While many studies have demonstrated that organic farms support greater levels of biodiversity, it is not known whether this translates into better provision of ecosystem services. Here we use a food-web approach to analyse the community structure and function at the whole-farm scale. Quantitative food webs from 10 replicate pairs of organic and conventional farms showed that organic farms have significantly more species at three trophic levels (plant, herbivore and parasitoid) and significantly different network structure. Herbivores on organic farms were attacked by more parasitoid species on organic farms than on conventional farms. However, differences in network structure did not translate into differences in robustness to simulated species loss and we found no difference in percentage parasitism (natural pest control) across a variety of host species. Furthermore, a manipulative field experiment demonstrated that the higher species richness of parasitoids on the organic farms did not increase mortality of a novel herbivore used to bioassay ecosystem service. The explanation for these differences is likely to include inherent differences in management strategies and landscape structure between the two farming systems.

The search for general properties in the structure of ecological networks is currently a very active area of research. Meta‐analyses of published networks are a widely used technique. To have the best chance of discovering common properties though, networks should be constructed using a standardized approach. However, this is rarely the case, and pollination networks are constructed using two main methods: transects and timed observations. To investigate the potential for variation in network structure arising from different construction techniques we constructed plant–pollinator networks using two different methods at a single site, repeating our protocol over three field seasons. Transects and timed observation methods differ in the evenness of observation effort allocated among plant species in the observed community. We show that the uneven allocation of observation effort significantly affects the number of unique interactions in the network, and we reveal a strong trend in effects on web asymmetry and evenness of marginal abundance distributions. However, these effects do not appear to extend to the higher‐order properties of connectance and nestedness.

Summary 1.Organic farming is thought to lead to increased biodiversity and greater sustainability than higher-yielding conventional farming systems. It is usually assumed that organic farms have both larger and higher quality areas of semi-natural habitats, although this assumption has not been unequivocally tested. 2.Here we test the hypothesis that in comparison to conventional farms, organic farms have larger areas of semi-natural and boundary vegetation, and organic farms support higher levels of plant abundance, richness and diversity within cropped and semi-natural areas. 3. Our study compared whole-farms: 10 organic farms were paired with 10 conventional farms in a complex landscape in the south-west of England. On average, organic farms were 7·3 years post conversion. Plant abundance, species richness and diversity were measured in all crop and non-crop landscape elements on each farm. 4. Organic farms had greater total areas of semi-natural habitat (woodland, field margins and hedgerows combined). Woodland area on it's own was also significantly greater. Organic farms had more continuous blocks of woodland (with simpler perimeters than similarly sized patches on conventional farms), whereas woodland on conventional farms often consisted of more linear patches. 5. Semi-natural habitats on organic farms did not have higher plant abundance, richness or diversity than their conventional counterparts. The only landscape element that showed a significant increase in plant abundance, richness or diversity was arable fields. 6. Synthesis and applications . Even within a complex agricultural landscape differences do exist between organic and conventional farms, these differences being larger areas of semi-natural habitats on organic farms. However, with the exception of arable fields, no habitats on organic farms were yet of a better quality than their conventional counterparts in terms of plant abundance and diversity. Conventional farmers may be able to achieve an increase in plant diversity within arable fields by adopting some organic management practices at the field scale (e.g. exclusion of synthetic herbicides), and whole-farm conversion to organic practice might not be required. However, further work is needed to determine any biodiversity benefits of larger areas of semi-natural habitat on conventional farmland.

Landscape management affects species interactions within a community, leading to alterations in the structure of networks. Modules are link-dense regions of the network where species interact more closely within the module than between modules of the network. Insufficient network resolution has meant that modules have proved difficult to identify, even though they appear important in the propagation of disturbance impacts. We applied a standardized approach across 20 farms to obtain well-resolved food webs to characterize network structure and explore how modularity changes in response to management (organic and conventional). All networks showed significantly higher modularity than random networks. Farm management had no effect on the number of modules per farm or module richness, but there was a significant loss of links between modules on conventional farms, which may affect the long-term stability of these networks. We found a significant association between modules and major habitat groups. If modules form as a result of interactions between species that utilize similar habitats, then ecosystem services to the crop components of the landscape, such as pest control by parasitoids originating in the non-crop vegetation, are less likely to occur on these farms.

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We examined whether estrogen receptor (ER)alpha is required for estrogen to stimulate cancellous bone formation in long bones of male mice. 17 beta-Estradiol (E(2)) was administered to ER alpha(-/-) male mice or wild-type (WT) littermate controls at 40, 400, or 4000 microg/kg by daily sc injection for 28 d and histomorphometric analysis performed at the distal femoral metaphysis. In WT mice, treatment with E(2) (40 microg/kg per d) increased the proportion of cancellous bone surfaces undergoing mineralization and stimulated mineral apposition rate. In addition, higher doses of E(2) induced the formation of new cancellous bone formation surfaces in WT mice. In contrast, E(2) had little effect on any of these parameters in ER alpha(-/-) mice. Immunohistochemistry was subsequently performed using an ER alpha-specific C-terminal polyclonal antibody. In WT mice, ER alpha was expressed both by cancellous osteoblasts and a significant proportion of mononuclear bone marrow cells. Immunoreactivity was also observed in cancellous osteoblasts of ER alpha(-/-) mice, resulting from expression of the activation function-1-deficient 46-kDa ER alpha isoform previously reported to be expressed in normal osteoblasts and bones of ER alpha(-/-) mice. Taken together, our results suggest that estrogen stimulates bone formation in mouse long bones via a mechanism that requires the presence of full-length ER alpha possessing activation function-1.

Cbfa1 is a transcription factor recognised as being involved in early osteoblast differentiation during embryonic skeletogenesis. To determine whether Cbfa1 plays a similar role in bone formation in the adult, we analysed whether its expression is altered during estrogen-induced osteogenesis, following our recent studies which suggest that this response involves the generation of early osteoblast precursors within bone marrow. To facilitate identification of Cbfa1-expressing cells, these studies were performed in mice heterozygous for a cbfa1 gene deletion (cbfa1(+/-)) using beta-galactosidase (lacZ) as a genetic marker. Cbfa1-expressing cells were identified by lacZ staining of longitudinal sections of the proximal tibial metaphysis. Treatment of cbfa1(+/-) mice with 17beta-estradiol 0.5 mg/week for 24 days led to the appearance of new cancellous bone surfaces. This response was associated with a marked increase in number of Cbfa1-expressing cells within the metaphysis, consisting not only of osteoblasts on bone surfaces but also of cells within the adjacent bone marrow. We subsequently enumerated Cbfa1-expressing cells at earlier time-points following estrogen, in sections co-stained for ALP activity. After 4 days of estrogen treatment, a population of cells appeared within the marrow cavity which expressed Cbfa1, but were negative for ALP. At later time-points, large numbers of Cbfa1 + bone marrow cells were still present, but the majority of these were close to new trabecular bone surfaces at sites which showed high levels of ALP activity. An equivalent distribution of Cbfa1-expressing cells was observed in further studies where Cbfa1 expression was analysed in wild-type mice by immunohistochemistry. We conclude that estrogen-induced osteogenesis is associated with the appearance of a population of Cbfa1-expressing cells within bone marrow, which we hypothesize to represent the osteoblast precursor population responsible for subsequent new bone formation.