added 2 research items
In forest ecosystems amphibians often represent the greater portion of biomass of vertebrates. Salamanders in particular are invertebrates’ predators and, being ectotherm, they are capable to efficiently convert the major part of ingested biomass, making it available for the upper trophic levels. As a consequence, they play a key role in the nutrient and carbon cycles. Both completely terrestrial and semi-aquatic amphibians need suitable terrestrial shelters. Trees are a natural source of refuges for amphibians, that may found many shelters in the buttresses or in the ground holes formed by roots. The spectacled salamander Salamandrina perspicillata is an Italian endemism, with mainly terrestrial habits, for which we aim at investigating the selection of trees as shelters, based on tree features, using occupancy probability as a proxy of tree suitability. This research is developed within the project Life ManFor C.BD, and is aimed at finding a synthetic and quickly measurable index of tree suitability, capable to link forest management and biodiversity conservation. We investigated one hectare of beech forest in the “Montedimezzo-Pennataro” test site. For 385 trees we recorded stem diameter (DBH, starting from 10 cm), number of buttresses (BUT) and number of cavities that are created between stumps and soil in the vicinity of the buttresses loops (HOL) in order to detect if there was a relationship between such variables and the use of trees by salamanders. We conducted six surveys in the study site from October to November (2013), recording salamanders’ presence/pseudo-absence for each tree. Based on our results, occupancy models that allowed salamanders’ detection probability to vary among surveys have the best empirical support, in particular the model including all of the three site covariates (DBH, BUT and HOL). Naïve and estimated proportion of tree occupied are 0.44 and 0.71, respectively. Our research has focused over a relatively small area, investigating single tree features, in order to provide a good proxy of tree suitability by means of occupancy level. Ground level holes and buttresses seems to be essential in providing shelter sites for Salamandrina perspicillata. Since these features are correlated with DBH, a forest management option aiming at conjugating forest harvesting and salamander communities conservation may focus on the retention of those trees, having a larger DBH along with a large number of buttresses and cavities at the ground level
Quantification of niche overlap represents an important topic in several aspects of ecology and conservation biology, although it could be potentially affected by imperfect detection, i.e., failure to detect a species at occupied sites. We investigate the effect of imperfect detection on niche overlap quan-tification in two arboreal rodents, the edible dormouse (Glis glis) and the ha-zel dormouse (Muscardinus avellanarius). For both species, we used Generalized Linear Mixed Models (GLMM) to estimate the occurrence probability and Occupancy Models (OM) to calculate occurrence and detection probabilities. By comparing these predictions through niche equivalency and similarity tests, we first hypothesised that methods correcting for imperfect detection (OM) provide a more reliable estimate of niche overlap than traditional presence/ absence methods (GLMM). Furthermore, we hypothesised that GLMM mainly estimate species detectability rather than actual occurrence, and that a low number of sampling replicates provokes an underestimation of species niche by GLMM. Our results highlighted that GLMM-based niche overlap yielded significant outcomes only for the equivalency test, while OM-based niche overlap reported significant outcomes for both niche equivalency and similarity tests. Moreover, GLMM occurrence probabilities and OM detectabilities were not statistically different. Lastly, GLMM predictions based on single sampling repli-cates were statistically different from the average occurrence probability predicted by GLMM over all replicates. We emphasized how accounting for imperfect detection can improve the statistical significance and interpretability of niche overlap estimates based on occurrence data. Under a habitat management perspective, an accurate quantification of niche overlap may provide useful information to assess the effects of different management practices on species occurrence.
A reasonably-complete bird inventory is the crucial starting point for the analysis of the bird community. We evaluated the efficiency of point counts in detecting forest birds and verified how many sampling points or occasions are needed to adequately characterize the bird community. We sampled birds in 5 forest stands (conifer and beech forests) from northern to southern Italy in 2012. Sampling (through aural and visual clues) lasted 5 minutes, during which species were recorded. Data were analysed in relation to both the number of sampling points and the number of sampling occasions. Then, estimates of species richness were compared to random resampling of subsets of the original data. Results showed that after 3.8 sampling occasions (out of 19–24 sampling points) or 10.4 sampling points (given points are sampled 5 times), the species coverage of each community approached, or exceeded, the 90% threshold. Also, no difference in the mean values emerged with the subset estimates, but the latter appeared less precise. Our results suggest that the density of 1 sampling point per every 5 ha, each repeated at least 3 times, can represent an adequate optimization of the sampling effort. We provided useful methodological information for planning bird inventories in forest environments (applicable at least for Mediterranean and south-European mountain forests) when personnel and financial resources are limited, leading to a thoughtful fund management whilst providing a method to evaluate the reliability of species coverage for bird surveys.
Ecological traits affect species’ responses to human impacts. Amphibians are declining worldwide and one of the major causes of such decline is habitat loss. Forestry practices have a primary role in determining habitat loss and fragmentation for amphibians. Thus, researchers should provide forest practitioners with essential information in order to address proper forest management plans. Here, we studied ecological requirements in the terrestrial phase of salamanders and we tested the feasibility of repeated counts to infer habitat determinants of salamanders’ abundance in order to guide forest management plans. We employed the N-mixture models for the analysis of repeated count data of an Italian endemic salamander (Salamandrina perspicillata) on seventy-seven 100 m² plots, within a central-Italian forest. Modelling salamanders abundance as a function of site specific habitat features allowed us to give precise guidelines for forest management. Harvesting should be conducted preferably on south facing slopes, since salamanders’ occurrence and abundance are higher on northern slopes. Forest operations should be avoided or reduced within a buffer of some 150 m from reproductive sites. Since salamanders use tree bases as shelters, patches of forest with larger trees and higher canopy cover should be retained, ensuring the availability of moist shelters. The amount of the cost for the whole monitoring, from plot installation to data analyses was 4872 Euros (about 5558 USD). Given the ease of application and inexpensiveness of this sampling protocol, we encourage its employment in similar situations, in order to gather useful information, which are essential to couple forestry practices with species conservation strategies.
Bats represent a major component of forest biodiversity. In forest, bats find many roosting and foraging opportunities. When foraging in forest, different bat species exploit a range of microhabitats according to their echolocation and flight style. When roosting, bats require sufficient numbers of suitable tree cavities. Overall, forest structure may influence both foraging and roosting behaviour, and in turn the number of bat species present and their population size. The exploitation of forests for commercial purposes may be a threat to biodiversity when logging leads to habitat loss, alteration or fragmentation. While some bat species may benefit from an increase in the amount of edge habitat determined by logging, others, more specialized to exploit forest interiors, may be potentially harmed. In this study we set out to assess the effect on foraging bats of different management approaches, comparing locally applied traditional approaches with innovative multifunctional management options and delayed logging. Within the framework of the LIFE+ ManFor C.BD. Project we surveyed the effects of thinning at four Italian forest sites, each representing a separate case study. We found that in logged plots bat activity either showed no difference from unlogged plots or resulted in an increase in foraging activity, suggesting that thinning, at least in the forest types we dealt with, has no adverse consequences on bat foraging. However, in our case the effects varied greatly across sites and were detected mostly when all bat species were pooled together for analysis. We conclude that forest exploitation may be sustainable and even favour foraging bats, but since our work neither covered direct mortality linked with forestry operations nor roost loss, further studies are needed to analyze these important aspects. We also highlight that total bat activity revealed by acoustic surveys carried out with automatic recorders may be used as an appropriate indicator of forestry effects on bats.
Environmental heterogeneity affects not only the distribution of a species but also its local abundance. High heterogeneity due to habitat alteration and fragmentation can influence the realized niche of a species, lowering habitat suitability as well as reducing local abundance. We investigate whether a relationship exists between habitat suitability and abundance and whether both are affected by fragmentation. Our aim was to assess the predictive power of such a relationship to derive advice for environmental management. As a model species we used a forest specialist, the short-toed treecreeper (Family: Certhiidae; Certhia brachydactyla Brehm, 1820), and sampled it in central Italy. Species distribution was modelled as a function of forest structure, productivity and fragmentation, while abundance was directly estimated in two central Italian forest stands. Different algorithms were implemented to model species distribution, employing 170 occurrence points provided mostly by the MITO2000 database: an artificial neural network, classification tree analysis, flexible discriminant analysis, generalized boosting models, generalized linear models, multivariate additive regression splines, maximum entropy and random forests. Abundance was estimated also considering detectability, through N-mixture models. Differences between forest stands in both abundance and habitat suitability were assessed as well as the existence of a relationship. Simpler algorithms resulted in higher goodness of fit than complex ones. Fragmentation was highly influential in determining potential distribution. Local abundance and habitat suitability differed significantly between the two forest stands, which were also significantly different in the degree of fragmentation. Regression showed that suitability has a weak significant effect in explaining increasing value of abundance. In particular, local abundances varied both at low and high suitability values. The study lends support to the concept that the degree of fragmentation can contribute to alter not only the suitability of an area for a species, but also its abundance. Even if the relationship between suitability and abundance can be used as an early warning of habitat deterioration, its weak predictive power needs further research. However, we define relationships between a species and some landscape features (i.e., fragmentation, extensive rejuvenation of forests and tree plantations) which could be easily controlled by appropriate forest management planning to enhance environmental suitability, at least in an area possessing high conservation and biodiversity values.
Research on species-habitat relationship implies that a specific parameter related to the species, such as abundance, has to be measured and compared to environmental features. Different methods have been implemented in the collection of abundance data on birds and different statistical techniques have been developed to deal with the great diversity of data collection. The aim of this study is to compare different sampling methods and statistical techniques currently used to estimate abundance, employing them in a dense forest environment: capture-mark-recapture vs. point counts. Short-toed treecreepers Certhia brachydactyla were captured through mist-netting and surveyed through song count. Capture data were analysed using a classical approach and a spatially-explicit approach (SECR), while count data were analysed with N-mixture models. Results show that classical capture analyses yield a lower abundance, while SECR and N-mixture models give similar and higher estimates. An optimization of the sampling design for studies regarding birdsàbundance and species-habitat relationship should consider the use of point counts for song/visual detection of individual birds while fitting N-mixture models for abundance estimation.