Fewer non-native insects in freshwater than in terrestrial habitats across continents

Aim: Biological invasions are a major threat to biodiversity in aquatic and terrestrial habitats. Insects represent an important group of species in freshwater and terrestrial habitats, and they constitute a large proportion of non-native species. However, while many non-native insects are known from terrestrial ecosystems, they appear to be less represented in freshwater habitats. Comparisons between freshwater and terrestrial habitats of invader richness relative to native species richness are scarce, which hinders syntheses of invasion processes. Here, we used data from three regions on different continents to determine whether non-native insects are indeed under-represented in freshwater compared with terrestrial assemblages. Location: Europe, North America, New Zealand. Methods: We compiled a comprehensive inventory of native and non-native insect species established in freshwater and terrestrial habitats of the three study regions. We then contrasted the richness of non-native and native species among freshwater and terrestrial insects for all insect orders in each region. Using binomial regression, we analysed the proportions of non-native species in freshwater and terrestrial habitats. Marine insect species were excluded from our analysis, and insects in low-salinity brackish water were considered as freshwater insects. Results: In most insect orders living in freshwater, non-native species were under-represented, while they were over-represented in a number of terrestrial orders. This pattern occurred in purely aquatic orders and in orders with both freshwater and terrestrial species. Overall, the proportion of non-native species was significantly lower in freshwater than in terrestrial species. Main conclusions: Despite the numerical and ecological importance of insects among all non-native species, non-native insect species are surprisingly rare in freshwater habitats. This is consistent across the three investigated regions. We review hypotheses concerning species traits and invasion pathways that are most likely to explain these patterns. Our findings contribute to a growing appreciation of drivers and impacts of biological invasions

Climate-induced changes in grapevine yield and must sugar content in Franconia (Germany) between 1805 and 2010

When attempting to estimate the impacts of future climate change it is important to reflect on information gathered during the past. Understanding historical trends may also aid in the assessment of likely future agricultural and horticultural changes. The timing of agricultural activities, such as grape harvest dates, is known to be influenced by climate and weather. However, fewer studies have been carried out on grapevine yield and quality. In this paper an analysis is undertaken of long-term data from the period 1805-2010 on grapevine yield (hl/ha) and must sugar content (°Oe) and their relation to temperature. Monthly mean temperatures were obtained for the same time period. Multiple regression was used to relate the viticulture variables to temperature, and long-term trends were calculated. Overall, the observed trends over time are compatible with results from other long term studies. The findings confirm a relationship between yield, must sugar content and temperature data; increased temperatures were associated with higher yields and higher must sugar content. However, the potential increase in yield is currently limited by legislation, while must sugar content is likely to further increase with rising temperatures

Modelling the Key Drivers of an Aerial Phytophthora Foliar Disease Epidemic, From the Needles to the Whole Plant

Understanding the epidemiology of infectious diseases in a host population is a major challenge in forestry. Radiata pine plantations in New Zealand are impacted by a foliar disease, red needle cast (RNC), caused by Phytophthora pluvialis. This pathogen is dispersed by water splash with polycyclic infection affecting the lower part of the tree canopy. In this study, we extended an SI (Susceptible-Infectious) model presented for RNC to analyse the key epidemiological drivers. We conducted two experiments to empirically fit the extended model: A detached-needle assay and an in vivo inoculation. We used the detached-needle assay data to compare resistant and susceptible genotypes, and the in vivo inoculation data was used to inform sustained infection of the whole plant. We also compared isolations and real-time quantitative PCR (qPCR) to assess P. pluvialis infection. The primary infection rate and the incubation time were similar for susceptible and resistant genotypes. The pathogen death rate was 2.5 times higher for resistant than susceptible genotypes. Further, external proliferation of mycelium and sporangia were only observed on 28% of the resistant ramets compared to 90% of the susceptible ones. Detection methods were the single most important factor influencing parameter estimates of the model, giving qualitatively different epidemic outputs. In the early stages of infection, qPCR proved to be more efficient than isolations but the reverse was true at later points in time. Isolations were not influenced by the presence of lesions in the needles, while 19% of lesioned needle maximized qPCR detection. A primary infection peak identified via qPCR occurred at 4 days after inoculation (dai) with a secondary peak observed 22 dai. Our results have important implications to the management of RNC, by highlighting the main differences in the response of susceptible and resistant genotypes, and comparing the most common assessment methods to detect RNC epidemics

Identifying new associations between invasive aphids and Pinaceae trees using plant sentinels in botanic gardens

Despite progress in prevention and management of biological invasions, challenges remain, including difficulties with assessing future invasion risks. Predicting the identity of potentially damaging invaders is complex because they are often unknown as pests in their natural range. We used a plant sentinel approach to assess host ranges of invasive aphids across 62 conifer species from around the world in Christchurch Botanic Gardens, as a model for risk assessment such as for the ‘International Plant Sentinel Network’. Using standardised sampling, we obtained ca. 600 observations of aphid abundances (4731 individuals), mainly of the pine aphids Eulachnus brevipilosus and Essigella californica and the spruce aphids Cinara pilicornis and Elatobium abietinum. These aphids were highly genus-specific, despite the spatially mixed distribution of genera. A phylogenetic analysis of pine aphid host preferences showed that abundances of species varied among pine subgenera and the geographic origin of trees, with significantly more aphids on pines in the subgenus Pinus than the subgenus Strobus. Essigella californica occurred abundantly on many pines across most subsections in the subgenus Pinus whereas E. brevipilosus was largely restricted to a few species in the subsection Pinus. Our study revealed several new host records (previously unknown aphid-host relationships) including the abundant occurrence of E. brevipilosus on Japanese red pine, P. densiflora, and of E. californica on P. yunnanensis, P. serotina, P. brutia, and P. nigra, among others. Our study identified numerous novel insect-plant interactions that are likely to materialise if these aphids colonise new host plants, confirming the utility of the plant sentinel approach

An alpine treeline in a carbon dioxide-rich world : synthesis of a nine-year free-air carbon dioxide enrichment study

ISSN:0029-8549ISSN:1432-193

No growth stimulation of tropical trees by 150 years of CO2 fertilization but water-use efficiency increased

The biomass of undisturbed tropical forests has likely increased in the past few decades (1, 2), probably as a result of accelerated tree growth. Higher CO2 levels are expected to raise plant photosynthetic rates (3) and enhance water-use efficiency (4), that is, the ratio of carbon assimilation through photosynthesis to water loss through transpiration. However, there is no evidence that these physiological responses do indeed stimulate tree growth in tropical forests. Here we present measurements of stable carbon isotopes and growth rings in the wood of 1,100 trees from Bolivia, Cameroon and Thailand. Measurements of carbon isotope fractions in the wood indicate that intrinsic water-use efficiency in both understorey and canopy trees increased by 30–35% over the past 150 years as atmospheric CO2 concentrations increased. However, we found no evidence for the suggested concurrent acceleration of individual tree growth when analysing the width of growth rings. We conclude that the widespread assumption of a CO2-induced stimulation of tropical tree growth may not be valid