Context, objectives & methods
Use of C, N and S stable isotope ratios to highlight resource
segregation among hermit crabs from tropical seagrass meadows
−16 −15 −14 −13 −12 −11 −10 −9 4.0 4.5 5.0 5.5 6.0 d13C d15N D. scutellatus C. tricolor 4 4.5 5 5.5 6 δ 15 N (‰) δ13C (‰) -16 -15 -14 -13 -12 -11 -10 -9 Dardanus scutellatus Ciliopagurus tricolor
Results & discussion
Isotopic ratios
of consumers
Significant differences in the isotopic
composition of all 3 elements ➔
The two species do not feed on the same items
According to literature from the area:
[Lepoint et al. 2008, Sci Mar 72: 109-117; Frédérich et al. 2009, Ichtyol Res 56: 10-17 ]
1. Both species are primary
consumers.
2. C. tricolor mostly relies on algal
production, while some D. scutellatus
could assimilate seagrass-derived
matter. Pelagic inputs to hermit crab diet are likely weak.
D. scutellatus C. tricolor 3 4 5 6 7 Species δ 15 N ( ‰ ) Unpaired t-test: p = 0.0096 D. scutellatus C. tricolor -18 -16 -14 -12 -10 -8 Species δ 13 C (‰ ) Unpaired t-test: p < 0.0001 D. scutellatus C. tricolor 8 10 12 14 16 18 20 Species δ 34 S (‰ ) Unpaired t-test: p = 0.0001 Toliara
Isotopic niche modeling
Loïc N. MICHEL
1,*, Bruno FRÉDÉRICH
2, Thierry LAVITRA
3& Gilles LEPOINT
11Laboratory of Oceanology, MARE Centre, University of Liege, Belgium. 2Functional and Evolutionary Morphology Laboratory, University of
Liege, Belgium. 3Institute of Fishery and Marine Sciences (IHSM), University of Toliara, Madagascar.
*E-mail: loicnmichel@gmail.com, publications available at http://goo.gl/xdxaHM
Conclusions & perspectives
Acknowledgements
0 1 2 3 4 5 Group Area (per mil^2) D. scutellatus C. tricolor Model-estimated standar d ellipse ar ea, SEA b (‰ 2 ) 5 4 3 2 1 0 D. scutellatus C. tricolor Species
LM is a BELSPO postdoctoral fellow. BF is a F.R.S.-FNRS postdoctoral researcher. GL is a F.R.S-FNRS research associate. LM and BF were supported by a F.R.S-FNRS travel grant. Authors would like to thank the staff of IHSM Toliara and Prof. I. Eeckhaut (UMons) for logistical support during sampling.
§
Differences
in
foraging ecology
of these two hermit crabs
è
could
limit
interspecific
competition
and
facilitate coexistence
of D. scutellatus and C. tricolor in Malagasy seagrass beds
§
Analysis of
food items
sampled at the same time and location will enable use of a
mixing model
and ultimately reveal which producers actually support hermit crabs populations
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➔
§ Tropical polyspecific seagrass meadows provide many ecological and
socio-economical services
§ These ecosystems undergo multiple anthropogenic threats (eutrophication,
overfishing, invertebrate overharvesting)
§ Data about functional ecology of meadows and structure of the associated
food webs are needed to understand how they could react to human impacts
§ As part of a larger study: examination of resource segregation between two
common, co-occurring, supposedly omnivore Diogenidae hermit crabs
➡
︎
§ Sampling of Dardanus scutellatus (n=28) and Ciliopagurus tricolor (n=17) on
the Toliara Great Reef (SW Madagascar, see map on left) in July 2014
§ Analysis of stable isotope ratios of C, N and S of their abdominal muscle using CF-EA-IRMS (Vario MicroCube EA coupled to Isoprime 100 MS)
§ Exploration of data using statistical hypothesis testing and isotopic niche
modeling (SIBER: Stable Isotope Bayesian Ellipses in R) [Jackson et al. 2011, J Anim Ecol 80:
595-602]
No overlap of standard ellipses (solid lines on the figure
on the left) of the two species ➔ they are supported by
different core resources
◀
︎
The area of the standard ellipse of D. scutellatus is
larger than the one of C. tricolor in 97.46% of 105 model
estimates ➔ D. scutellatus exploits more food items
than C. tricolor.
