Seed demography

Abstract

"Some seeds fell by the way side, … some fell upon stony places,... and some fell among thorns;.... but other fell into good ground" (The Bible, St. Matthew's gospel, Chapt. 13).Much of modern plant ecology is concerned with demography. One major topic is the study of mortality rates. A common belief, originating with Charles Darwin's Origin of Species is that the seedling stage of the plant's life cycle exhibits the highest mortality rates. Evidence is provided in this paper to show that the highest rates of mortality for many species occur at the seed stage. The major causes of mortality associated with five major functions served by seeds are discussed. These functions enable the population to (i) invade new areas, (ii) occupy all possible microsites within a habitat, (iii) survive unfavorable periods, (iv) avoid predators and pathogens, and (v) recruit new genotypes which will be more successful in growth, survival, and reproduction than their predecessors. Seed mortality, somewhat paradoxically, has an integral role in each of these functions. The discussion includes a consideration of mortality at all stages of the seed's life history from formation through to germination.