Sex ratio and gender-dependent neighboring effects in Podocarpus nagi, a dioecious tree

Abstract

We analyzed sex ratio, growth rates, and spacing among individuals of Podocarpus nagi, a dioecious tree, on Mt. Mikasa, Nara City, Japan. The sex ratio of reproductive trees ‡ 5 cm in stem diameter at breast height (dbh, 130 cm above ground level) was significantly male-biased. The sex ratio was male-biased in the < 20 cm and ‡ 50 cm size classes, while it did not depart from 1:1 in the 20 £ dbh < 50 cm class. Growth rate varied with tree size in males but not in females. The precocity and vigor of males suggests that differences in reproductive costs between sexes induce the biased sex ratio. Random labeling tests on the positions of reproductive trees showed that in the < 30 cm class, males and females were distributed randomly and independently from each other. In the ‡ 30 cm class, males were significantly clumped, whereas females were randomly distributed. Males and females showed significant repulsion, i.e., a spatial segregation of sexes. Both intra-and intersexual effects on the growth rate of crowding by neighbors were significant for females, but not for males. Maximum competitive interference was observed at a distance of 5 m, which corresponded approximately to the radius of clumps of large males and to the significant repulsive distance between large males and females. These results suggest that sexual differences in sensitivity to local crowding are related to the formation of gender-dependent spatial patterns. Formation of female-repulsive male clumps and a male-biased sex ratio may intensify the decreased probability of regeneration near males, as suggested by the limited seed-dispersal range of this species, thereby promoting coexistence with other species.

Araucaria angustifolia grafting: techniques, environments and origin of propagation material

“…It is assumed that females allocate more resources for reproduction than males do, generating an asymmetry between sexes. This is a result of differences in distribution of resources for growth and reproduction of these individuals, also including differences in photosynthetic activity and transpiration rate Bliss 1993, Dawson andEhleringer 1993), making female gender most sensitive to environmental conditions (Dawson et al 2004, Nanami et al 2005, Iszkuło et al 2008, Rozas et al 2009). …”

Sex ratio and spatial distribution of male and female Antennaria dioica (Asteraceae) plants

“…In addition, this segregation could be a consequence of intrasexual competition. For example, Nanami et al 2005 reported females in Podocarpus nagi (Podocarpaceae) were more sensitive to the presence of neighbours because of higher reproductive costs than males.…”

Spatial distribution patterns of old-growth forest of dioecious tree Torreya nucifera in rocky Gotjawal terrain of Jeju Island, South Korea

“…Several studies in recent years have also emphasized the effects of both biotic and abiotic conditions on plant spatial patterns. For example, old trees tend to be randomly distributed as a result of stochastic mortality and intra-or interspecific competition for resources (Nanami et al 2005). Dying seedlings under large trees are frequently found in Torreya Forest.…”

“…Reproductive costs are age-specific and reproductive investment is variable during lifespan of plants (Silvertown and Dodd 1999;Montesinos et al 2006). Nanami et al (2005) have reported that dioecious individuals tend to shift from clumped distribution to random distribution as tree size increases due to density-dependent mortality caused by intraspecific competition. Therefore, interactions between sex and size in dioecious species should be considered in spatial structure study of dioecious population.…”