I have seen in several publications on paleoecology that the C3/C4 diet, inferred by carbon isotopes, is treated as exactly the same as the difference between browsing and grazing. Nevertheless it appears that the non tropical grasses use mostly the C3 pathway and tropical grasses use more the C4 pathway.
So my questions are: Does a C4 diet mean necessarily predominantly grazing behaviour? And is C3 diet clearly browsing or could it be both?
Hey Charalambos, check the following link in RG. I quote some parts that are relevant to your question:
" Following the shift in photosynthesis in tropical grasses around 7 Ma, from a
C3 carbon cycle to a C4 carbon cycle, the dental enamel of tropical grazers contains
a different composition of enamel isotope from that of browsers, and mixed feeders
have intermediate values between browsers and grazers. While dental isotopes are
only applicable in the rather limited case of fairly recent ungulates (i.e., within the
past 7 Ma or so) in tropical or subtropical settings, they can be extremely useful in
such palaeoecological situations, especially in combination with morphological
features (e.g., Sponheimer et al. 1999)."
"Around 8 Ma, there was a shift in grass photosynthetic biochemistry from the C3 cycle to the C4 cycle in lower latitudes in North America and Asia (Cerling et al. 1993, 1997). It has been claimed that this event had a significant impact on the grazing mammals: a greater diversity of hypsodont artiodactyls, including bovids, appeared in Pakistan at thistime while brachydont taxa such as suids and giraffids declined (Barry et al. 1995),
but there was little overall impact on the hypsodonty levels of ungulates in North
America (Janis et al. 2000)."
Make sure to check the references therein, as there is a large literature in the topic.
Chapter An Evolutionary History of Browsing and Grazing Ungulates
A C4 diet indicates grasing, but only in the tropics. In the tropics many grasses, especially the savannah grasses, use the C4 pathway, while all trees use C3. However, outside the tropics most grasses also uses C3. For instance, the cows in Europe eat C3 grasses.
Hi! I will give my point of view on that interesting topic (note that my research is focused on Africa).
As already mentioned, there is a HUGE literature on the complicated task of interpreting stable carbon isotopic data in terms of vegetation and diets.
That is true that C3 grasses are pretty rare in modern tropical low-altitude environments in Africa (but not totally absent), and that most grasses in those environments are C4 grasses. Therefore, the C3/C4 dichotomy is usually interpreted as a browser/grazer dichotomy, and that should work well most of times in modern environments (not every time).
But the situation is much less clear in the fossil record. For many years, researchers have assumed that C3 grasses were present in negligible proportions starting from the Miocene and the spread of C4 grasses. However, recent paleobotanic publications, notably on phytoliths from Laetoli and Olduvai sites, seem to indicate that C3 grasses were present in non-negligible proportions. That complicates a lot the interpretation of enamel d13C values that are dominated by C3 plants: the animal could have eaten C3 browse, C3 grasses, or a combination of both. Unfortunately, most recent studies just totally ignore this complicating factor and still assume that C3 grasses are not worth considering when interpreting stable carbon isotopic data in past landscapes of tropical environments.
Cheers!
Antoine
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