According to this paper, there is. See this post for a brief analysis.
Following the trend might be the most rational decision to do to get a job. It takes some irrationality and some extra passion to do the dissertation research on a topic that is not hot. But if there is a very serious commitment by the student chances are she will also get an academic job.
Demand for hot topics drive researchers as well, for the most part.
This is the best paper I know that motivates scholars to adventure themselves into foreign areas.