Reevaluation of dialect boundaries in the Yellowhammer(Emberiza citrinella)based on citizen science data:Should we split or lump?

Dialects are a specific form of geographic variation of birdsong with relatively sharp boundaries between distinct song characteristics,which provide opportunities for focused studies of processes underlying the emergence of spatial patterns in vocalization.Several songbird species that exhibit dialects became models for such research,and for some of them large-scale datasets were assembled that included recordings provided by the public.Among them,the Yellowhammer(Emberiza citrinella,Emberizidae) is particularly prominent,as it has been recently a subject of dedicated citizen science projects focusing on its dialect distribution.The most successful,in terms of public participation as well as the number and density of obtained recordings,was the Dialects of Czech Yellowhammers(DCY) project,which assembled detailed data at the whole-country level.A mosaic of almost all common song variants known across Europe was observed in Czechia,but the results indicated that some of the traditionally recognized Yellowhammer dialects may not represent geographically clustered song variants,at least not in Central Europe.We quantitatively analysed variation(frequency and temporal characteristics and modulation) of the terminal song element in three dialects defined by arbitrary frequency thresholds in DCY.Multivariate analyses indicated that pooling these to two distinct groups reflects the variation in the songs,as well as their spatial distribution,better than retaining the current classification to three dialects or their finer splitting to even more categories.We provide simple measures that may be used for classification of these Yellowhammer song variants in Central Europe.However,we warn from indiscriminate transposing of results from one region to another,as that may lead to substantial biases.Future studies of birdsong variation will benefit from big data assembled by citizen scientists,but to maximise their usefulness for further dialect research,careful delineation of dialect boundaries is essential.

Timing is everything:does early and late germination favor invasions by herbaceous alien plants?

Aims Plant invasions represent a unique opportunity to study the mechanisms underlying community assembly rules and species distribution patterns.While a superior competitive ability has often been proposed as a major driver of successful plant invasions,its significance depends crucially on the timing of any competitive interaction.We assess whether a mismatch in germination phenology can favor the establishment of alien species,allowing them to exploit vacant niches where competition is low.As well as having important effects on the survival,growth and fitness of a species,asymmetric competition and potential soil legacies resulting from early or late germination can also impact on species recruitment.However,early or late germination comes at a cost,increases the risks of exposure to unfavorable conditions and requires an enhanced abiotic resistance if it is to lead to successful establishment.Important Findings While there are several anecdotal accounts of early and late ger-mination for invasive species,there are limited comparative data with resident species growing under natural conditions.Available evidence from grassland communities indicates that a short-term germination advantage or priority(few days/weeks)provides inva-sive species with a strong competitive advantage over native species and is a critical factor in many invasions.While the exploitation of periods of low competition is a plausible mechanism for the suc-cessful establishment of many invasive plants,direct evidence for this strategy is still scarce.This is particularly true with regard to the exploitation of late germination niches.Consequently,long-term comparative monitoring of the germination phenology of invasive and native plants in situ is needed to assess its significance in a range of ecosystems and its impact on community dynamics.

Plant invasions

Almost everyone now seems to have a view about alien plant introductions and their significance and there is an ever increasing body of information,both in the scien-tific and popular press,about the dangers of allowing the uncontrolled spread of alien species.Virtually all possible impacts of plant invasions have been reported,including alterations in biogeochemical cycling,disruption of food webs,alterations in plant-plant,plant-insect and plant-microbe interactions and reductions in biodiversity,leading to the proposal that this is resulting in the creation of novel or emerging ecosystems that have no historical analogue(Hobbs et al.2009).

Genotypic diversity and genotype identity of resident species drive community composition

Aims Species-rich plant communities are more resistant to invasions.In the past decade it was demonstrated that genetic variation also has many ecological effects.In our study we aimed to test whether the patterns of response to the genetic diversity of a resident species differ between colonizing species of different growth forms and whether the response is affected by soil nutrients.Methods We established experimental stands of a common grass,Festuca rubra,harbouring three levels of genetic diversity(1,6 or 18 clonal genotypes,referred to as genotypic diversity)under two soil nutrient levels.In the fourth year after the stands were established,we sowed a mixture of four colonizers into the stands:a stoloniferous legume(Trifolium repens),a broad-leaf tussock grass(Anthoxanthum odoratum),a largerosette forb(Plantago lanceolata)and a small-rosette forb(Campanula rotundifolia).We observed species establishment and growth over 3 years.We tested whether colonization success depended on genotypic diversity,specific Festuca genotypes,soil nutrients and colonizer growth form.Important Findings The colonization success and biomass of the colonizers were significantly affected by the genotypic diversity and the genotype identity of the resident clonal grass.The response,however,differed between the colonizers.The strongest response to the genotypic diversity of the resident species was observed in the tussock grass with a growth form and architecture similar to the resident species.The large-rosette species responded in early stages of growth whereas the stoloniferous legume did not respond at all.The intraspecific genotypic diversity and genotype identity of the resident species play an important role in the assembly of plant communities.