive datasets. In this study, the evolution of ant climatic niches is investigated at a global scale based on bioclimatic data associated with 163 481 ant occurrence records. The resulting dataset was subjected to principal component analysis, and the scores obtained were used to characterise the main axes of ant climatic niche evolution. 2. Principal component axis 1 (PC1) reflected variation in average temperature and seasonality – consistent with typical tropical/temperate gradients – whereas PC2 was associated with varying levels of aridity. Evolution along these two niche axes was markedly different: differences in the amount of explained variance between PC1 (65%) and PC2 (19%) suggest that climatic niche evolution was nearly three times more pronounced along a tropical–temperate climate axis. 3. There was statistically significant phylogenetic signal on PC1, with genera occupying more tropical conditions diversifying at a faster rate, yet neither of these results is significant on PC2. In addition, most of the ancient ant lineages are associated with conditions of low seasonality and high temperatures. 4. These results provide partial support for the tropical conservatism hypothesis as an explanation for geographical patterns of ant species richness.     

Realized climatic niches of deciduous trees: comparing western Eurasia and eastern North America

Aim  Assessment of cross-continental similarities and differences in climatic limiting values for deciduous tree species and of the possible deterministic influence of past and present climatic differences on the modern tree flora in two regions.
Location  The deciduous forest regions of western Eurasia and eastern North America.
Methods  Based on species distribution data (range maps) and climate site data, the realized climatic niches of 137 deciduous tree species from the two regions were quantified using climatic envelopes. To compare these envelopes on the two continents, a hierarchical cluster analysis was performed, and principal components analysis was used to check cluster consistency.
Results  Significant differences do exist for upper limits of winter temperatures and for lower limits of summer temperatures between Western Eurasia and eastern North America. Lower limits for the annual water balance also appear different, suggesting that the deciduous trees may be more drought-tolerant in western Eurasia than in eastern North America. Climatic range types generated by the cluster analysis can be characterized, according to the distribution of the species, as boreal-temperate, northern temperate, temperate, southern temperate, and Appalachian. Five of the eight clusters contain trees from both regions, but three groups consist only of American species that have no European counterparts.
Main conclusions  Differences in temperature limitations can be explained by location on the east versus west side of the continents and by the almost complete lack of warm moist areas in western Eurasia. The difference in drought tolerance, on the other hand, is more likely to be the product of a deterministic sorting process that occurred during the Plio-Pleistocene.     

Fractal dimension of birds population sizes time series

Information about fractal dimension is collected so that it can be applied to time series interpreting Hurst coefficient. The population size of a species is modelled as a dynamic system. The Hurst coefficient is calculated for these times series. A computer programme has been elaborated to compute the Hurst exponent of time series using the algorithms of range increment, second order moment increment and local second order moment increment. It has been applied to time series of birds' populations.     

Overlap of temporal niches among four sympatric species of shrews

Hypotheses about the dependence of circadian activity from metabolic rate and the segregation of temporal niches among competing species were verified by the study of activity patterns in a shrew community of two semiaquatic species,Neomys anomalus Cabrera, 1907 andN. fodiens (Pennant, 1771), and two terrestrial species,Sorex araneus Linnaeus, 1758 andS. minutus Linnaeus, 1766, co-existing in wet habitats of Białowieża Forest (E Poland). In ten trapping sessions, performed in early summer between 1991 and 2000, traps were open 24 hours continuously and patrolled at 1:00, 5:00, 10:00, 15:00, and 20:00. All the shrew species were most active between 20:00 and 1:00, and least active around mid-day (10:00–15:00). However, activity of the twoSorex species was lower than that of the twoNeomys species in the period 20:00–1:00, but higher in the period 15:00–20:00. BothNeomys species displayed clearly nocturnal, unimodal patterns of activity. In contrast, activity of bothSorex species was relatively evenly distributed over 24 hours and they increased their activity earlier (ie after 15:00) than bothNeomys species (after 20:00). These results confirm the idea that small shrew species with higher metabolic rate have more frequent and more equally distributed activity bouts than large species. Overlap of temporal niches was the highest within genera (99.29% between bothNeomys species and 98.36% between bothSorex species), the lowest betweenN. fodiens andS. araneus (88.26%) andS. minutus (89.34%), and intermediate betweenN. anomalus and bothSorex species (91.78 and 93.34%, respectively). Such high interspecific overlaps in activity suggest a joint-action of other mechanisms that separate ecological niches of these species also in other dimensions (eg food, microhabitat).     

The temporal dimension of marine speciation

Speciation is a process that occurs over time and, as such, can only be fully understood in an explicitly temporal context. Here we discuss three major consequences of speciation’s extended duration. First, the dynamism of environmental change indicates that nascent species may experience repeated changes in population size, genetic diversity, and geographic distribution during their evolution. The present characteristics of species therefore represents a static snapshot of a single time point in a species’ highly dynamic history, and impedes inferences about the strength of selection or the geography of speciation. Second, the process of speciation is open ended—ecological divergence may evolve in the space of a few generations while the fixation of genetic differences and traits that limit outcrossing may require thousands to millions of years to occur. As a result, speciation is only fully recognized long after it occurs, and short-lived species are difficult to discern. Third, the extinction of species or of clades provides a simple, under-appreciated, mechanism for the genetic, biogeographic, and behavioral ‘gaps’ between extant species. Extinction also leads to the systematic underestimation of the frequency of speciation and the overestimation of the duration of species formation. Hence, it is no surprise that a full understanding of speciation has been difficult to achieve. The modern synthesis—which united genetics, development, ecology, biogeography, and paleontology—greatly advanced the study of evolution. Here we argue that a similarly synthetic approach must be taken to further our understanding of the origin of species.     

Niche-tracking migrants and niche-switching residents: evolution of climatic niches in New World warblers (Parulidae)

Differences in life-history traits between tropical and temperate lineages are often attributed to differences in their climatic niche dynamics. For example, the more frequent appearance of migratory behaviour in temperate-breeding species than in species originally breeding in the tropics is believed to have resulted partly from tropical climatic stability and niche conservatism constraining tropical species from shifting their ranges. However, little is known about the patterns and processes underlying climatic niche evolution in migrant and resident animals. We evaluated the evolution of overlap in climatic niches between seasons and its relationship to migratory behaviour in the Parulidae, a family of New World passerine birds. We used ordination methods to measure seasonal niche overlap and niche breadth of 54 resident and 49 migrant species and used phylogenetic comparative methods to assess patterns of climatic niche evolution. We found that despite travelling thousands of kilometres, migrants tracked climatic conditions across the year to a greater extent than tropical residents. Migrant species had wider niches than resident species, although residents as a group occupied a wider climatic space and niches of migrants and residents overlapped extensively. Neither breeding latitude nor migratory distance explained variation among species in climatic niche overlap between seasons. Our findings support the notion that tropical species have narrower niches than temperate-breeders, but does not necessarily constrain their ability to shift or expand their geographical ranges and become migratory. Overall, the tropics may have been historically less likely to experience the suite of components that generate strong selection pressures for the evolution of migratory behaviour.     

Potential impacts of climatic change on European breeding birds

Background

Climatic change is expected to lead to changes in species'' geographical ranges. Adaptation strategies for biodiversity conservation require quantitative estimates of the magnitude, direction and rates of these potential changes. Such estimates are of greatest value when they are made for large ensembles of species and for extensive (sub-continental or continental) regions.

Methodology/Principal Findings

For six climate scenarios for 2070–99 changes have been estimated for 431 European breeding bird species using models relating species'' distributions in Europe to climate. Mean range centroid potentially shifted 258–882 km in a direction between 341° (NNW) and 45° (NE), depending upon the climate scenario considered. Potential future range extent averaged 72–89% of the present range, and overlapped the present range by an average of 31–53% of the extent of the present range. Even if potential range changes were realised, the average number of species breeding per 50×50 km grid square would decrease by 6·8–23·2%. Many species endemic or near-endemic to Europe have little or no overlap between their present and potential future ranges; such species face an enhanced extinction risk as a consequence of climatic change.

Conclusions/Significance

Although many human activities exert pressures upon wildlife, the magnitude of the potential impacts estimated for European breeding birds emphasises the importance of climatic change. The development of adaptation strategies for biodiversity conservation in the face of climatic change is an urgent need; such strategies must take into account quantitative evidence of potential climatic change impacts such as is presented here.     

The climatic drivers of long-term population changes in rainforest montane birds

Climate-driven biodiversity erosion is escalating at an alarming rate. The pressure imposed by climate change is exceptionally high in tropical ecosystems, where species adapted to narrow environmental ranges exhibit strong physiological constraints. Despite the observed detrimental effect of climate change on ecosystems at a global scale, our understanding of the extent to which multiple climatic drivers affect population dynamics is limited. Here, we disentangle the impact of different climatic stressors on 47 rainforest birds inhabiting the mountains of the Australian Wet Tropics using hierarchical population models. We estimate the effect of spatiotemporal changes in temperature, precipitation, heatwaves, droughts and cyclones on the population dynamics of rainforest birds between 2000 and 2016. We find a strong effect of warming and changes in rainfall patterns across the elevational-segregated bird communities, with lowland populations benefiting from increasing temperature and precipitation, while upland species show an inverse strong negative response to the same drivers. Additionally, we find a negative effect of heatwaves on lowland populations, a pattern associated with the observed distribution of these extreme events across elevations. In contrast, cyclones and droughts have a marginal effect on spatiotemporal changes in rainforest bird communities, suggesting a species-specific response unrelated to the elevational gradient. This study demonstrated the importance of unravelling the drivers of climate change impacts on population changes, providing significant insight into the mechanisms accelerating climate-induced biodiversity degradation.     

水稻纹枯病时空生态位施药干扰研究

以施药作为干扰因子,研究干扰条件下水稻纹枯病菌的时间和空间生态位变化.结果表明,各施药处理与对照纹枯病菌的空间生态位存在差异,其中孕穗期施药+齐穗期施药和孕穗期施药+灌浆期施药两处理的空间生态位宽度指数分别为0.520、0.572,与对照的空间生态位宽度指数0.8563相差最大;分蘖盛期一次施药处理的空间生态位宽度指数为0.8577,与对照相差最小.各施药处理和对照的时间生态位宽度无显著差异,表明施药对纹枯病菌的时间生态位宽度影响不大.空间生态位宽度指数、病叶(鞘)率、病情指数及防治效果等计测结果表明,两次施药对病害的控制好于一次施药,其中两次施药中以孕穗期施药+齐穗期施药和孕穗期施药+灌浆期施药对病害的控制作用最强.施药不但压缩了水稻纹枯病菌的空间生态位宽度,限制了其在产量形成较为重要的上部叶位的扩张,而且压缩了水稻纹枯病菌的时间生态位宽度,限制了其在水稻产量形成时期的扩张.但施药只改变了病菌生态位的分布,调整压缩了水稻产量形成期的病害生态位,病菌生态位势的总和不变.