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Schott T.,University of Tromso | Hagen S.B.,Bioforsk Soil and Environment | Ims R.A.,University of Tromso | Yoccoz N.G.,University of Tromso
Journal of Animal Ecology

1. Larval parasitoids (i.e. parasitoids attacking host larvae) constitute a major source of mortality in many ecologically and economically important forest insects, but how this mortality affects spatio-temporal population dynamics is often not clear. 2. In sub-arctic Fennoscandian birch forest, the two geometrids Epirrita autumnata and Operophtera brumata exhibit pronounced outbreak cycles with significant ecosystem impacts. As mortality owing to larval parasitoids often is very high, the hypothesis that parasitism terminates outbreaks has been advocated, but without decisive empirical evidence. 3. We analysed the altitude- and species-specific timing of population outbreaks typically seen in the coastal section of the sub-arctic birch forest ecosystem to evaluate the critical premise that parasitoid-inflicted larval mortality ought to predict geometrid population growth. 4. However, despite temporally high rates of parasitism, this did not influence the strongly species and altitude-patterned geometrid outbreaks. We therefore conclude that termination of cyclic outbreaks in these geometrids is caused by other regulatory mechanisms than larval parasitoids. 5. Regardless of their lack of effect on the altitude-specific outbreak dynamics, larval parasitoids accounted for some of the local spatial variance in the temporal dynamics. This implies that results from spatially localized observations and experiments, which dominate research on parasitoid- host interaction, may be misinterpreted with respect to their relevance for large-scale and longterm population dynamics. © 2010 The Authors. Journal compilation © 2010 British Ecological Society. Source

Vindstad O.P.L.,University of Tromso | Hagen S.B.,Bioforsk Soil and Environment | Schott T.,University of Tromso | Ims R.A.,University of Tromso
Ecological Entomology

1. Wide temporal fluctuations in host abundance are a potential source of instability and stochasticity in the spatiotemporal population dynamics of associated parasitoid species. Within parasitoid guilds (i.e. parasitoids with similar modes of host utilisation), a conceivable outcome is guild organisation according to a lottery model, in which guild members attain local dominance by colonising previously emptied habitats during increasing host density, before other guild members. In the spatial dimension, an expected manifestation of such dynamics is variable guild structure even across homogeneous habitats. 2. We examined the extent of large-scale spatial patterning of guild characteristics in larval parasitoid wasps associated with cyclically outbreaking populations of the geometrid moth Operophtera brumata in northern Fennoscandia. The study was performed at the onset of the crash-phase of the geometrid's outbreak cycle, along a 70-km transect in costal northern Norway, characterised by largely homogeneous environmental conditions, except for a small climatic gradient. 3. There was a distinct large-scale spatial turnover in dominance among the major parasitoid groups (i.e. guild structure) in O. brumata along the transect, whereas the total prevalence rate of the guild and its diversity showed no consistent variation. Guild structure was unrelated to host density. 4. Although group-specific responses to a slight spatial climatic gradient cannot be rejected as a causal mechanism, we conclude that our results are consistent with the expectation from large-scale stochastic extinction-recolonisation dynamics among functionally equivalent parasitoids relying on a host with strongly cyclic population fluctuations. © 2010 The Authors. Journal compilation © 2010 The Royal Entomological Society. Source

Hagen S.B.,Bioforsk Soil and Environment | Jepsen J.U.,Norwegian Institute for Nature Research | Schott T.,University of Tromso | Ims R.A.,University of Tromso
Biology Letters

For trophic interactions to generate population cycles and complex spatio-temporal patterns, like travelling waves, the spatial dynamics must be matched across trophic levels. Here, we propose a spatial methodological approach for detecting such spatial match-mismatch and apply it to geometrid moths and their larval parasitoids in northern Norway, where outbreak cycles and travelling waves occur. We found clear evidence of spatial mismatch, suggesting that the spatially patterned moth cycles in this system are probably ruled by trophic interactions involving other agents than larval parasitoids. © 2010 The Royal Society. Source

Coutris C.,Norwegian University of Life Sciences | Joner E.J.,Bioforsk Soil and Environment | Oughton D.H.,Norwegian University of Life Sciences
Science of the Total Environment

Sewage sludge application on soils represents an important potential source of silver nanoparticles (Ag NPs) to terrestrial ecosystems, and it is thus important to understand the fate of Ag NPs once in contact with soil components. Our aim was to compare the behavior of three different forms of silver, namely silver nitrate, citrate stabilized Ag NPs (5nm) and uncoated Ag NPs (19nm), in two soils with contrasting organic matter content, and to follow changes in binding strength over time. Soil samples were spiked with silver and left to age for 2h, 2days, 5weeks or 10weeks before they were submitted to sequential extraction. The ionic silver solution and the two Ag NP types were radiolabeled so that silver could be quantified by gamma spectrometry by measuring the 110mAg tracer in the different sequential extraction fractions. Different patterns of partitioning of silver were observed for the three forms of silver. All types of silver were more mobile in the mineral soil than in the soil rich in organic matter, although the fractionation patterns were very different for the three silver forms in both cases. Over 20% of citrate stabilized Ag NPs was extractible with water in both soils the first two days after spiking (compared to 1-3% for AgNO3 and uncoated Ag NPs), but the fraction decreased to trace levels thereafter. Regarding the 19nm uncoated Ag NPs, 80% was not extractible at all, but contrary to AgNO3 and citrate stabilized Ag NPs, the bioaccessible fraction increased over time, and by day 70 was between 8 and 9 times greater than that seen in the other two treatments. This new and unexpected finding demonstrates that some Ag NPs can act as a continuous source of bioaccessible Ag, while AgNO3 is rapidly immobilized in soil. © 2012 Elsevier B.V. Source

Lapied E.,Bioforsk Soil and Environment | Moudilou E.,University of Lyon | Exbrayat J.-M.,University of Lyon | Oughton D.H.,Norwegian University of Life Sciences | Joner E.J.,Bioforsk Soil and Environment

In terrestrial ecotoxicology there is a serious lack of data for potential hazards posed by engineered nanoparticles (ENPs). This is partly due to complex interactions between ENPs and the soil matrix, but also to the lack of suitable toxicological end points in organisms that are exposed to ENPs in a relevant manner. Earthworms are key organisms in terrestrial ecosystems, but so far only physiological end points of low sensitivity have been used in ecotoxicity studies with ENPs. We exposed the earthworm Lumbricus terrestris to silver nanoparticles and measured their impact on apoptosis in different tissues. Increased apoptotic activity was detected in a range of tissues both at acute and sublethal concentrations (down to 4 mg/kg soil). Comparing exposure in water and soil showed reduced bioavailability in soil reflected in the apoptotic response. Apoptosis appears to be a sensitive end point and potentially a powerful tool for quantifying environmental hazards of ENPs. © 2010 Future Medicine Ltd. Source

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