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SCALETOOL IntroductionDriversBiodiversityPolicies and managementConnectivity and protected areas

Functional connectivity study of the natterjack toad (Bufo calamita) for regulatory study of an industrial area in southwestern France

In south-western France (44°11'36.32"N, 0°31'14.23"E), MetaConnect was used in the context of regulatory study for implantation of economic area (ZAC) and terrestrial transport infrastructure (high-speed railway). We used MetaConnect to determine the potential impact of such infrastructures on the functional connectivity in Bufo calamita. We also evaluate the cumulative impact of the infrastructures on the functional connectivity (Art. L122-1 modified by Loi n° 2010-788 du 12 juillet 2010 - art. 230 of the French environmental legislation).

MetaConnect setting up

The philosophy of this analysis was not to determine the absolute functional connectivity for B. calamita but rather to estimate the landscape potentialities in regard to B. calamita functional connectivity.

Habitat patches were determined a priori based on expert assessment. Landscape rugosity coefficient were derived from those experimentally determined by Stevens et al.1. B. calamita was assumed to disperse following the stochastic-movement-simulator (SMS) assumptions2. The rational for this choose is that, even though, Stevens et al.1 found that least-cost-path assumption is consistent with the population genetic structure of B. calamita in their study site, Palmer & Stevens recently improved the fit between simulated dispersal of B. calamita and the observed population genetic structure using the SMS model (2012, unpublished datas). Finally, MetaConnect was setup with LHTs values found in the literature.

Functional connectivity for B. calamita

Expert survey of the site performed for the regulatory study (cabinet ECTARE) confirmed the presence of B. calamita (adults and eggs) on the most important habitat patches a priori assumed from habitat suitability (Figure 1). Simulation results showed that the building of the ZAC will probably not change strongly the persistence of B. calamita within the study site. Even though, the habitat patch which would be destroyed by the building of the ZAC (figure 1) plays an important role in the local functioning of the meta-population as a relay for the dispersal of B. calamita along the North-South axis (Figure 1), this destruction will have little influence on B. calamita persistence because this role would be ensured by a patch nearby (Figure 1). In contrast, the addition of the high-speed-railway will disrupt the flow of individual along the North-South axis which would increase patches extinction probabilities and total extinction probabilities and would greatly reduce B. calamita's movements within the study site (Figure 1).


Figure 1: Graphical representation of metapopulation functioning of the focal area derived from MetaConnect outputs for the current situation (A) with the addition of the industrial area (B) and with both the industrial area and the high-speed railway added (C). Node sizes are proportional to patch population sizes (mean ± SE). Arrows represent dispersal intensity (mean ± SE) and direction (bidirectional arrow values correspond to symmetrical dispersal). For clarity, only dispersal superior to 1 individual a year has been represented and dispersal superior to 5 individuals a year has a width reduced by 10 and shown as a plain arrow. Maps represent the variation of extinction probabilities per patch where variation = patch extinction probability in scenario B - patch extinction probability in scenario A (from brown for an extinction probability variation of -1 to purple for a variation of 1 where white is used if no differences are recorded) and of cell occupancy during efficient dispersal (from red for a loss superior to 3 individuals a year to dark blue for a gain of 1 where a constant number of individual per year corresponds to light blue). The D scenario corresponds to change in the metapopulation functioning after the development of the industrial area. The E scenario presents the change between post-development of the industrial area and after the construction of the high-speed railway. Finally, the F scenario summarizes the differences between the current metapopulation functioning and the expected functioning after the cumulative development of the industrial area and the high-speed railway.



Conclusion

The use of MetaConnect detected that the ZAC will destroy an important patch for the functional connectivity of the natterjack toad in the study site. However, the functional redundancy of this patch with an eastern patch (Figure 1) suggests that this other patch would functionally replace the destroyed patch.
In addition, the detection of this second patch as a key patch will allow informing the city nearby as required by the French legislation. This patch would then benefit from the compensatory measure induced by the ZAC build to ensure its conservation and functionality.

References

1 Stevens, V. M., Leboulenge, E., Wesselingh, R. A. & Baguette, M. Quantifying functional connectivity: experimental assessment of boundary permeability for the natterjack toad (Bufo calamita). Oecologia 150, 161-171, doi:10.1007/s00442-006-0500-6 (2006).

2 Palmer, S. C. F., Coulon, A. & Travis, J. M. J. Introducing a 'stochastic movement simulator' for estimating habitat connectivity. Methods in Ecology and Evolution (2011).
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