LEC 30 - ISOTOPES

Question 1

what is the compensatory dynamic of fish harvesting? conversely, what are depensatory dynamics, and how can this lead to ‘invisible collapse’

Answer 1

when fish get fished, relatively there are more resources to go around so the fish that are left behind have the opportunity to repopulate

depensatory dynamics continue if fish don’t get a chance to repopulate before getting harvested, so growth falls.
this can be due to things like juvenile fish that don’t get fished eating the fish that need to repopulate, never letting them have the change.

this can reach a critical point called the ‘invisible collapse’ where collapse occurs despite numbers appearing to be fine

Question 2

ok so recall an isotope is a element w diff # neutrons but same # protons. what is fractionation

Answer 2

fractionation: bc mass differs bw isotopes, they will behave differently in chem reactions

ex. heavier isotopes of water are less likely to evaporate

Question 3

isotopes mix conservatively - describe this, perhaps through the analogy of mixing two buckets of paint

Answer 3

so u can mix two buckets of paint and, analyzing the saturation of colour, can determine how much of each bucket was put in. u can do the same w isotopes by looking at how much of either is in the mix.

Question 4

from the atmosphere to the water, and ultimately to the cell, what is the fractionation that 13C CO2 experiences?

Answer 4

-7 –> -8 –> -29 in photosynth and -37 in organic matter

Question 5

ideally, photosynthetic cells prefer to take up lighter 12C CO2, but we do not live in an ideal world. what does this mean for, say, phytoplankton vs submerged macrophytes?

Answer 5

ppton will get the lighter 12C CO2 bc they have access to it first. this means that, even if its ideal, submerged macrophytes will take up the heavier 13C isotope, even if it isn’t ideal

Question 6

what are isotopes of C and N used for?

Answer 6

diet and looking at trophic level, respectively

Question 7

why are isotopes useful for looking at diet?

Answer 7

isotopes stay in tissue for long time, so u can get a longer time span when looking at diet (in contrast, to looking at the diet of what the organism ate in the last day or so)

Question 8

isotopes can be used to indicate omnivory. how so?

Answer 8

by looking at 15N isotope, u can see what they’re feeding on. if its mostly veggies, itll be lower amt of 15N, whereas if its mostly animals, itll be higher amt of 15N