RESOURCE PARTITIONING BY 3 SPECIES OF NEWTS DURING THEIR AQUATIC PHASE

This paper describes the multidimensional niche of syntopic smooth newts Triturus vulgaris, alpine newts Triturus alpestris, and Italian crested newts Triturus carnifex, which constitute a complex community of eight components (the three species and their larvae, plus juvenile and neotenic alpine newts). All the potentially limiting resources (seasonal time, diel time, habitat and food) are analyzed as single niche dimensions, and then the real multidimensional niche is calculated. Resource states are objectively defined, using an algorithm that groups the significant resource categories. The larvae were segregated by prey, season, habitat, and water depth, in order of decreasing importance; their overlap was very low when their complete multidimensional niche was considered, and therefore they have few opportunities for present-day competition. The adults were largely segregated by season and water depth, and to a lesser degree by habitat and prey; their multidimensional niches overlapped to a certain degree, thus leaving conditions for ongoing competition. Considering all the species and the life stages together, the order of importance for segregation was season, prey, habitat, water depth and diel activity, with a low overlap in the complete niche. Differences in prey size were probably due to morphological constraints; differences in diel activity had very little effect on segregation, except in separating larvae from the adults, and were likely promoted by need to avoid mutual predation and cannibalism. It remains to be tested whether seasonal, habitat, and water depth differences are due to competitive pressures or to ecophysiological constraints.