Macfadyen, S., Craze, P., Polaszek, A., van Achterberg, K. & Memmott, J. (2011) Parasitoid diversity reduces the variability in pest control services across time on farms. Proceedings of the Royal Society B, 278: 3387-3394.
doi:10.1098/rspb.2010.2673

Abstract

Recent declines in biodiversity have increased interest in the link between biodiversity and the provision and sustainability of ecosystem services across space and time. We mapped the complex network of interactions between herbivores and parasitoids to examine the relationship between parasitoid species richness, functional group diversity and the provision of natural pest control services. Quantitative food webs were constructed for 10 organic and 10 conventional farms. Parasitoid species richness varied from 26 to 58 species and we found a significant positive relationship between parasitoid species richness and temporal stability in parasitism rates. Higher species richness was associated with lower variation in parasitism rate. A functional group analysis showed significantly greater parasitoid species complementarity on organic farms, with on average more species in each functional group. We simulated parasitoid removal to predict whether organic farms experienced greater robustness of parasitism in the face of local extinctions. This analysis showed no consistent differences between the organic and conventional farm pairs in terms of loss of pest control service. Finally, it was found that the different habitats that make up each farm do not contribute equally to parasitoid species diversity, and that hedgerows produced more parasitoid species, significantly more so on organic farms.

The full reference is:

Nico Blüthgen (2010) Why network analysis is often disconnected from community ecology: A critique and an ecologist’s guide. Basic and Applied Ecology 11:185-195.

Link to Journal website

Stefano Allesina and Mercedes Pascual
PLoS Computational Biology Vol 5, Issue 9, e1000494

The authors have developed an algorithm based on the one Google uses to rank web-pages to order species in a network in terms of their importance for coextinctions. Their algorithm outperformed other measures of robustness to species loss. When examining 12 published food webs their results suggest that the position of a species in the food web is an important determinate of impact on extinction cascades.

1. Understanding the community of bees that occurs  in an agricultural landscape with bee-pollinated crops.  Canola is grown in fields not far from Canberra and we want to know how many different bee species occur in these fields, when these bees are active, and whether the bee community is influenced by other parts of the landscape such as woodland patches and pastures. Blandine has been putting traps to catch native bees each week during spring and the start of summer. This work is being completed with the help of Saul Cunningham.

Blandine and Mick return after placing a bee trap in a canola field

A bee trap on the edge of a canola field

2. Examining the parasitic natural enemies of a  leaf-mining moth (Dialectica scalariella) that was released as a biocontrol agent for patterson’s curse (Echium plantagineum). Blandine has been collecting the miners and rearing them in the laboratory to see if they have been attacked by parasitic wasps.

Patterson's curse: a common agricultural weed in our area

doi: 10.1111/j.1461-0248.2009.01327.x

Rezende et al. examined network structure in a marine food web (containing 3313 interactions between 249 species/trophic groups!) and unequivocally showed the presence of compartments (or subunits) in this network. These are link-dense regions of the network where species interact more closely with other species within the module than between modules. Modules may may be important for the propagation of disturbance impacts throughout a network.  More importantly Rezende et al. identified some potential mechanisms behind this interesting network structure (body size, phylogeny and spatial structure).  Shark species played an important role in this network.

I am due to give a presentation in the Ecosystem Services symposium (Tuesday 18th 3:15pm Mezzanine 2). The presentation abstract is here:

The provision of the ecosystem service of pest control on farms now and in the future

Sarina Macfadyen¹, Rachel Gibson², Paul Craze³, William O.C. Symondson⁴, Jane Memmott²

1CSIRO Entomology
2School of Biological Sciences, University of Bristol
3Biology and Environmental Science, University of Sussex
4Cardiff School of Biosciences, Cardiff University

A precautionary approach to biodiversity management is often justified on the basis that the maintenance of a diversity of species is useful for the provision of a particular ecosystem service now and as a form biological ‘insurance’ against disturbances in the future. Natural pest control is one ecosystem service that is thought to be threatened by agricultural intensification. Here we examine the complex network of interactions between insect herbivores and their parasitoids to understand the relationship between parasitoid species richness, functional group diversity and the provision of natural pest control services across time. We utilise 20 farms that display a gradient of parasitoid species richness as a result of farming system. We hypotheses firstly, that there will be a strong correlation between parasitoid species richness and variability in parasitism rate at the whole-farm level. Secondly, those farms with greater parasitoid species richness within functional groups will experience better pest control services in the future. Finally, we use species interactions to identify the key parasitoid species important for providing pest control services in this context.