Introduction

Tropical alpine environments impose unique selection pressures on plants, producing a number of special adaptations. Among these are caulescent and acaulescent rosettes, nyctinasty, semelparity, and resistance to nightly frost. For each of these adaptations there are a number of possible evolutionary explanations. To discriminate between among explanations, and to understand better tropical alpine environments in general, integrated long-term studies of particular species are necessary. Such studies include morphology, ecological physiology, demography and reproductive biology. Long-term population biology studies of tropical alpine plants are rare; most are presented in this volume. These studies are helping us to understand the nature of adaptation in tropical alpine environments.

Giant rosette plants make ideal research subjects for a number of reasons. They are conspicuous and characteristic members of virtually all tropical alpine communities. Their morphologically discrete form makes their growth and individual dynamics easy to quantify. Lastly, they are relatively long-lived, enabling us to examine the effects of long-term changes in local environment.

Since 1977, I have been studying two closely related giant rosette species on Mount Kenya, Lobelia telekii and L. keniensis. I present here a summary of the first 7 years of that study, concentrating on the comparative population biology of these two species.

A number of factors make Mount Kenya lobelias particularly attractive as research subjects. (i) The alpine environment of Mount Kenya is one of the most intensively studied ecosystems in the tropics (Hedberg 1957, 1964; Coe 1967; Coe & Foster 1972; Young & Peacock 1985; Young 1990a).