Effects of population size and structure on reproductive success of a Pistacia chinensis population

Abstract

The Thousand-Island Lake region, a highly fragmented landscape in Zhejiang Province, China, was selected as a natural laboratory to examine how the reproductive success of a Pistacia chinensis (Anacardiaceae) population was affected by population size and structure. Thirty local island populations and one large mainland population were studied. Pollen density during the flowering season differed significantly among four differently sized populations. The number of pollen grains on the female stigma was positively related to the size of the male population. The 100-seed weight and seed-setting rate of fruits were also significantly correlated with the size of the male population. These results indicated that pollen limitation caused by a reduction in the size of the male population in this fragmented landscape was the main factor that reduced the female reproductive success of the P. chinensis population. In the small population, artificial pollination resulted in significant increases in the 100-seed weight and the seed-setting rate compared with those of untreated individuals. However, artificial pollination did not significantly increase the 100-seed weight or seed-setting rate in the large population. Pollen limitation caused by a reduction in the size of male population was the main factor that reduced the female reproductive success of the P. chinensis population in this fragmented landscape. Thus, the size of populations is an important factor in developing conservation and protection strategies for dioecious plant species in fragmented habitats.