Lecture 8 Flashcards
What is the migration of zoo plankton when fish are present?
Dinural migration occurs. Zooplankton remain close to the bottom of the lake at mid day as there’s less chance of predation. At midnight, the zoo plankton migrate to their preferred position and the majority of seeding occurs
What is cyclomorphosis
A process where cytoplnakton attempt to make themselves appear smaller, in order to avoid predation ( they appear as a less favourable food source)
Explain cyclomorphosis in daphnia
In summer their heads are rounded, their bodies smaller and more transparent. In winter the head become more helmet shaped
Which two invertebrate species undergo cyclomorphosis?
Rotifera and cladocerans
What is the zooplankton and fish distribution in oligotrophic lakes?
Zooplankton: high diversity, low biomass
Fish: few species, low biomass
What is the zooplankton and fish distribution in eutrophic lakes?
Zooplankton: high biomass but few species
Fish: many species with high biomass
What is the difference between a planktivorous fish and a pescivorous fish?
Planktivorous fish predate plankton And invertebrates
Pescivrous fish predate other fish (eg pike)
What is meant by: pike have a threshold density?
Pike have a threshold entity for the available biomass of prey. In regions of low biomass, there will be very low pike concentrations. Pike DO NOT have a threshold for diversity, just the available biomass
How do pike control the productivity of the rest of the food web?
They are top down predators
What would happen if the top tropic level predators(eg pike) were removed from the food web?
- there would be an increase in planktivorous fish concentration (tropic level three) as they would no longer be predated
- there would be a decrease in zooplankton (tropic level 2) as the increase in planktivorous fish would cause their population concentrations to decrease
- they’re would be a decrease in algae. Although zooplankton concentrations are decreased, Protozoa will still eat the algae and regulate their populations
- more algae means a decrease in available nutrients
In isotope analysis, what does the carbo value plus one indicate?
An organism with a carbon value plus one (in relation to another organism) is that organisms predator
What does nitrogen indicate in stable isotope methods?
The tropic level
What does an n value increase of 3.4% show?
A move from one tropic level to another
What is the name given to carbon produced by phytoplankton in lakes?
Autochtnous
What is the name given to carbon bought into lakes from “elsewhere”?
Allochtonous
