Does Landscape Fragmentation Influence Sex Ratio of Dioecious Plants? A Case Study of Pistacia chinensis in the Thousand-Island Lake Region of China

Abstract

The Thousand-Island Lake region in Zhejiang Province, China is a highly fragmented landscape with a clear point-in-time of fragmentation as a result of flooding to form the reservoir. Islands in the artificial lake were surveyed to examine how population sex ratio of a dioecious plant specie Pistacia chinensis B. was affected by landscape fragmentation. A natural population on the mainland near the lake was also surveyed for comparison. Population size, sex ratio and diameter at breast height (DBH) of individuals were measured over 2 years. More than 1,500 individuals, distributed in 31 populations, were studied. Soil nitrogen in the different populations was measured to identify the relationship between sex ratio and micro-environmental conditions. In accordance with the results of many other reports on biased sex ratio in relation to environmental gradient, we found that poor soil nitrogen areas fostered male-biased populations. In addition, the degree of sex ratio bias increased with decreasing population size and population connectivity. The biased sex ratios were only found in younger individuals (less than 50 years old) in small populations, while a stable 1∶1 sex ratio was found in the large population on the mainland. We concluded that the effects of landscape fragmentation on the dioecious population sex ratio were mainly achieved in relation to changing soil nitrogen conditions in patches and pollen limitation within and among populations. Large populations could maintain a more suitable environment in terms of nutrient conditions and pollen flow, subsequently maintaining a stable sex ratio in dioecious plant populations. Both micro-environmental factors and spatial structure should be considered in fragmented landscape for the conservation of dioecious plant species.

Biodiversity, Species Interactions and Ecological Networks in a Fragmented World

“…Characteristics of breeding systems, for example, the degree of protandry, self-incompatibility or sex ratios, might be affected by fragmentation Jennersten (1988), Yu and Lu (2011) Growth form Specific growth forms (e.g. clonal plants) might be more strongly affected than others (e.g.…”

Population size, sex-ratio and sexual dimorphism in <em>Fuchsia parviflora</em> (Onagraceae) an endemic dioecious shrub

“…Unfortunately, we could not estimate fruit production in some of the smaller populations. Yu & Lu (2011) found that small populations of the dioecious Pistacia chinensis had a male-biased sex ratio, compared with larger, nonfragmented populations. They found that male-biased populations were established in soils with low nitrogen availability and they concluded that fragmentation affects soil nitrogen conditions at the microhabitat scale.…”

“…The fact that sex ratio did not vary along the flowering season gives us more confidence on our sex ratio estimations. Few studies have reported the effect of population size on sex ratios (Soldaat et al 1997, Somanathan & Borges 2000, Yu & Lu 2011. If most individuals in a small population are males this may reduce the chances of fruit production and therefore the viability of populations.…”

“…Fragmentation may reduce population sizes and consequently may affect pollen flow (Rosas et al 2011), reproductive success and finally the viability of populations (Murren 2002, Leimu et al 2006. Fragmentation may especially affect biotic pollinated, endemic dioecious species, and it is thus essential to assess their population sizes and sex ratios (Leo et al 1997, Yu & Lu 2011. A recent review on dioecious species, found that sex-ratio deviates from equality in half of the studied species being male-biased almost twice as common as female-biased (Field et al 2013).…”

Reproductive allocation of two dioecious Rhamnus species in temperate forests of northeast China

“…The sex ratio is affected at germination by sex-linked genes (Shelton 2010), pollination intensity (Field et al 2012) and soil nitrogen (Yu & Lu 2011). Sex ratios are affected by other factors as well, e.g., sexually different mortality rates (Stehlik & Barrett 2005).…”