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- Developed in 1962 by Karel Hrbacek (Czech Rep) à John L. Brooks & Stanley I. Dodson 1965
- Seen in ponds by Hrbacek Small zooplankton in areas where fish were present, large zooplankton in areas where fish were not present, in the same system.
- Fish tend to eat the larger prey size, making zooplankton want to be smaller to avoid being preyed upon, hoping something else is bigger than them.
Describe the role of predation and competition in explaining the differences in thezooplankton community of Crystal Lake (CT) in 1942 and 1964. Why do large zooplankton dominate lakes after a fish kill? Give examples of fish that are planktivorous and fish that are piscivorous
- Lakes with Alosa (Alewife) had smaller zooplankton and smaller Daphnia, Lakes without Alosa had larger zooplankton and larger Daphnia.
- Large zooplankton dominate after a fish kill because if the fish (being the largest predator in the lake) being lessened, the major threat now lies from invertebrate predators, which prefer smaller prey, (less handling cost, energy waste, feasibility, ect), so the larger the plankton is, the less likely it is to be eaten.
-Alosa, Bleak, Perch, Rainbow Trout are planktivorous.
-Large Mouth Bass and Northern Pike Are Planktivorous.
1) With loss of piscivorous fish, planktivorous fish would become more abundant, large zooplankton would decrease in abundance and smaller zooplankton would remain the same (over time) or increase in abundance.
2) Alsoa (Alewife) feed on smaller zooplankton (finer gill rakes to pick up smaller zooplankton) decrease in zooplankton abundance and size. Alosa feed on larger zooplankton causing larger zooplankton to become less abdunant.
-Planktivorous fish eat zooplankton such as daphnia Ex. Alosa
-Zooplankton grazers eat smaller-sized zooplankton such as Bosmina Ex. Daphnia-Piscivorous fish eat other, smaller planktivorous fish such as perch, alosa Ex. Large Mouth Bass and Pike
-The setup of terrestrial land around the given lake can contribute, “moontraps”, areas where the sun doesn’t come up for extended periods of time.
- Lakes that have constant temperatures all the time, even at night and evenly mixed lakes will not have the triggers that cause the migration pattern.
-Tested how fish emitted chemicals/kairomones can affect the trigger of DVM.
- Ploen Plankton Towers: Two long tubes, one with fish kairomones, other with plain water. The plankton in the kairomone filled tube migrated down at night, and came up to the surface during the day.
-Experiment Example: In Mozambique, full moon would fool the plankton into thinking it was time to migrate, and the bright moonlight would allow fish to see the plankton rising to the surface and the fish can eat plankton during the night.
- Vertical migration is a predator avoidance mechanism despite the drawbacks of lack of food and prolonged egg incubation times from migrating to colder water in order to avoid predators.
-D. galeata does not migrate and remains at the surface and has a higher birth rate but has a high mortality due to predation
-D. hyaline migrates to the deeper water in a diurnal pattern, however, there’s less food and the colder water prolongs the time it takes for eggs to hatch.
-Daphnia can be seen by fish swimming underneath them when light filters through the surface of the water, so they do have an effect on the clarity of water.
-If the zooplankton grazer is an invertebrate (smaller), the smaller zooplankton tend to decrease. If the zooplankton grazer is a planktivorous fish (larger), the larger zooplankton tend to be eaten.
-See SEH above for examples
In what habitat type is transparency useful as a form of camouflage? Namesome examples of transparent species in lakes and oceans. Why are transparent animals rare in terrestrial environments?
-When DVM’s could put a species in harms way from casting shadows below to where fish could easily find and eat them. Also, shallower water conditions can cause damage to the zooplankton from the UV light. Transparency is a way to duck the damage and exposure.
-Leptodora Kinti (cladoceran)
-Any pigment that can help with life processes cannot be present in a transparent zooplankton, as this would make them able to be spotted. A work around for this pigments (amino acids, ect) can be used. Also, hiding of any food ingested can be a problem.
Where is Lake Constance and what are its features (size, depth, trophic state, mixing pattern, water clarity)?
- 531 Sq. km Surface Area
- 85 253 km depth range
- Eutrophic (by agriculture, high population density, high traffic and tourism)
- Highly stratified in Summer, monomictic in winter
- Clear in third week of May, less clear rest of year, major alga bloom in spring.
What factors in the watershed contributed to its eutrophication?
- Introduction of 3 – 5 new plankton species and extinction or severe decrease in one species
- Phytoplankton production increases in the middle of May, followed by Daphnia population spike the following week, resulting in the Daphnia taking in the phytoplankton in massive amounts, causing a clear water effect and competition with Cyclops, who also decrease in abundance, making the water have less particulate matter to cloud up the water.
Exactly how did the introduction of a predatory copepod affect the succession of
phytoplankton in the lake?
- Introduction of a predatory copepod decreased the populations of the phytoplankton grazers (Daphnia), which allowed the biomass of phytoplankton to spike due to the lack of control. Daphnia birthrates greatly increase the population in May and that can be supported due to the temporary spike in food (Phytoplankton). Cyclops decreases while Daphnia increase to take in the phytoplankton, causing the lake to become less cloudy.
-Daphnia dominate during the small mid-May to mid-June period, Cyclops dominate pre-May.
-Mixis – Stratifies April – November, mixes entirely November to April = Turnover raises nutrients (P) to the surface to trigger blooms in spring
- Phosphorus: Spike in P causes a spike in Phytoplankton, which begins the Clear Lake effect, mixing rises P to the surface from deep water
-Predation: Cyclops predation on Daphnia most of the year, until birth rate of Daphnia increases causes Phytoplankton spike until Daphnia can clean
-Competition: Daphnia quickly out-compete the Cyclops when food is highly available, spiking its population-Grazing: Daphnia graze, feed on, phytoplankton, cleaning up the water from the P spike
Where is the English Lake District? Describe the origin and morphometry of the lakes. What type of seasonal mixing pattern is found? How does this affect the timing of nutrient regeneration and the seasonal succession of the diatom Asterionella?
-Glacier developed lakes, thin and spoke-like, glacial valleys
-Monomixis, mixes from November to March
-When mixed, less DO available, P loading is increasing, N:P ratio has decreased, SI:P ratio is decreasing
-Silica goes down when Asterionella goes up. When SI arrives in the lake (mixed up into epilimnion) the diatoms use it to form.
-Eutrophic. Less DO in deeper water, typical of Oligotrophic (during Nov. – March). Spring = Oligotrophic, Fall/Winter is well mixed, meromictic.
Where are the Italian Alpine Lakes located? In what ways are they similar to the English Lake District lakes? Describe the mixing pattern of these lakes, such as Lago Maggiore, and the current change that is occurring in the mixing pattern.
-Northern Italy, 300m above sea level
- Glacial Valleys, carved from mountain glaciers
-Warm monomixis (1950’s) à Oligomixis à (7year cycle) Meromictic (1998)
- Overall becoming less mixed from the bottom to top as time goes on
How and why is the N/P ratio in Lago Maggiore changing? How might this affect the
composition of the phytoplankton and the entire aquatic food web?
-Nitrogen remains constant despite acidic rain (NO3 and NH4)
- Industrial areas to the south moving the pollution to deposit in the lakeà Human population density
-N/P Ratio increasing since Total P is decreasing
-A physiological morph in structure induced by
some trigger from the environment.
-It is induced in the Brachionus Caliciflorus only when a predator, Asplanchna is present.
-If no Asplancha is present, they will not have spines. When Asplancha is present, they’ll be triggered to grow spines, as to prevent predation; harder to eat.
- Experiment: When Asplancha are not present, Brachionus rubens (does not produce spines), Brachionus Caliciflorus (can produce spines, but only when triggered) loses the competiton. However, B.c. wins when a predator is present.
Kairimones can trigger a defense polymorphism in species of zooplankton simply from chemicals the predator emits
What is “cyclomorphosis”? In what organisms has it been observed? Give an example of a species that exhibits it (and draw it). What are four hypotheses (& authors) concerning the adaptive significance of cyclomorphosis in Daphnia?
-Cyclomorphosis is a seasonal change that occurs in a species of zooplankton.
-Observed in Daphnia à Neckteeth and the hoods/helmets
-Buoyancy Hypothesis (Wesenburg-Lund): Helmet reduces sinking rates (form resistance), compensating for warm water & lower viscosity
-Steering Hypothesis (German Author): Helmet
aids Daphniain swimming horizontally in layers or strata of phytoplankton
-Predator defense Hypothesis (James): Helmet reduces visible outline of Daphnia & smaller eye size (i.e. defense against fish predation)
-Predator defense Hypothesis (Tolrian): Chaoborus kairomone induction of helmet in Daphnia cuculata (i.e. defense against invertebrate predation)
-Able to see the effects of the environment on the aquatic ecosystems as well and get fossils of plankton that lived in the water at the time
- Can be achieved through coring in sediment and analyzing the layers and content
EX- Niches of algae/plankton are defined by nutrients requirements at different levels
1. Diurnal (morning)
2. Crepuscular (twilight)
3. Nocturnal (night)
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