Integration of Demographic Annual Variability in a Clonal Desert Cactus

Abstract

Spatial and temporal variability influence the structure and dynamics of perennial plant populations. In order to investigate the consequences of this environmental heterogeneity on population and life history traits of a perennial plant with a complex life history, four size‐classified population matrix models were employed (i.e., annual, mean, periodic, and stochastic simulations) in a clonal cactus, Opuntia rastrera, in the Chihuahuan Desert, Mexico. This species was studied over a seven‐year period in two contrasting, neighboring habitats (nopalera and grassland). The specific aims were: (a) to assess the effect of annual environmental variability on the long‐term dynamics of both populations; and (b) to estimate the relative contribution of sexual reproduction and clonal propagation to the populations' rates of increase. Projections from each model provided complementary information on population dynamics and life history in the two habitats. The finite rate of population growth (λ) varied among matrix projections. Mean, periodic, and stochastic projections yielded λ > 1 for nopalera and λ ≈ 1 for grassland. The relative contributions of size classes and demographic processes to changes in λ differed widely between years and habitats for annual matrices. In contrast, elasticities of periodic matrices showed a stable habitat‐dependent pattern. The proportional change in λ produced by sexual recruitment and clonal propagation showed wide spatial variation in which the most distinctive difference between habitats was the predominance of clonal recruitment at the nopalera and seedling recruitment at the grassland. Elasticities also showed temporal variation whereby clonal propagation decreased as precipitation increased, while sexual reproduction and growth tended to increase with precipitation. The striking spatial and temporal differences found in the structure, dynamics, and life history traits of O. rastrera are aptly summarized by the periodic analyses. These differences reflect both the varying influence of the selective pressures operating on this species and the ways in which demographic plasticity deals with them.

Impacts of insect herbivory on cactus population dynamics: experimental demography across an environmental gradient

“…Our demographic results, which are consistent with those for other Opuntia species (e.g., Mandujano et al 2001, Godinez-Alvarez et al 2003, indicate that such individual-level damage has the potential of imposing negative effects on the population dynamics of the native cacti attacked, especially in combination with damage by the native cactus-feeding insects. The ''pre-invasion'' data presented here may be useful in quantitatively evaluating the ecological effects of Cactoblastis if this invasive herbivore reaches the Opuntia populations of the Chihuahuan Desert.…”

Cacti community structure in a tropical Mexican dry forest under chronic disturbance

“…The proportion of adults under conditions of chronic disturbance may decrease due to high mortality of small size-classes and slow growth rates (Jiménez-Sierra et al, 2007;Alba-García, 2011;Martorell et al, 2012). Also, some studies have shown that even when recruitment is higher in grasslands, cacti growth faster in sites denuded of grasses (Mandujano et al, 2001) because belowground competition (Briones et al, 1996). This seems to be supported by the average height of adults of Pachycereus grandis in this study which was three times higher in the conserved forest (468 ± 43) compared to the secondary one (148 ± 81; Table 3).…”

Population Dynamics of the Western Prickly Pear, Opuntia macrorhiza (Cactaceae)

“…The genus is native to the New World, but some species introduced elsewhere have naturalized and are invasive (Benson, 1992;Pinkava, 2003;Reyes-Agü ero et al, 2006). Many species of Opuntia live for a long time; e.g., Mandujano and coworkers (Mandujano et al, 1996(Mandujano et al, , 1998(Mandujano et al, , 2001 reported that Opuntia rastrera (nopal) lived for decades. This species dominates the nopal ecosystem through its long life span and ability to reproduce vegetatively by rooting of cladodes (Mandujano et al, 1998).…”

“…Elasticities (Table 2) In many species of Opuntia, reproduction by seeds is infrequent (Godínez-Á lvarez et al, 2003;Reyes-Agü ero et al, 2006;Piñ a et al, 2007). Relative success of reproduction by vegetative means and by seeds for Opuntia rastera depended on habitat (Mandujano et al, 1998(Mandujano et al, , 2001). Success of recruitment of O. macrorhiza in our study was .50% (Table 1), which is an order of magnitude higher than reported for most species of cacti (Palleiro et al, 2006;ReyesAgü ero et al, 2006).…”