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Temperate
Subtropical
Piscivorous fish
Other fish
Shrimps
Lit. invertebrates (c) (×10)
Pel. invertebrates (c) (×10)
Lit. invertebrates (h) (×10
2
)
Cladocerans (×10
3
)
Periphyton
250
200
150
100
50
0
50
100
150
200
250
Density (ind m
-2
/mg chl
a
m
-2
)
Piscivorous fish
Piscivorous fish
Other fish
(omnivorous)
Shrimps
Other fish
Lit. invertebrates (c)
Pel. invertebrates (c)
Lit. invertebrates (c)
Lit. invertebrates (h)
Cladocerans
Lit. invertebrates (h)
Pel. invertebrates (c)
Phyto
Cladocerans
Periphyton
Phyto
Periphyton
Figure 6.3
Structure of the littoral communities in artificial plant beds in temperate
(Denmark, left) and subtropical (Uruguay, right) lakes. Above: Density of potentially
piscivorous fish (numbers of individuals m
−2
, all other fish, shrimps, littoral carnivorous
macro-invertebrates (×10), pelagic carnivorous invertebrates (×10), littoral herbivorous
macro-invertebrates (×10
2
), pelagic herbivorous cladocerans (×10
3
) and biomass of
periphyton (as chlorophyll
a
) ). Below: Simplified schematic depiction of trophic
interactions among the same trophic groups as above, showing densities in the
subtropics relative to those in temperate lakes. Shrimps were absent in the temperate
lakes, and except for fish, the same taxa received the same trophic classification in both
climate zones. Abbreviations: (c), carnivorous; (h), herbivorous; Pel., pelagic; Lit., littoral,
phyto, phytoplankton. Data are sample means (± 1 SE) of five lakes paired between
climate regions in terms of phytoplankton biomass and physico-chemical and
morphometric characteristics (adapted from Meerhoff
et al
. 2007b).
Notable differences were found between the two climate zones, regardless of
other variables, supporting our first two hypotheses (Meerhoff
et al
. 2007a, b).
The littoral food web was more complex and less hierarchically structured in the
subtropical lakes (Fig. 6.3). Their fish communities had higher diversity, greater
density (on average 11-fold) and biomass, less piscivory and widespread omnivory,
smaller individual size (90% of fish smaller than 3.0 cm standard nose to tail-fork
length) and stronger association with the submerged plants than in the temperate
lakes. Fish communities in the warm lakes were dominated by omnivorous
cyprinodontids, whereas somewhat larger cyprinids and percids dominated in
the temperate lakes (Teixeira de Mello
et al
. 2009). More fish species co-occurred
with fewer cladoceran and littoral invertebrates genera in the subtropical lakes,
with the opposite in the temperate lakes.
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