Resistant invaders can convey benefits to native species

Introduced species are recognized as a major threat to native species. One factor that facilitates their spread is that they are often resistant to natural enemies of their native competitor. Negative effects of the invaders are often documented, but invaders may also convey benefits to the natives if they interfere with the native host-parasite interactions. If invaders act as resistant targets for the native parasites, they may reduce the density of the infectious transmission stages ('dilution effect') and decrease the risk of infection for the natives. We tested this hypothesis by exposing coexisting native and introduced freshwater snails to infectious stages of a native parasite. The native hosts showed a significantly reduced infection rate when exposed together with the resistant invader. A significant amount of the parasite transmission stages was wasted on the resistant invader leading to lower risk of infection for the natives. Our results show that invaders may convey benefits to the native competitors by perturbing the native host-parasite interaction and support the idea that the 'dilution effect' could be important for invaded communities.     

Loss of migration and urbanization in birds: a case study of the blackbird (Turdus merula)

Many organisms have invaded urban habitats, although the underlying factors initially promoting urbanization remain poorly understood. Partial migration may facilitate urbanization because such populations benefit from surplus food in urban environments during winter, and hence enjoy reduced fitness costs of migratory deaths. We tested this hypothesis in the European blackbird Turdus merula, which has been urbanized since the 19th century, by compiling information on timing of urbanization, migratory status, and population density for 99 cities across the continent. Timing of urbanization was spatially auto-correlated at scales up to 600 km. Analyses of timing of urbanization revealed that urbanization occurred earlier in partially migratory and resident populations than in migratory populations of blackbirds. Independently, this effect was most pronounced in the range of the distribution that currently has the highest population density, suggesting that urbanization facilitated population growth. These findings are consistent with the hypothesis that timing of urbanization is facilitated by partial migration, resulting in subsequent residency and population growth.     

Case study on the carbon consumption of two metropolitan cities

Purpose  

The cities merit special attention in global warming since they produce up to 80% of the global greenhouse gas emissions. Even though this has been widely acknowledged, only few papers exist that have studied cities holistically from a demand, i.e., consumption, perspective. The study presents a detailed analysis of the carbon footprint of two metropolitan cities from a consumption perspective. With the analysis of consumer carbon footprints (carbon consumption), the distribution of emissions in the key source categories is presented and compared.     

DOC and N<Subscript>2</Subscript>O dynamics in upland and peatland forest soils after clear-cutting and soil preparation

Forest clear-cutting followed by soil preparation means disturbance for soil microorganisms and disruption of N and C cycles. We measured fluxes of N₂O and dissolved organic carbon (DOC) in upland soil (podzol) and adjacent peat within a clear-cut forest catchment. Both soil types behaved in a similar way, showing net uptake of N₂O in the first year after the clear-cutting, and turning to net release in the second. The N₂O flux dynamics were similar to those of N content in logging residues, as reported from a nearby site. As organic matter is used in the food web of the decomposers, we attempted to explain the dynamics of N₂O uptake and release by measuring the concurrent dynamics of the low molecular weight (LMW) fraction and the aromaticity of DOC in a soil solution. The labile and most readily available LMW fractions of DOC were nearly absent in the year following the clear-cutting, but rose after two years. The more refractory high molecular weight (HMW) fraction of DOC decreased two years after the clear-cutting. The first year’s net uptake of N₂O could be accounted for by the growth of decomposer biomass in the logging residues and detritus from the degenerating ground vegetation, resulting in immobilization of nitrogen. Simultaneously, the labile, LMW fraction of DOC became almost completely exhausted. The low availability of the LMW fraction could retard the growth and cause the accumulated decomposer biomass to collapse. During the following winter and summer the fraction of LMW clearly increased, followed by increased N₂O emissions. The presence of LMW DOC fractions, not the concentration of DOC, seems to be an important controller for N₂O liberation after a major disturbance such as clear-cutting and site preparation. The complex connection between DOC characteristics, nitrification or denitrification merits further studies.     

Natural range expansion and human-assisted introduction leave different genetic signatures in a hermaphroditic freshwater snail

Colonization events like range expansion or biological invasions can be associated with population bottlenecks. Small population size may lead to loss of genetic diversity due to random genetic drift, to loss of heterozygosity due to increased inbreeding and should leave a signature on the genetic polymorphism and genetic structure of populations. The mating system might additionally influence the outcome of such a process. Here, we compare invasive and native populations of the hermaphroditic freshwater snail Lymnaea stagnalis. In the native range we included populations that were ice-free during the last glaciation period and populations that were glaciated and are located at the edge of the species’ native distribution range. The microsatellite data show substantial loss of genetic variation in the introduced range and no signs of high propagule pressure or admixture. The expressed polymorphism was so low that mating system analysis was not possible. In the native region, all populations display strong levels of differentiation (global F _ST: 0.341) independent of colonization history and exhibit no significant pattern of inbreeding. However, the populations in more recently colonized habitats show diminished genetic diversity. Overall, these results illustrate how dramatic the reduction in genetic diversity can be for hermaphroditic animals and that gene flow in the native range can be surprisingly low despite short distances.     

The macrophyte, Stratiotes aloides, protects larvae of dragonfly Aeshna viridis against fish predation

Predation could be one force determining which contemporary species occupy a certain habitat. Aeshna viridis is an endangered dragonfly species with a larval distribution strongly associated with lakes where the water plant, water soldier, Stratiotes aloides, occurs. In this study, the larvae were almost exclusively found in patches of S. aloides. To study larval association with S. aloides further, we conducted a series of laboratory experiments. Behavioural experiments indicated that larvae preferred S. aloides. Aeshna viridis larvae were nocturnal and rather inactive. Larvae on S. aloides were less susceptible to predation by the perch, Perca fluviatilis, than larvae on another water plant, Myriophyllum alterniflorum. According to our study it seems that occurrence of S. aloides may limit the distribution of A. viridis, and the protection of refuges may be essential in planning the conservation of this endangered species.     

Meiofauna of springs in Finland in relation to environmental factors

The meiofauna was studied from springs in Finland which wascompletely ice-covered during the last glacial epoch. Of the31springs that were examined, 15 were in areas considered to bein anatural state and 16 had catchment areas subject toanthropogenicdisturbance from one of four sources: agriculture,inhabitation,gravel extraction or winter road de-icing with NaCl. The taxarecorded were a mixture of those already described fromepigeicwaters or groundwaters and some which may be regarded ascharacteristic of springs Statistical analysis revealeddifferencesin the meiofaunal taxa in relation to the water quality orcatchment area variables. Of the major meiofaunal groups thenematodes favoured springs influenced by agriculture,oligochaeteswere most tolerant of road de-icing, cladocerans and copepodspreferred springs in a natural state, ostracods couldwithstand theinfluence of road de-icing and gravel extraction, whilstdipteranlarvae could withstand the influence of agriculture.Oligochaetescomprised 13.4% of meiofaunal numbers. The most abundantspecieswas Aeolosoma quaternarium, which was most numerous insprings in a natural state, while Dero digitatapreferredeutrophic conditions. Harpacticoids comprised 14.1% ofindividualsand clearly preferred a natural state, Bryocamptusechinatusand Moraria brevipes being the most abundant species.Ostracods, of which the most abundant species was Potamocyprispallida, were the most numerous animal group, constituting21% ofthe meiofaunal population, and their numbers were greatest insprings influenced by road de-icing or gravel extraction.Dipteranlarvae, of which the majority were chironomids, comprised14.9% ofindividuals. The ostracods Potamocypris pallida andthreespecies of Candona and the harpacticoid Bryocamptuscuspidatus are new records for Finland.     

Variation in the fatty acid profiles of two cold water diatoms grown under different temperature,light, and nutrient regimes

There is a growing demand for marine omega-3 fatty acids (FAs) that is produced in high amounts by some microalgae. Here we determined the FA profiles of two cold water adapted diatoms, Chaetoceros wighamii and Thalassiosira baltica. The cultures were acclimated to different temperatures (3, 7, 11, 15, and 19 °C) and irradiance (20, 40, 130, and 450 μmol photons m^?2 s^?1) and the FA profiles were determined in exponential and stationary growth phases, the latter induced by different nutrient limitation (N, P, and Si). The maximum growth rate was obtained by both species at 11 °C, ≥ 130 μmol photons m^?2 s^?1 and was 0.8 day^?1 and 0.6 day^?1 for C. wighamii and T. baltica, respectively. Both species contained relatively high amounts of eicosapentaenoic acid (EPA). Thalassiosira baltica accumulated maximally ~ 30 mg EPA g^?1 ash-free dry weight (AFDW) under Si-limitation. The content of docosahexaenoic acid (DHA) was lower, reaching up to 4 mg DHA g^?1 AFDW in T. baltica. The concentration of EPA correlated positively with the chlorophyll a:carbon ratio, suggesting that it is bound to membranes in the photosynthetic apparatus and the EPA content in T. baltica was high enough to consider it as a potent candidate for cultivation under cold (< 15 °C) conditions. Covering a wide range of environmental conditions, the strongest differentiation in FA profiles was observed between the species with the growth phase/nutrient limitation pattern as the second most important driver of the FA composition.