The effects of serotiny and rainfall‐cued dispersal on fitness: bet‐hedging in the threatened cactus Mammillaria pectinifera

Abstract

Serotiny-the retention of seeds in the mother plant for over a year-in unpredictable environments may increase the probability that at least some seeds are dispersed during favorable periods. Propagules may be expelled when environmental cues announcing favorable conditions occur, or be gradually released into the environment. This could be a bet-hedging strategy increasing the long-term fitness by reducing interannual variability in reproduction. However, the impact of seed retention on the population dynamics of serotinous species and its contribution to fitness has been barely explored under field conditions. We assessed these issues in the threatened Mammillaria pectinifera, a small globose cactus that gets established only in exceptionally rainy years. This species expels some seeds actively during unusually rainy periods, while dispersing others passively over several years. Dynamics of the seeds in the mother plant over two very contrasting years in terms of precipitation was incorporated into a stochastic matrix model. Seed retention was found to increase significantly the probability that some of the seeds retained in any given year are dispersed within a subsequent rainy period. Active seed-expulsion raises this probability even further. As expected in bet hedgers, seed retention increased fitness in the presence of temporal variability. Active fruit expulsion did not affect fitness, but reduced demographic stochasticity. The incomplete serotiny and fruit expulsion observed is the evolutionary outcome expected for the environment and life-history attributes of the species.

Ruderality in extreme‐desert cacti? Population effects of chronic anthropogenic disturbance on Echinocereus lindsayi

“…These discontinuous outbreaks may allow the population size to recover or even increase between insect surges. As in our study, Peters et al (2011) found evidence for predation only in some years, with very low adult mortality in the remaining period. In May 2011, we surveyed both sites, and found that mortality at NDS remained low (annual average 0.9%) and had diminished in DS since 2009 (7.7%), confirming that the low survival observed during years 3 and 4 was a transitory event.…”

“…In the cactus Mammillaria pectinifera, a cerambicid outbreak was observed to cause a stronger reduction in k in a disturbed site (Valverde and Zavala-Hurtado 2006) compared to a relatively preserved one (Peters et al 2011). Insect outbreaks may be more probable on plants exposed to pulsed water stress (Huberty and Denno 2004), which seems to be amplified by CAD.…”

“…Many of the large individuals that died during the third and fourth years in DS were found hollowed. Cerambicids have been widely reported to cause massive mortalities in several cacti species, causing strong reductions in k (Kass 2001;Valverde and Zavala-Hurtado 2006;Martínez-Á valos et al 2007;Peters et al 2011). …”

Dinámica poblacional de Mammillaria humboldtii una cactácea endémica de Hidalgo, México

“…hutzilopochtli, Flores-Martínez et al, 2010;M. gaumeri, Ferrer et al, 2011;Peters et al, 2011;M. mystax, Saldivar y Navarro, 2012), es un gé-nero poco estudiado dada su riqueza y amplitud de hábitats en los que se encuentra en México y EUA.…”

“…El ciclo de vida fue dividido por el diámetro de los individuos en cinco categorías de tamaño (0.01 > a < 1 cm Plántula, 1 ≤ a < 2 cm Juvenil, 2 ≤ a < 3 cm Adulto 1, 3 ≤ a < 4 cm Adulto 2 y ≥ 4cm Adulto 3) y una categoría de semilla a la que se le asignó una probabilidad pequeña (0.0005) al desconocer la probabilidad real de permanencia en el banco de semillas. Los experimentos de germinación (ver apartado de germinación) mostraron que las semillas > 1 año siguen germinando lo que sugiere al menos la posibilidad de un banco de semillas semi-permanente de corta duración para Mammilaria humboldtii, además de que se han reportado bancos de semillas para otras especies del género Mammillaria (Bowers, 2005;Valverde y Zavala-Hurtado, 2006;Peters et al, 2011). El crecimiento y supervivencia se registraron en el mes de mayo de 2012 y 2013 después de la época reproductiva.…”