Host preferences and differential contributions of deciduous tree species shape mycorrhizal species richness in a mixed Central European forest

Mycorrhizal species richness and host ranges were investigated in mixed deciduous stands composed of Fagus sylvatica, Tilia spp., Carpinus betulus, Acer spp., and Fraxinus excelsior. Acer and Fraxinus were colonized by arbuscular mycorrhizas and contributed 5% to total stand mycorrhizal fungal species richness. Tilia hosted similar and Carpinus half the number of ectomycorrhizal (EM) fungal taxa compared with Fagus (75 putative taxa). The relative abundance of the host tree the EM fungal richness decreased in the order Fagus > Tilia >> Carpinus. After correction for similar sampling intensities, EM fungal species richness of Carpinus was still about 30–40% lower than that of Fagus and Tilia. About 10% of the mycorrhizal species were shared among the EM forming trees; 29% were associated with two host tree species and 61% with only one of the hosts. The latter group consisted mainly of rare EM fungal species colonizing about 20% of the root tips and included known specialists but also putative non-host associations such as conifer or shrub mycorrhizas. Our data indicate that EM fungal species richness was associated with tree identity and suggest that Fagus secures EM fungal diversity in an ecosystem since it shared more common EM fungi with Tilia and Carpinus than the latter two among each other

Avaliação auditiva objetiva através de potenciais evocados

Analisaram-se 1300 exames de Potencial Evocado Auditivo. Classificaram-se os pacientes segundo faixa de idade, apresentação clínica, relato de fatores de risco que levam a deficiência auditiva e limiar auditivo determinado pelo exame. Distribuíram-se os resultados em 5 faixas de limiar auditivo: audição normal (até 25 dBHL); perda auditiva moderada (25-50 dBHL); perda acentuada (50-70 dBHL); perda severa (70-90 dRHL); e sem resposta ao estímulo auditivo. Estudaram-se os fatores de risco relativos a gestação, parto e período neonatal, história familiar de deficiência auditiva, malformações do aparelho auditivo, anomalias crânio-faciais, síndromes associadas a deficiência auditiva, certas modalidades de doenças infecciosas e uso de determinadas drogas. Investigaram-se também os itens Retardo do Desenvolvimento Neuropsicomotor, Paralisia Cerebral e os casos sem antecedentes conhecidos. Entre as conclusões destacam-se: 82,8% dos pacientes eram portadores de alguma forma de deficiência auditiva; o encaminhamento é tardio, evidenciado pelo fato de 54,1% dos pacientes situarem-se entre 1 e 3 anos de idade; 54,0% da totalidade dos casos apresentavam-se sem linguagem; o fator de risco «Rubéola Congênita» possui a elevada incidência de 14,8%, e este percentual distribuído nas faixas de limiar auditivo revelou um crescimento exponencial, demonstrando inequívoca e acentuada correlação da moléstia com deficiência auditiva

Knowledge networks in high-tech clusters: a multilevel perspective on interpersonal and inter-organizational collaboration

This study contributes to research on knowledge networks in high-tech clusters by adding a multilevel perspective. We show that while informal individual-level and formal organizational-level knowledge networks created by nested actors partly follow their own structural logic, they are at the same time logically intertwined. Interpersonal knowledge ties influence the maintenance of formal R&D collaborations and vice versa. To fully understand knowledge exchange in high-tech clusters it is therefore necessary to take a multilevel network perspective. Our study shows how these organizational-level and individual-level knowledge networks are mutually influential. Focusing on knowledge networks emerging in the context of regional clusters, we highlight how R&D collaborations among organizations impact the interpersonal exchange of knowledge among managers and researchers and vice versa. Taking a multilevel network perspective, we extend the existing understanding of knowledge networks by demonstrating that individuals who are willing to share their knowledge with colleagues belong to organizations involved in many R&D collaborations. These managers and their organizations thus benefit from each others’ central positions in the networks by having access to extensive sources of external knowledge. However, the opposite holds true when managers and researchers informally ask for knowledge from many of their colleagues. Our results show that extensive knowledge-seekers belong to organizations with fewer formal R&D collaborations. This can either be a sign of them trying to compensate for the lack of organizational-level collaborations or that they are harming their organizations’ chances to find collaboration partners. Finally, if two organizations collaborate on a joint R&D project there is a good chance that their managers and researchers also informally exchange knowledge with each other. Formal and informal knowledge networks thus overlap and open up the potential to realize synergies. We draw conclusions about whether individuals acquire knowledge independent of the opportunity structures provided by their organizations and thus fully exploit the possibilities provided by clusters