Spatial and temporal variations in mortality of the biennial plant, Lysimachia rubida: effects of intraspecific competition and environmental heterogeneity

Abstract

Summary 1We studied mortality, growth and spatial distribution of individuals of Lysimachia rubida to elucidate causes and consequences of temporal and spatial variations in mortality. This short-lived monocarpic biennial grows in open dry habitats on rocky coastal cliffs of the subtropical Bonin (Ogasawara) Islands, Japan. 2 All individuals of two successive cohorts that appeared in a 8 × 8-m quadrat were mapped, and their fate and size were recorded at 2-3 month intervals from March 1998 to July 2000. We analysed spatial and temporal changes in the relative importance of plant size, local densities of neighbouring plants and ground surface conditions to determine plant mortality. We also examined spatially non-random mortality and its spatial scales. 3 Patchy seed dispersal from scattered mother plants resulted in a clumped distribution of seedlings. During the growth cycle of L. rubida , we recognized two growth stages that differed in the relative importance of the factors affecting plant mortality. 4 At the earlier growth stage, after germination in March until July, mortality was caused mainly by local density. Smaller plants within areas of high local densities were more likely to die. The spatial patterns of surviving and dead plants tended to be regular and aggregated, respectively, in comparison with those expected from random mortality. The spatial scale of aggregation of the dead plants was 5-25 cm, corresponding to the distance of direct interactions between neighbours. 5 At the later growth stages, in October until May of the following year, mortality was affected mainly by ground surface conditions. Both surviving and dead plants were spatially aggregated at spatial scales of 20-100 cm. Plants tended to survive in microhabitats of smaller gravel, which had a greater water-holding capacity. 6 This study also showed the consequence of spatial variations in mortality on population structures of L. rubida . Patchy seed dispersal and subsequent temporal and spatial variations in mortality are likely to contribute to the scattered distribution of L. rubida individuals observed at the study site.

Effect of temporal variation in precipitation on the demography of four herbaceous populations in a tropical dry forest area in Northeastern Brazil

“…In the present study, the birth rates recorded for the four populations during the rainy season, followed the pattern found for several vegetation types in Brazil and in the world. Water shortage is the main factor responsible for the mortality of herbaceous plants in dry (Mondragón et al, 2004;Volis et al, 2004;Nippert et al, 2006;Silva et al, 2008) and humid (Zotz, 1998;Castellani et al, 2001;Nordbakken et al, 2004;Vilà, Bartolomeus, Gimeno, Traveset, & Moragues, 2006) forest areas during dry seasons; however, herbivory (Maron, & Crone, 2006;Gotelli, 2007), intraspecific competition (Suzuki, Kudoh, & Kachi, 2003;Volis et al, 2004) and interspecific competition (Miller & Duncan, 2003;Nordbakken et al, 2004;Thomson, 2005) have been identified as the main causes of mortality during the rainy season.…”

Influencia de microhábitats en el desempeño de especies herbáceas en áreas de bosque maduro y secundario en la región semiárida de Brasil

“…For example, individuals established in the "between canopies" microhabitat lose faster water to the environment, suffering water deficit more quickly and more intensely (characteristic of the caatinga), being unable to keep themselves alive in these microhabitats. In addition to water stress, other environmental factors can cause mortality of individuals in both microhabitats, such as the impact of rain on newly germinated seedlings or frail individuals who survived the previous drought ; intra and interspecific competition for resources (Nordbakken, Rydgren, & Okland, 2004;Suzuki, Kudoh, & Kachi, 2004;Vilá, Bartolomeus, Gimeno, Traveset, & Moragues, 2006); attack by pathogens (Araújo, & Ferraz, 2003;Silveira, Araújo, Araújo, & Willadino, 2005); and herbivory (Belsky, 1990;Hanley, 1998;Leimu, & Lehtila, 2006).…”

The influence of microhabitat on the population dynamics of four herbaceous species in a semiarid area of northeastern Brazil

“…Studies of the population dynamics of herbaceous species in dry (Miller and Duncan, 2003;Santos et al, 2013b;Vega and Montaña, 2004;Volis et al, 2004;Wang, 2005) and wet forests (Baeten et al, 2009;Flores-Torres and Montaña, 2012;Kolb et al, 2007;Pino et al, 2007;Suzuki et al, 2003;) around the world have shown that heterogeneity in establishment conditions (microhabitats) for seedlings may limit population sizes and occurrence. This phenomenon was observed for some herbaceous populations in the dry forest (Caatinga) of Brazil (Andrade et al, 2007;Araújo et al, 2005;Lima et al, 2007;Reis et al, 2006;Santos et al, 2012;Silva et al, 2008), and it was also observed in this study.…”

“…García- Cháves et al, 2014;Vega and Montaña, 2004;Wang, 2005). In rocky outcrops that occur within forested areas, the occurrence of a moss layer and sediment accumulation in rocky outcrop crevices are sufficient to provide a substrate and promote the development of a dense layer of herbaceous plants during the growing season, when temperature and humidity conditions are favorable for seedling recruitment, establishment and survival (Araújo et al, 2005;Nordbakken et al, 2004;Silva et al, 2008;Suzuki et al, 2003). Water accumulation in rocky outcrop crevices may explain the high density of individuals of the four species in the rocky microhabitat, especially C. obliqua, which has a preference for this microhabitat.…”