PARENT SESSION
Monday, August 7, 8:00-11:30 am
COS 2 - Population dynamics I: plants
Chickasaw, Mezzanine Level, Cook Convention Center
Presiders: K Klemow

What do survivorship curves tell us about senescence in plants?

Spindler, Lori^*,1, Casper, Brenda¹, ¹ University of Pennsylvania, Philadelphia, PA

ABSTRACT- It is not known whether senescence is a general feature in the life cycle of annual and perennial plants. One way to approach this problem is to examine survivorship curves from studies where plants of known ages are individually marked and followed throughout their entire lifespan. Age-specific survivorship rates can increase, decrease or remain constant, but only those that decrease with age provide evidence for senescence. Using this criterion, it is clearly apparent that annual plants are the only group that consistently shows senescence. Herbaceous perennials are much more likely to have constant or increasing survivorship with age, but few studies are available for long-lived species. This result can be explained by the different morphological and physiological properties possessed by the two types of plants. Recently, many survivorship curves have been constructed with data generated by population projection matrices that use size as a proxy for age. There are several assumptions which must be taken into account when interpreting these curves and one that may not always be valid is that size increases with age. If plants shrink with age, then data on the oldest age classes will be lost since it will be pooled with that of younger, but similarly sized plants. Survivorship curves are an excellent way to visualize age-specific survival and an easy way of comparing dynamics between populations or species as long as the underlying assumptions used in constructing the curves are understood.

Key words: survivorship curves, senescence, annual and perennial plants