LEC 32 - ECOLOGICAL STOICH Flashcards
what is seston?
shit that can be measured in filter nets, usually ppton
when primary producers have a nutrient in excess, they dont do anything to it… unless?
they undergo “luxury consumption” where they store extra of the nutrient in case it ever becomes scarce
when looking at seston, what do we observe w respect to the redfield ratio?
its rarely maintained - redfield ratio is the exception, not the rule
- in lakes, terre inputs have huge impacts
- decoupled growth w nutrient avail may occur, where prim prods keep undergoing photosynth to keep the lights on
in general ur more likely to have higher C than P
comparing seston to zpton, how does stoich homeostasis stay? what does this imply for the top down/bottom up controls?
seston dont stay at stoich homeostasis, but zpton do –> mismatch bw communities
this mismatch means that zpton biomass is partly controlled by ‘quality of food’ aka seston C:P ratios; ultimately nutrients are important for predators (ex. P inputs can supplement seston stoich homeostasis problems)
in lake 227, cyanobacteria briefly lost their competitive advantage, primarily due to P-rich daphnia. why was this the case.
P treated food accidentally led to a huge burst in cladoceran daphnia. because there were more daphnia, more excretion was occurring, and thus N incr –> N:P ratio increased
we know that cyanobacteria thrive in N:P environ bc they are N fixers; the sharp rise in daphnia ultimately resulted in the loss of advantage for cyanobacteria
caddisfly grazing increases the nutrient concentration of periphyton. through what mechanism?
unlike daphnia in the lake 227 ex, caddisfly are not nutrient sinks for P (ie they dont have super high P reqs), but instead act as nutrient regenerators through grazing, excretion, etc
how does stoich homeostasis regulate trophic cascades?
limits consumer growth, which affects the transfer of energy up the trophic cascade. in a sense, regulation occurs through the nutrient requirements of consumers
why is N likely to be more abundant in FW systems than marine systems?
excretions, agriculture, etc
but also bc they tend to be closed off w limited inflow/outflow, FW systems tend to be affected way more than marine systems
in redfield ratio C:P biomass quality of food, daphnia do really well (60% of C apportioned to growth). however, as C (and thus the ratio) gets higher and higher, daphnia actually grow less. why is this the case? do we have any examples?
daphnia have no need for all the excess carbon, but instead need P. thus, growth increases at a slower rate, bc P becomes increasingly scarce
this was demonstrated in the experimental lakes, where food treated w P (exact same amt of C in control and P addition) was found to be correlated w incr daphnia growth.
another ex. daphnia biomass was measured w respect to amt of C, and then quality of food (C:P). amt of C was not correlated, but quality of food was.
ELA 110: pisciv fish were stocked, causing a drop in minnows, the main ptoniv. we should expect to see a rise in zpton, but this was not the case. what happened?
once again, food quality! (C:P increased - P was declining)
in other words, seston were poor in P which was inhibiting the growth of zpton
