Record Details

Werner, Dagmar I
Reproduction in the iguana Conolophus subcristatus on Fernandina Island, Galapagos: clutch size and migration costs
American Naturalist
Journal Article
Conolophus subcristatus
The concept of reproductive effort has received increasing attention since it was first formulated by Fisher (1930). Reproductive effort can loosely be defined as an organism's investment in any current act of reproduction (Fisher 1930; Pianka 1976). For females, reproductive effort is essentially synonymous with parental investment which is "any investment by the parent in an individual offspring that increases the offspring's chances of surviving (and hence reproductive success) at the cost of the parent's ability to invest into other offspring" (Trivers 1972, p. 55). Both definitions imply the importance of insight into the competing demands of an organism (such as maintenance, growth, and reproduction) as characteristics of life history patterns. Within a given environment the commitment of a given amount of energy to each of the demands should be balanced so that the probability of producing surviving offspring is maximized. Williams (1966) proposed that the ratio of clutch weight to female weight can be used to approximate reproductive effort. Subsequent work, however, showed that important parameters concerning life history evolution had not yet been recognized or measured, and that the clutch weight to female weight ratio is a poor or only partial indicator of reproductive effort in lizards (Tinkle and Hadley 1975; Hirshfield and Tinkle 1975). The same authors and Pianka (1976) have discussed the difficulties in exactly defining and quantifying reproductive effort, concluding that it is unlikely that these difficulties will ever be overcome. I think it is at least as relevant to determine ratios of effort (energy) invested into competing demands as to quantify absolute values, as has been pointed out by Stearns (1976). This approach was used in the present field study. The research on Conolophus was undertaken as a long-term study to gain insight into the wide spectrum of adaptations of the population to a most peculiar environment, Fernandina Island in the Galapagos. Here I will present data on reproductive effort in females. The findings will be discussed on the basis of current life history theories (see Stearns 1976 for review) and compared with results from other lizards, especially the iguanine group. Adaptations to the peculiarities of the island will be emphasized.