Sex-linked Niche Differentiation in Two Species of Thalictrum

The possibility that staminate (male) and pistillate (female) individuals of Thalictrum dioicum and Thalictrum polygamum occupy different niches and thereby par- tition potentially limiting resources was investigated. Data on spatial segregation be- tween sexes and comparison of microsite quality, nutrient uptake, photosynthetic responses and survivorship for male and female plants were used to assess niche dif- ferentiation. Spatial segregation occurred in some populations but could be attributed to the effects of vegetative reproduction. Differences between the sexes in microsite quality and nutrient uptake were indicated but need to be further substantiated. No significant differences in photosynthetic responses between sexes were observed. Sur- vivorship data indicate that females may be more stress-tolerant than males. None of the intersex differences is striking, which suggests that factors other than male-female resource partitioning were more important as the impetus for the evolution of dioecy in these plants.