Ontogenetic niche shifts and their implications for recruitment in three clonalVacciniumshrubs:Vaccinium myrtillus,Vaccinium vitis-idaea, andVaccinium oxycoccos

Abstract

Ontogenetic niche shifts, i.e., changes in niche breadth and (or) position during the life of individuals, have received rather limited attention in plant ecology. An experiment was designed to assess ontogenetic niche shifts in three clonal Vaccinium shrubs in order to examine their recruitment behavior. Seeds were sown, and juveniles transplanted, at sites along a gradient of changing occurrence of the three species. Recruitment was seed limited, varied among sites, and was correlated with juvenile survivorship. No niche shift occurred during seed to seedling stages for any of the plants. For Vaccinium myrtillus L., recruitment was not related to adult occurrence, whereas for Vaccinium oxycoccos L., recruitment was highest at the site where adults dominated. However, for both of these species, recruitment also occurred outside the range of adult occurrence. Vaccinium vitis-idaea L. exhibited a negative relationship between adult occurrence and recruitment and between adult occurrence and juvenile survivorship, indicating an ontogenetic niche shift. For V. myrtillus the results suggested an uncoupling of niche requirements of juvenile and adult stages, whereas for V. oxycoccos the results suggested a niche contraction towards the requirements for adults. Thus, the form of ontogenetic niche shifts differs among the species. These differences in niche shifts contribute to understanding dispersal and recruitment behavior of the species.Key words: clonal plants, dispersal, niche shifts, recruitment.