Effects of disturbance on sandy coastal ecosystems of N-Adriatic coasts (Italy)

Coastal sand dune landscapes hold habitats of high economic, social and ecological value on a global scale. At the same time, they are among the most threatened ecosystems worldwide, facing escalating anthropogenic pressures, drawing attention to their resilience as a necessary condition for both biodiversity conservation and sustainable development. This study describes the vegetation zonation of the North-Adriatic coastal landscape which suffers from a severe and complex human utilization meanwhile holding high landscape, faunal and floral values. As plant communities, because of their specific nature, are considered good indicators of overall biodiversity and of ecosystem integrity of coastal dune environments, effects of both human and natural disturbance have been analysed through a comparison between real and potential coastal vegetation, using a hierarchical landscape classification approach. To provide a comprehensive framework for sustainable coastal management and development, a multiscale method for the assessment of the conservation status of sandy coastal environment has been applied. The assessing methodology focused first on landscape level by means of structural and compositional indicators. At a more detailed scale, floristic, vegetational and structural aspects of plant communities were analyzed along the main environmental gradient, which develops moving inland from the sea edge. Conservation status of N-Adriatic coastal zonation resulted fairly good at only few sites along the coast, mostly located where urban development and tourism are limited by legislation or simply because of the difficulty in reaching them. Elsewhere, real vegetation is deeply different from the potential zonation: erosion and tourism pressures truncate the first elements of the zonation, while towns and villages, coastal roads, pines plantations and agriculture truncate the last stages and sandy systems are trapped between erosion on the sea side and human settlements inlands, with no space for natural sediment dynamics and communities development

Successful reproduction of feral Trachemys scripta (Schoepff, 1792) in an inland wetland of the Veneto region, Le Basse del Brenta, Italy

Successful reproduction of feral Trachemys scripta (Schoepff, 1792) in an inland wetland of the Veneto region, Le Basse del Brenta, Ital

Pollinator distribution in patches of suitable habitat depends more on patch isolation than on floral abundance

Intrinsic complexity of real-world systems makes particularly difficult to decipher which factors influence the dispersal of pollinators in the landscape matrix and their distribution among patches of suitable habitat. Saltmarshes are an ideal and naturally simplified landscape to study the ability of different groups of pollinators to disperse across a landscape matrix, as they consist of a matrix of flooded areas surrounding patches of suitable habitat with different degrees of isolation from the mainland and different levels of floral abundance. We hypothesise that pollinator distribution to flowering plants depends more on patch isolation than on floral abundance with pollinator richness and visitation rates to flowering plants decreasing with increasing distance from the mainland. To this end, we established 60 permanent plots at varying distances from the mainland and monitored pollinator visitation to entomophilous plants. We also quantified the reproductive success of entomophilous species in the surveyed plots by calculating fruit set. We found that the pollinator community of saltmarshes consisted only of flying pollinators with good dispersal abilities, while we recorded no flightless pollinator species. Both pollinator richness and visitation rate decreased with increasing distance of patches of suitable habitat from the mainland, affecting reproductive success of a non-autogamous entomophilous species. Interestingly, floral abundance did not affect pollinator richness and visitation rate to flowering plants, nor did it affect reproductive success of target plant species. In saltmarshes, the pollinator distribution depends more on patch distance from the mainland than on floral abundance. Our results suggest that the presence of patches of suitable habitat in a landscape matrix does not necessarily ensure the maintenance of pollinators. Rather, our results suggest that suitable habitat isolation is the critical factor in pollinator dispersal and distribution that should be considered to improve landscape matrix permeability to pollinators

Patterns of pollination interactions at the community level are related to the type and quantity of floral resources

1. A fundamental question in community ecology is how the quantity of floral resources affects pollinator activity and how this relates to the structure and robustness of pollination networks. The issue has been mainly addressed at the species level, while at the community level several questions are still open. 2. Using a species-rich semi-natural grassland as model ecosystem, we explored the relationship between community-level quantity of floral resources, the number of flower visits at community level and descriptors of the structure and robustness of pollination networks. To assess whether patterns of pollination interactions were consistent when using different types of floral resources, we measured three types of floral resources, namely the volume of nectar, the number of pollen grains and the number of flowers. 3. Community-level pollinator visitation rate showed a hump-shaped relationship with the quantity of floral resources. Results were consistent among models employing different measures of floral resources as independent variables. The relationship between the quantity of floral resources and the structure and robustness of the network was not consistent among different types of floral resources; only intermediate levels of nectar volume were associated with high levels of network robustness. 4. The pattern we found is in contrast with some former studies which reported positive linear relationships between the community-level visitation rate of pollinators and the quantity of floral resources. Rather, the observed hump-shaped pattern resembles the relationship previously found between the quantity of floral resources of a given plant species and its visitation rate per flower. Our results highlighted that, by using specific types of floral resources (e.g. the volume of nectar and the number of pollen grains), it is possible to reveal ecological processes that would be masked by using the number of flowers as the sole measure of floral resource

Trade-offs between sampling effort and data quality in habitat monitoring

The transect method has been widely used to monitor habitat conservation status and has been recently recommended as the best tool to monitor steep ecological gradients, such as those in coastal systems. Despite that, the effectiveness of the transect approach can be limited when considering the sampling effort in terms of time needed for sampling. Our work aimed at evaluating the efficacy of the transect approach in a Mediterranean coastal system. Specifically we aimed at evaluating the sampling effort versus the completeness of datasets obtained by performing belt transects in different ways specifically designed to progressively reduce the sampling effort: (i) sampling plots adjacently (“adjacent-plot transect”); (ii) sampling plots alternately (“alternate-plot transect”); (iii) sampling one plot at each plant community along the vegetation zonation (“zonation-plot transect”). We evaluated method efficiency in terms of number and type of habitats identified, spatial extent, species richness and composition, through multivariate analyses, null models and rarefaction curves. The sampling effort was measured in terms of time needed for sampling. The zonation-plot transect had the lowest sampling effort, but provided only an approximation of the state of the dunal communities. The alternate-plot transect showed the best trade-off between the sampling effort and the completeness of information obtained, and may be considered as a efficient option in very wide coastal systems. Our research provides guidelines that can be used in other coastal systems to choose the most cost-effective monitoring method thereby maximising the efficient use of monitoring resources

The resilience of pollination interactions: importance of temporal phases

Aims The loss of species that engage in close ecological interactions, such as pollination, has been shown to lead to secondary extinctions, ultimately threatening the overall ecosystem stability and functioning. Pollination studies are currently flourishing at all possible levels of interaction organization (i.e., species, guild, group and network), and different methodological protocols aimed to define the resilience of pollination interactions have been proposed. However, the temporal dimension of the resilience of pollination interactions has been often overlooked. In the light of these considerations, we addressed the following questions: does a temporal approach help to reveal critical moments during the flowering season, when pollination interactions are less resilient to perturbations? Do pollination interactions evaluated at species, guild, group and network level show different patterns when assessed through time? Methods We monitored contacts between plant and pollinator species in dry grassland communities every 15 days during the overall community flowering season (12 surveys). For each survey, we built a quantitative plant–pollinator interaction matrix and we calculated two sets of metrics characterizing, respectively, the diversity and the distribution of interactions across hierarchical levels. To describe the diversity of interactions, we calculated partner diversity (PD) at the species level, vulnerability/generality (V/G) at the guild level, and interaction diversity and evenness at the network level. The distribution of interactions was characterized by calculating selectiveness at the species and the network level, and modularity at the group level. We assessed the temporal variation of PD, V/G at the level of plants and pollinators, and species selectiveness, by means of Linear Mixed Models (LMMs). To investigate the temporal variation of indexes calculated at group and network level, we applied simple linear and quadratic regressions after checking for temporal autocorrelation in residuals. Important Findings When taking into account the temporal dimension of interactions, the diversity of interactions showed different patterns at different levels of organization. At the species level, no relationship was disclosed between PD and time, when assessing the temporal trend of V/G separately for the guild of plants and pollinators we observed an asymmetric structure of interactions. Pollination interactions showed to be asymmetric throughout the flowering season; however, evenness of interactions and network selectiveness showed significant positive relationships with time, revealing a poorer network of interactions during the end of the flowering season. The temporal analysis of pollination interactions revealed a stronger risk of secondary extinctions at the end of the flowering season, due to a lower degree of redundancy and thus of resilience of the overall network of interactions

Patterns of floral resources and pollination interactions along dry grassland succession

Succession following the abandonment of traditional management practices can pose severe consequences for the conservation of semi-natural dry grassland communities. In the present study, we investigated whether the quantity of floral resources changes during succession of semi-natural dry grasslands and how this is related to pollinator richness and the number of pollination interactions at the community level. We addressed this issue by quantifying floral resources (i.e., number of flowers, nectar volume and number of pollen grains) and monitoring pollination interactions in dry grassland communities at different stages of succession, defined as the total cover of plant species of forest edges. The relationship between the quantity of floral resources and cover of plant species of forest edges was significantly hump-shaped, i.e., regardless of the type of floral resource, all peaked at intermediate values of cover of plant species of forest edges. The richness of animal-pollinated plants in bloom also showed a hump-shaped relationship with the cover of plant species of forest edges, while the richness of pollinator species and the number of pollination contacts were indirectly related to the cover of plant species of forest edges, as they were significantly associated with the number of flowers and the richness of animal-pollinated plants in bloom. Results suggest that succession of dry grasslands after abandonment may affect a crucial function in terrestrial ecosystems, namely animal-mediated pollination. Nevertheless, the conditions of early succession, which could be achieved by the presence of scattered shrubs, could ultimately be favourable for the pollination function in dry grasslands

Disturbance affects the contribution of coastal dune vegetation to carbon storage and carbon sequestration rate

Coastal dune vegetation has been proved to contribute to several crucial ecosystem services, as coastal protection, water purification, recreation; conversely, its capacity to regulate the concentration of greenhouse gases received less attention. To fill this gap, the present work focalized on the assessment of the contribution of coastal dune herbaceous vegetation to carbon storage and carbon sequestration rate, also in relation to possible effects of disturbance. To this aim, we measured the dry biomass and carbon sequestration rate in three different vegetation types (foredune, dry grasslands, humid grasslands), and habitat patch attributes as proxies of the disturbance regime. Relationships between disturbance, and carbon storage and sequestration rate have been analysed by GLMMs. The target vegetation types did not equally contribute to the medium-long term sequestration of carbon with a gradient that increased from the seashore inlands and related to both the growth form and the strategy of resource acquisition of dominant species, and plant community attributes. Disturbance in the form of trampling negatively affected carbon sequestration rate. Results suggest that, when different plant communities are spatially interconnected, the landscape scale results in a better understanding of ecosystem dynamics, functioning and resistance to perturbations and allows to plan coherent management strategies

Increasing the germination percentage of an endangered native orchid (Himantoglossum adriaticum) by pollen transfer and outbreeding between populations

The endangered native orchid Himantoglossum adriaticum H. Baumann is a European endemic species of priority interest (92/43/ EEC, Annex II). Italian populations of H. adriaticum are small and isolated, with depressed germination (< 5%) and seed set. Given the important implications for plant population conservation, we tested the efficacy of artificial pollen transfer (hand pollination) and outbreeding between populations for increasing the germination percentage. Artificial cross-pollination included a). pollen transfer from one large population to two small and isolated populations; b). pollen transfer between two small but not very isolated populations; c) within-population pollen transfer used as a control. Seeds were sown on a modified Malmgren’s medium in vitro and cultured in a controlled environment. Total germination was recorded when no further germination was observed. Germination percentage was compared using a Kruskall-Wallis analysis of variance. Pollen transfer produced a significant increase in total germination but increases were not homogeneous between crosses nor between ramets. Pollen transfer from the largest population to the smaller ones enhanced the germination capacity in one population (1.1% vs. 3.1%; p=0.019). Cross pollination between small-sized and less isolated populations resulted in the largest increase of germination (6.1% vs. 1.58%; p=0.028). The largest differences in total germination occurred between ramets within each crossed-pollinated population. Although germination capacity was essentially ramet-specific and was never high, the results of pollen transfer between the small populations are particularly encouraging, since the mean increase in germination was almost four times that of the control. Our results suggest that pollen transfer and outbreeding between small populations can be considered as a valuable tool to increase genetic flow and germination capacity in natural populations, limit the accumulation of detrimental effects on their fitness driven by the repeated breeding with closely-related individuals, thereby increasing the possibility of conservation of endangered native species

Altitudinal patterns of floral morphologies in dry calcareous grasslands

A central goal in vegetation ecology is the identification of processes that influence species assemblage and distribution within a community. Among the wide variety of biotic interactions, plant-pollinator interactions are assumed to have a marked influence on plant communities assemblage and dynamics. The aim of this work was to verify if in dry grasslands there is a non random distribution of different blossom types along an altitudinal gradient, which may exert a selective pressure on both plants and insects, as well as on their mutualistic relationships. We sampled 85 plots in pre-alpine and hilly reliefs of the Veneto Region, finding that different blossom morphologies were patterned along the altitudinal gradient. Wind blossom type was dominant at low altitude while disk shaped flowers prevailed at high altitude. Our study revealed that altitude might affect species assemblage in dry grassland communities not only by selecting plant species according to their tolerance to different environmental conditions, but also according to their floral morphology, evoking the possibility of an indirect pollination filtering to occur