Sex ratio and spatial pattern of males and females in the dioecious sandhill shrub, Ceratiola ericoides ericoides (Empetraceae) Michx

Abstract

Sex ratio, size, age, and spatial pattern were investigated for males and females of the dioecious shrub Ceratiola ericoides ericoides (Empetraceae) Michx. within seven mapped populations in Georgia and South Carolina, USA. Among the sites studied, two are regularly burned and one site long-unburned. Age was estimated from node counts of individual shrubs. Only one (fire-suppressed) population showed a female-biased sex ratio, while all others did not differ significantly from 1:1. Mean age estimates did not differ between sexes at any site nor did mean shrub canopy diameter. Bivariate Ripley's K analysis with a null hypothesis of random labeling was used to investigate whether any of the mapped populations exhibited spatial segregation of the sexes (SSS). No population showed strong evidence of SSS. Rather all sites but one showed males and females to be associated (though not significantly) at a scale of 1-10 m. At a scale of 10-35 m male and female shrubs were located randomly with respect to one another at all sites.

Sex ratios and spatial structure of the dioecious tree Torreya nucifera in Jeju Island, Korea

“…However, in this study, we did not find a significant pattern of spatial structure, similar to other more recent studies (Ueno et al 2007, Schmidt 2008, Gao et al 2009, Forero-Montaña et al 2010). Male and female T. nucifera were distributed randomly in all quadrats except D, in which a weak pattern of female clumping could be observed at a distance of r = 7 m. Nonetheless, we acknowledge that this study has limitations, largely due to the following reasons.…”

“…For example, female Acer negundo (Freeman et al 1976), Populus tremuloides (Grant and Mitton 1979), and Salix arctica (Dawson and Bliss 1989) are found in sites with a relatively greater amount of moisture. However, conflicting results for SSS have recently been documented in diverse plants (Osunkoya 1999, Ueno et al 2007, Schmidt 2008, Gao et al 2009, Forero-Montaña et al 2010. Due to the fact that the distance and distribution between male and female plants influences the level of outcrossing, and consequently seed production (Bawa and Opler 1977), SSS is one of the major components determining dioecious plants' fitness levels.…”

“…If the reproductive costs of male and female plants are equivalent, frequency-dependent selection should result in a 1:1 sex ratio (Fisher 1930). Mixed patterns have been reported, though malebiased sex ratios (Opler and Bawa 1978, Ornduff 1985, Sakai 1990, Allen and Antos 1993 are more common than female-biased ones (Crawford andBalfour 1990, Ueno et al 2007) or 1:1 sex ratios (Ortiz et al 1998, Schmidt 2008. Male-biased sex ratios are generally ascribed to the effects of higher reproductive costs of females than males.…”

Sex-different response in growth traits to resource heterogeneity explains male-biased sex ratio

“…However, SSS has been observed mostly in herbaceous plants (Bierzychudek and Eckhart, 1988;Eppley, 2005;Mercer and Eppley, 2010; but see Varga and Kyt€ oviita, 2011), but rarely in shrubs (Rocheleau and Houle, 2001;Schmidt, 2008;Hughes et al, 2010;Alvarez-Cansino et al, 2013) or in trees (Vasiliauskas and Aarssen, 1992;Nicotra, 1998). A few studies reported SSS for dioecious woody plants (Nanami et al, 2005;Nuñez et al, 2008;Zhang et al, 2010).…”

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

“…For example, female Acer negundo (Dawson and Ehleringer 1993), Juniperus virginiana (Lawton and Cothran 2000), and Salix glauca (Dudley 2006) are found on sites with relatively greater amounts of moisture. However, conflicting results relevant to SSS have recently been documented in several plant species (Ueno et al 2007, Schmidt 2008, Gao et al 2009, Forero-Montaña et al 2010Garbarino et al 2015).…”