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TL PhD Comprehensive Exam
  • Introduction
  • Tasklist
  • 1. Basics
    • 1.1 Basic Biology Review
    • 1.2 Basic Genetics Review
    • 1.3 Light & Photosynthesis
  • 2. Coral Biology
    • 2.1 Basic Coral Biology
      • 2.1a Food Webs
    • 2.2 Reef Structure
    • 2.3 Growth & Reproduction
    • 2.4 Morphology
    • 2.5 Physiology
    • 2.6 Mixotrophy & Energy
    • 2.7 Symbiosis
    • 2.8 Reef Mortality
      • 2.8a Conservation
  • 3. Ecology & Evolution
    • 3.1 Evolution & Plasticity
    • 3.2 General Ecology
    • 3.3 Species
    • 3.4 Cryptic Species
  • 4. Isotopes
    • 4.1 Isotope Basics
      • 4.1a Instrumentation & methodology
      • 4.1b Environmental O & H
      • 4.1c Environmental C and N
      • 4.1d Organismal Isotopes
    • 4.2 Fractionation in Corals
    • 4.3 Trophic Niche Analysis
    • 4.4 CSIA
      • 4.4a C: Essential vs. Nonessential
      • 4.4b N: Trophic vs. Source
  • 5. Other
    • 5.1 Science & Society
    • 5.2 Stats
  • 6. Summary & Resources
    • 6.1 Glossary
    • 6.2 Resources
    • 6.3 Questions From Exam
    • 6.4 Recommendations & Reflections
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  1. 4. Isotopes
  2. 4.4 CSIA

4.4b N: Trophic vs. Source

16

Last updated 1 year ago

Trophic amino acids

  • heavily fractionating

  • glutamic acid

  • commonly undergo transamination

Source amino acids

  • minimally fractionating - not zero fractionation

  • phenylalanine

  • commonly undergo hydroxylation

  • show the baseline

Trophic position = trophic - source = Glu - Phe

  • same source with different trophic means variation in diet

  • same trophic position/difference between trophic & source means baseline variability

TDF

  • measured TDF glu-phe values are consistently lower than expected

    • diet quality - amino acid imbalance with low diet quality leads to more de novo biosynthesis -> increased Glu transamination = higher TDF

      • In carnivores: higher protein content = higher excretion rate = higher TDF

      • In Herbivores: lower protein content = lower excretion rate = lower TDF

    • Waste type - ammonia producers have higher TDFs than urea/uric acid producers

    • This change can be included in trophic position models by using multiple TDFs as you move up the food chain

  • Basically the same things as TEF except for the rationale behind the word choice (Kelton prefers TEF)

Beta

  • β = δ15NGlu - δ15NPhe in 1° producers

  • vascularization drives beta values (not habitat or mode of photosynthesis)

  • Phe is the main precursor to many secondary compounds in plants, including lignin

  • non vascular plants have higher beta value than vascular

Microbial N

  • Microbial N metabolism is highly complex

  • mixotrophic organisms

  • Microbes have a very low & highly variable TDF

SumV

  • degree of microbial working of organic matter