Life-history diversification in the Middle Danubian fish fauna - a conservation perspective
I evaluated the diversity of the life-history attributes of Middle Danubian fish species in relation to a trilateral life-history continuum model. Life-history strategies could be characterized for 70 species. Multivariate analysis identified a gradient in life-history variables from species having larger body size, delayed maturation, longer life span, larger fecundity and no marked parental care to species with the opposite suite of traits. A second gradient further delineated species based predominantly on egg size and the development of parental care. Diversity of life-history strategies tended to increase from headwater to large river habitats. A comparison of life-history attributes between native and exotic fishes showed that exotic species modify the general life-history diversification of the native fauna. Exotic species were rather small, performed relatively well developed parental care and laid a small number of large eggs (i. e. they displayed intermediate-equilibrium strategist features). Temporal changes in the patterns of life-history diversification (i. e. the rarity or disappearance of large bodied, highly fecund species with late maturation (i. e. periodic strategist sturgeons), and the invasion of the intermediate-equilibrium strategist exotic species) could be well associated with the alteration of the Middle Danubian hydrosystem. The present study supports the prediction that life-history variables can be useful in the monitoring and conservation management of running water habitats.