Emerging complexity: Evolutionary and ecological processes shaping interaction networks

Background/Question/Methods

How patterns of organization in natural communities emerge through ecological and evolutionary processes is an important question. This complexity stems from the fact that ecological and evolutionary processes are often linked by complex feedbacks, the impact of which can be difficult to distinguish. Building on the analysis of a mathematical model and field surveys using a microbial model system (the bacterium Pseudomonas fluorescens and its lytic phages), I will synthesize results pertaining to two questions. (i) What is the impact of resources on the assembly and structure of food webs, with and without coevolution? Different patterns of resource dynamics lead to the emergence of different bipartite networks, which differ notably in their epidemiological properties. (ii) How do we expect the structure of coevolving networks to change through space and time?

Results/Conclusions

(i) We show that coevolution under different patterns of resource dynamics leads to the assembly of networks that differ by their structural properties (specialization, connectance), and discuss the epidemiological consequences of these patterns [1]. We show that the emergence of such networks relies on simple ecological mechanisms, namely that the availability of resources will regulate the contacts between antagonists, thus limiting both the efficiency of coevolution and the establishment of links within the network [2]. (ii) We show that local phylogenetic structure of the bacterial host is a good predictor of network local adaptation, and that the similarity of networks through time and space can be predicted from the phylogenetic similarity between host populations. In conclusion, these results reinforce the necessity to understand the interactions between ecological and evolutionary processes to predict the patterns of interaction network structure in complex environments.

1.        Poisot T, Thrall PH, Hochberg ME (submitted) Trophic network structure emerges through antagonistic coevolution in temporally varying environments. submitted to Proceedings of the Royal Society B: Biological Sciences.

2.        Poisot T, Lepennetier G, Martinez E, Ramsayer J, Hochberg ME (2010) Resource availability affects the structure of a natural bacteria-bacteriophage community. Biology Letters. doi:10.1098/rsbl.2010.0774