The Saguaro Cactus Yetman, David; Búrquez, Alberto; Hultine, Kevin ...
02/2020
eBook
The saguaro, with its great size and characteristic shape-its arms stretching heavenward, its silhouette often resembling a human-has become the emblem of the Sonoran Desert of southwestern Arizona ...and northwestern Mexico. The largest and tallest cactus in the United States, it is both familiar and an object of fascination and curiosity. This book offers a complete natural history of this enduring and iconic desert plant. Gathering everything from the saguaro's role in Sonoran Desert ecology to its adaptations to the desert climate and its sacred place in Indigenous culture, this book shares precolonial through current scientific findings. The saguaro is charismatic and readily accessible but also decidedly different from other desert flora. The essays in this book bear witness to our ongoing fascination with the great cactus and the plant's unusual characteristics, covering the saguaro's: history of discovery, place in the cactus family, ecology, anatomy and physiology, genetics, and ethnobotany.The Saguaro Cactus offers testimony to the cactus's prominence as a symbol, the perceptions it inspires, its role in human society, and its importance in desert ecology.
A review of the agricultural value of plants that use crassulacean acid metabolism, spanning traditional knowledge and uses, recent genomic discoveries, physiological adaptations, and known ...commercial values.
Abstract
The potential for crassulacean acid metabolism (CAM) to support resilient crops that meet demands for food, fiber, fuel, and pharmaceutical products far exceeds current production levels. This review provides background on five families of plants that express CAM, including examples of many species within these families that have potential agricultural uses. We summarize traditional uses, current developments, management practices, environmental tolerance ranges, and economic values of CAM species with potential commercial applications. The primary benefit of CAM in agriculture is high water use efficiency that allows for reliable crop yields even in drought conditions. Agave species, for example, grow in arid conditions and have been exploited for agricultural products in North and South America for centuries. Yet, there has been very little investment in agricultural improvement for most useful Agave varieties. Other CAM species that are already traded globally include Ananas comosus (pineapple), Aloe spp., Vanilla spp., and Opuntia spp., but there are far more with agronomic uses that are less well known and not yet developed commercially. Recent advances in technology and genomic resources provide tools to understand and realize the tremendous potential for using CAM crops to produce climate-resilient agricultural commodities in the future.
The family Cactaceae contains some of the most iconic species of succulent plants, many of which are valued for their cultural, economic, and ecological value. However, over 75% of all species of ...cacti are in decline, largely because of the effects global environmental changes (GEC), including climate change. Mitigating the impacts of GEC on cacti will require a coordinated effort that combines conservation, research, and education. Botanical gardens are uniquely positioned to lead such an effort because their living collections and programs focus on conservation and research. A coordinated network of botanical gardens—with living collections serving as experimental gardens—could become a crucial hub for studying the impacts of climate change on cacti. A network of botanical gardens could open previously untapped funding avenues to support the research, education, and conservation of cacti and provide resources for underfunded botanical gardens in Latin America.
Cacti usually grow in areas with severe resource limitations, making them vulnerable to local extinction. To ensure their survival, cacti have evolved a differential allocation of resources that is ...reflected in trade-offs among vital rates. In this study, we assess the effect of interannual climatic variation on resource allocation to vital rates in a cactus with biogeographical rarity (Thelocactus leucacanthus ssp. schmollii). Eight-year observations were used to relate vital rates to climatic data using population projection matrix models and Spearman correlations. The finite rate of population growth (λ) indicates, on average, a population in equilibrium. The transition from seeds to seedlings and the growth of seedlings, juveniles, and adults are the stages of the lifecycle with the highest selection pressure, with adults and juveniles being the categories with the greatest contribution to λ. This species allocates more resources to survival than to growth or reproduction during its lifecycle. The trade-off between the survival of adult individuals and fertility seems more marked in years with higher rainfall and minimum temperature turned out to be a key factor for population maintenance. This research provides new insights into the strategies used by rare globose cacti to avoid extinction in these limiting environments.
•Cacti differential allocation of resources is reflected in trade-offs among vital rates.•Interannual climatic variation influences the resource allocation to vital rates.•Minimum temperature a key factor for population maintenance in a cactus with biogeographical rarity.•Trade-off between survival of adult individuals and fertility more marked in years with higher rainfall.•New insights into the strategies used by rare globose cacti to avoid extinction in limiting environments.
Genetic differentiations and phylogeographical patterns are controlled by the interplay between spatial isolation and gene flow. To assess the extent of gene flow across an oceanic barrier, we ...explored the effect of the separation of the peninsula of Baja California on the evolution of mainland and peninsular populations of the long-lived columnar cactus Stenocereus thurberi. We analyzed twelve populations throughout the OPC distribution range to assess genetic diversity and structure using chloroplast DNA sequences. Genetic diversity was higher (Hd = 0.81), and genetic structure was lower (GST = 0.143) in mainland populations vs peninsular populations (Hd = 0.71, GST = 0.358 respectively). Genetic diversity was negatively associated with elevation but positively with rainfall. Two mainland and one peninsular ancestral haplotypes were reconstructed. Peninsular populations were as isolated among them as with mainland populations. Peninsular haplotypes formed a group with one mainland coastal population, and populations across the gulf shared common haplotypes giving support to regular gene flow across the Gulf. Gene flow is likely mediated by bats, the main pollinators and seed dispersers. Niche modeling suggests that during the Last Glacial Maximum (c. 130 ka), OPC populations shrank to southern locations. Currently, Stenocereus thurberi populations are expanding, and the species is under population divergence despite ongoing gene flow. Ancestral populations are located on the mainland and although vicariant peninsular populations cannot be ruled out, they are likely the result of gene flow across the seemingly formidable barrier of the Gulf of California. Still, unique haplotypes occur in the peninsula and the mainland, and peninsular populations are more structured than those on the mainland.
Abstract Background and Aims Climate change is a global phenomenon affecting species, which in arid regions will translate into more frequent and intense periods of drought. The Sonoran Desert is ...becoming hotter and drier, and many organisms are rapidly changing in abundance and distribution. These population attributes depend directly on the dynamics of the population, which in turn depends on the vital rates of its individuals; yet few studies have documented the effects of climate change on the population dynamics of keystone species such as the saguaro cactus (Carnegiea gigantea). Although saguaros have traits that enable them to withstand present environmental conditions, climate change could make them vulnerable if forced beyond their tolerance limits. Methods We evaluated the effect of climate change on 13 saguaro populations spanning most of the species’ distribution range. Using field data from 2014 to 2016, we built an integral projection model (IPM) describing the environmentally explicit dynamics of the populations. We used this IPM, along with projections of two climate change scenarios and one no-change scenario, to predict population sizes (N) and growth rates (λ) from 2017 to 2099 and compared these scenarios to demonstrate the effect of climate change on the future of saguaro cactuses. Key Results We found that all populations will decline, mainly due to future increases in drought, mostly hindering recruitment. However, the decline will be different across populations, since those located near the coast will be affected by harsher drought events than those located further inland. Conclusions Our study demonstrates that climate change and its associated increase in drought pose a significant threat to the saguaro cactus populations in the Sonoran Desert. Our findings indicate that the recruitment of saguaros, vital for establishing new individuals, is particularly vulnerable to intensifying drought conditions. Importantly, regional climate trends will have different impacts on saguaro populations across their distribution range.
Terrestrial carbon stock mapping is important for the successful implementation of climate change mitigation policies. Its accuracy depends on the availability of reliable allometric models to infer ...oven‐dry aboveground biomass of trees from census data. The degree of uncertainty associated with previously published pantropical aboveground biomass allometries is large. We analyzed a global database of directly harvested trees at 58 sites, spanning a wide range of climatic conditions and vegetation types (4004 trees ≥ 5 cm trunk diameter). When trunk diameter, total tree height, and wood specific gravity were included in the aboveground biomass model as covariates, a single model was found to hold across tropical vegetation types, with no detectable effect of region or environmental factors. The mean percent bias and variance of this model was only slightly higher than that of locally fitted models. Wood specific gravity was an important predictor of aboveground biomass, especially when including a much broader range of vegetation types than previous studies. The generic tree diameter–height relationship depended linearly on a bioclimatic stress variable E, which compounds indices of temperature variability, precipitation variability, and drought intensity. For cases in which total tree height is unavailable for aboveground biomass estimation, a pantropical model incorporating wood density, trunk diameter, and the variable E outperformed previously published models without height. However, to minimize bias, the development of locally derived diameter–height relationships is advised whenever possible. Both new allometric models should contribute to improve the accuracy of biomass assessment protocols in tropical vegetation types, and to advancing our understanding of architectural and evolutionary constraints on woody plant development.
Bats are the main pollinators and seed dispersers of Stenocereus thurberi, a xenogamous columnar cactus of northwestern Mexico and a good model to illustrate spatial dynamics of gene flow in ...long-lived species. Previous studies in this cactus showed differences among populations in the type and abundance of pollinators, and in the timing of flowering and fruiting. In this study we analyzed genetic variability and population differentiation among populations. We used three primers of ISSR to analyze within and among populations genetic variation from eight widely separated populations of S. thurberi in Sonora, Mexico. Sixty-six out of 99 of the ISSR bands (P = 66.7%) were polymorphic. Total heterozygosity for all populations sampled revealed high genetic diversity (Hsp = 0.207, HBT = 0.224). The AMOVA showed that most of the genetic variation was within populations (80.5%). At the species level, estimates of population differentiation, θ = 0.175 and θB = 0.194, indicated moderate gene flow among populations. The absence of a significant correlation between genetic and geographic distances indicated little isolation by geographic distance. The large genetic variation and diversity found in S. thurberi is consistent with its open reproductive system and the high mobility of bats, a major pollinator. However, small changes in number or kind of pollinators and seed dispersal agents, in the directionality of migratory routes, and/or in the timing of flowering and fruiting among populations, can critically affect gene flow dynamics.
Abstract
Reconstructing accurate historical relationships within a species poses numerous challenges, not least in many plant groups in which gene flow is high enough to extend well beyond species ...boundaries. Nonetheless, the extent of tree-like history within a species is an empirical question on which it is now possible to bring large amounts of genome sequence to bear. We assess phylogenetic structure across the geographic range of the saguaro cactus, an emblematic member of Cactaceae, a clade known for extensive hybridization and porous species boundaries. Using 200 Gb of whole genome resequencing data from 20 individuals sampled from 10 localities, we assembled two data sets comprising 150,000 biallelic single nucleotide polymorphisms (SNPs) from protein coding sequences. From these, we inferred within-species trees and evaluated their significance and robustness using five qualitatively different inference methods. Despite the low sequence diversity, large census population sizes, and presence of wide-ranging pollen and seed dispersal agents, phylogenetic trees were well resolved and highly consistent across both data sets and all methods. We inferred that the most likely root, based on marginal likelihood comparisons, is to the east and south of the region of highest genetic diversity, which lies along the coast of the Gulf of California in Sonora, Mexico. Together with striking decreases in marginal likelihood found to the north, this supports hypotheses that saguaro’s current range reflects postglacial expansion from the refugia in the south of its range. We conclude with observations about practical and theoretical issues raised by phylogenomic data sets within species, in which SNP-based methods must be used rather than gene tree methods that are widely used when sequence divergence is higher. These include computational scalability, inference of gene flow, and proper assessment of statistical support in the presence of linkage effects. Phylogenomics; phylogeography; rooting; Sonoran Desert.
Germination traits are components of invasion potential, and comparing seed traits in sympatric native and invasive species can offer insights into the invasion process. We characterized seed ...germination traits and how they influenced the success of
, a native species, and
an exotic species (Poaceae) in Mexico, in the context of their potential for biological invasion. Seeds from both species were collected from four sites in a natural protected area in Mexico City, and the germination of seeds of different ages was conducted in experiments at different temperatures.
exhibited higher germination percentages than the native
across all treatments. Seed age had differential effects, with older seeds of the native
germinating better, while
performed better with younger seeds. Temperature positively impacted germination for both species, although
was limited at lower temperatures. Exotic
can germinate over a wider temperature range with earlier germination rates, and generate a seed bank lasting several years, which may contribute to naturalization. The importance of germination traits in the context of invasive species establishment underscores the potential role of seed banks in facilitating biological invasions.
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