Gradients of life-history variation:: an intercontinental comparison of fishes

Multivariate analysis identified a two-dimensional continuum of life-history variation among 301 fish species from Europe, North America, South America and the Atlantic and Pacific coasts of North America. The first axis was associated with larger body size, higher fecundity, delayed maturation, fewer reproductive events, and shorter breeding season on one end and small size, low fecundity, early maturity, multiple reproductive events per year, and prolonged breeding season on the other. The second axis contrasted fishes having larger eggs and more parental care against fishes with the opposite suite of traits. Phylogenetic affiliations of species were apparent in the general patterns of ordination of species within orders, indicating evolutionary divergences in life-history patterns. In fact, partitioning the variance of life-history traits showed that taxonomic order and latitude were the most important factors and geographic region and habitat the least. Despite phylogenetic constraints, basic life-history patterns showed consistency between distantly geographical regions, latitudinal ranges and basic adult habitats, indicating convergences in life-history patterns. Although the basic life-history patterns seemed repeatable among distantly related taxa, geographical and latitudinal affiliations were apparent. Species from South America are skewed toward the opportunistic endpoint, whereas North American marine species are skewed toward the periodic endpoint of the trilateral continuum model. Most of the fish species from South American data set came from fluctuating environments, so an opportunistic strategy of early maturation and continuous spawning permits efficient recolonization of habitats over small spatial scales. In contrast, most species in the North American and European data sets came from seasonal habitats that are nonetheless more hydrological stable, so a periodic strategy of delaying maturation to attain large clutches enhances adult survivorship during suboptimal environmental conditions and recruitment when early life stages encounter suitable environmental conditions. Similarly, latitudinal affiliations were also observed: opportunistic strategists more common in tropical latitudes and periodic strategists more common in temperate and Arctic latitudes.