No uniform associations between parasite prevalence and environmental nutrients

The resource quality of the host has been shown to affect parasite transmission success, prevalence, and virulence. Seasonal availability of environmental nutrients alters density and stoichiometric quality (carbon–nutrient ratios) of both producers and consumers, suggesting that nutrient availability may drive fluctuations in parasite prevalence patterns observed in nature. We examined the interactions between the population dynamics of a keystone herbivore, Daphnia, and its parasites, and their associations with water nutrient concentrations, resource quantity and quality, and other environmental variables (temperature, pH, oxygen concentration) in a small lake, using general linear models. We found that the prevalence of two gut endoparasites was positively related to food source and quality as well as nitrogen content of Daphnia, whereas the prevalence of an epibiont and overall parasite species richness was negatively related to phosphorus content of Daphnia. When only endoparasite species richness was considered, no connections to nutrients were found. Daphnia density was not connected to parasites, but we found interactions between Daphnia fecundity and parasite prevalence. Overall, our results suggest that environmental nutrient concentrations and stoichiometric quality of the host have the potential to affect seasonality in parasite epidemics, but the connections between environmental carbon : nutrient ratios and parasite prevalence patterns are diverse and species specific.peerReviewe

Männyn siitepölytuotannon määrittäminen neulastuotannon avulla metsänrajalla : väline menneen ilmaston rakentamiseen

TutkimusselosteSeloste artikkelista: Jalkanen, R., Hicks, S., Aalto, T. & Salminen, H. 2008. Past pollen production reconstructed from needle production in Pinus sylvestris at the northern timberline: a tool for evaluating palaeoclimate reconstructions. Silva Fennica 42(4): 499–513

Comparative LCA of the use of biodiesel, diesel and gasoline for transportation

Silva Fennica 39(4): 467–480. The foliage status in the main stem of Scots pines (Pinus sylvestris) was studied ret-rospectively using the needle trace method (NTM) on a stand, seriously defoliated by the pine sawfly (Diprion pini) in the 1980s. Needle density increased abruptly in the seasons following the defoliation. The strongest reduction in annual needle production occurred one year later. As a consequence of lower needle production, the annual number of attached needles decreased three to five years after the defoliation. Needle retention and the average age of attached needles tended to increase after defoliation. In analyses of covariance with the NTM variables, needle density (logarithmic transformed values) and average age of attached needles, had the highest, significant, negative relationship with radial and height increments both in the period prior to the defoliation and in the time when the trees were suffering from defoliation. The relationships between height increment and the number of needles and needle loss were positive and significant. Also radial increment had a positive relationship with the number of needles but not with needle loss. Interestingly, an abrupt increase in the needle density gave a good indication of the effects of a sudden defoliation in pines