Ecología de poblaciones y conservación de escarabajos y pseudoescorpiones que habitan en robles huecos en Suecia

This paper aims at giving a summary of recent research on the habitat requirements and population structure of beetles and pseudoscorpions living in old, hollow oaks in Sweden. An inventory of old oaks in pasture woodlands revealed that the species richness of beetles is higher at sites that are originally open and are still grazed. The trees in these plots are preferred for two reasons: they are more sun–exposed and have a larger trunk diameter. Many species are harmed by forest regrowth and, thus, to preserve the rarer saproxylic fauna it is important to continue the management of areas with old oaks. In four of thirteen species (Osmoderma eremita, Tenebrio opacus, Elater ferrugineus and Larca lata), the occupancy per tree were found to be significantly positively correlated with the number of trees in the stand. This finding is noteworthy as there is little scientific evidence available to support that saproxylic beetles suffer from habitat fragmentation. The population dynamics were investigated on a certain study species, O. eremita. The results suggest that the individuals of each tree could be seen as a local population, and the populations in all occupied trees in a stand together form a metapopulation.Este trabajo pretende ofrecer un resumen de investigaciones recientes sobre los requerimientos de hábitat y la estructura de las poblaciones de escarabajos y pseudoescorpiones que viven en viejos robles huecos en Suecia. Un inventario de viejos robles situados en pastos de zonas boscosas reveló que existe mayor riqueza de especies de escarabajos en lugares originalmente abiertos y que todavía se utilizan para el pasto. Los árboles situados en estos terrenos son preferidos por dos razones: están más expuestas a los rayos del sol y el diámetro del tronco es mayor. Muchas especies sufren los perjuicios del recrecimiento del bosque, por lo que para preservar la fauna saprofita más rara es importante proseguir con la gestión de las áreas pobladas por robles viejos. En cuatro de trece especies (Osmoderma eremita, Tenebrio opacus, Elater ferrugineus y Larca lata) se encontró que la ocupación por árbol estaba correlacionada positivamente y de forma significativa con el número de árboles de la zona. Este hallazgo es notable dado que existen pocas evidencias científicas disponibles que apoyen que los insectos saprofitos sufran fragmentación del hábitat. Se estudia la dinámica de población de una especie determinada del estudio, O. eremita. Los resultados sugieren que los individuos de cada árbol pueden considerarse como poblaciones locales y que las poblaciones de todos los árboles ocupados de una zona próxima constituyen metapoblaciones

Population ecology and conservation of beetles and pseudoscorpions living in hollow oaks in Sweden

This paper aims at giving a summary of recent research on the habitat requirements and population structure of beetles and pseudoscorpions living in old, hollow oaks in Sweden. An inventory of old oaks in pasture woodlands revealed that the species richness of beetles is higher at sites that are originally open and are still grazed. The trees in these plots are preferred for two reasons: they are more sun-exposed and have a larger trunk diameter. Many species are harmed by forest regrowth and, thus, to preserve the rarer saproxylic fauna it is important to continue the management of areas with old oaks. In four of thirteen species (Osmoderma eremita, Tenebrio opacus, Elater ferrugineus and Larca lata), the occupancy per tree were found to be significantly positively correlated with the number of trees in the stand. This finding is noteworthy as there is little scientific evidence available to support that saproxylic beetles suffer from habitat fragmentation. The population dynamics were investigated on a certain study species, O. eremita. The results suggest that the individuals of each tree could be seen as a local population, and the populations in all occupied trees in a stand together form a metapopulation

Estructura genética de dos especies de pseudoescorpión que viven en los huecos de árboles en Suecia

Two saproxylic pseudoscorpions, Larca lata and Allochernes wideri, were compared in an analysis of genetic structure in southern Sweden. Allochernes wideri is a relatively widely distributed species that occurs in single–standing trees and in small tree hollows, while L. lata is on the Swedish red list and confined to larger assemblages of very old trees with hollows containing large amounts of wood mould. In A. wideri, the polymorphism of PGM was used, whereas in L. lata the variation for PGI was studied. The genetic differentiation between trees within a site was low for both species, indicating that the migration between nearby trees is considerable despite the fact that phoretic dispersal has only been occasionally observed in these species. Between sites, situated four to 900 km from each other, the genetic differentiation was small both in A. wideri and L. lata with no difference between the species, when considered on the mainland only. The small differentiation suggests the habitat was fragmented recently (100–170 years ago). The relation between the rate of migration and long–term population survival and the risk of mis–interpretation due to selection for alleles is discussed.Se comparan dos pseudoescorpiones saproxílicos, Larca lata y Allochernes wideri, del sur de Suecia mediante un análisis de su estructura genética. Allochernes wideri es una especie de distribución relativamente amplia que se encuentra en árboles aislados y en pequeños huecos de árboles, mientras que L. lata aparece en la lista roja sueca y se encuentra confinado en grandes agrupaciones de árboles muy viejos cuyos huecos contienen gran cantidad de moho. En A. wideri se empleó el polimorfismo de PGM mientras que en L. lata se estudió la variación por PGI. La diferenciación genética entre árboles de un mismo lugar fue baja para ambas especies, indicando que la migración entre árboles cercanos es considerable aun cuando sólo se observó dispersión forética ocasionalmente en ambas especies. Entre zonas situadas a una distancia de 4 a 900 km, la diferenciación genética fue escasa en ambas especies, A. wideri y L. Lata, sin ninguna diferencia entre las mismas cuando se consideró únicamente la zona principal. Esta pequeña diferenciación sugiere que el hábitat se fragmentó recientemente (100–700 años antes). Se discute la relación entre la tasa de migración y la supervivencia de la población a largo plazo y el riesgo de una mala interpretación debida a la selección de los alelos

Riqueza en nutrientes del mantillo de la madera en cavidades arbóreas donde está presente el escarabeideo Osmoderma eremita

Trunk hollows with wood mould harbour a rich invertebrate fauna with many threatened species, and it has been suggested that the beetle Osmoderma eremita (Coleoptera, Scarabaeidae) is a keystone species in this community. We estimated the amount of nitrogen and phosphorus in wood mould and compared the coarse fraction which constitutes frass of O. eremita with the finer fraction of wood mould, and found that the nutrient richness was higher in frass. O. eremita larvae have a fermentation chamber that harbours nitrogen fixing bacteria. As the levels of absorbable nitrogen are a limiting factor in insect growth, an increase in nutrient richness is one of several possible explanations why the species richness of saproxylic beetles is higher in hollow oaks where O. eremita is present in relation to similar trees where the beetle is absent.Las cavidades de los troncos con mantillo de la madera albergan una rica fauna de invertebrados, entre los que se incluyen numerosas especies amenazadas. Se ha sugerido que Osmoderma eremita (Coleoptera, Scarabaeoidea) constituye una especie clave de esta comunidad. Se estimó la cantidad de nitrógeno y fósforo presentes en el mantillo de la madera, y se comparó la fracción gruesa formada por las deyecciones de O. eremita con la fracción más fina del mantillo de la madera y se vió que la riqueza en nutrientes era más elevada en la fracción gruesa. Las larvas de O. eremita contienen una cámara de fermentación que alberga el nitrógeno fijado por las bacterias. Puesto que los niveles de nitrógeno absorbible constituyen un factor limitador del crecimiento de insectos, un aumento de la riqueza en nutrientes es una de las posibles explicaciones del porqué la riqueza en especies de los escarabajos saproxílicos es más elevada en los robles huecos donde O. eremita está presente que en otros árboles similares donde está ausente

Drivers of lichen species richness at multiple spatial scales in temperate forests

Only few studies analysing lichen diversity have simultaneously considered interactions among drivers that operate at different spatial and temporal scales. Aims: The aims of this study were to evaluate the relative importance of host tree, and local, landscape and historical factors in explaining lichen diversity in managed temperate forests, and to test the potential interactions among factors acting at different spatial scales. Methods: Thirty-five stands were selected in the Őrség region, western Hungary. Linear models and multi-model inference within an information-theory framework were used to evaluate the role of different variables on lichen species richness. Results: Drivers at multiple spatial scales contributed to shaping lichen species richness both at the tree and plot levels. Tree level species richness was related to both tree and plot level factors. With increasing relative diffuse light lichen species richness increased; this effect was stronger on higher than on lower part of the trunks. At the plot-scale, species richness was affected by local drivers. Landscape and historical factors had no or only marginal effect. Conclusions: Lichen conservation in temperate managed forests could be improved if the complex interactions among host tree quality and availability, micro-climatic conditions, and management were taken into consideration

Development of Secondary Woodland in Oak Wood Pastures Reduces the Richness of Rare Epiphytic Lichens

Wooded pastures with ancient trees were formerly abundant throughout Europe, but during the last century, grazing has largely been abandoned often resulting in dense forests. Ancient trees constitute habitat for many declining and threatened species, but the effects of secondary woodland on the biodiversity associated with these trees are largely unknown. We tested for difference in species richness, occurrence, and abundance of a set of nationally and regionally red-listed epiphytic lichens between ancient oaks located in secondary woodland and ancient oaks located in open conditions. We refined the test of the effect of secondary woodland by also including other explanatory variables. Species occurrence and abundance were modelled jointly using overdispersed zero-inflated Poisson models. The richness of the red-listed lichens on ancient oaks in secondary woodland was half of that compared with oaks growing in open conditions. The species-level analyses revealed that this was mainly the result of lower occupancy of two of the study species. The tree-level abundance of one species was also lower in secondary woodland. Potential explanations for this pattern are that the study lichens are adapted to desiccating conditions enhancing their population persistence by low competition or that open, windy conditions enhance their colonisation rate. This means that the development of secondary woodland is a threat to red-listed epiphytic lichens. We therefore suggest that woody vegetation is cleared and grazing resumed in abandoned oak pastures. Importantly, this will also benefit the vitality of the oaks