Fate of cohorts in Melocactus (Cactaceae) species is affected by rainfall uncertainty and microrelief structures

Demographic processes and anthropogenic threats of lithophytic cacti in eastern Brazil

“…Thus, the population distribution and growth of this lithophylic species depend on special microhabitats where recruitment and survival are higher. This is consistent with observations of other rupicolous globose cacti, in which individuals were rarely associated with other perennial plants (Munguía-Rosas and Sosa 2008;Martorell et al 2015;Hughes et al 2016). Furthermore, plants in MeC are larger, which may be the result of less precipitation in this locality (i.e., 670 mm year -1 and 5-6 months of drought), and thus selection for individuals that are able to store more water to compensate for the long droughts (Mauseth 2000).…”

“…Secondly, Melocactus seedlings have high surface:volume ratio (S/V) due to their very small size (& 1.90 mm wide) and reduced number of ribs (Mauseth 2000). The combination of C3 metabolism and high S/ V ratio reduces water usage efficiency and intensifies transpiration, thus restricting recruitment in environments with multiple stress factors, such as rocky outcrops (Porembski and Barthlott 2000;Lüttge 2004), to very specific mesic microhabitats (Mauseth 2000;Munguía-Rosas and Sosa 2008;Hughes et al 2016). Thirdly, cacti seeds can germinate quickly, in the first week after contacting moist substrate (& 5-20 days), or after developing physiological dormancy in ephemeral environments (Rojas-Aréchiga and Vásquez-Yanes 2000).…”

“…Study system and field research -The genus Melocactus is found from Central America to the western portion of the Peruvian Andes, with its center of diversity and endemism in eastern Brazil (Taylor and Zappi 2004). Most species colonize oligotrophic microsites within landscapes with high topographic and edaphoclimatic heterogeneity (Hughes et al 2016). Melocactus ernestii and M. bahiensis are lithophytic cacti endemic to eastern Brazil and occur on rocky outcrops scattered in landscapes subjected to high inter-annual rainfall fluctuations (Taylor and Zappi 2004;Gomes et al 2013).…”

“…1). They are lithophytic cacti and generally occur in depressions and crevices, or are partially protected by rock fragments (Hughes et al 2016). Two populations represent the M. ernestii species: MeM-located in the southern limit of the species distribution in the municipality of Itaobim, Minas Gerais state (16°35 0 41.22 00 S, 41°34 0 35.53 00 W; 334 m a.s.l.…”

“…In the case of endangered populations, basic understanding of the demographic behavior and population response to harvesting may be necessary to guide conservation and management actions (PAN 2010). Currently, there are no demographic studies of cacti in Brazil (Godínez-Á lvarez et al 2003;PAN 2010), and few studies have documented cacti population dynamics on rocky outcrops in South America (Munguía-Rosas and Sosa 2008;Martínez et al 2010;Hughes et al 2016).…”