Top Predators
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Top Predators Forage fauna Zoo Phyto on trophic ecology of top predators Stomach Content Analyses Stable Isotope Analyses (Acoustics) • To investigate feeding ecology & trophic structure in high-sea ecosystems • To document the diversity of the forage fauna (micronekton)
description
Data on trophic ecology of top predators. Stomach Content Analyses Stable Isotope Analyses ( Acoustics ). Top Predators. Forage fauna. To investigate feeding ecology & trophic structure in high - sea ecosystems To document the diversity of the forage fauna ( micronekton ). - PowerPoint PPT Presentation
Transcript of Top Predators
Top Predators
Foragefauna
Zoo
Phyto
Data on trophic ecology of top predators
Stomach Content Analyses
Stable Isotope Analyses(Acoustics)
• To investigate feeding ecology& trophic structure in high-sea
ecosystems
• To document the diversityof the forage fauna
(micronekton)
stomachs are frozen
Stomachsare taken
from freshlycaught fishes
and analysed in the lab
Diet indices on preyOccurrence
Mean NumberMean Reconstituted Weight
DietFeeding rangeTrophic overlap
Prey size distributionsSize ratios
Stomach content data
INDIAN OCEAN: 2 databases
– YugNIRO 1962 to 1990 (Soviet Union)Low level of prey identification – Heterogeneity of data
– STOMAC 2000 to 2010 (IRD)Small spatial and temporal scales – High identification prey level
YugNIRO (Indian Ocean) STOMAC (West Indian Ocean)
> 20,000 stomachs6 main predators
300 prey taxa5 functional groups
6 main predators
Yellowfin tuna (Thunnus albacares)
Bigeye tuna (Thunnus obesus)
Skipjack (Katsuwonus pelamis)
Dolphinfish (Coryphaena hippurus)
Longnose lancetfish (Alepisaurus ferox)
Swordfish (Xiphias gladius)
Epi-Pel
Epi-Meso
Meso
Bathy
Meso-Bathy
Functional prey groups vs >300 prey taxa
dept
h
+ΔN +ΔN +ΔN +ΔN
15N = n‰ 15N = n + 4ΔN‰ΔN = Trophic enrichment
15Nbaseline
15Npredator
Stable isotope ratios of N in consumers reflect thoseof their prey as they are enriched in a predictable manner15N serve as indicators of consumer trophic position
Stable Isotope Analyses (15N, 13C)a tool to investigate trophic relationships (trophic tracers)
″ You are what you eat, plus a few per mil "
PRINCIPE : les processus biologiques, physiques et chimiques induisent une répartition différentielle des éléments légers et lourds
Cause : essentiellement dus aux différences de masse
- variation de certaines propriétés physico-chimiques
- modification des vitesses des réactions chimiques
réactivité différentielle
changement du rapport entre éléments lourds et légers
Nitrogen Isotope Fractionation
Rate of 14NH4+ excretion is
greater than the rate of 15NH4
+ excretion
δ15Npredator = ~3.0 + δ15Nprey (‰)NO3
-, NH4+ N2
14NH4+
14NH4+
14NH4+
14NH4+
14NH4+
2
4
6
8
10
12
14
16
-22 -21 -20 -19 -18 -17 -1613C
15N
Top predators
Micronekton
Gelatinous zooplankton
Tuna postlarvae
Fish
Crus Ceph
SWO
BET
YFT
• Multispecies trophic models of ecosystems depend on accurate depiction of trophic links
• Trophic level estimation using 15N
Stable Isotope Analyses (d15N, d13C): a tool to investigate trophic relationships
Latitudinal effect on d15N : differences in nitrogen dynamics existing at the base of the food web propagate along the food chain up to top predators
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13
15
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-30 -20 -10 0 10
Latitude
Pred
icte
d 1
5 N
YFT SWO Body Size = 160cm
• Isoscapes…
15N isoscapes for bigeye (n = 196) and yellowfin (n = 387) tunaValues were normalized against the average within the study region (Graham et al.)
Residuals between the interpolated 15N values
for the two species
bigeye
yellowfin
