Globose cacti (Mammillaria) living on cliffs avoid high temperatures in a hot dryland of Southern Mexico

POPULATION BIOLOGY OF THE MELON CACTUS Melocactus violaceus subsp. violaceus (CACTACEAE) ON A BRAZILIAN SANDY COASTAL PLAIN

“…The majority of the cacti individuals were located near enough to adjacent vegetation to be shadow-covered and avoid direct sunlight during some part of the day. This reduction to sunlight exposure enables the establishment of the individuals on exposed sand, as the overheating is an important issue to globose cacti germination (Rojas-Aréchiga & Vasquez-Yanes 2000) and survival (Martorell & Patiño 2006). On the same area, Zaluar & Scarano (2000) reported the positive association between A. arenaria and P. arrabidae, a columnar cactus, and the possible positive effect of the palm on the germination and establishment of this cactus, and both Reyes-Olivas et al (2002), working on a Mexican desert, and Hughes et al (2011), on the Brazilian caatinga, states that some species of globose cacti do not depend on scrubs to its establishment, but the effect of shading on their survival cannot be neglected.…”

“…violaceus was sampled during a week in August 2006, on a one hectare plot (100 x 100 m) divided in 16 plots of 625 m² (25 x 25 m). Each plots was considered a sample unity where every cacti individual was identified, had its reproductive stage recorded, and its diameter and distance to the nearest vegetation above 50 cm measured (both in cm), in order to represent potential shadow cover in the area, as soil temperature is one of the main factors affecting the survival of globose cacti seedlings (Martorell & Patiño 2006). The cacti individuals were classified according their stage of growth as: immature (all green, without cephalium), pre-breeding (with cephalium, but no flowers or fruits) and reproductive (with cephalium and flowers or fruits).…”

What can the demography of Astrophytum ornatum tell us of its endangered status?

“…There are only a handful of studies that have addressed the problems of habitat specificity (García, 2003;García et al, 2002;Pico and Riba, 2002) and the population dynamics in rupicolous cacti (Flores-Martinez et al, 2010) even though Martorell and Patiño (2006) suggest rupicolous habitats in the Cactaceae (specifically members of the Supertextae) to be remnants of more widely distributed populations that have been restricted to remnant populations in inaccessible areas. We still do not know if A. ornatum populations are relict populations or have specific habitat preferences.…”

Demography of an endangered endemic rupicolous cactus

“…Few studies have addressed endangered species in rupicolous habitats (Picó and Riba 2002; García et al 2002;García 2003); so there is little information on their population dynamics. Specifically for the Cactaceae, Martorell and Patiño (2006) have suggested that some of the species of the Series Supertextae included in the Mammillaria (like M. huitzilopochtli and M. crucigera) that are susceptible to chronic disturbance were once more widely distributed (Martorell and Peters 2005) and are currently restricted to remnant populations (e.g., Picó and Riba 2002). Poor recruitment, the continuously decreasing fruit and seed production and high mortality over time could be driving the decline of M. huitzilopochtli populations.…”