Ernesto Vicente Vega-Peña’s research while affiliated with National Autonomous University of Mexico and other places

Los resultados preliminares de analizar las historias de vida de la familia Cactaceae [sin incluir especies clonales y corrección filogenética] nos muestran que: Se presenta un eje correspondiente al continuo rápido-lento. Las especies grandes en talla tardan en madurar sexualmente, presentan mayor esperanza de vida adulta y se achican menos. Las especies pequeñas asignan menos recursos a las flores y semillas. Tienden tener un crecimiento positivo y reproducción sexual mayores. Presentan semillas fotoblásticas positivas.

Cacti are threatened mainly by loss of habitat and illegal commerce. Because of this, it is essential to know their demographic characteristics. We systematically reviewed the publications with matrix population models (MPM) and integral projection models (IPM) in indexed journals, databases like the COMPADRE Plant Matrix Database and grey literature. In each publication, we recorded the literature characteristics, the population attributes, and the methods and metrics applied to describe them. We reviewed studies published until April 2022. We found 83 publications applied demographic modeling, 43 of which were of grey literature. Most studies were conducted in North America and on the tribe Cacteae, with a scarce representation of South American cactus. Compared to a previous review from 20 years ago, our study recorded a 488% increase in the number of publications and a 33.3% increase in the COMPADRE demographic database. We found demographic data for 65 taxa and very few studies covered a medium-to long-term period. MPMs were the most used until the 2009 when IPMs began to gain popularity. Population growth rates were commonly close to the unit (λ ≈ 1), but we identified a wide range of λ values. Species position in the demographic triangle showed that the populations in the tribes Echinocereae, Cereeae and Cylindropuntieae were located towards the end of the survival axis, while those in the tribes Cacteae, and Opuntieae had a more variable location. Applications of demographic models have focused on the analysis of life history traits (growth and turnover) and employing numerical simulations to simulate the consequences of variations in vital rates on λ. Interactions with the climate and the nurse-protected system are analyzed frequently. Nonetheless, a limited number of research explores the socioeconomic and political components of management and conservation. Finally, even though Cactaceae is the plant group with the most extensive demographic research, models are available for only 3.5% of the species.

Fractal dimension ( D ) can be used to characterise temporal changes of crown architecture of individual trees. Our goal in this study was to analyse seasonal changes in tree crown fractal dimension of two species of deciduous oaks ( Quercus castanea and Q. obtusata ) coexisting in a natural forest in central Mexico using low cost sampling, and relate these changes to morphological attributes and environmental variables. Every two months, from May 2017 to September 2018, for each oak species, we photographed fixed portions of the crowns of individual trees, measured their trunk diameters, and obtained average temperature and accumulated precipitation data recorded for the sampling date. From the obtained images, we calculated D values by the semivariogram method using three different variability estimators (square increment, isotropic, and transect variation). We identified a positive correlation between D and temperature, and a negative correlation between temperature and crown cover. The fractal dimension ( D ) of crowns of two deciduous oak species changes according to the tree’s phenological stage. D values varied through time in relation to tree crown phenological variation, but not with crown cover dimension. We propose a model of annual D value fluctuation in deciduous trees, characterised by two high complexity peaks and two low complexity valleys, corresponding to the effects on crown cover of annual periods of leaf abscission and development.

Los seres vivos tienen un “objetivo” común: dejar descendencia. A través de millones de años, han evolucionado diferentes maneras de vivir y dejar descendencia en diferentes especies. No obstante esta diversidad de historias de vida, encontramos ciertos patrones a los cuales llamamos “estrategias”. Durante su vida, cada organismo realiza muchas tareas, como alimentarse, crecer, reproducirse y migrar. Sin embargo, ningún ser vivo puede dedicarle todo su tiempo, energía y otros recursos (agua, proteínas, azúcares, etc.) a una de esas tareas sin descuidar otras, por lo que se generan “disyuntivas”, es decir, sacrificios en el desarrollo de una tarea para poder realizar otra. Las múltiples disyuntivas de los organismos pueden estudiarse con modelos matemáticos de “optimización multiobjetivo”, los cuales pueden enfocarse en analizar su forma, fisiología e incluso su demografía. La demografía analiza el cambio numérico de una población y permite estimar las tasas de nacimientos y muertes que determinan cuánto crece una población. Actualmente, un grupo interdisciplinario de investigadores mexicanos estudia las estrategias óptimas de las poblaciones y rasgos morfoecológicos de plantas de interés para la conservación. La finalidad es identificar cuáles y cómo son estas estrategias, así como su posible origen.