Researchers examined several species of monkey teeth in order to determine the microwear patterns produced by a variety of different diets. They then turned their attention to the teeth of Australopithecus africanus and A. robustus:
The new study by Ungar, Brown, and colleagues suggests that, on average, A. africanus probably ate a greater share of soft and tough foods than P. robustus, which probably ate more hard and brittle foods.
The researchers found, however, that there was substantial overlap between the two species in their dental microwear, and presumably, in their diets.
Both species would probably have preferred to eat easy-to-consume, energy-rich foods, such as fruits, when they were available.
A similar phenomenon can be seen in modern chimpanzees and gorillas that live in the same geographical area. These so-called sympatric animals share food resources much of the year, but differ mostly during times of food scarcity.
At these times, gorillas fall back on tougher foods, such as leaves and stems, because their teeth and guts allow them to do so.
This study tends to confirm the idea that A. africanus and A. robustus were specializing in different diets - although not to the extent one would have thought. Seems like a good example of the competitive exclusion principle.