Integrated Plankton Ecology

I. Plankton distribution
    A.     Regional –
        Biogeography
        ·        cosmopolitan – e.g., many rotifers
        ·        Some species (many cladocera and copepods) not distributed worldwide – good study organisms for questions of biogeography
    Understudied in general for plankton vs. other organisms
        1.      tropics vs. arctic
        2.      flowing versus still water -- negative correlation of plankton size, diversity and numbers with water velocity
        3.      lake size
        4.      endemism
                Baikal
                Tanganyika

        5.      chemistry
              a. example of crater lake district -  most similarity where lakes have most similar chemistry
              b. conductivity
                At conductivity >400 mS, start to lose zooplankton species
            c. pH
            d. Specific Ions –
                    1.      e.g., Changes in [Fl-] in East Africa; copepods
                    2.       calcium
 
        6.      geography
            a.       mountain ranges – may prohibit movement of species
            b.      events not now apparent
                                                                         i.      plate tectonics
                                                                         ii.      glacial relict species
                                        a.       Mysis relicta (opossum shrimp)
                                        b.      Limnocalanus
        7. other abiotic factors
            a.       temperature
            b.      lake morphology – variability in habitat
        8. biotic controls
            a competition
            b. predation
    B. Local
        1. horizontal
            a. pelagic versus littoral -- 'avoidance of shore'
            b. patchiness – random, uniform, clumped
                
                scales of patchiness
                    1.       large scale >1km (e.g., windward vs. leeward)
                    2.      small scale, wind induced circulation; Langmuir circ.
                    3.       swarms (biotic)
        2. vertical – zooplankton can adjust their depth
            a.       types – Diel vertical migration
                    1)      nocturnal
                    2)      twilight
                    3)      reversed
            b.      patterns
                    1)      increased lake transparency – increased vertical migration
                    2)      increased organism body size – increased migration
                    3)      migration related to life history
                    4)      seasonal patterns
            c. causal evaluation
                    (1)   proximate cue is light
                    (2)   ultimate or adaptive (plankton towers)
                        a)      metabolic boost hypothesis
                        b)      protection from damaging light
                        c)      protection from predation
                                 vertebrate predators are visual predators
                                                                   why come up ever? Food
                                                            another proximate cue – fish kairomones
II. Role of predation
    A.     Size structuring of fish – large bodied versus small bodied zooplankton
-1941 Crystal Lake – no Alosa, large bodied zooplankton
-1950s Alosa added to the lake
-1964 Crystal lake re-sampled – found small bodied zooplankton
WHY AREN’T ALL ZOOPLANKTON SMALL?
  B.     Size-efficiency hypothesis
 
            -Invertebrate vs. Vertebrate Predators
 
    C. Cyclomorphosis – changes in body form/shape over seasons – development of spines and changes in body shape – WHY?
        1. resistance to sinking?
 
        2. temperature?
 
        3. predation?
                a. vertebrate – Tom Zaret; Lake Gatun (Isthmus of Panama); 2 forms of Ceriodaphnia cornutaMelaniris fish


                b. invertebrate
                    So, why have a short form? 
    greater reproductive output


    D. Developmental polymorphisms
        1. inducible defenses
            a. chemical signals – morphogen chemicals
o       Brachionus (loricate rotifer); predator Asplanchna releases a chemical (‘Asplanchnin’) that induces Brachionus to become spined;
o       spines induced with only the water from an Asplanchna culture
o       inducibility only in early developmental stages
            b. certain lifestages induced
            c. costs of induction
            d. phytoplankton inducible as well
            e. density
                ·        Asplanchna (cannibalistic at high densities)– 3 forms – sacchate, campanulate, cruciform (large, resistant to predation by campanulate form)
            f. reverse vertical migration

- TO AVOID INVERTEBRATE PREDATORS – CHANGE SHAPE
(makes predation more difficult)
-TO AVOID VERTEBRATE PREDATORS - REDUCE VISIBILITY
(makes finding prey more difficult)
-Also escape ability important
III. Summary of effects of invertebrate and vertebrate predators
 
            Average body size of zooplankton in the community
            Phytoplankton that can be grazed – size and amount
 

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