intplankecol

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

-Hrbacek, 1962, reservoirs in Poland and Czechoslovakia; fish species were correlated with zooplankton species
-Brooks and Dodson 1965, Alosa (blue-backed herring) efficient predator on zooplankton:

lakes with Alosa – Bosmina, small Cyclops and Tropocyclops – small zooplankton
lakes without Alosa – large Daphnia, Diaptomus, Epischura, Leptodora – large zooplankton – correlational evidence

-1941 Crystal Lake – no Alosa, large bodied zooplankton
-1950s Alosa added to the lake
-1964 Crystal lake re-sampled – found small bodied zooplankton

-size and escape ability both important
-arctic – depth of the lake determines the presence/absence of fish -- fish lakes have small bodied zooplankton; fishless lakes have large bodied zooplankton
-are exceptions – lakes with lots of piscivorous fish – effect of an extra trophic level
-better to be small in the face of vertebrate predation - size selective predation

WHY AREN’T ALL ZOOPLANKTON SMALL?
B. Size-efficiency hypothesis –

- Brooks and Dodson – large zooplankton are competitively superior
- can take a larger size range of food
- allometric (changes with body size) respiration function – lower respiration rate at larger size
- holds sometimes, but not always (e.g., between cladocera and rotifers)
- alternative hypothesis – INVERTEBRATE PREDATION

            -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 cornuta – Melaniris fish

                b. invertebrate

Effective size
Invertebrate predators choose small or medium size prey – opposite to vertebrate predation
example: Kerfoot - Bosmina and Epischura

So, why have a short form?

greater reproductive output

Epischura versus sticklebacks

    D. Developmental polymorphisms
        1. inducible defenses
            a. chemical signals – morphogen chemicals

Gilbert:

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

Daphnia with a Chaoborus predator

            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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