Enrico Caprio

The effects of body mass on dung removal efficiency in dung beetles.

Understanding of the role of body mass in structural-functional relationships is pressing, particularly because species losses often occur non-randomly with respect to body size. Our study examined the effects of dung beetle body mass on dung removal at two levels. First, we used the lab experiment to evaluate the efficiency of eight dung beetle species belonging to two functional groups (tunnelers, dwellers) on dung removal. Second, the same species employed in the lab were used in field mesocosms to examine the effects of the two functional groups on dung removal maintaining realistic differences in the total body mass between tunneler and dweller assemblages. Furthermore, the experimental assemblages contained one and four species within each functional group, so the effect of body mass heterogeneity was examined. We used a statistical approach (offset method) which took into account a priori constraints due to the study design allowing us to analyse the effect of larger species in mesocosm style experiments. Body size played a crucial role in dung removal: large beetles were more efficient than small ones and the percentage of removed dung increased with higher body mass heterogeneity. Tunnelers were more efficient than dwellers over both short and long time periods (one month and one year). Significant effects of dwellers were found only after one year. Moreover, our study showed that not including the body mass as an offset in the model resulted in sometimes different results, as the offset expresses dung removal independently of the body mass. This approach confirmed that body size is likely a pivotal factor controlling dung removal efficiency at multiple levels, from single species to overall dung beetle assemblages. Even though other specific traits should be examined, this study has begun to address the consequences of losing individuals with specific traits that are especially sensitive to perturbations.

Can forest management have season-dependent effects on bird diversity?

Forest management modified the original structure of most European forests, and in the most extreme cases, genuinely natural and semi-natural forests were turned into plantations through clear felling and replanting, often using non-native species. We compared the bird community structure of native oak woods of northern Italy with that of their anthropogenic counter-parts: black locust and sweet chestnut woods. The three stand types were compared in terms of vegetation structure, bird species richness, diversity and abundance of foraging guilds. We analysed both the overwintering and the breeding community, to assess whether management had specific seasonal effects on bird diversity. Forestry-imposed disturbances affected bird diversity more consistently in winter than in breeding time: bird species richness and diversity were significantly greater in oak and chestnut stands, which were the preferred habitat for bark foragers and foliage gleaners. In the breeding period, bird diversity of black locust woodlands increased, and inter-stand differences were not significant. At this time of year, understorey gleaners were more abundant in black locust stands (where shrubs were denser). In winter, species richness, diversity and the abundance of several guilds were positively correlated with stand age, whereas in the breeding period canopy gleaners preferred younger woodlots. Despite the lack of inter-stand differences in breeding bird diversity, young-managed woods benefited generalist birds that need no particular conservation efforts. Conversely, priority species for forest conservation such as specialised bark foragers positively selected native and mature stands throughout the year. We suggest that detailed year-round studies on diversity and community composition could sharpen the precision with which it is possible to prescribe conservation measures in forested areas.

Alpine bird distributions along elevation gradients: the consistency of climate and habitat effects across geographic regions

Many species have shown recent shifts in their distributions in response to climate change. Patterns in species occurrence or abundance along altitudinal gradients often serve as the basis for detecting such changes and assessing future sensitivity. Quantifying the distribution of species along altitudinal gradients acts as a fundamental basis for future studies on environmental change impacts, but in order for models of altitudinal distribution to have wide applicability, it is necessary to know the extent to which altitudinal trends in occurrence are consistent across geographically separated areas. This was assessed by fitting models of bird species occurrence across altitudinal gradients in relation to habitat and climate variables in two geographically separated alpine regions, Piedmont and Trentino. The ten species studied showed non-random altitudinal distributions which in most cases were consistent across regions in terms of pattern. Trends in relation to altitude and differences between regions could be explained mostly by habitat or a combination of habitat and climate variables. Variation partitioning showed that most variation explained by the models was attributable to habitat, or habitat and climate together, rather than climate alone or geographic region. The shape and position of the altitudinal distribution curve is important as it can be related to vulnerability where the available space is limited, i.e. where mountains are not of sufficient altitude for expansion. This study therefore suggests that incorporating habitat and climate variables should be sufficient to construct models with high transferability for many alpine species.

The dynamics of alternative male mating tactics in a population of Black Grouse Tetrao tetrix in the Italian Alps

The Black Grouse Tetrao tetrix is primarily a lekking species, although in some populations solitary display is also common. We analysed data from a 25-year-long survey of an increasing Black Grouse population in the western Italian Alps in order to test whether the numbers of males adopting different tactics conformed to patterns expected, based on the hypothesis that dominant birds occupy the leks and solitary displaying birds are subordinate, and that the tendency for birds to be excluded from leks increases with lek size. Four predictions were made to test this hypothesis: (1) the proportion of solitary males would increase as the overall population increases, (2) there would be a threshold at which there is little or no increase in the size of the lekking population, but continued increase in the population of solitary displaying birds, (3) available lek habitat would be occupied prior to an increase in solitary displaying males, and (4) there would be an increase in the use of less preferred habitat by solitary displaying males as the total population increases. Population trends varied according to display status, in that the lekking population reached an apparent threshold while the number of solitary males continued to increase, and there was an expansion of the range of solitary males into higher altitudes in years when the population was larger. However, there was no increase in the proportion of solitary males as the total population increased. Furthermore, there was no suggestion that suitable lek habitat was limiting, as the number of leks and the mean size of those leks continued to increase throughout the study period. Although two predictions were supported, the precise patterns of trends, and results of additional analyses, suggested that solitary display is more likely to be an alternative rather than a subordinate tactic. Several factors may promote this apparent dual display tactic in Black Grouse, but habitat structure in this and other Alpine populations is likely to be a key influence.ZusammenfassungDynamik alternativer männlicher Paarungsstrategien bei einer Population des BirkhuhnsTetrao tetrixin den Italienischen Alpen Das Birkhuhn Tetrao tetrix balzt vor allem in Arenen (Leks), bei manchen Populationen kommt häufig aber auch Einzelbalz vor. Analysiert wurden Daten aus einer 25-jährigen Bestandserfassung einer wachsenden Birkhuhnpopulation in den westlichen italienischen Alpen, um festzustellen, ob die Anteile der Männchen mit verschiedenen Taktiken den Mustern entsprechen, die man aufgrund der Hypothesen erwarten würde, dass dominante Vögel die Leks besetzen, einzeln balzende Männchen einen niedrigeren Rang innehaben und die Wahrscheinlichkeit, vom Lek ausgeschlossen zu bleiben, mit dessen Größe zunimmt. Um diese Hypothesen zu überprüfen, wurden vier Annahmen gemacht: (1) der Anteil an Einzelgängern nimmt mit wachsender Gesamtpopulation zu, (2) es gibt einen Grenzwert, ab dem die Größe der Lek-Population wenig oder gar nicht zunimmt, die Einzelgänger-Population aber weiterhin ansteigt, (3) das verfügbare Lek-Habitat wird besetzt, bevor es zu einer Zunahme einzeln balzender Männchen kommt, und (4) mit steigender Gesamtpopulation kommt es zur verstärkten Nutzung weniger bevorzugter Habitate durch einzeln balzende Männchen. Die Populationstrends unterschieden sich hinsichtlich des Balzverhaltens dahingehend, dass die Lek-Population offenbar einen Grenzwert erreichte, während die Anzahl der Einzelgänger weiterhin anstieg. Außerdem war in Jahren mit größerer Population eine Ausdehnung der Verbreitung der Einzelgänger in höher gelegene Bereiche zu beobachten. Allerdings gab es bei wachsender Gesamtpopulation keinen Anstieg im Anteil der Einzelgänger. Des Weiteren gab es keine Anzeichen dafür, dass geeignete Lek-Habitate einen limitierenden Faktor darstellen, da die Anzahl der Leks und deren durchschnittliche Größe über die Laufzeit der Studie weiter zunahmen. Obwohl zwei der gemachten Annahmen bestätigt wurden, legen die genauen Trendmuster sowie die Ergebnisse weiterer Analysen nahe, dass die Einzelbalz eher eine alternative als eine untergeordnete Taktik darstellt. Mehrere Faktoren könnten diese offenbar zweigleisige Balztaktik beim Birkhuhn begünstigen, allerdings kommt der Habitatstruktur bei dieser und anderen alpinen Populationen vermutlich eine entscheidende Bedeutung zu.

Greenhouse gas emissions from dung pats vary with dung beetle species and with assemblage composition

Cattle farming is a major source of greenhouse gases (GHGs). Recent research suggests that GHG fluxes from dung pats could be affected by biotic interactions involving dung beetles. Whether and how these effects vary among beetle species and with assemblage composition is yet to be established. To examine the link between GHGs and different dung beetle species assemblages, we used a closed chamber system to measure fluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) from cattle dung pats. Targeting a total of four dung beetle species (a pat-dwelling species, a roller of dung balls, a large and a small tunnelling species), we ran six experimental treatments (four monospecific and two mixed) and two controls (one with dung but without beetles, and one with neither dung nor beetles). In this setting, the overall presence of beetles significantly affected the gas fluxes, but different species contributed unequally to GHG emissions. When compared to the control with dung, we detected an overall reduction in the total cumulative CO2 flux from all treatments with beetles and a reduction in N2O flux from the treatments with the three most abundant dung beetle species. These reductions can be seen as beneficial ecosystem services. Nonetheless, we also observed a disservice provided by the large tunneler, Copris lunaris, which significantly increased the CH4 flux–an effect potentially traceable to the species’ nesting strategy involving the construction of large brood balls. When fluxes were summed into CO2-equivalents across individual GHG compounds, dung with beetles proved to emit less GHGs than did beetle-free dung, with the mix of the three most abundant species providing the highest reduction (-32%). As the mix of multiple species proved the most effective in reducing CO2-equivalents, the conservation of diverse assemblages of dung beetles emerges as a priority in agro-pastoral ecosystems.

Ski-piste revegetation promotes partial bird community recovery in the European Alps

ABSTRACT Capsule: Restoration of grasslands on ski-pistes caused a recovery in the bird community, but not to the extent that it was equivalent to a natural Alpine grassland community. Aim: To test whether revegetation of ski-pistes in open habitat areas results in bird community recovery. Methods: The bird communities in two ski resorts in the Italian Maritime Alps were surveyed using a standardized area count method in three different plot types: non-restored ski-pistes (newly constructed), restored ski-pistes and control plots in grassland far from ski-pistes. Results: In 49 independent plots, 32 species were recorded. Species richness and abundance of birds were significantly higher on restored than on non-restored ski-pistes, independently of the species group considered and the analyses carried out. Bird community parameters of restored ski-pistes were still lower than those of natural grassland, as shown by results of typical grassland species. Conclusion: Our results suggest that an apparently successful restoration of ski-pistes may be not enough to promote a complete recovery of bird communities. The complete recovery of local bird communities may be promoted only if an integral recovery of the original vegetal communities is achieved. We suggest the best conservation option is to adopt techniques to maintain as far as possible original grassland if construction of new ski-pistes is unavoidable.