Reproductive strategies in waterfowl: the effect of ultimate enviromental factors, size and phylogeny

Abstract

Using data extracted from the literature, I studied the world's waterfowl species (142 species from the total of 149) in order to reveal the ultimate factors contributing to the evolution of their reproductive strategies . As the differences between species reflect not only optimal adaptations to the environment, but also phylogenetic relationships or differences in size, special care was given to separate the effects of ecological factors from those due to size and phylogeny. Body weight scaled allometrically to all traits studied. Increased body size was accompanied by decreasing clutch size and an increasing trend in all other dependent variables. When reproductive traits were adjusted for the effect of weight, a rapid rate of development in the young accompanied northern distribution and ground-nesting habits. Largeeggs were combined with young that were at an advanced stage at hatching. In general, late age at maturity and decreasing nest concealment were associated with small clutches,butthereasonsforevolving asmallclutch didnotseem to be the same in different species. Using principal component analysis, the factors influencing reproductive traits were grouped into three main components, interpreted as size, geography and tribe . Together these explained 84-95% of the variation in other traits, but only 55% of the clutch size variation. Thus given the size, distribution and phylogeny of a waterfowl species, its reproductive strategy is determined to a great extent. Away to change reproductive strategy, therefore, is to change body size . Further adaptation can be achieved by modifying clutch size, as it is the trait least determined by the three main factors .