Local and landscape effects in a host-parasitoid interaction network along a forest-cropland gradient

Osorio S., Arnan X., Bassols E., Vicens N., Bosch J. (2015) Local and landscape effects in a host-parasitoid interaction network along a forest-cropland gradient. Ecological Applications. 25: 1869-1879.
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Doi: 10.1890/14-2476.1

Resum:

Land-use driven habitat modification is a major driver of biodiversity loss and impoverishment of interaction diversity. This may affect ecosystem services such as pollination and biological control. Our objective is to analyze the effects of local (nesting environment: farms vs. tree stands) and landscape (forest-cropland gradient) factors on the structure and composition of a cavity-nesting bee-wasp (CNBW) community, their nests associates (henceforth parasitoids), and their interactions. We set up 24 nest-trapping stations in a fragmented, extensively farmed area of ∼100 km2. We obtained 2035 nests containing 7572 brood cells representing 17 bee and 18 wasp species, attacked by 20 parasitoid species. Community structure and composition, as well as network structure, were much more dependent on local than on landscape factors. Host abundance and richness were higher in farms. In addition, host abundance was positively correlated to cropland cover. We also found highly significant differences between nesting environments in host community composition. Structure and composition of the parasitoid community were conditioned by the structure and composition of the host community. Network structure was affected by nesting environment but not by landscape factors. Interactions tended to be more diverse in farms. This result was mostly explained by differences in network size (greater in farms). However, generality was significantly higher in farms even after controlling for network size, indicating that differences in species' interaction patterns associated to differences in community composition between the two nesting environments are also affecting network structure. In conclusion, open habitats associated with extensively farmed exploitations favor local CNBW diversity (especially bees) and result in more complex host-parasitoid interaction networks in comparison to forested areas. The conservation value of this kind of open habitat is important in view of the progressive abandonment of extensively cultivated farmland taking place in Europe at the expense of agricultural intensification and reforestation. © 2015 by the Ecological Society of America.

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Pre-wintering conditions and post-winter performance in a solitary bee: Does diapause impose an energetic cost on reproductive success?

Sgolastra F., Arnan X., Pitts-Singer T.L., Maini S., Kemp W.P., Bosch J. (2015) Pre-wintering conditions and post-winter performance in a solitary bee: Does diapause impose an energetic cost on reproductive success?. Ecological Entomology. : 0-0.
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Doi: 10.1111/een.12292

Resum:

1. Diapause is a dynamic process of low metabolic activity that allows insects to survive periods of harsh conditions. Notwithstanding the lowered metabolism, and because diapausing insects have no access to food, diapause has an energetic cost that may affect post-diapause performance. 2. Previous studies on the solitary bee Osmia lignaria have shown that prolonged pre-wintering periods (the time during which individuals already in diapause remain at warm temperatures) are associated with elevated lipid consumption, fat body depletion, and body weight loss. The present study investigated whether prolonged pre-wintering also affects reproduction, i.e. whether the costs associated with diapause could have an effect on post-diapause performance in this species. 3. Females were exposed to a range of pre-wintering conditions, and ovary development and individual post-wintering performance were monitored throughout their adult life span. 4. No evidence of an effect of pre-wintering duration on post-diapause reproductive success was found. Expected differences in the timing of establishment were not observed because ovary maturation was, surprisingly, not arrested during pre-wintering. Prolonged pre-wintering duration did not result in decreased life span, probably because emerging females could rapidly replenish their metabolic reserves through feeding. However, there was a very strong effect of the duration of the pre-emergence period on the likelihood of nest establishment. 5. Longevity, the main factor determining fecundity in Osmia, is subjected to high levels of intrinsic variability, even among females of similar size exposed to identical conditions during development and nesting. © 2015 The Royal Entomological Society.

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