Migratory strategy drives species-level variation in bird sensitivity to vegetation green-up

Accumulating evidence suggests that density dependence, whether at early or late life stages, is an important mechanism regulating plant population structure. However, the opposing effects of habitat heterogeneity and species-level variation might have confounded the prevalence of density dependence in natural forests. These compatible ideas were rarely considered simultaneously. In this study, we applied a spatial statistical technique to examine (i) the prevalence of density dependence at late life stages after controlling for habitat heterogeneity and (ii) the relationships between species traits and the strength of density dependence in a newly established, 25 ha subtropical mountain forest plot in central China. Of the 88 (75%) tree species analyzed, 66 were found to exhibit density dependence predominantly at very close distances among neighbors in the species-rich subtropical forest. In addition, the strength of density dependence was associated with species traits. Our findings identified strong density dependence among trees that had greater stature and were rarer. We concluded that density dependence was a prevalent mechanism for regulating the population structure of most tree species and both habitat heterogeneity and species-level variation played crucial roles in shaping the strength of density dependence in natural forests.

Despite the central role of species distributions in ecology and conservation, occurrence information remains geographically and taxonomically incomplete and biased. Numerous socio-economic and ecological drivers of uneven record collection and mobilization among species have been suggested, but the generality of their effects remains untested. We develop scale-independent metrics of range coverage and geographical record bias, and apply them to 2.8M point-occurrence records of 3,625 mammal species to evaluate 13 putative drivers of species-level variation in data availability. We find that data limitations are mainly linked to range size and shape, and the geography of socio-economic conditions. Surprisingly, species attributes related to detection and collection probabilities, such as body size or diurnality, are much weaker predictors of the amount and range coverage of available records. Our results highlight the need to prioritize range-restricted species and to address the key socio-economic drivers of data bias in data mobilization efforts and distribution modeling.

Abstract Species delimitation requires a broad assessment of population-level variation using multiple lines of evidence, a process known as integrative taxonomy. More specifically, studies of species limits must address underlying questions of what limits the distribution of populations, how traits vary in association with different environments, and whether the observed trait differences may lead to speciation through reproductive isolation. While genomic data have revolutionized the process of delimiting species, such data should be analyzed along with phenotypic, behavioral, and ecological traits that shape individuals across geographic and environmental space. The integration of multiple traits promotes taxonomic stability and should be a major guiding principle for species delimitation. Equally important, however, is thorough geographic sampling to adequately represent population-level variation—both in allopatry and across putative contact zones. We discuss the importance of both of these factors in the context of species concepts and traits and present different examples from birds that illustrate criteria for species delimitation. In addition, we review a decade of proposals for species-level taxonomic revisions considered by the American Ornithological Society’s North American Classification Committee, and summarize the basis for decisions on whether to split or lump species. Finally, we present recommendations and discuss challenges (specifically permits, time, and funding) for species delimitation studies. This is an exciting time to be studying species delimitation in birds: many species-level questions remain, and methodological advances along with increased access to data enable new approaches to studying age-old problems in avian taxonomy.

Despite the central role of species distributions in ecology and conservation, occurrence information remains geographically and taxonomically incomplete and biased. Numerous socio-economic and ecological drivers of uneven record collection and mobilization among species have been suggested, but the generality of their effects remains untested. We develop scale-independent metrics of range coverage and geographical record bias, and apply them to 2.8M point-occurrence records of 3,625 mammal species to evaluate 13 putative drivers of species-level variation in data availability. We find that data limitations are mainly linked to range size and shape, and the geography of socio-economic conditions. Surprisingly, species attributes related to detection and collection probabilities, such as body size or diurnality, are much weaker predictors of the amount and range coverage of available records. Our results highlight the need to prioritize range-restricted species and to address the key socio-economic drivers of data bias in data mobilization efforts and distribution modeling.

Despite the central role of species distributions in ecology and conservation, occurrence information remains geographically and taxonomically incomplete and biased. Numerous socio-economic and ecological drivers of uneven record collection and mobilization among species have been suggested, but the generality of their effects remains untested. We develop scale-independent metrics of range coverage and geographical record bias, and apply them to 2.8M point-occurrence records of 3,625 mammal species to evaluate 13 putative drivers of species-level variation in data availability. We find that data limitations are mainly linked to range size and shape, and the geography of socio-economic conditions. Surprisingly, species attributes related to detection and collection probabilities, such as body size or diurnality, are much weaker predictors of the amount and range coverage of available records. Our results highlight the need to prioritize range-restricted species and to address the key socio-economic drivers of data bias in data mobilization efforts and distribution modeling.

In response to environmental stressors, organisms often demonstrate flexible responses in morphology, life history or behaviour. However, it is currently unclear if such plastic responses are coordinated or operate independently of one another. In vertebrates, this may partly result from studies examining population- or species-level mean responses, as opposed to finer grained analyses of individuals or families. We measured predator-specific morphological and coloration plasticity in 42 families of tadpoles of the treefrog Dendropsophus ebraccatus and behavioural plasticity from 18 of these families, allowing us to examine the correlation between three predator-induced plastic responses. For all three plastic responses, tadpoles showed strong opposing responses to each of two predators, providing the appearance of covariation in plasticity. However, the examination of individual families revealed a strong correlation between morphological and coloration plasticity, but no correlations between either morphology or colour and behavioural plasticity. Thus, our analysis shows that some aspects of the plastic phenotype develop together while others function independently. This highlights the importance of examining individual- and family-level variation for understanding the adaptive significance of developmental plasticity, which is crucial for a holistic appreciation of phenotypic plasticity and its importance in ecology and evolution.

Molecular and cellular mechanisms underlying differences in adult form remain largely unknown. Adult pigment patterns of fishes in the genus Danio, which includes zebrafish, D. rerio, include horizontal stripes, vertical bars, spots and uniform patterns, and provide an outstanding opportunity to identify causes of species level variation in a neural crest derived trait. Yet understanding such variation requires quantitative approaches to assess phenotypes, and such methods have been mostly lacking for pigment patterns. We introduce metrics derived from information theory that describe patterns and pattern variation in Danio fishes. We find that such metrics used singly and in multivariate combinations are suitable for distinguishing general pattern types, and can reveal even subtle phenotypic differences attributable to mutations. Our study provides new tools for analyzing pigment pattern in Danio and potentially other groups, and sets the stage for future analyses of pattern morphospace and its mechanistic underpinnings.