AgriPop Friday Talks

Friday's Agripop Talk

19 April 2013 - 11:30 - Salle Seminaire (!)

From habitat use to habitat selection: which key factors drive breeding little bustard distribution?

Pierrick Devoucoux

 This week's talk will be about a really cool species, the Little Bustard (Tetrax tetrax). This species is also of high conservation concern (Near Threatened on the IUCN Red List) as it prefers open grasslands and undisturbed habitat -- requirements which often conflict with agricultural practices.

Whilst the species has gone extinct in several parts of Europe, especially in the east, several populations still survive in southern and western France. One remarkably high density population lives in France, in the Costière Nîmoise, near the city of Nîmes in southern France, with around 700 breeding males in an area of just 40km length! Not surprisingly the area is protected since 2006 and a current question of interest is understanding which are the key factors allowing to obtain such high population densities, as this would be quite handy to know for improving the conditions for other breeding populations.

All fine, hence? Well, not really. This year a new TGV train line will start to be build right across this protected area...

 Yeah, indeed an unfortunate state of affairs. Apparently the decision cannot be reversed, but Pierrick's work is part of an initiative funded to find ways to mitigate the impact on this important breeding population. As part of this, Pierrick has already concluded one field season last year and will present us some new results on the patterns and drivers of Little Bustard breeding habitat selection. Here the official abstract of the talk:

Conservation measures generally act on landscape composition at large and fine scale. However, global distribution and local density are not only under environmental influences. Social factors play an important role, especially in species with complex mating system. Hence the real question is about habitat selection. This study will investigate the relative weight of social and environmental factors in habitat selection on  a protected species in a high sensibility  context of conservation.

Especially, the population lives in an agricultural landscapes and agricultural practices profoundly determine and change the landscape structure. The different roles of soil occupancy on vegetation type and structure, and hence foraging availability, will be studied and the role of intra and inter sexual interactions explored. Conclusions are expected to help managers to build efficient conservation measures.

So, a really interesting talk - and as you have seen Pierrick has taken also great pictures of Little Bustards during his last field season -- so come, listen, and enjoy! And let's hope his work will help improve mitigation measures, so that also in the future we'll be able to see flocks of this bird flying and breeding in this population.

AgriPop Friday Talks

Friday's Agripop Talk

05 April 2013 - 11:30 - Salle Ragondin

Musings on community ecology by a lonely plant ecologist stuck in the forest of Chizé: Can we infer process from pattern?

Nicolas Gross

 

Image from www.stuckincustoms.com/

Stuck in the forest. Can you imagine this happening to a guy who's spent most of his (research) life so far studying nice open grasslands? Well, our research centre is indeed in the middle (sort of) of a forest but Nico is surviving, has been making escapes to study grasslands in Spain (more on that on Friday) and even started to explore the grasslands in our study area outside the forest.

So, why does Nico study grasslands? Well, plants do not escape or hide from researchers and in general do not move (except as seeds or pollen). Hence, a quite convenient study system to investigate what drives the strcture of ecological communities - the main interest of Nico's research. 

OK, but what is that 'pattern vs. process' bit? Well, that's actually a highly contentious one - here an example (hey, I know, it's a paper from 1989, so what! Still interesting to read, isn't it?). A pattern is what we see, like the configuration or traits of a system, but what we actually want to understand is which processes did generate these patterns. Unfortunately, it is often the case that a multitude of contrasting processes could have created the same patterns, which has led to decade-long debates. In general this is related to the problem of distinguishing correlation from causation (here a recent paper on that). One key process that has been often debated is the role of biotic interactions and this is what Nico will talk about this Friday. To exemplify his points he will use a grassland study system in New Zealand, similar to this:

from: http://bit.ly/SSmJZb

Well, nearly -- just 500km more south of that. And the title will actually be slightly less informal. So, here's the official abstract:

Importance of biotic interactions in structuring plant communities: Moving from patterns to processes

How biotic interactions determine the structure of plant communities is a central question in ecology. Different approaches have been used to address this question. These can be broadly separated in two categories: (i) the individual-centered approach; (ii) the community scale approach. The first approach has mainly focused on the species response to local biotic interactions (competition, facilitation) along large ecological gradients. This approach has led to a better understanding on how the intensity of biotic interactions changes depending on local environmental conditions. However, it is difficult from this approach to evaluate how biotic interactions observed at the individual scale translate at the community level and determine the properties of the whole system. 

The second approach has focused on observed pattern of species similarities or dissimilarities within communities in order to evaluate the community scale impact of biotic interactions. In this context, the use of plant functional traits has been proposed as a key metric to quantify species convergence and divergence across communities, the central assumption being that trait divergence reflects competition while trait convergence reflects the effect of environmental filtering. 

However, inferring the impact of biotic interactions from community scale patterns remains challenging because many alternative processes can lead to similar trait distributions at the community scale. For instance, while competition has been primarily hypothesized to promote trait divergence at the community level, superior competitors can also have a disproportionally large effect on local resources and thus act as an environmental filter. Facilitation has also been shown to increase trait divergence at the community level by promoting the coexistence of functionally contrasted species. Finally, abiotic factors are usually considered to cause community trait convergence. They may also act as a disruptive force when different functional strategies exhibit equal fitness in response to similar abiotic constraints (e.g. stress-avoidance vs. tolerance strategies). 

Here, I present some results from a study conducted in highly invaded grasslands (New-Zealand) where we have evaluated how biotic interactions between alien and native species determine the success of aliens in their new environment. I will show how we have tried to merge species and community scale approaches to explicitly test the importance of biotic interactions at the whole community scale.

Figure 1. Highly invaded grasslands in New-Zealand. View from Mt Herbert, 920 m (Banks Peninsula, South Island). Semi-natural grasslands are constituted by a mix of native and alien species (tussock species are Poa cita and Festuca Novae-Zelandiae). Small alien plant species dominate inter-tussock area (e.g. Poa pratense; Lolium perenne; Agrostis capillaris), while tall alien species are more abundant close to the tussocks (e.g. Holcus Lanatus; Dactylis glomerata; Arrhenatherum elatius).

So, see you all this Friday, usual time (11:30) and place.