1. Widespread omnivory in warmer shallow lakes
determines different food web structures than
observed in temperate ones
Carlos Iglesias , Mariana Meerhoff, Liselotte S. Johansson, Mariana
Vianna, Néstor Mazzeo, Juan Pablo Pacheco, Franco Teixeira de
Mello, Guillermo Goyenola, Iván González-Bergonzoni, Torben L.
Lauridsen, Martin Søndergaard, Thomas A. Davidson & Erik Jeppesen
XIII Congresso Brasilero de Limnologia
4-8 de Setembro 2011, Natal, RN

2. SUMMARY:
Framework
Objectives
Methodology
Results
Conclusions
XIII Congresso Brasilero de Limnologia

3. What is a Shallow lake ?
• Medium depht ca. 3 m
• Light can reach bottom
• No or very short-term stratifications
• Strong water-sediments link
• Wide distributed, very important to
humans
P
P
P
Very well studied in cold temperate areas
Theoretical
framework
XIII Congresso Brasilero de Limnologia
ALTERNATIVE STATES
(Scheffer et al., 1993)

4. Alternative (stable) states hypotheses
Total P(g L-1) concentration
25
only
submerged
plants
50
100
1000
Transparency and plant -associated mechanisms
clear water submerged plants
Forward switches
scarce
plants
Biomanipulation
turbid water
phytoplankton
phytoplankton
dominance
Turbid water-associated mechanisms
higher probability of phytoplankton OR free-floating plants
higher probability of submerged plants dominance
XIII Congresso Brasilero de Limnologia

5. Role of submerged plants in temperate lakes
 BOTTOM-UP
Nutrients/Light
Sedimentation rate
+
turbidity
+
-
phytoplankton
allelopathy
submerged plants
-
+
+
nutrients
Modified from Scheffer et al. 1993
XIII Congresso Brasilero de Limnologia
+
periphyton

6. Role of submerged plants in temperate lakes
+
piscivorous fish
submerged plants
planktivorous fish
zooplankton
Modified from Scheffer et al. 1993
 TOP DOWN
Direct trophic Interactions
Cascading effects (Carpenter & Kitchell 1986)
 REFUGE
Diel migrations (Timms & Moss, 1984)
Behavioural cascades (Romare & Hansson 2002)
XIII Congresso Brasilero de Limnologia

7. Role of submerged plants in warmer lakes
Temperate lakes
Subtropical lakes
high submerged plant cover with low
phytoplankton
loss of clear patterns
high phytoplankton biomass with
low plant %PVI
high plant %PVI simultaneous with
phytoplankton biomass
Jeppesen et al in 2007
XIII Congresso Brasilero de Limnologia

8. Role of submerged plants in warmer lakes
Subtropical lakes
Effects of macrophytes on trophic interactions more complex and
water clarity less improved
This is apparently a consequence of markedly different trophic web
interactions (zooplankton & fish)
XIII Congresso Brasilero de Limnologia

9. Changes on fish community structure
High diversity
(TdeM 2009)
High density (specialy in plants)
Small-sized species with high abundances
(Meerhoff et al., 2007)
Few large-sized strict piscivores
(Quiros, 1998)
Dominance of omnivorous species
(Lazzaro, 1997)
Several reproduction events. No window of
opportunity for zooplankton (Van Leeuwen et al.,
2007)
XIII Congresso Brasilero de Limnologia

10. Food webs changes among climatic regions
Denmark
Uruguay
11x higher density in the subtropical
lakes
temperate fish more “pelagic”
subtropical fish more “littoral”
Large-bodied
zooplankters infrequent
or absent.
5.5x lower density in
subtropical lakes
8x lower density of macroinvertebrates
4x lower periphyton biomass, despite better
growing conditions of light & temperature
(Meerhof et al GChB 2008)
XIII Congresso Brasilero de Limnologia

11. Food webs changes among climatic regions
More complex and less hierarchically structured
More fish co-ocurred with fewer cladocerans and invertebrates
Lower biomass of periphyton than expected (less grazing high light and temp)
(Meerhof et al GChB 2008)
XIII Congresso Brasilero de Limnologia

12. Objectives and Methodological approach
Are the food webs more truncated
in subtropical lakes?
and fuelled by periphyton to a larger
extent?
From Hugie & Dill 1994
XIII Congresso Brasilero de Limnologia

13. Objectives and Methodological approach
Stable isotopes analysis +
Community-wide measures of trophic structure
(Vander Zanden & Vadeboncouer, 2002/Post, 2002/Layman et al., 2007)
dN indicates trophic position and dC carbon sources
Uruguay 30-35 。 S
Denmark 55-57 。N
XIII Congresso Brasilero de Limnologia

14. Food webs changes among climatic regions
Stable isotopes analysis + Community-wide
measures of trophic structure
• Trophic position
• Trophic web length (Max TP)
• % Littoral Contribution
• Carbon range (amplitude of C sources)
• Total area (niche space ocupied)
• Mean nearest neighbour distance
(redundancy)
CR3
CR2
TA
CR= max –min carbon
TWL
XIII Congresso Brasilero de Limnologia

15. Food webs changes among climatic regions
%CONT
LITT
TA
NND*
3.5
53.5
10.1
0.4
9.7
5.9
54.7
9.2
0.4
9.9
9.4
7.6
64.5
15.5
0.6
4.1
8.5
7.7
5.1
50.7
16.0
0.6
4
4.4
7
7
3.4
46.1
10.7
0.7
11
4.0
8.5
7.7
5.1
53.5
10.7
0.6
Range
4-13
3.4-4.4
7.0-9.9
4.5-9.7
3.4-7.6
46.1-64.5
9.2-16.0
0.4-0.7
VAENG
8
5.1
4.9
4.3
2.6
52.7
8.6
0.6
TRANEVIG
6
5.8
10.5
7.3
0.6
58.3
16.1
0.9
GAMMELMOSE
4
4.6
4.6
4.4
3.0
98.2
10.2
1.2
DENDERUP
3
4.4
9.9
9.9
4.1
31.6
15.4
0.6
DK Median
5
4.8
7.4
5.9
2.8
55.5
12.8
0.8
3-8
4.4-5.8
4.6-10.5
4.3-9.9
0.6-4.1
31.6-98.2
8.6-16.1
0.6-1.2
Zvalue
1.85
2.2
0.1
0.7
1.96
0.25
0.0
1.98
p
0.06
0.02
0.9
0.5
0.05
0.6
0.99
0.05
Lake
FR*
TLW*
CR
CR 2
CISNE
13
4.0
7.7
4.5
DIARIO
11
3.4
9.7
GARCIA
11
3.9
CLOTILDE
9
BLANCA
UY Median
Range
CR 3*
In warmer lakes
Temperate = Subtropical lakes
Reliance in Littoral (ca. 50%)
Carbon range
Total extent of trophic diversity
2X Fish richness
-1 Trophic Levels
2x CR3
More redundant species
XIII Congresso Brasilero de Limnologia

16. Food webs changes among climatic regions
Temperate = Subtropical lakes
Reliance in Littoral (ca. 50%)
Carbon range
Total extent of trophic diversity
Implicances on Trophic webs architecture
-1 Trophic Levels
2x CR3
More redundant species
XIII Congresso Brasilero de Limnologia

17. Food webs changes among climatic regions
(Meerhoff et al,2007)
XII Congresso Brasilero de Limnologia

18. Food webs changes among climatic regions
Implicances on Trophic webs architecture
-1 Trophic Levels
2x CR3
More redundant species
3 Structural mechanisms
XIII Congresso Brasilero de Limnologia
(Post & Takimoto,2007)

19. Food webs changes among climatic regions
Omnivory may explain the observed architecture
(Post & Takimoto,2007)
Gonzalez-Bergonzoni subbmited
XIII Congresso Brasilero de Limnologia

20. Conclusions
submerged plants
piscivorous fish
+
+
piscivorous fish
submerged plants
OMNIVOROUS
fish
planktivorous fish
zooplankton
zooplankton
Modified from Scheffer et al. 1993
Different structure of trophic webs (and probably also functioning).
Omnivory appears as the most plausible explanation
Strong effects to whole system functioning.
Asymmetries in some important feed backs probably weak alternative
states to occur
XIII Congresso Brasilero de Limnologia

21. Conclusions
ONE FINAL REMARK: We do have plant dominated clear water systems, even
with quite high nutrient levels that seems to be persistent in time.
XIII Congresso Brasilero de Limnologia

22. Thanks!!
Thanks for finantial support to AU, NERI and the Ministry of Science, Technology and Innovation in
DK. PDT, ANII, CSIC –Udelar in Uruguay
XIII Congresso Brasilero de Limnologia

26. Methods