Habitat availability in forests and clearcuts for saproxylic beetles associated with aspen

To maintain biodiversity in managed, boreal forest in Scandinavia, aspen trees (Populus tremula) are often retained at clearcutting. In this study, the habitat availability for beetles associated with aspen coarse woody debris (CWD) was predicted for forests and clearcuts with a model of CWD dynamics. Habitat requirements of eight beetle species (Agathidium bicolor, Cerylon ferrugineum, Cyphaea curtula, Endomychus coccineus, Homalota plana, Mycetophagus fulvicollis, Ptilinus fuscus and Xylotrechus rusticus) were obtained from their occurrence patterns in relation to characteristics of CWD objects in forest and on clearcuts in a study landscape in central Sweden. Three species were more frequent in forest and three at clearcuts. Five species increased with increasing girth of the CWD. Three were more frequent on standing CWD, and two on lying CWD. From the same study area, we also obtained field data on the recruitment of CWD (i.e., tree mortality) and amounts of different types of CWD. Annual tree mortality of aspen was higher for recent clearcuts (6.3%) compared with older clearcuts (1.1%). For all species, the habitat availability was higher on clearcuts, because enhanced tree mortality increased the amount of recently dead CWD. As a conclusion, green-tree retention of aspen is a conservation effort that is beneficial for species associated with aspen CWD.     

Individual food niche specialization in stream-dwelling charr

Food niche variation within a population of white-spotted charr, Salvelinus leucomaenis, was investigated by means of mark and recapture to examine the simplification that conspecific individuals are ecologically equivalent. Food diversity measured on the basis of living form of dietary organisms demonstrated variability in food niche in incidence, degree, and stability. As inferred from body size distribution and fish movement, niche variation was inexplicable by social rank hierarchy or foraging habitat rotation, and occasional niches were deemed to be realized individually. Higher annual growth rate shown by those with a larger niche width indicated the adaptive significance in niche variation. Assuming trade-off between feeding efficiency and predation risk, phenotypic plasticity was suggested to determine the food niche specialization of individuals to maximize lifetime fitness.     

On testing temporal niche differentiation in carabid beetles

Summary It is first shown that den Boer's (1985) claims that competition should be rejected as a factor explaining community structure are not warranted by his tests on temporal niche differentiation in carabid beetles. The power of these tests is so low that they are unlikely to detect even the most extreme pattern of niche differentiation. A major factor that affects their power is the procedure of building up an artificial species pool from the local communities to which the test is to be applied. Alternative tests are then presented, and applied to data on annual activity cycles of carabids in three forest biotopes in Belgium. Three factors are shown to strongly affect their outcome: the unit into which the time scale is divided, the criteria used to incorporate constraints, and the set of species selected. Nevertheless, they provide some evidence that there is a growing niche differentiation from the successional to the climax forest, as predicted by competition theory. Other hypotheses, however, could explain the observed pattern.     

Micro and macro-habitat associations in saproxylic beetles: implications for biodiversity management

Restoration of habitats is critically important in preventing full realization of the extinction debt owed as a result of anthropogenic habitat destruction. Although much emphasis has been placed on macrohabitats, suitable microhabitats are also vital for the survival of most species. The aim of this large-scale field experiment was to evaluate the relative importance of manipulated microhabitats, i.e., dead wood substrates of spruce (snags, and logs that were burned, inoculated with wood fungi or shaded) and macrohabitats, i.e., stand types (clear-cuts, mature managed forests, and forest reserves) for species richness, abundance and assemblage composition of all saproxylic and red-listed saproxylic beetles. Beetles were collected in emergence traps in 30 forest stands in 2001, 2003, 2004 and 2006. More individuals emerged from snags and untreated logs than from burned and shaded logs, but species richness did not differ among substrates. Assemblage composition differed among substrates for both all saproxylics and red-listed saproxylic species, mainly attributed to different assemblage composition on snags. This suggests that the practise of leaving snags for conservation purposes should be complemented with log supplementation. Clear-cuts supported fewer species and different assemblages from mature managed forests and reserves. Neither abundance, nor species richness or assemblage composition differed between reserves and mature managed forests. This suggests that managed stands subjected to selective cutting, not clear-felling, maintain sufficient old growth characteristics and continuity to maintain more or less intact assemblages of saproxylic beetles. Thus, alternative management methods, e.g., continuity forestry should be considered for some of these stands to maintain continuity and conservation values. Furthermore, the significantly higher estimated abundance per ha of red-listed beetles in reserves underlines the importance of reserves for maintaining viable populations of rare red-listed species and as source areas for saproxylic species in boreal forest landscapes.     

Vertical distribution of saproxylic beetles within snag trunks retained in plantation forests

Retention of snags (standing dead trees) is considered to have important effects on saproxylic species conservation in plantation forests because snags would provide vertically stratified deadwood habitats. However, the vertical distribution of saproxylic insects within snag trunks is still unclear. We felled 33 naturally occurring snags of Todo fir Abies sachalinensis in plantation forests and extracted insects from 99 logs sampled from three vertical positions of the snag trunks (basal stem: <2.5 m, lower trunk: 2.5–5 m and upper trunk: >5 m). The mean number of species that emerged from a single log was only 2.69, but we identified 51 morphospecies of saproxylic beetles in total. The total number of species that emerged from the basal stem (34 spp.) was greater than those that emerged from the lower trunk (25 spp.) or the upper trunk (30 spp.). However, rarefaction-extrapolation analysis did not demonstrate a significant difference in species richness among the log positions. Beetle assemblages were separated into two groups by constrained correspondence analysis; one group emerged only from lower and upper trunk logs, while another emerged mainly from basal stem logs. Additionally, vertical position had a significant effect on the distribution of the five main species. Our results show that beetle assemblages within snags in the plantation forests were highly variable, and retaining a sufficient number of high stumps may be important for saproxylic beetle conservation in plantation forests. We propose ‘retention thinning’ as an appropriate method to combine efficient timber production with biodiversity conservation in plantation forests.     

A comparison of three methods to survey saproxylic beetles in hollow oaks

One of the most endangered assemblages of species in Europe is insectsassociated with old trees. For that reason there is a need of developing methodsto survey this fauna. This study aims at comparing three methods – windowtrapping, pitfall trapping and wood mould sampling – to assess speciesrichness and composition of the saproxylic beetle fauna in living, hollow oaks.We have used these methods at the same site, and to a large extent in the sametrees. Useful information was obtained from all methods, but they partiallytarget different assemblages of species. Window trapping collected the highestnumber of species. Pitfall trapping collected beetles associated with treehollows which rarely are collected by window traps and therefore it isprofitable to combine these two methods. As wood mould sampling is the cheapestmethod to use, indicator species should preferably be chosen among specieswhich are efficiently collected with this method.     

Isolation by distance in Middle Dalmatia-Yugoslavia

Parameters of Malécot's isolation-by-distance model are estimated for biological (anthropometric head and body dimensions, morphometric dimensions of metacarpal bones, quantitative and qualitative dermatoglyphic traits, and physiological/cardiorespiratory/variables) and linguistic distances and migrational kinship on the island of Korcula and the Peljesac peninsula in Middle Dalmatia, Croatia, Yugoslavia. Resulting parameters and the fit of the model are compared, for both regions, as well as with results of similar analysis in other parts of the world. The fit of the model is highly significant for migrational kinship and linguistic distances and less so for biological traits. Differences between these two populations, which live under basically similar ecological conditions, are explained by variation in biological and sociocultural history.     

Head shape variation in cerambycid saproxylic beetles as a function of host plant selection

Saproxylic insects depend on deadwood for larval development, and a certain degree of specialization may be involved in their choice of host plants and/or wood in a particular stage of degradation. The plant species chosen for oviposition in turn act as an environmental pressure on the head morphology of larvae and it is expected that head shape plasticity varies directly with the number of woody plant species used for larval development in each insect species. We analyzed head shape variation in saproxylic beetles with respect to host plant species, maximum time of larval emergence and season of the year when insects colonized branches. Generalist species in the use of host plants showed significant variation in head shape and size. Time of emergence and season did not appear to affect head shape, although season was a determinant factor of abundance and possibly head size variation.     

Some of the rarest European saproxylic beetles are common in the wilderness of Northern Mongolia

Natural landscapes characterized by heavy disturbance regimes were displaced in Europe by managed cultural landscapes over the past centuries. The associated loss of biological legacies, such as dead or dying trees, has exposed numerous saproxylic species to high risks of extinction. In contrast, extensive wilderness forests in Northern Mongolia have been sustained owing to significant cultural differences. Here we used saproxylic beetle abundance data gathered during two sampling campaigns in the Mongolian taiga to address whether (1) the saproxylic beetle fauna of the Mongolian taiga is comparable to that of European boreal forests, (2) fires are a natural disturbance regime, indicated by the occurrence of many pyrophilous species, and (3) species rare in Europe are also rare in the Northern Mongolian wilderness. Of 191 saproxylic beetle species identified, 150 (79 %) were also found in Europe. The high number of pyrophilous beetle species (20) indicated that natural species communities are well adapted to this disturbance regime. The species rarity in Germany was significantly positively correlated with the species rarity in Finland, but the species rarity in these two countries was negatively correlated with that in the Mongolian wilderness. Our results indicated that wilderness areas with natural disturbances provide biological legacies important for rare species. Therefore, exploitation of the unique, remaining natural landscapes of the Palaearctic wilderness areas should be stopped. Moreover, we urge conservationists to expand controlled burning for restoration at relict sites of rare boreal species also outside Fennoscandia.     

Life-history specialization was not an evolutionary dead-end in Pyrenean cave beetles

Research on subterranean organisms has focused on the colonization process and some of the associated phenotypic changes, but little is known on the long-term evolutionary dynamics of subterranean lineages and the origin of some highly specialized complex characters. One of the most extreme modifications is the reduction of the number of larval instars in some Leptodirini beetles from the ancestral 3 to 2 and ultimately a single instar. This reduction is usually assumed to have occurred independently multiple times within the same lineage and geographical area, but its evolution has never been studied in a phylogenetic framework. Using a comprehensive molecular phylogeny, we found a low number of independent origins of the reduction in the number of instars, with a single transition, dated to the Oligocene–Miocene, from 3 to 2 and then 1 instar in the Pyrenees, the best-studied area. In the Pyrenees, the 1-instar lineage had a diversification rate (0.22 diversification events per lineage per million years) significantly higher than that of 3- or 2-instar lineages (0.10), and similar to that seen in other Coleopteran radiations. Far from being evolutionary dead-ends, ancient lineages fully adapted to subterranean life seem able to persist and diversify over long evolutionary periods.     

Evidence that niche specialization explains species-energy relationships in lake fish communities

1. Interspecific niche differences have long been identified as a major explanation for the occurrence of species-rich communities. However, much fieldwork studying variation in local species richness has focused upon physical habitat attributes or regional factors, such as the size of the regional species pool. 2. We applied indices of functional diversity and niche overlap to data on the species niche to examine the importance of interspecific niche differentiation for species richness in French lake fish communities. We combined this information with environmental data to test generalizations of the physiological tolerance and niche specialization hypotheses for species-energy relationships. 3. We found evidence for a largely non-saturating relationship (relative to random expectation) between species richness and functional evenness (evenness of spacing between species in niche space), while functional richness (volume of niche space occupied) peaked at moderate levels of species richness and niche overlap showed an initial decrease followed by saturation. This suggests that increased niche specialization may have allowed species to coexist in the most species-rich communities. 4. We tested for evidence that increased temperature, local habitat area, local habitat diversity and immigration affected species richness via increased niche specialization. Temperature explained by far the largest amount of variation in species richness, functional diversity and niche overlap. These results, combined with the largely non-saturating species richness-functional evenness relationship, suggest that increased temperature may have permitted increased species richness by allowing increased niche specialization. 5. These results emphasize the importance of niche differences for species coexistence in species-rich communities, and indicate that the conservation of functional diversity may be vital for the maintenance of species diversity in biological communities. Our approach may be applied readily to many types of community, and at any scale, thus providing a flexible means of testing niche-based hypotheses for species richness gradients.     

Species richness of saproxylic beetles in woodlands is affected by dispersion ability of species,age and stand size

This study examines the occurrence of saproxylic beetles in woodlands of different size and age and their potential to leave woodland areas and cross open grassland in northern Germany. The beetles were recorded by emergence traps and flight-intercept-traps. The investigated sites were dominated by beech, oak and alder, but other tree species also occurred in low abundance. Species richness showed a positive relation to stand size and age of woods. Both total and rarefaction species richness were the lowest in small and young woods and highest in old and large woods. Species richness decreased asymptotically from the inner-wood habitat to a distance greater than 80 m from the wood margin. 80 species were classified into 46 low mobile species found at a distance <30 m from wood margins and 34 high mobile species found >30 m from wood margins. The most mobile species were found the most frequently in all woods; but they contributed less to species richness in wood stands than did the species with low mobility. The contribution of the least mobile species to species richness in wood stands increased with the age and size of the stands, with the effect of stand size being the greater. We conclude that in our study region woods larger than 100 ha are necessary to maintain the highest richness of the least mobile saproxylic beetles.     

Habitat niche specialization in an understory species in a warm temperate forest

Relationships between microhabitat variables; understory light conditions in summer and winter, altitude, slope inclination and topographic categories (valley, ridge, and slope) and the distribution of Aucuba japonica Thunb. (Cornaceae), a common understory shrub species in Japan were examined using non-contagious 66, 20 × 20 m² quadrats. The Morishita’s I _δ suggested that A. japonica distributions were strongly heterogeneous among the quadrats. Therefore positive spatial autocorrelation of A. japonica at a within-quadrat level (≤20 m) was obvious. Moran’s I statistics showed a significant positive spatial autocorrelation in A. japonica abundance within the distance shorter than 60 m. But the partial Mantel tests suggested that the mass effect from neighboring quadrats would little explain A. japonica abundance in a quadrat. The partial Mantel tests also clearly showed that A. japonica distributions were strongly structured by topography and understory light conditions. Using Monte Carlo randomization tests, we found that A. japonica was aggregately distributed in quadrats in valley which were covered by deciduous canopies. Better understory light conditions in winter together with valley edaphic conditions may increase the abundance of A. japonica there. It is concluded that habitat niche specialization is important in structuring distribution of A. japonica in this forest community.     

Diversity distribution of saproxylic beetles in Chilean Mediterranean forests: influence of spatiotemporal heterogeneity and perturbation

Mediterranean ecosystems have been recognized as a priority for biodiversity conservation due to their high levels of species richness and endemism. In South America, these environments are restricted to central Chile and represent a biodiversity hotspot. The study of saproxylic beetles in this area is an unexplored topic, despite the ecological role they play in these ecosystems and their potential usefulness for monitoring the degree of forest conservation. We investigated the diversity distribution of trophic guilds of saproxylic beetles in Chilean Mediterranean forests, to identify the main environmental variables that influence their distribution. We also analyzed seasonal dynamics as a key factor influencing insect communities and the effect of human disturbance on their diversity and composition. We identified characteristic species of perturbation degree as bioindicators for habitat monitoring. A total of 40 window traps were used to survey three Mediterranean forest types in the Río Clarillo National Reserve and the adjacent non-protected areas. We found that the diversity, abundance and composition of saproxylic beetles varied significantly spatiotemporally among the studied forest types and among perturbation degrees, showing different patterns depending on the trophic guild. Results indicated that conservation decisions should include the preservation of a larger range of different vegetation types and the nearby zones that have suffered low levels of disturbance or fragmentation and where actions promoting the presence of old native trees would have a significant conservation value.     

Selection by parasites may increase host recombination frequency

Meiotic recombination destroys successful genotypes and it is therefore thought to evolve only under a very limited set of conditions. Here, we experimentally show that recombination rates across two linkage groups of the host, the red flour beetle Tribolium castaneum, increase with exposure to the microsporidian parasite, Nosema whitei, particularly when parasites were allowed to coevolve with their hosts. Selection by randomly varied parasites resulted in smaller effects, while directional selection for insecticide resistance initially reduced recombination slightly. These results, at least tentatively, suggest that short-term benefits of recombination--and thus the evolution of sex--may be related to parasitism.