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Fish and Zooplankton Interactions

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Fish and Zooplankton
Interactions
Wetzel
Chapter 16, pp. 460-468
Interactions between Fish and ZP
• Predation
• Alteration of trophic structures
• Nutrient cycling
Feeding Relationships Among Fish
• Feeding defined: acquisition of both energy
and nutrients for growth and reproduction
• Cost/Benefit Analysis: do the costs of food
acquisition exceed energy gained from
consumption – Maximize return per unit
effort
Prey Density and Diet Shifting
• If prey are large and scarce, fish consume
them one at a time
• If prey are small and abundant, fish will
filter water column – Mechanical Sieving
• Obviously, these statements apply to fish
capable of doing this and of the correct
trophic status – i.e. adult walleye will not do
this, but walleye larvae will
Ontogenetic Diet Shift in Yellow Perch –
Wu and Culver 1992
• As zooplankton occur less and less
frequently, yellow perch young-of-year
switch from zooplankton to benthic
macroinvertebrates
• This was found both in the lab and in nature
• Function of the development of digestive
organs
Ontogenetic Diet Shift
Ontogenetic Diet Shift
Predation of ZP by Fish
• Study from Liu and Herzig
– Distribution in lake of possible prey
Distribution of Prey Species
Predation of ZP by Fish
• Study from Liu and Herzig
– Distribution in lake of possible prey
– Selectivity of larger sized individuals
• Prey sizes present in gut vs. prey sizes in nature
Selectivity of Large Individuals
Predation of ZP by Fish
• Study from Liu and Herzig
– Distribution in lake of possible prey
– Selectivity of larger sized individuals
• Prey sizes present in gut vs. prey sizes in nature
– Selectivity vs. Length
Selectivity vs. Length
Predation of ZP by Fish
• Study from Liu and Herzig
– Distribution in lake of possible prey
– Selectivity of larger sized individuals
• Prey sizes present in gut vs. prey sizes in nature
– Selectivity vs. Length
– Selectivity vs. Eye Diameter
Selectivity vs. Eye Diameter
Predation of ZP by Fish
• Study from Liu and Herzig
– Distribution in lake of possible prey
– Selectivity of larger sized individuals
• Prey sizes present in gut vs. prey sizes in nature
– Selectivity vs. Length
– Selectivity vs. Eye Diameter
• Conclusion: Prey visibility and parts that
are visible make a difference
Predation of ZP by Fish
• Predation by fish can shape communities of zooplankton
• Relationship between size selection and foraging
efficiency
• Ex: Bluegill (p. 462 in Wetzel & refs therein)
– Selects prey on basis of size
– Growth rates increase with increasing food size
• Increased efficiency (higher return with large prey)
– Size selection based on search time and handling time
– When there is low density of prey, more likely to take
prey of any size
– As prey density increased, search time decreased and
small classes are consumed less frequently
Predation of ZP by Fish
• Another example of Size
Selectivity
• Crystal Lake, Connecticut
(Brooks and Dodson,
1965)
• No alewife – large zp
• Alewife introduced – shift
to smaller zp
• But why were larger
present in the first place
and no coexistence of all
sizes?
Size Efficiency Hypothesis
•
When size-selective predation not occurring in
lakes, small zooplankton not found to occur with
larger zooplankton
• The Hypothesis:
(1) Planktonic herbivore zp compete for small food
particles in the pelagic zone of a lake
(2) Larger zp filter more efficiently and can take
larger particles – this allows for reduced
metabolic maintenance demands allowing for
more devotion of energy to reproduction
Size Efficiency Hypothesis
(3) Therefore, larger forms come to dominate
(4) However, if fish size-selective predation is
intense, larger forms are selected to be eaten,
allowing smaller forms to dominate
(5) If predation pressure is moderate, large forms are
reduced and this allows coexistence of forms
- Some evidence for this – Threshold food
concentrations
- Amount of food to satisfy metabolic upkeep decreases
with increasing body sizes
- In Cladocerans, Gliwicz 1990; however, rotifers may
not follow the same patterns
Food Limitations in ZP
• If food is limiting, body sizes and mass are
reduced and reproduction is minimal
• Interaction of food limitation and size
selective feeding shapes the community
– Which is more important depends on lake
characters
Conclusions
• Fish and ZP interact through predation
• How this actually shapes the communities is
dependent of many different forces
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