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

Abstract

Ruderal species, i.e., those that increase their numbers in the presence of disturbance, are not expected to occur in extreme environments. We test whether Echinocereus lindsayi, a cactus from an extreme desert, follows the ruderal trend observed in similar species from mild deserts, or, as theory suggests, it is a non ruderal. Contrary to expectations, its density and fraction of small individuals in the population increased with disturbance. This seemingly results from increased establishment, as it is nursed by rocks exposed by disturbance. A demographic model for two populations, one nearly pristine and another highly disturbed, showed that at the latter site recruitment was more frequent and likely. At the disturbed site the performance of E. lindsayi individuals was usually poor, except on favorable years. Then, competition release caused by disturbance apparently allowed for a better performance compared to the less disturbed site. Despite that this opportunistic behavior would suffice to maintain the population size stable, the large mortality produced by an insect outbreak in two of the four study years caused the population to diminish. In contrast, the population at the less disturbed site was near equilibrium. If the insect outbreak is associated to disturbance, E. lindsayi at the disturbed site would be already experiencing more disturbance than it tolerates. This agrees with the fact that no populations were found at greater disturbance intensities. While, contrary to our hypothesis, E. lindsayi is ruderal, this extreme desert species appears to tolerate far less disturbance than its counterparts from milder areas.

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

“…Studies at the population level have shown positive, negative or neutral effects of disturbance in cacti density. Some species (called ruderal cacti sensu Martorell and Peters, 2005) may benefi t from moderate levels of human activities as the globose species Coryphantha werdermannii in Coahuila, North Mexico (Portilla-Alonso and Martorell, 2011) and the cylindrical cactus Echinocereus lindsayi in Baja California, Mexico (Martorell et al, 2012). In the present study, further analysis at species level revealed that Opuntia velutina and O. puberula were significantly more abundant in the secondary forest under chronic disturbance compared to the conserved forest (t (1,10) = 2.6, P < 0.05 and t (1,10) = 6.4, P < 0.0001, respectively).…”

“…These results are in line with others studies at population level; for example for Ferocactus histrix (del Castillo, 1987) and Coryphantha werdermannii (Portilla-Alonso and Martorell, 2011), a higher proportion of adults were found at the sites with less 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).…”

Demography of Euterpe precatoria and Mauritia flexuosa in the Amazon: application of integral projection models for their harvest

“…We estimated the λ s value of each harvest scenario by iterating the kernels 1000 times, out of which we took the last 900 λ values so that the simulation model reached its stationary ergodic properties (Martorell et al . ), to obtain the geometric mean of lambda. To obtain the number remaining adults, we obtained the first 100 iterations of the IPM population structure proportions, starting with the observed size structures.…”

“…In this paper, we used Integral Projection Models (IPMs, Ellner & Rees ), a relatively novel approach in plant demography to project harvest impact, because it provides smaller confidence intervals in the parameters estimation since the model uses continuous variables and the variation in all the individuals and avoids size‐class subjective categorization (Martorell et al . ).…”

Reconstructing shifts in vital rates driven by long‐term environmental change: a new demographic method based on readily available data

“…To mention but one, altitude ranged from 640 to 2500 m a.s.l. Third, climate fluctuations are important in drylands (Schwinning et al 2004), and thus vital rates are not likely to be deterministic (Fieberg and Ellner 2001;Martorell et al 2012) as assumed by our model. Furthermore, given that we are working with an endangered species, the samples were relatively small (130 AE 97 individuals per site), limiting the amount of information supplied to the model.…”