Various explanations for hunter-gatherer mobility have been offered, for
example, that it is an attribute of the interplay between social-political concerns
and ecological constraints. There is no need to review the classical debates here (for
which, see Kelly 1995). For Southeast Asia, mobility is often linked to rainforest
characteristics. Given that the rainforest has a great diversity of resources but few
numbers of any species in a given location, the most effective subsistence strategy
is broad-spectrum foraging. This in turn requires hunter-gatherers to move widely
over a large area, traveling to resources rather than to bring them back to a central
place (Hutterer 1988). For Batek, there were clear ecological reasons for some of
the group movements, such as the search for widely scattered forest products and
fruits, but for individuals the most commonly given reason for leaving one camp
group and joining another was to reunite with friends and relatives. In line with
the overall opportunism (see below), once individuals joined a group, they would
participate in whatever activity was most common there. For example, people who
spent most of their time collecting forest products would switch to making crafts
for national park tourists when they joined their relatives in tourism camps. When
they moved on, they would switch activities again.