Summary

1. A systems model of the socioecology of extant gelada is used to predict maximum group sizes for populations of extinct theropiths living under various climatic conditions.

2. Under present climatic conditions, poor nutritional quality of the graze at low and high altitudes restricts the extant gelada to habitats lying between 1500–4000 m in altitude, but higher latitudes or lower global temperatures would make the colonization of lower altitudes possible.

3. The theropiths of the Plio-Pleistocene were not large enough to be able to exploit poorer quality vegetation at lower altitudes; consequently, they must have had an even more restricted distribution than the extant gelada.

4. The largest theropiths of the later Pleistocene could only have survived in the localities where they are known to have occurred if ambient temperatures were at least 6°C cooler than at present or graze quality was at least three times greater than is the case in modern grassland habitats; this suggests that they were restricted to the immediate vicinity of permanent water and thus that they would have been particularly vulnerable to extinction.

5. The analyses suggest that the largest species could not have lived in groups as large as those of contemporary gelada; nor could they have grown much larger in body size than they did.

Introduction

In this chapter, I use a model of the behavioural ecology of the extant gelada (Theropithecus gelada) to explore the likely constraints acting on the ecology the extinct congeners of this species.