Gradients of salinity and plant community richness and diversity in two different Mediterranean coastal ecosystems in NW Sardinia

This study aimed to test if differences in soil salinity, plant richness and diversity were significantly affected by habitat, site and distance from the seashore at three sandy and three rocky coastal sites in north-western Sardinia. Each site has been divided into three belts placed at an equal distance of 50 m from the shoreline. We measured soil salinity using a probe and vascular plants richness and diversity using linear transects at all sites. Average soil salinity varied from 0.115 g/l to 0.180 g/l; it was higher in the rocky habitats than in the sandy ones. A total of 21 species were found per transect/site at the rocky sites and 30 species per transect/site at the sandy sites, with an average of Shannon and Weaver's Diversity Index of 1.8 per each belt at each site. These data confirm that, also in the Mediterranean islands, there are coastal gradients of soil salinity from the seashore to inland areas and that also vascular plant richness and diversity are influenced by the distance from the sea. Soil salinity was strongly affected by the type of habitat, being average at the rocky coasts and negligible at the sandy shores. The site effect was not significant for both soil salinity and plant richness and diversity.

Climate, Land use and Plant Richness Differently Shape Herbivory on Major Plant Functional Groups

Interactions between plants and herbivorous invertebrates drive the nutritional quality of resources for higher trophic levels, nutrient cycling and plant-community structure. Thereby, shifts in functional composition of plant communities particularly impact ecosystem processes. However, the current understanding of herbivory is limited concerning climate, land use and plant richness, as comparative studies of different plant functional groups are lacking. This study was conducted on 81 plots covering large climatic and land-use gradients in Bavaria, Germany. We investigated foliar invertebrate herbivory rates (proportional leaf-area loss, following ‘herbivory’) in three major plant functional groups (legumes, non-leguminous forbs, grasses). As drivers we considered multi-annual mean temperature (range: 6.5–10.0 °C), local habitat type (forest, grassland, arable field, settlement), local plant richness (species and family level, ranges: 10–50 species, 5–25 families) and landscape diversity (0.2–3-km scale). Our results largely confirm higher herbivory on legumes than on forbs and grasses. However, herbivory in forests was similar across plant functional groups since herbivory on legumes was low, e.g. lower than on legumes in grasslands. We also observed differential responses of herbivory among plant functional groups in response to plant richness (family level only), but not to landscape diversity. Temperature did not affect overall herbivory, but in grasslands higher temperature decreased herbivory on legumes and increased on forbs and grasses. We conclude that climate, habitat type and family-level plant richness likely assert different effects on herbivory among plant functional groups. This emphasises the importance of functional groups for understanding community-level herbivory and ecosystem functioning.

Hymenopteran Parasitoid Diversity & Tri-Trophic Interactions: the Effects of Habitat Fragmentation in Wellington, New Zealand

<p>Habitat fragmentation and the resulting decline in biodiversity through the loss of habitat are thought to be the main threat to insect extinctions. According to the trophic level hypothesis, habitat fragmentation affects parasitoids more severely than their herbivorous hosts. Parasitoids also may be correlated with plant species richness, because plants host a variety of phytophagous insects acting as hosts for parasitoids, or plants provide food or act as shelter for parasitoids. In this study, the effects of the forest fragment properties; area, isolation, percentage of residential area surrounding focal fragments and plant richness on parasitic wasps and their interactions were examined. These fragmentation effects were examined in 10 urban native bush remnants in the Wellington and Hutt Valley region of the lower North Island, New Zealand. Fragmentation effects on species abundance, richness and diversity and on community assemblages were examined for the wasp families Ichneumonidae, Pompilidae and Proctotrupidae. Correlations between beta diversity of the plant community and the parasitoid community were analysed and the study investigated whether individual parasitoid occurrences can be predicted by the range of their host's host plants. This study focused on interactions between the kawakawa moth larva Cleora scriptaria, its primary host plant Macropiper excelsum and the parasitism rates by two parasitoids Aleiodes declanae (an endemic species) and Meteorus pulchricornis (an exotic species) and the herbivory caused by C. scriptaria larvae. In addition to interaction responses to forest fragmentation properties, interaction responses were also examined with respect to the properties of the plot and individual plant. Individual species showed different trends in response to the fragmentation properties, making interpretation of a general community response difficult. The abundance, richness and diversity of small-bodied parasitoids were inversely related to increasing area and plant species richness. Parasitoid community composition changed with fragment isolation and plant species richness. Ichneumonidae strongly responded to isolation in one year, whereas the Pompilidae responded to plant species richness. The Proctotrupidae community structure showed no response to any of the fragmentation properties. Correlations between plant and parasitoid community structures were not significant and individual parasitoid-plant associations were weak and inconclusive. Parasitism rates for A. declanae were significantly higher in more isolated fragments with smaller trees, and were negatively affected by overall parasitism rates, more so in isolated fragments. Parasitism rates by M. pulchricornis responded positively to larval densities and declined with increasing plant richness. Herbivory was positively related to the abundance of M. excelsum, tree size and larval density. The current study provides evidence that the forest fragment properties examined are, on their own, not always sufficient predictors of community structure and interactions for parasitoids. Aspects of the results from this thesis conflict with the trophic-level hypothesis with species responding in a negative or positive way, or not responding at all to forest fragmentation effects. The findings of this thesis support to conserving species diversity by maintaining and enhancing all types of existing forest fragments to prevent species extinctions.</p>

Hymenopteran Parasitoid Diversity & Tri-Trophic Interactions: the Effects of Habitat Fragmentation in Wellington, New Zealand

<p>Habitat fragmentation and the resulting decline in biodiversity through the loss of habitat are thought to be the main threat to insect extinctions. According to the trophic level hypothesis, habitat fragmentation affects parasitoids more severely than their herbivorous hosts. Parasitoids also may be correlated with plant species richness, because plants host a variety of phytophagous insects acting as hosts for parasitoids, or plants provide food or act as shelter for parasitoids. In this study, the effects of the forest fragment properties; area, isolation, percentage of residential area surrounding focal fragments and plant richness on parasitic wasps and their interactions were examined. These fragmentation effects were examined in 10 urban native bush remnants in the Wellington and Hutt Valley region of the lower North Island, New Zealand. Fragmentation effects on species abundance, richness and diversity and on community assemblages were examined for the wasp families Ichneumonidae, Pompilidae and Proctotrupidae. Correlations between beta diversity of the plant community and the parasitoid community were analysed and the study investigated whether individual parasitoid occurrences can be predicted by the range of their host's host plants. This study focused on interactions between the kawakawa moth larva Cleora scriptaria, its primary host plant Macropiper excelsum and the parasitism rates by two parasitoids Aleiodes declanae (an endemic species) and Meteorus pulchricornis (an exotic species) and the herbivory caused by C. scriptaria larvae. In addition to interaction responses to forest fragmentation properties, interaction responses were also examined with respect to the properties of the plot and individual plant. Individual species showed different trends in response to the fragmentation properties, making interpretation of a general community response difficult. The abundance, richness and diversity of small-bodied parasitoids were inversely related to increasing area and plant species richness. Parasitoid community composition changed with fragment isolation and plant species richness. Ichneumonidae strongly responded to isolation in one year, whereas the Pompilidae responded to plant species richness. The Proctotrupidae community structure showed no response to any of the fragmentation properties. Correlations between plant and parasitoid community structures were not significant and individual parasitoid-plant associations were weak and inconclusive. Parasitism rates for A. declanae were significantly higher in more isolated fragments with smaller trees, and were negatively affected by overall parasitism rates, more so in isolated fragments. Parasitism rates by M. pulchricornis responded positively to larval densities and declined with increasing plant richness. Herbivory was positively related to the abundance of M. excelsum, tree size and larval density. The current study provides evidence that the forest fragment properties examined are, on their own, not always sufficient predictors of community structure and interactions for parasitoids. Aspects of the results from this thesis conflict with the trophic-level hypothesis with species responding in a negative or positive way, or not responding at all to forest fragmentation effects. The findings of this thesis support to conserving species diversity by maintaining and enhancing all types of existing forest fragments to prevent species extinctions.</p>

Pioneer annual vegetation of gravel-bed rivers: first insights on environmental drivers from three Apennine streams

A huge knowledge gap exists on riverine pioneer herbaceous vegetation. Despite its relevance in regulating the C metabolism at the catchment scale, and the triggering role in shrubs and trees establishment along riverbanks, little data is available on its environmental determinants. Indeed, most existing knowledge in this field refers to woody species or aquatic macrophytes neglecting the ecosystem relevance of ephemeral herbaceous vegetation. Focusing on three gravel bed rivers located in northern Italy (Baganza, Nure and Parma streams), the present study is aimed to evaluate the riverine ephemeral plant richness, considering both native and alien taxa, and the role of hydrogeomorphological disturbance and sediment quality in the observed richness patterns. At higher disturbance rates (e.g., larger river sizes), our data indicates a progressive decrease in overall plant richness, but also an increase in the coverage-abundance rates mainly due to alien species. This evidence confirms that variations in hydrology imply changes in pioneer plant species richness at in-stream periodically exposed sediments. More attention must be given to the vulnerability of pioneer vegetation to climate change and direct human impacts to fully understand the functioning of lotic ecosystems, especially the non-perennial ones.

Variations in Plant Richness, Biogeographical Composition, and Life Forms along an Elevational Gradient in a Mediterranean Mountain

Despite the increasing interest in elevational patterns in biodiversity, few studies have investigated variations in life forms and biogeographical composition, especially in the Mediterranean biome. We investigated elevational patterns in species richness, biogeographical composition (chorotypes) and life forms (Raunkiaer classification) along an elevational gradient in a Mediterranean mountain (Central Italy). We found a general hump-shaped pattern of species richness, which can be explained by harsher conditions at the lowest and highest elevations. This pattern is distinctly related to prevalence at mid elevations of species with European and Euro-Asiatic distribution, which are favored by a temperate climate. Phanerophytes and geophytes (which are mainly associated with woods) were concentrated at mid elevations where woodlands prevail. Hemicryptophytes increased with elevation, consistently with their ability to cope with high altitude climatic conditions. Mediterranean species declined with elevation because they are negatively affected by decreasing temperatures. Chamaephytes showed a U-shaped pattern, suggesting they are able to cope with arid and cold conditions at the extremes of the gradient. Endemics increased with elevation because of their association with mountainous areas as key places for endemism evolution. These results illustrate how elevational patterns in species richness, biogeographical composition and life forms are interrelated and demonstrate reciprocal insights for understanding current vegetation settings.

High resolution ancient sedimentary DNA shows that alpine plant biodiversity is a result of human land use

Alpine areas are well known biodiversity hotspots, but their future may be threatened by expanding forest and changing human land use. Here, we reconstructed past vegetation, climate, and livestock over the past ~ 12,000 years from Lake Sulsseewli (European Alps), based on sedimentary ancient DNA, pollen, spores, chironomids, and microcharcoal. We assembled a highly-complete local DNA reference library (PhyloAlps, 3,923 plant species), and used this to obtain an exceptionally rich sedaDNA record of 366 plant taxa. The vegetation mainly responded to temperature during the first half of the Holocene, while human activity drove changes from 6 ka onwards. Land-use shifted from episodic grazing (Neolithic, Bronze Age) to agropastoral intensification (Medieval Age). This prompted a coexistence of species typically found at different elevational belts, thereby increasing plant richness to levels that characterise present-day alpine diversity. Our results indicate that traditional agropastoral activities should be maintained to prevent reforestation and preserve alpine plant biodiversity.

Effects of Patch Size, Fragmentation, and Invasive Species on Plant and Lepidoptera Communities in Southern Texas

Habitat loss, fragmentation, and invasive species are major threats to biodiversity. In the Lower Rio Grande Valley (LRGV) of southern Texas, a conservation hotspot, few studies have examined how land use change and biotic disturbance influence biodiversity, particularly among Lepidoptera. We surveyed 24 habitat fragments on private lands in the LRGV and examined how patch size, edge to interior ratio (EIR), prevalence of invasive, exotic, and pest (IEP) plant species, and other environmental factors influenced plant and Lepidoptera communities within four habitat classes. Biotic disturbance was widespread and intense. IEP plants represented three of the four most common species in all but one habitat class; yet, classes largely had distinctive plant and Lepidoptera communities. Larger habitat patches had lower IEP prevalence but also lower plant richness and lower Lepidoptera richness and abundance. Conversely, patches with higher EIRs had greater IEP prevalence, plant richness, and Lepidoptera richness and abundance. IEP prevalence was negatively related to plant diversity and positively related to woody dominance, blooming plant abundance, and, surprisingly, both plant cover and richness. However, plant richness, abundance, and diversity were higher where a greater proportion of the plants were native. Lepidoptera diversity increased with plant cover, and Lepidoptera richness and abundance increased with plant richness. More individual Lepidoptera species were influenced by habitat attributes than by availability of resources such as host plants or nectar sources. Our results illustrate extensive landscape alteration and biotic disturbance and suggest that most regional habitats are at early successional stages and populated by a novel species pool heavy in IEP species; these factors must be considered together to develop effective and realistic management plans for the LRGV.