Tracing the Source of the Elephant And Hippopotamus Ivory from ...

22‰ to -38‰ (average -26‰). Compared to C3 plants, C4 plants have a reduced
discrimination against 13 C isotopes, and consequently have values that range from -9‰ to
-21‰ (average -12.5‰) (Tykot and Staller 2002; Larsen 1997: 271; Sukumar and
Ramesh 1992).
Notice these values do not overlap, thereupon making it possible to differentiate
between animal diets based solely on either type of plant. C4 plants have δ 13 C values that
are on average about 14‰ less negative than C3 plants. Different carbon isotope ratios
may occur between plants of the same species due to differences in 1) atmospheric CO2 in
forested and high altitude areas, and 2) latitude, which will affect the amount of sunlight
and therefore the efficiency of photosynthesis. Moreover, carbon isotope ratios will
differ within the plant from one part to another. Considering that most animals eat a
variety of plants, these intra-species and intra-plant differences in carbon isotope ratios
are of little concern when reconstructing diets since the analysis is aimed at a larger scale,
that is, the relative contribution of C3 versus C4 plants to the diet (Larsen 1997: 271).
An additional consideration, however, is the CAM photosynthetic pathway. This
pathway is designed in such a way as to allow the plant to switch between a C3 or C4
pathway depending on the environmental conditions, and CAM plants (cacti and other
succulents) have δ 13 C values intermediate between and overlapping those of C3 and C4
plants. Marine plants also have δ 13 C values between and overlapping those of C3 and C4
plants (Larsen 1997: 272; Tykot and Staller 2002).
The isotopic signature of the plants are passed on to herbivores, after a trophic
shift due to fractionation by metabolic processes (van der Merwe et al. 1988: 165).
Generally the trophic level shift is around 5‰ from plant to the collagen of the animal
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