Variation and covariation in life-history traits of sharks

Walsh, Stephen J. (1990) Variation and covariation in life-history traits of sharks. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (14MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

I used the comparative method to examine the interspecific variation of seven life-history traits across Euselachiians, the modern sharks, in relation to adult body size, phylogeny, mode of reproduction, and ecology. Life-history traits included adult female length, length at maturity, birth length, fecundity, gestation, age at maturity, and life span. Body size accounted for a significant amount of explained variation. Phylogenetic history (order, family, and genus) explained only a small amount of variation and covariation of these life-history traits. Genera within families and families within orders tended to show similar levels of variation in most life-history traits, but a larger proportion of the variance occurred at the family level of analysis. Principal component analysis on a reduced number of traits defined an axis ordering sharks from large fecund forms giving birth to many large offspring and small forms with low fecundity and small offspring. The analysis also defined a secondary gradient in which many small offspring versus few large offspring resulted in an inverse relationship between fecundity and birth length. Perception of these patterns of covariation fit r/K selection theory. Analysis within individual families revealed differences from family to family in distribution along the first principal component. Patterns of covariation at the family level appeared also to be constrained by mode of reproduction (oviparity vs viviparity strategies) interacting with size. There is some evidence to indicate that the patterns of covariation may be partitioned according to the mode of reproduction, with a separate axis defining each mode. Ecological associations appeared to have some effect on the evolution of life-history traits, independent of size and phylogeny. Dietetic and habitat differences were linked to the pattern of covariation of life-history traits. Birth length differences were associated with geographic distribution, and gestation differences were associated with inshore or offshore residency. The comparative method was useful in suggesting the kinds of attributes and ecological relationships that could be used in detailed comparisons of life-histories at the intraspecific level.

Actions (login required)

View Item