Googling Food Webs: Can an Eigenvector Measure Species’ Importance for Coextinctions?
Predicting the consequences of species’ extinction is a crucial problem in ecology. Species are not isolated, but connected to each others in tangled networks of relationships known as food webs. In this work we want to determine which species are critical as they support many other species. The fact that species are not independent, however, makes the problem difficult to solve. Moreover, the number of possible “importance’” rankings for species is too high to allow a solution by enumeration. Here we take a “reverse engineering” approach: we study how we can make biodiversity collapse in the most efficient way in order to investigate which species cause the most damage if removed. We show that adapting the algorithm Google uses for ranking web pages always solves this seemingly intractable problem, finding the most efficient route to collapse. The algorithm works in this sense better than all the others previously proposed and lays the foundation for a complete analysis of extinction risk in ecosystems.
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.
We have a visitor from France here as part of a work placement traineeship. Blandine Prache is doing some research focused on understanding the ecology and identity of insect species involved in the provision of ecosystem services in agricultural landscapes. Her work is in two areas:
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
We (Mick Neave and I) recently spent a few nights in Toowoomba QLD as part of the first project meeting for the ‘Pest suppressive landscapes’ project (funded by GRDC). Amongst other activities we went on a quick tour of the grain growing region around near Toowoomba to examine potential sites for this project and had a go at beat sheeting for invertebrates in native vegetation patches. Many thanks to the QLD team members for their hospitality.
Nancy, Felix and Dave selecting a shrub to beat
Nancy using her 'shaking' method to collect invertebrates onto the beat sheet
Compartments in a marine food web associated with phylogeny, body mass, and habitat structure
Ecology Letters (2009) 12(8), 779-788
Enrico L. Rezende, Eva M. Albert, Miguel A. Fortuna, Jordi Bascompte
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.
The 10th International Congress of Ecology is on in Brisbane next week (16-21st August)
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.
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