INTRODUCTION

So far we have dealt with how plant systems work to promote, sustain, and preserve life. But what do we know about the processes leading to decline and death in plants?

We tend to imagine death as a process that begins at birth and progresses to an end, sometime. “Lifespan” is the maximum length of time an organism could live if all the conditions of life were at their most favorable; the human lifespan, for example, is about 120 years, but most of us do not expect to be around that long. “Life expectancy” more closely describes the reality. The question is not “How long could I live?” but rather, “How long can I expect to live?” which is dependent on prevailing environmental, social, and cultural conditions. In some parts of the world, human life expectancy may be only 30 or 40 years, about the same as it was some 2500 years ago at the height of ancient Greek culture, whereas in others we know it to be over 80 years. Disease, starvation, predation, accident, and polluted environments are just some of the hazards faced by all living things which affect how long they survive.

LIFE HISTORY STRATEGIES

All species share one basic aim in life: the survival of at least some individuals to reproductive age is crucial to the passing on of genetic traits to descendants. What is important is the different strategies living things have evolved to achieve this fundamental aim.