THE INFLUENCE OF CLONALITY ON DEMOGRAPHY: PATTERNS IN EXPECTED LONGEVITY AND SURVIVORSHIP

Abstract

Although clonal organisms dominate many habitats, relatively little is known about their demography in comparison to the more familiar unitary species commonly studied by ecologists. While studies of the population dynamics of clonal species are becoming more common, and methods have recently been developed to examine their demography in more detail, there have been few attempts to calculate such parameters as survivorship and expected remaining life-span (ERL) of ramets for these species. I use published stage-class transition probability matrices to compare the demography of clonal and aclonal species. Clonal species tend to have an increase in their ERL as they increase in size, whereas most aclonal species have a peak in ERL at intermediate sizes which decreases for larger individuals. These patterns indicate that, while aclonal species tend to experience senescence, it is less common for clonal species even at the ramet level. Patterns in genet survivorship are less distinct, with type III survivorship predominating for clonal species, but also being common for aclonal species. Many aclonal species have a “mixed” survivorship curve, which starts out as type III, but becomes type I later in life, indicating high juvenile mortality followed by low adult mortality and eventually senescence. In general, type III survivorship was associated with an increasing ERL, type II with a constant ERL, and mixed with a peaked ERL. The only species with a typical type I survivorship curve was aclonal and had a mixed ERL, first decreasing and then reaching a peak before declining again.