The effect of anthropization on sedentary landbirds occurring in late summer on a small Mediterranean island (San Pietro, SW Sardinia) has been studied comparing abundance and biomass among different ecological guilds. The two specialized insular guilds (Mediterranean warblers and rocky cliff species) represent about half of the total individual abundance (47%) but only 16% in terms of biomass. Although almost all the surface of the island is covered by Mediterranean scrub (maquis), Mediterranean warblers were not as dominant as the guild of strictly synanthropic species. This latter guild was the most represented in frequency both for abundance and biomass. I hypothesize that (i) here the anthropization could be considered a locally relevant process disrupting the resource flow and lowering the trophic level and (ii) the dominance of synanthropic birds in terms of biomass could be a general phenomenon extended to a large set of Mediterranean islands. The three most abundant synanthropic species, linked to highly disturbed habitats, showed a larger body mass when compared to specialized species as Mediterranean warblers: when applying the Abundance/Biomass Comparison (ABC), an early cumulating biomass curve was observed, partially overlapping with abundance curve. This pattern did not match with the classic predictions for the ABC model (i.e., species with higher biomass are typical of undisturbed assemblage) and could be wrongly interpreted. Therefore, I suggest that the ABC assumptions are not universal but limited only to assemblages where high body mass species coincide to species of a higher trophic level.
Wetlands are naturally patchy habitat types that in fragmented landscapes are usually immersed inside a sea of anthropogenic habitat matrix. Decrease in patch size area and increase of patch isolation are two important components of wetland fragmentation. We investigated the effects of fragment area on bird species richness at four-level assemblages in a highly fragmented Mediterranean wetland system of Central Italy. Our results indicate that fragment area influenced differently the species richness for distinct assemblages in wetland fragments. Area was significantly correlated to total species richness, vagrant, breeding and
-related breeding species (PBS). A comparison of the various regression equations showed that the log-log relationship was the best-fitted model and the amount of variation (
of log-log regression line) was much higher for PBS and breeders than for vagrants. This pattern confirmed that when including vagrants in studies based on the equilibrium theory of island biogeography, the ‘insularity of islands’ is reduced. We also found that higher z-values (regression slope) were associated with PBS and breeding birds, supporting the idea of a ‘matrix effect’ on the studied species.
Authors:L. Redolfi De Zan, C. Battisti, and G. Carpaneto
The awareness of the importance of deadwood in forest ecosystems has increased in recent decades. Today, dead wood is recognized as a key factor affecting diversity of forest communities. Hole-nesting birds and saproxylic organisms represent an active part of the animal community through the recycle of decaying wood into the forest soils. Three relict beech forests of central Italy were surveyed for both saproxylic beetles and hole-nesting birds, using two different types of interception traps for the former group and point count method for the latter. The variables of dead wood quality were recorded from ten plots, particularly the decaying class and typology of all the wood debris with a diameter ≥ 5 cm. In order to correlate richness and abundance of beetles and birds in a symmetric way, we used co-inertia analysis (CoIA). To correlate in a predictive way the dead wood attributes (dead wood typology and class decay) with birds and beetles assemblages we used partial redundancy analysis (RDA). Our results showed a significant relationship between saproxylic beetle and hole-nesting bird communities. Three dead wood variables (the volume of standing dead trees, stumps and large branches on the ground) appeared to be good predictors of saproxylic beetle richness while the volume of standing dead tree and of dead trees on the ground were the same for hole-nesting birds. These results suggest specific recommendations useful for forest management and planning.
Authors:C. Battisti, L. Luiselli, B. Frank, and E. Lorenzetti
Breeding bird assemblages and species present in two ‘archipelagos” of wood fragments, included in fragmented landscape of Central Italy, were studied in springs 2002 and 2003 with line transect method (1: Cornicolan hills study area: 20 fragments; 2: Anzio-Nettuno study area: 13 fragments). An area effect was shown in diversity/dominance analyses carried out by species rank/frequency diagrams obtained for the wood fragment assemblages of two ‘archipelagos’. Smaller fragments showed a lower species richness, a higher relative frequencies of first dominant species and a higher value of angular coefficient of assemblage lines. When fragment area decreases, the assemblage tendency lines in diversity/dominance diagrams show a higher slope (i.e., higher angular coefficient). Simpson dominance index was inversely correlated to fragment area: smaller fragments concentrate dominance in less species compared to larger ones. This approach suggests that the reduction in area of wood fragments could be comparable to a stress on breeding bird assemblages induced by anthropogenic habitat conversion and fragmentation, here considered as a disturbance at landscape level.
Authors:G. Amori, S. Gippoliti, L. Luiselli, and C. Battisti
Changes in taxa composition among different communities in a landscape or along an environmental gradient are defined as β-diversity. From a biogeographic point of view, it is interesting to analyse patterns of β-turnover across latitudinal bands, and to understand whether P-diversity is significantly associated with endemism at lower latitudes, as predicted by theory. We inspected these issues by using squirrels (Rodentia, Sciuridae) as a study case. Distribution data for each genus were obtained from literature and mapped. The two hemispheres were subdivided into 23 latitudinal bands of equal area, and we calculated a β-turnover index between latitudinal bands with two formulae: Wilson and Shmida’s (1984) and Lennonetal.’s (2001) indices. We found that the peak of number of Sciuridae genera significantly corresponded to the peak in β-turnover scores at the same latitudes (25–31°N) with Wilson and Shmida’s (1984), but not with Lennon et al.’s (2001) index. We also found that the turnover between ground and tree squirrels corresponded to the grassland vegetation latitudinal bands (around 40° N), and the beginning of the latitudinal bands characterized by tropical and subtropical forests is accomplished with the occurrence of tree and flying squirrels
Authors:C. Battisti, E. Ukmar, L. Luiselli, and M. Bologna
Breeding bird communities were studied by line-transect in burnt pinewood and unburnt pinewoods, during three years subsequently to a fire event, in a coastal woodland of Mediterranean central Italy. We analyzed data following a diversity/dominance approach that ranks the species in order of their abundance, to obtain rank/abundance diagrams (‘Whittaker plots’). Although it is generally accepted that fire may induce structural changes in forest communities of breeding birds, we observed more evident effects when considering the assemblage of forest-specialist species. When considering the whole community of birds, ordinate intercepts of the regression between rank and relative abundance of species were not significantly different between unburnt and burnt plots in any of the three years of study. However, when considering only the forest-related species, there was a significant difference between unburnt and burnt plots in all the years of study. Evenness showed lower values that were explicited by the diversity/dominance diagrams (lower collocation of the curves of burnt pinewoods if compared to unburnt ones). Overall, the patterns observed in this study suggest that the effects of fire disturbance were more evident at the ecological level than at the taxonomic-level assemblages. The gradual decline of the more sensitive species due to fires and the proportional increase of edge/generalist species may induce a species turnover in burnt woods with cascade and relaxation effects which could be evidenced by diversity/dominance diagrams. Consequently, it is useful to separate the effects of fires at community-level and at assemblage-level when studying bird communities in areas subjected to fires.
Authors:C. Battisti, G. Fanelli, D. Pavel, L. Redolfi De Zan, S. Rossi de Gasperis, and G. Caneva
We tested the application of the concept of hemeroby and generalism at community level, on a set of birds occurring in various habitats of central Italy characterized by different level of disturbance. In each habitat-related bird community, we applied the recently published species-specific score in hemeroby (a proxy of habitat-related disturbance; HSi) and hemerobiotic diversity (a proxy of generalism; H’Hi) to local species frequency, obtaining weighted values at community level (HStot and H’Htot). The relationship between HStot vs. H’Htot showed an increasing trend moving from reed beds through forests and mosaics to urban communities. Quadratic model (best fit) evidenced a significant correlation between these variables and a tendency toward a hump-shaped curve, corroborating results already observed at species level (intermediate generalism hypothesis). The co-inertia analysis discriminated four groups of habitat-related communities, characterized by species with different levels of disturbance-sensitivity (expressed by HSi) and generalism (expressed by hemerobiotic diversity; H’Hi): (i) forest type-related, where mature wood communities were separated from a coppiced wood one; (ii) communities of moderately disturbed agricultural habitats; (iii) communities embedded in highly disturbed mosaics, and (iv) a group including either a highly disturbed urban habitat or a low disturbed wetland reed bed, with highly specialized species (respectively, synanthropic species and water-related species). Total scores in hemeroby and hemerobiotic diversity, expressing the composition in species with different disturbance preference and generalism, might act as good community-based indicators of degree of naturalness, especially for forest habitat types.