Ana Mendoza

comparative plant demography - relative importance of life-cycle components to the finite rate of increase in woody and herbaceous perennials

Stage projection (Lefkovitch) matrices for 21 species of woody plants and 45 herbaceous perennials were extracted from the plant demographic literature or compiled from published data. Each matrix was divided into six regions representing: recruitment of seeds to the seed pool; recruitment of seedlings or juveniles from current seed production; clonal growth; retrogression, due to plants decreasing in size or reverting in stage; stasis, (survival from one year to the next in the same stage class); progression to later stage classes. Matrix analysis was used to calculate the finite rate of increase λ for each population and to calculate the elasticities of each transition coefficient in the matrices (...)

Effects of experimental defoliation on growth, reproduction and survival of Astrocaryum mexicanum

(1) The effects of three levels of defoliation at four stages of development on leaf production, reproduction probability, fruit production and survival of an understorey palm, Astrocaryum mexicanum, were studied from 1978 to 1981. (2) Three portions of the crown were factorized with the partial defoliation treatments. (3) Completely defoliated juvenile and immature palms produced significantly fewer leaves than control plants. In mature palms, the removal of the oldest portions of the crown increased leaf production by 30%. (4) Complete defoliation and the removal of two-thirds of the oldest leaves had the effect of reducing leaf abscission in all stages, except for seedlings. (5) Defoliation had a significant effect on reproduction during all years, except 1978. Completely defoliated palms had a lower probability of reproduction and produced no fruits for three years. The removal of a small proportion of the oldest tissue significantly increased fruit production. Defoliations greater than 33% of the total number of leaves reduced the reproductive capacity of palms, except when the oldest tissue was removed. (6) The survival of totally defoliated juvenile and immature individuals was 50% less than that of undefoliated plants. The survival of mature individuals was not significanly affected by the defoliation.

Sexual reproduction and clonal growth in Reinhardtia gracilis (Palmae), an understory tropical palm.

Patterns of sexual reproduction and clonal growth were investigated in the understory palm Reinhardtia gracilis var. gracilior over a 3-yr period. R. gracilis is a very abundant clonal palm in the tropical rain forest of Los Tuxtlas, Veracruz, México. Because ramets form clumps, genets are easily identified in the field. Genets were monitored in a 0.5-ha area, and classified by size according to the number of ramets they possessed. In contrast to clonal growth, sexual reproduction was highly dependent on genet size. The probability of reproduction, the number of inflorescences, and the number of fruits produced were positively correlated with genet size. However, neither the probability of producing a ramet, nor the number of ramets produced per genet were correlated with genet size. Over the 3 yr of study, 55% of the genet population had at least one ramet with reproductive structures, while <1% (a single genet in one year) had six ramets with flowers. Thirty-two percent of the mature genets reproduced during each of three consecutive years. In contrast, 58% of the genets produced no new ramets during these 3 yr. No evidence was found of a trade-off between clonal growth and sexual reproduction. Ramet production increases genet size and this in turn increases genet reproductive performance. Clonal growth in this species may be viewed as a growth strategy that tends to maximize genet fitness.

Clonal and genetic structure of two Mexican oaks: Quercus eduardii and Quercus potosina (Fagaceae)

Quercus eduardii and Q. potosina are dominant oak species in Sierra Fría, Aguascalientes, Mexico. These species have been exploited for multiple purposes since the 16th century. Both species produce clonal offspring through root suckering and acorns through sexual reproduction. To understand clonality for the implementation of the most adequate actions for the conservation of these species, we addressed the following questions: (a) what is the spatial clonal structure of both species? (b) How much clonal and genetic diversity is maintained in these species? Random Amplified Polymorphic DNAs (RAPDs) were used as molecular markers for these analyses. Genets of both species have few ramets and these grow close the parent tree. Autocorrelation analyses at the ramet level showed an aggregated distribution at short distances and a random spatial distribution at larger distances. Also, at the genet level the autocorrelation analyses showed a random distribution. Clonal diversity was high in both species (Q. eduardii: D=0.963, G/N=0.60; Q. potosina: D=0.985, G/N=0.65). Genetic diversity was high within populations (Q. eduardii: He=0.33±0.11; Q. potosina: He=0.35±0.11). Low levels of genetic differentiation among populations were observed (Q. eduardii ϕst=0.19, P < 0.002; Q. potosina ϕst=0.13, P < 0.002). Both species maintain high levels of clonal and genetic diversity, probably due to successful sexual reproduction, which allows gene flow among populations. Conservation and/or reforestation programs must include seed collections and germplasm banks. Due to the small genet size and the high clonal diversity of these species, seeds can be collected in any place in Sierra Fría, Aguascalientes.

Association between individual genetic diversity of two oak host species and canopy arthropod community structure

Numerous oak species have wide geographical distribution and canopy dominance and they may influence the structure and functioning of the community. Therefore, they can be considered as foundation species. In the present study, we tested the potential association between individual genetic diversity of the host plant (microsatellites), host tree species (Quercus castanea and Q. crassipes), and seasonality (dry vs. rainy) with their arthropod community structure [diversity (H′), density, biomass and composition]. Forty individual oak canopies were fogged (10 individuals per species per season) in the Parque Ecológico Ciudad de México. We identified 338 arthropod morphospecies belonging to 21 orders. NMDS showed a separation of host tree species during both seasons, suggesting a different community structure between host tree species. Q. crassipes showed the highest values for H′, richness, and density in comparison with Q. castanea. In contrast, Q. castanea showed the highest values for arthropod biomass. Homozygosity by locus index (HL), a measure of individual diversity, showed that the more genetically diverse host individuals registered more H′ and density of arthropods, independently of the season. On the contrary, arthropod biomass registered an inverse pattern. This study suggests that genetic diversity of foundation species is an important element in the structuring of the canopy arthropod community.