AgriPop Friday Talks

Friday's Agripop Talk

21 March 2013 - 11:15 - Salle Ragondin

The structuring processes of passerine’s communities, the share of the stochastic, environment and biotic interactions

Laura Henckel

Actually, it's a thursday talk!

Which mechanisms drive the assembly of communities is a longstanding question in ecololgy. However there is a renewed of interest for this problematic since the last decades due to some original studies : coexistence theory of Chesson (2000), Hubbell’s unified neutral theory (2001), or due to new available tools (ie. phylogenetic). But notwhithstanding the numerous studies, the debate remain open and there is no consensus amoung the various theories. The controversies concern in particular the relative importance of the processes involved (stochasticity, dispersal, biotic interactions or environmental screen).

Because it is difficult to test directly the effect of these processes via a mechanistic model, a wide range of indirect approachs were proposed in recent years. This great diversity of methods can partly explained the divergence of conclusions. Furthermore, it appears that these results are strongly dependent on the scale of analysis (spatial extent and grain), on taxa and even on the characteristic of the study site. Another thing is that a wide part of the studies on community assemblages remain theoretical and most of the others concern micro-organisms or plant communities. For these reasons further studies are needed, combining both a consistent set of methods and a multi-scale approach in a way to strengthen the results and reduce biases or misinterpretation. We therefore use some of these methods in way to understand the assembly processes that structure the passerine community in the particular context of the intensive agro-ecosystems.

This question constitutes both a scientific and societal challenge in the context of the strong decline of farmland birds observed during the past decades due to agricultural intensification.  For this purpose I will use the point count data collected between 2009 to 2012 on the workshop area “Plaine et Val de Sevre”, which are distributed on the whole area (every 1km²) allowing me to conducted a multi-scale approach by varying the grain and the extent of analysis.  A set of different methods will be used to distangle the processes involved (ie. multiple regressions on distance matrix, co-occurrence analysis) and different models will be compared (stochastic vs different determist models) to try to identify which processes are involved and at which scale. This work constitutes a preliminary study for my PhD which will focus more specifically on the environmental factors and in particular on the landscape heterogeneity effect (crop composition and configuration) on farmland birds.