Intro to Stable Isotopes Flashcards
Historically, food web structures were developed with a focus on what 2 components?
taxonomy and organization
life history
Which guy developed a highly influential paper that most current methods of food web ecology are still based on? What important number did he figure out?
Lindeman - looking at the ‘trophic-dynamic aspect of ecology’ in a pond ecosystem
he figured out that the loss value between trophic levels is ~10x
What was unique and novel about Lindeman’s ‘trophic-dynamic perspective’ compared to the historical animal ecology food cycle?
Lindeman organized his food web:
- focused less on taxonomy and grouped organisms based on function
- focused on the math to organize the species
his had two distinct chains from distinct sources and showed that they interact - microbes and nutrients from abiotic contributions - included the recycling nutrients
the animal ecology one provides more taxonomic info, the Lindeman one is more informative and provides a functional understanding
What does the study about fiddler crabs and the stable carbon isotope tracer tell us?
looking at the stable carbon isotope in various photosynthetic life which the fiddler crab consumes (C3 and C4 plants) in salt marshes tells us about the diet
how well does the crab’s signature match the photosynthetic plants?
T or F: carbon isotopes vary among dietary sources
true
What does the 1:1 linear line in a graph tell us?
the 1:1 line shows us what the relationship would look like if the carbon isotopes in the animal do not vary from the carbon isotope in the primary producer that is thought to be the dietary source
what happens to the nitrogen stable isotope as you go up the trophic levels?
it increases (gets heavier)
What does carbon tell us about the organism?
dietary source - ‘you are what you eat’
What does nitrogen tell us about the organism?
trophic position
“you are what you eat + more”
T or F: there is only variation in the stable nitrogen isotope between trophic levels
false, there can also be variation between individuals of the same species/same trophic level
Explain the details of the carbon stable isotope graph we’re always shown (diet C v. animal C)
there is some variation within the dietary source species but not much between trophic levels (between the dietary source species)
most of them are close to the 1:1 line
‘you are what you eat’
Explain the details of the nitrogen isotope graph we’re always shown (diet N v. animal N)
vary a bit within dietary sources (species), but more variation between dietary sources =
more variation from the 1:1 line (most of them are above the line)
‘you are what you eat + more’
When you put the stable carbon and nitrogen isotopes together, what do you get?
a food web
with d13C on the x axis and d15N on the y axis
What does the atomic mass of an element represent?
the number of protons + neutrons (each one has mass = 1)
What does the atomic number of an element represent?
the number of protons (and same as number of electrons)
So, for 12C where atomic mass = 12 and atomic number = 6; how many protons, neutrons, and electrons are there?
atomic mass = 12
atomic number = 6
there are 6 protons and 6 electrons (atomic number)
and 6 neutrons (atomic mass - atomic number)
What is an isotope?
an element with the same number of protons and electrons but different number of NEUTRONS
What number of neutrons do 13C and 14C have?
13C has: 13-6 protons = 7 Neutrons
14C has: 14-6 protons = 8 neutrons
What does it mean for an isotope to be stable?
it means the element does not decay over time, it is stable
What does it mean for an isotope to be radioactive?
it decays overtime as its nucleus changes, it is not stable
How do isotopes behave?
heavier isotopes chemically behave like carbon, but physically behave different
How are isotopes ‘hidden’ in the periodic table?
‘iso’ = same
‘topos’ = place
found in the same place
ie., isotopes are hidden in the periodic table because it is organized by atomic number (number of protons) and isotopes have the same atomic numbers/number of protons
What are nuclides?
isotopes
How is the chart of nuclides (isotopes) arranged?
rows are by element (same element across) = number of protons
columns are by the number of neutrons (increasing order)
each row represents a list of isotopes
each column represents a list of isotones (different protons but same neutron numbers)
on a diagonal to the left = isobars (different elements with same atomic mass)
on a diagonal to the right = isodiapher (difference between stable isotopes is the same)
What predicts whether an isotope will be stable or radioactive?
how different the number of neutrons and number of protons are
the more different neutrons and protons are = the more likely to be radioactive
What is the ratio of neutrons/protons for radioactive elements ?
neutrons/protons > or = 1.5
so for example, C and 13C and 14C
13C: 6 protons and 7 neutrons = difference of 1 < 1.5 = stable
14C: 6 protons and 8 neutrons = difference of 2 > 1.5 = radioactive
What 5 major elements have stable isotopes used in ecology? what are they?
- carbon - d13C
- nitrogen - d15N
- Sulfur - d34S
- hydrogen (deuterium) - dD
- oxygen - d18O
plus other trace elements like silicon and iron
Which isotope of carbon is most naturally abundant?
12C
Which isotope of nitrogen is most naturally abundant?
14N
what do the most naturally abundant isotopes of carbon and nitrogen (and others) have in common?
these are the balanced elements - where the number of protons = number of neutrons (= number of electrons)
What 3 ways can ecologists represent the relative distribution of heavy: light isotopes in a sample?
- fraction (atomic percent) = % heavy isotope in a sample (F or AP)
- ratio = heavy: light in a sample (R)
- delta = most common ; a ratio of ratios
What is the equation for delta?
[(Rsample / Rstandard) - 1] x 1000
where R = ratio of heavy to light isotopes (ex. 15N/14N)
Calculate the AP(F), R and delta for the following sample:
sample 1 has 0.38 15N atoms for every 99.62 14N
