Download Size-structured aquatic systems M2 EBE 2014

Ecole Normale Supérieure - Master EBE (M2 - 2014-2015)
UE: Ecologie et dynamique des populations structurées
(Responsable: David CLAESSEN)
Size-structured aquatic systems
Gérard LACROIX
UMR 7618 iEES-Paris – Institute of Ecology and Environmental Sciences
Université Pierre et Marie Curie, 7 quai St – Bernard. 75005 Paris.
[email protected]
Body size: a central trait
in physiology, ecology, and evolution
•  Body size correlated with numerous characteristics:
- Metabolism (Brown et al., 2004, Ecology)
- Demographic traits (Hone & Benton, 2005, TREE)
- Plasticity in life-history traits (Piersma & Drent, 2003, TREE)
- Behaviour of organisms (Dial et al., 2008, TREE)
- Trophic strategies of organisms (Lafferty & Kuris, 2002, TREE)
- Structure of trophic networks (Woodward et al., 2005, TREE)
- Abundance of organisms (White et al., 2007, TREE)
•  Body size appears as a key link between population and
community ecology
A metabolic theory of ecology
•  Basal metabolic rate = fundamental constraint that underpins
many size-related patterns and processes in ecology:
Towards a metabolic theory of ecology
(Brown et al., 2004, Ecology)
•  Body size = means of integrating approaches based on
biomass and energy flux with those based on abundances
and populations.
Why is body size so important in aquatic systems?
•  Role of body size in terrestrial systems explored extensively at very large
spatial scales (e.g. latitudinal gradient)
•  Prominent role in thinking about community structure in aquatic ecosystems:
- Importance of particles and organisms in suspension in the water (also true for
plants [planktonic algae] an detritus [detritic particles + algae = seston])
- Predation (including herbivory) frequently size-dependent in pelagic systems.
In terrestrial systems, herbivory might be closer to parasitism.
- Frequent use of body size when analysing aquatic organisms (flow, cytometry,
coulter counter, continuous plankton recorder, remote sensing of fish with
Passive Integrated Transponder [PIT])
See: Woodward G. & P. Warren (2007). Body size and predatory interactions in freshwaters:
scaling from individuals to communities. In: Hildrew et al. (Eds): Body Size: the Structure and
Function of Aquatic Ecosystems. Cambridge University Press, Cambridge: 98-117.
Aquatic communities
along size gradient
Range of
body sizes
in aquatic
ecosystems
Classification according to plankton size
Term
Size range
Organisms
Macroplankton
2 - 20 mm
Large carnivorous cladocerans, insect
larvae, fish larvae
Mesoplankton
0.2 - 2 mm
Large rotifers, copepods, cladocerans
20 - 200 µm
Phyto-, small eukariotic protists, ciliates,
rotifers, nauplii
2 - 20 µm
Phytoplankton, small eukariotic protists,
small flagellates
Microplankton
Nanoplankton
Bacteria, picoalgae,
Picoplankton
0.2 - 2 µm
small eukariotic protists
Femtoplankton
0.01 - 0.2 µm
Virus
Feeding modes and sizes
of predators and prey
Trophic interactions: suspension feeding
•  Filter feeders (or suspension feeders) are animals that feed by straining
suspended matter and food particles from water, typically by passing the
water over a specialized filtering structure.
•  A lot of categories of animals use this method of feeding, both in :
- freshwater ecosystems (cladocerans [Daphnia, Ceriodaphnia], bivalves
[Dreissena, Anodonta], fish [gizzard shad, bream, tilapia], birds [ducks])
- marine ecosystems (copepods [Acartia], krill, sponges, bivalves, some
fish and sharks, baleen whales, birds [flamingos])
•  Filter feeders can play an important role by clarifying water.
intra-specific variation in body size
and particle selection by filter feeders
Positive relationship between predator
size and maximum bead size
Constant minimum bead size
Relationship between prey size and body size in the copepod Acartia tonsa
capturing plastic beads (from Humphries [2007]. Body size and suspension feeding.
In: Hildrew et al. (Eds): Body Size: the Structure and Function of Aquatic
Ecosystems. Cambridge University Press, Cambridge: 98-117).
Largest particle ingested (diameter µm)
Body size of herbivorous Cladocerans (planktonic
microcrustacea) and maximum size of filtered particles
Carapace length (mm)
Relationship established for 7 species of Cladocerans
(From Burns C. W., Limnology and Oceanography, 1968)
Feeding behaviour of planktivorous fishes
A complex set of feeding strategies
Visual feeders
Bluegill,
juveniles of percids
(perch,walleye),
Post-larvae of most
fish species
Gulpers
Pump filter feeders
Tow-net filter feeders
(suction feeders)
(ram feeders)
Filtreurs par pompage Filtreurs par déplacement
Cyprinids such
as bream,
Coregonus,
tilapia
Visual selective predation
Gizzard shad,
tilapia,
herring
Padlefish,
Some marine
fishes
Passive escape selective predation
Fish filter feeders: Dead-end and crossflow filtration
a. In dead-end filtration, fluid flow is perpendicular
to the filter surface and the filter rapidly
becomes clogged with particles. Particles may
be retained by sieving when they are larger
than the filter’s pore size (particle 1), or by
hydrosol filtration when they are smaller than
the pore size (particle 2); in this case, the small
particles stick to the elements of the filter.
b. In crossflow filtration, fluid flows
parallel to the filter surface and
particles become more concentrated as filtrate leaves through
the filter’s pores.
(From Brainerd, E. L. 2001. Caught in the
crossflow. Nature 412: 387-388).
Fish filter feeders: some complex feeding behaviours
Suspension-feeding
fishes filter water through
complex structures in
their throats. Food
particles could clog the
filters, but the fishes seem
to have an efficient
crossflow filtration system
to prevent that happening.
Oesophagus
Gill raker
Gill arch
(From Brainerd, E. L. 2001. Caught in the
crossflow. Nature 412: 387-388).
Fish filter feeders: some complex feeding behaviours
Values are means ± s.d.
100
Frequency %
Movement frequency of 100
randomly selected particles (38 µm
- 1mm diameter) in the oral cavities
of each of 3 specimens belonging
to 3 fish species:
- no contact (particles did not touch
any oropharyngeal surface)
-  Bounce (particles bounced off the
floor or roof of the oral cavity and
proceeded posteriorly)
-  Slide (particles maintained contact
with the arches and rakers)
-  Rest (particles remained immobile
on an arch)
Goldfish
Gizzard shad
Ngege tilapia
75
50
25
0
No contact
Bounce
Slide
Rest
(From Sanderson et al. 2001.Crossflow filtration in
suspension-feeding fishes. Nature 412: 439-441).
Maximal prey length (mm)
intra-specific variation in body size
and particle selection by invertebrate raptors
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
3
4
5
6
7
8
9
10
11
12
Predator length (mm)
Relationship between length of the carnivorous planktonic Cladocera
Leptodora kindtii and the maximal body size of its prey (doted lines = 95%
interval). (from Herzig & Auer.1990. Hydrobiologia 198: 107-117).
intra-specific variation in body size
and particle selection by invertebrate raptors
Control prey
Spined prey
4
3
2
1
0
Female Copepods (1.5 mm)
Male Copepods (1.0 mm)
Predation rate (prey predator-1 day-1) exerted by females and males of the cyclopoid
copepod Acanthocyclops robustus on the 5 first instars of the cladocera Daphnia
galeata (from Caramujo & Boavida. 2000. Freshwat. Biol. 45: 413-423).
(Sizes of microcrustaceans are approximated)
variation in predator body size and fish selection by piscivorous fish
Mean prey size consumed (LT, mm)
(a)
(b)
Yellow perch predator size (LT, mm)
(a) Round goby and (b) alewife
total length eaten by yellow perch
in the extreme southern area of
Lake Michigan during summer.
Each point represents either the
LT of the fish found in the yellow
perch stomach when n=1, or the
mean LT value when n>1.
The lines ---- represent the
theoretical maximum size prey
that could be ingested by the
yellow perch based upon yellow
perch gape and prey maximum
morphological measurements.
From Truemper & Lauer. 2005.
J. Fish Biol. 66: 135-149
Contrasted predation pressures of similar-sized species
on the different components of pelagic communities
Planktivorous fish
Dorosoma cepedianum
(Gizzard shad, alose à gésier)
Cupleid
Lepomis machrochirus
(Bluegill, crapet arlequin)
Centrarchid
Invertebrate
Carnivores
Herbivores
Primary producers
Feeding behaviour and trophic position
of similar-sized planktivorous fishes
Mesocosm experiment on effects of fish total
biomass (B) and feeding behaviour (F)
Dorosoma cepedianum
(Gizzard shad, suspension feeder)
54 ± 10 g ind-1 (13-16 cm SL)
Lepomis machrochirus
(Bluegill, particulate feeder)
17 ± 9 g ind-1 (5-10 cm SL)
Trophic position
F: 0.0001 B: 0.32 FxB: 0.030
Invertebrate carnivores
4,0
3,8
3,6
3,4
3,2
3,0
10
30
50
75 g m-3
0
10
30
50
75
The predation process:
the different stages of a predation event
Search
Encounter
Attack
Capture
Ingestion
from Brönmark and Hansson, 1998. The Biology of Lakes and Ponds.
Oxford University Press, New-York, 216 pp.
Size constraints and effects on foraging can arise :
-  At each of the individual stages of the predation sequence
-  At different points within each stage, for example for attack rate:
-  Reactive distance of the predator
-  Speed of movement of both predator and prey
-  Probability of capture
Feeding and size: processes at the individual level
Handling time (i.e. for prey
capture to complete ingestion)
for Cordulegaster boltonii
larvae (Odonata) as a function
of predator body mass.
Prey = one Nemurella pictetii
(Stone fly larva, Plecoptera)
[head capsule width = 1 mm]
From Woodward G. & P. Warren (2007). Body size and predatory interactions in freshwaters:
scaling from individuals to communities. In: Hildrew et al. (Eds): Body Size: the Structure and
Function of Aquatic Ecosystems. Cambridge University Press, Cambridge: 98-117.
Feeding and size: processes at the individual level
Maximum daily
consumption of
Nemurella pictetii
(Stone fly larva) by
Cordulegaster boltonii
larvae (Odonata) as a
function of predator
body mass.
From Woodward G. & P. Warren (2007). Body size and predatory interactions in freshwaters:
scaling from individuals to communities. In: Hildrew et al. (Eds): Body Size: the Structure and
Function of Aquatic Ecosystems. Cambridge University Press, Cambridge: 98-117.
From individual behaviours
to community patterns
From individual predation events to structure of food webs
-  The set of processes encountered during the predation cycle emphasize the
predator view.
-  Frequently, single species of prey with single species of predators.
-  How to extrapolate to complex food webs?
-  Simple way: species are equivalent in all respects except size
-  However many prey species differ (e.g. proportion of digestible tissues, cost
of handling, mechanisms for avoiding capture, etc.)
-  What proportion of the variation in individual feeding interactions between a
predator and a suite of prey is determined by size?
-  If size predominates, modelling the patterns and determinants of trophic
links in food webs might be essentially modelled on a single niche axis.
From Woodward G. & P. Warren (2007). Body size and predatory interactions in freshwaters:
scaling from individuals to communities. In: Hildrew et al. (Eds): Body Size: the Structure and
Function of Aquatic Ecosystems. Cambridge University Press, Cambridge: 98-117.
From individual predation events to structure of food webs
The prey species
was eaten
The prey species
was not eaten
Results of separate laboratory feeding trials, in which 11 species of
freshwater invertebrate predators were presented a range of prey species
of different sizes (from Woodward G. & P. Warren, 2007).
Weak cross-specific relationships between body size of
species and their trophic position
Relationship between relative trophic level (expressed as
maximum body mass of North sea fishes.
15N)
(From Jennings et al. 2001. J. Anim. Ecol. 70: 934-944).
and the
Relationship between mean body size and trophic position
Decrease of the
mean trophic
level due to the
appearance of
filter-feeding
sharks and
whales
Relationship between relative trophic level (expressed as 15N) and the body
mass for the whole community of North sea fishes by body mass class.
(From Jennings et al. 2001. J. Anim. Ecol. 70: 934-944).
Frequent intra-specific increase
of trophic position with body size
Relationship
between
body mass
and relative
trophic level
( 15N) for
the central
North sea
invertebrate
and fish
community
(broken line).
Relationship
between body
mass and
relative trophic
level for the 10
most abundant
individual
species in this
community
(solid lines).
(From Jennings et al. 2002. Mar. Ecol. Prog. Series 226: 77-85)
Variation in prey-size range with predator size
Relationship between the log-log
transformed data of total length
anfd gape size for pikeperch
(Stizostedion lucioperca) in
Bautzen Reservoir (From Dörner
et al., 2007. Ecol. Freshwat. Fish,
16: 307-314).
- 
- 
- 
- 
Predators tend to take prey smaller than themselves
Prey maximum size tends to increase with predator size (gape limitation)
Thus, larger predators tend to take larger prey individuals in average
But, the minimum size of prey tends to grow much more slowly that their
maximal size (=> upper triangularity in predator-prey relationships)
Aggregating individuals within species and
ontogenetic changes
Ontogenetic diet shift in perch ( from
Brönmark and Hansson, 1998. The
Biology of Lakes and Ponds. Oxford
University Press, New-York, 216 pp).
-  Organisms can move through 3 or more orders of magnitude of body
mass over the course of their development
-  Ontogenetic changes within species can far exceed taxonomic
differences between species
(see : Woodward and Hildrew. 2002. Body-size determinants of niche overlap and
intraguild predation within a complex food web. J. Anim. Ecol. 71: 1063-1074)
-  Interpretation of food webs where individuals are aggregated within
species can be difficult.
Species averaging effects in food webs
Community matrix for
Skiptwith Pond with species
ordered according to body
length (mm)
-  Black circles represent
feeding links
-  White circles represent the
average size across all prey
species for each predator.
From Woodward G. & P. Warren (2007). Body size and predatory interactions in freshwaters:
scaling from individuals to communities. In: Hildrew et al. (Eds): Body Size: the Structure and
Function of Aquatic Ecosystems. Cambridge University Press, Cambridge: 98-117.
log (predator mass/prey mass)
Scaling to species
Distribution of predator:prey
body-mass ratio for feeding links
in aquatic systems. Boxplots (a)
and (b) show species-averaged
consumer-resource ratios for
species pairs taken in the Brose
et al.’s (2005) data set (Ecology
86 (9): 2545-2546) for freshwater
and marine food webs
respectively.
Wide range of possible values
-  mean log-ratio 1.8 - 1.9
(2 orders of magnitude)
-  Wider range in marine systems
-  ratios either < or > 1
(modular organisms such as
cnidaria: what is true mean
individual biomass?)
From Woodward & Warren (2007)
log (predator mass/prey mass)
Scaling to species
Different scales of
resolution within
Broadstone Stream food
web. The true value of
predator:prey size ratio
is underestimated by
one order of magnitude
(roughly from 100 to 10)
when considering mean
size of species).
(from Woodward &
Warren, 2007)
(c) Species-averaged values.
(d) Average body mass of consumers and that of the prey found in their guts for
each species pair (only individuals involved in a predation event).
(e) Values from all individual events.
(f) Distribution of predator:prey body-mass ratio from the gut of single predator.
Species averaging effects in food webs
(a)
(b)
(a) Community matrix for the
Broadstone Stream food
web, with species ordered
according to body mass.
Size of each circle
represents per capita
interaction strength for each
feeding link.
(triangularity in the speciesaveraged feeding matrix)
(b) Individual predation
events for the Broadstone
Stream food web (n = 1825
observations).
The triangularity tends to
disappear)
From Woodward & Warren (2007)
size and food-web topology
Food-web topology
Neo Martinez, www
A simplified food web from the
Northern Atlantic (www.ifaw.org)
Topological analysis
•  Specific richness: S
•  Number of feeding links: L
•  Link density: L/S
•  Connectance: C = L/S2
(ratio of realized feeding links
compared to the maximum
theoretical number of links )
•  Chain length (mean, min., max.)
•  Omnivory and generality indices
of species or functional groups
•  Mean species trophic position
•  Basal, intermediate and top-species…
Community-size distributions and realized niches
-  Distribution of feeding links
within the Skipwith Pond
food web across a gradient
of potential consumer:
resource body-mass ratios.
The clear bars show
potential values, as derived
from the full community
matrix
-  The dark bars show the
frequency of consumerresource pairs for which
feeding links are realized
(From Woodward & Warren,
2007)
Effect of foraging behaviour of top species
on food-web topology
Mesocosm experiment on the effects of biomass and foraging
behaviour of two planktivorous fishes
Particulate feeder
Lepomis machrochirus
(Bluegill, Centrarchidae)
Filter feeder
Dorosoma cepedianum
(Gizzard shad, Cupleidae)
Lazzaro, Lacroix, Gauzens, Gignoux & Legendre (2009). Journal of Animal Ecology
Contrasted topological characteristics
Topological variable
Visual
feeder
Filter
feeder
Probability of
absence of effect
Richness
-
+
0.0004
Number of basal species
-
+
0.009
Number of herbivorous species
-
+
0.0001
Number and % of top species
-
+
0.0001
Mean /max chain length
+
-
0.0001 / 0.0006
Number of chains
-
+
0.0001
Number of links (link density)
-
+
0.0001
L/S and connectance
-
+
0.0001 / 0.0002
Number of edible algal species
-
+
0.0001
Number and % of algal inedible species
+
-
0.0001
Invertebrate / food-web omnivory index
-
+
0.0005 / 0.0003
Lepomis machrochirus
(grasper)
Dorosoma cepedianum
(filter feeder)
Functional patterns revealed by the analysis
of instantaneous trophic networks, really
observed in the experimental enclosures
X17taille
25
25
P = 0,007
15
15
Potential network in the
enclosures if all species initially
present develop and coexist
c
10
10
5
5
0
0
A chlorophyl
Chlorophyll a (µg L-1)
20
20
0
0
20
20
40
40
% of inedible basal species
60
60
Percentage of poorly edible algae
80
80
Realized (instantaneous) food
web in enclosures after a
specific treatment
Body size, abundance patterns and structure of food webs
Food web of Broadstone Stream in England. Trivariate relationships between log10 body mass,
log10 abundance and trophic links. Basal species are shown in green, intermediate species in
green, and top-species in red.
(From Woodward et al. 2005. Body size in ecological networks.
Trends in Ecology and Evolution 20: 402-409).
Body size, abundance patterns and structure of food webs
Food web of Tuesday Lake in the USA. Trivariate relationships between log10 body mass, log10
abundance and trophic links. Basal species are shown in green, intermediate species in green,
and top-species in red.
(From Woodward et al. 2005. Body size in ecological networks.
Trends in Ecology and Evolution 20: 402-409).
Body size, abundance patterns and structure of food webs
Food web of Ythan Esturay in Scotland.
Trivariate relationships between log10 body
mass, log10 abundance and trophic links. Basal
species are shown in green, intermediate
species in green, and top-species in red.
The three Food webs on the same
figure, suggesting the occurrence
of strong metabolic constrains.
(From Woodward et al. 2005.
TREE 20: 402-409).
From individual feeding events
to size-dependent
global patterns
An important limitation: defining food webs
Extreme difficulty for constructing matrices:
- several dozens to several hundreds of species
- Several hundreds of trophic links
- Moderate help expected from specific feeding experiments
- Moderate benefits expected from tracers
An important limitation: defining food webs
Extreme difficulty for constructing matrices:
- several dozens to several hundreds of species
- Several hundreds of trophic links
- Moderate help expected from specific feeding experiments
- Moderate benefits expected from tracers
⇒  General database on trophic links within
freshwater and marine communities
General database on aquatic food webs
-  Freshwater or marine systems
-  Qualitative or quantitative data on feeding links
-  Prey size (weight), predator size (weight) or prey/predator size ratio.
-  Characterization of taxa (taxonomy, life-history and functional traits, etc.)
-  Characterisation of ecosystems (country, latitude, longitude, ecosystem
type) and environmental conditions (t°C, season, period of the day, light…)
-  Introduction of the data sources…
A never ending story…
Beginning of the construction of the database Aquatic web in 2010
August 2014:
- 14650 feeding links arising from 532 scientific articles
Today, punctual information on:
- 6 kingdoms
- 36 phyla
- 90 classes
- 246 orders
- 616 families
- 1044 genera
- 1391 species
Number of links
Prey-predator size ratios
Dominance of small prey
Prey / predator size ratio (x 100)
log (prey size)
Feeding behaviour and prey-predator size ratios
log (predator size)
Probability of feeding links
Graspers
Frequency
Frequency
Filter feeders
Residuals
Residuals
Possibility of determining statistically probability of links from:
- The feeding behaviour of consumer
- The size ratio of the studied taxa
Towards weighted predator-prey matrices
Establishment of predator-prey weighted matrices from :
-  Consumer and prey specificities
-  Species biomasses
- Consumer size and behaviour and predator /prey size ratio
- Life history traits other than body size
Improvement compared to the most frequently used theoretical food webs
models such as the niche model (Williams & Martinez, Nature, 2000)
- More realistic weighted models
Study of the role of interaction strength knowing that:
- Food webs are dominated by weak links
- Interaction strength seems to affect food-web stability
From topological networks to energy fluxes
Body size involved in many
biological processes and energy
fluxes at all level of organization.
Allometric scaling
For a given property Y of an
organism of mass M:
Y = Y0Mb.
log Y = Log Y0 + b log M
Slope b constant for
a given property
=> variability of Y0 according to
(From Woodward et al. 2005. TREE 20: 402-409)
specific features of organisms (e.g.
sit-and-wait predators versus active
foragers)?
Integrating energy fluxes and nutrient constraints
Possibility of lumping species a posteriori into trophic groups (necessity of
defining appropriate algorithms for minimizing loss of information)
-  Dynamical models with fluxes of energy and matter transfers
-  Stoichiometric characteristics (C:N:P ratios) of trophic species
Elaboration of algorithms for simplifying networks
Mesocosm food web defined
at the species levels
Mesocosm food web defined at the trophic
groups level (groups of species interacting
with similar prey and predators)
Mesocosm food web defined as a set of
distinct modules (main vertical pathways
of energy flow)
From theory to experimentation
Elaboration of theoretical food webs (« Cascade model», « niche model »)
and comparison to empirical food webs
• 
• 
• 
• 
• 
Poor knowledge of real food webs
Species aggregation into vague categories (« kind of organisms »)
Pooling of data on several dates and sites
Comparison of systems with strong dissimilarities in nature, scale, and details
Scarce use of experimental approaches for testing theories
From theory to experimentation
Elaboration of theoretical food webs (« Cascade model», « niche model »)
and comparison to empirical food webs
• 
• 
• 
• 
• 
Poor knowledge of real food webs
Species aggregation into vague categories (« kind of organisms »)
Pooling of data on several dates and sites
Comparison of systems with strong dissimilarities in nature, scale, and details
Scarce use of experimental approaches for testing theories
Experimental approaches on aquatic food webs
• 
• 
• 
• 
• 
Food webs often described at the species level
Identical rules across the data set
Food webs close to natural ones
Large variety of controlled factors
Important source of data sets for testing theories
on food-web architecture
Mesocosm experiment on
Lake Créteil (Paris suburb)
Size-dependent
functional food webs
Biotic determinants of zooplankton body size in lakes
%
1942
0,4
0,8
1,0
1,2
1,4
1,6
L (mm)
%
1962
+ glut herring (Alosa aestivalis)
0,2
0,4
0,8
1,0 L
(mm)
From Brooks et Dodson
(Science, 1965)
Respective effects of competition and predation on
size structure of zooplankton communities
•  Brooks & Dodson (1965):
« Size-efficiency hypothesis »
1. Competitive superiority of large herbivorous
zooplankton
2. Selective predation of large zooplankton by
vertebrate predators
Size efficiency hypothesis: competitive superiority
of large herbivorous zooplankton
Threshold food
concentration
Gliwicz (1990) presents experimental data from eight filter-feeding
species (family Daphnidae) that strongly support the cornerstone
assumption of the competitive aspect of the size-efficiency hypothesis.
Daphnid body size
The threshold food concentration, necessary to assure that assimilation
equals respiration, is lower for the large-bodied species than it is for the
small-bodied species under steady-state and low-mortality conditions.
Gliwicz Z. M.(1990). Food thresholds and body size in cladocerans. Nature 343: 638-640.
Size efficiency hypothesis: competitive superiority
of large herbivorous zooplankton
Daphnia
species
Size at birth
(mm)
Size at
maturity
(mm)
Threshold
concentration
(µg C L-1)
D. ambigua
0.4
0.8
47
D. galeata
0.6
1.2
43
D. pulicaria
0.7
1.6
30
Modified from Kreutzer C. & W. Lampert (1999). Exploitative competition
in differently sized Daphnia species: a mechanistic explanation. Ecology
80: 2348-2357.
Respective effects of predation by invertebrate and
vertebrate organisms on size structure of
zooplankton communities
•  Dodson (1974, Ecology): « alternative hypothesis »
1. Selective predation of small zooplankton by invertebrate predators.
2. Selective predation of large zooplankton by vertebrate predators.
Invertebrate predators
Vertebrate predators
Prey body size
Prey body size
Selective predation on zooplankton and filtering
capacity of herbivorous zooplankton
With
fish
Without
fish
(From Burns C. W., Limnol. Oceanogr., 1968)
Predation
and size
structure of
phytoplankton
ALGAE
Highly edible
Poorly edible
(mesocosm
experiment on
Lake Créteil)
% of highly
edible algae
Fish m-3
‘Large’
Algal
size
‘Small’
‘Small’
Zooplankton size
‘Large’
An increase in mean zooplankton body size induces a decrease in mean
phytoplankton size.
From Brönmark et Hansson (1998). The Biology of
Lakes and Ponds, Oxford University Press
Theoretical prey-dependent models
When supposing that it is possible to segregate species within
a food web into distinct trophic levels, the response of a given
trophic level to an increase of the limiting resource for primary
producers, depends upon the number of trophic levels
(see Oksanen et al. 1981. Am. Nat. 118)
Trophic
level
Phytoplankton
Zooplankton
Planktivorous fish
Piscivorous fish
Number of levels
1
2
3
4










Comparison between predictions of the prey dependent model and results of mesocosm experiment
Mesocosm experiment
With fish
With fish
Without fish
Nutrients
Chlorophyll a
(µg L-1)
Biomass of
primary producers
Prey-dependent
model
Prey
- dependent model
Without fish
0.32
1.6
3.2
Phosphorus loading (µg L-1 d-1)
Modified from Lacroix et al. (1996). Trophic interactions, nutrient supply, and structure of
freshwater pelagic food webs. In : Hochberg, M., J. Clobert & R. Barbault (eds), Aspects in the
genesis and maintenance of biological diversity. Oxford University Press : 162-179.
With
fish
Abundance of phytoplankton
Prey-dependent model
Without
fish
(µg D.W. L-1)
Without
fish
Herbiovorous Cladoecerans
Abundance of zooplankton
Comparison between predictions of the prey dependent model and results of mesocosm experiment
With fish
Chlorophyll a (µg L-1)
Results of a mesocosm
experiment
Discrepancies between the responses of functional groups within
food webs and the predictions of the prey-dependent model
F
Z
+
+
Z 0
+
A 0
A
N
N 0
+
Bottom-up and top-down control of body size within food webs
%
1942
Zooplankton
body length
%
1962 (+ glut herring)
Zooplankton
body length
From Brooks & Dodson
(Science, 1965)
Selectivity of herbivores
(From Burns C. W.,
Limnol. Oceanogr., 1968)
Construction of functional food webs
of intermediate complexity
Simplified pelagic food web
Based on functional groups
(« trophic species »), differentiated
according to body size.
(From Carpenter et Kitchell, 1993,
The trophic cascade in lakes,
Cambridge University Press).
Mathematical model
Experimental results
Taking in account body size
allows better accordance between
theoretical predictions and
observations
(From Hulot, Lacroix, Lescher-Moutoué & Loreau, Nature, 2000)
Experimental results
Mathematical model
Taking in account body size allows
better accordance between theoretical
predictions and observations
(From Hulot, Lacroix, Lescher-Moutoué & Loreau, Nature, 2000)
Predation and evolution of life-history traits
Relationships between the size of Daphnia
galeata ovigerous females and the size of their
eggs, in enclosures with different abundances
of planktivorous fish (roach, Rutilus rutilus)
F0=0, F1=1, F2=2, F3=3 ind. m-3)
Modifications of life-history traits (in
particular of body size) of organisms
within populations, according to
ecological and selective pressures of
the environment
Mean size of eggs of Daphnia galeata in
enclosures according to the abundance of
planktivorous fish (roach, Rutilus rutilus)
Prey plasticity in response to predation
Conclusion
Towards better integration of body size in networks
Static topological models could be revisited by:
-  explicitly using body size as a niche dimension
-  Using size-specific rules for link allocations
-  Switching from binary topological food webs to weighted networks,
which take into account interaction strengths or link probability
-  Better generalizing interactions between predator:prey size ratios and
functional responses of predator.
-  Integrating allometric rules
-  Integrating density-dependence in link probability
-  Working on realized networks
-  Taking into account species plasticity