Lecture 7-bottom up control of zooplankton Flashcards
what is the difference between bottom up and top down control?
Bottom up control: controlled by food sources lower down the train
Top down control: controlled by predators higher up the food chain
where are metazooplankton commonly found in aquatic environments? why?
- metazooplankton are commonly found at the deep chlorophyll maxima
- this is because algae are positioned at this point, near the thermocline. They are her to acquire maximum nutrients etc, and as metazooplankton predate them, it benefits then to be located in the same region
explain the seasonal distribution in algae?
-in winter there is little abundance due to sunlight being a limiting factor for photosynthesis. the increase in light intensity in spring causes the formation of spring blooms,-in summer overpredation by zooplankton causes the formation of a clearwater phase. algae recover in later summer, undergoing a second summer bloom
explain the edibleness of the spring bloom
- the spring bloom is composed of edible algae species, such as:
- phytoflagellates
- chlorophytes
- centric diatoms
explain the edibleness of the summer bloom
- begins with edible species, but growth is limited by phosphorous
- diamtoms become the dominating species due to their ability to tolerate low p conditions
- as diatoms require silica to make their glass casing, silica becomes limiting
- these are then replaced by cyanobacteria, which are very efficient at nutrient utilization and are NON EDIBLE
- in autumn diatoms and flagellates appear in low number (as stratification is over)
what happens to metazooplankton in the winter famine?
- cladocerans and rotifers produce by sexual reproduction due to resource scarcity
- copepods go into diapause
what triggers the end of copepod diapause?
- food concentration
- food quality
- temperature
what is threshold density?
the lowest available food concentration required to produce a positive population growth. This determines when cladoceran EPHIPPIUMS hatch
how does threshold density relate to growth rate?
-the greater the organisms threshold density, the greater the growth rate
what happens to organisms with high threshold densities during times of famine?
-theyre the first to disappear
what is the wakeup order of rotifer, cladocerans and copepods?
rotifers and copepods wake up together, then cladocerans
why do copepods wake up early?
because they have six stages of nauplis growth, they must wake up early to acquire food and avoid being out competed
how does rotifer “wake up” relate to algae type?
-rotifers have a very low threshold density for edible algae species. but a high one for inedible species
which metazooplnakton is active in the spring bloom?
-cladocerans
explain the feeding of the two dominant cladoceran types in the spring bloom
-both bosmina and daphnia hatch in may, but the lower threshold density of bosmina means that they hatch later. bosmina eat phytoflagellates, and when these become limiting daphnia becomes the limiting form. daphnia have no carry capacity for resources, so overgraze algae and cause the clearwater phase
what happens to metazooplnakton in the clear water phase?
cladocerans +rotifers: large species die off of cladocerans
- rotifer populations still increase slowly
copepods: use lipid reserves as a food source to avoid die off
describe claodceran species populations during feast 2 in the peg model
two types of cladocerans:
- left overs, who survived the famine
- newly hatched species, including: Ceriodaphnia, Diaphanosoma and Chydorus
- newly hatched species can consume cyanobacteria
describe copepod species populations during feast 2 in the peg model
- high correlation with algae abundance, suggesting that they are the dominant grazers
- populations are now mature
- can consume cyanobacteria (typically non-edible algae)
describe rotifer species populations during feast 2 in the peg model
-activity is completely temperature dependant
they preferentially predate cilliates over algae, giving them a poor correlation to algae populations
why do cladocerans switch from large genera to small genera from the spring feast- summer famine?
- starvation
- fish predation
what are the two main problems of the peg model?
- no mention of indirect feeding
- bacteria and protezoa not included
explain algae and bacteria correlation in the BACTERIA INITIATED CASCADE MODEL
-as bacteria feed on algae waste products (DOC), population is closely correlated to the increase/decreases of algae populations
what organisms feed on bacteria in the clearwater phase? why?
- ALL metazoplankton (copepods,cladocerans,rotifers)
-protezoa
because algae is limiting
what is the other food source for zooplankton in the clear water phase?
-protezoa
explain flagellate and cilliate distribution over the peg model?
- as they are a food source for bacteria when algae are limiting, population changes are closely related to those of bacteria.
- however cilliate populations do not increase during the summer feast as they are over predated by rotifers (who choose to not eat the non-edible algae)
