Ernesto Vega

Ecological and socio-cultural factors influencing plant management in Náhuatl communities of the Tehuacán Valley, Mexico

BackgroundManagement types and their intensity may vary according to indicators such as: (1) practices complexity, (2) degree of techniques specialization, (3) occurrence and types of social regulations, (4) artificial selection intensity, (5) energy invested, (6) tools types, and (7) amounts of resources obtained. Management types of edible plants were characterized and analyzed in Náhuatl communities of the Tehuacán Valley. We expected that both natural and human pressures generate risk on plant resources availability, influencing human responses of management directed to decrease risk. We particularly hypothesized that magnitude of risk would be a direct function of human pressures favored by cultural and economic value and ecological factors such as scarcity (restricted distribution and abundance). Management practices may decrease risk of plant resources, more effectively when they are more intense; however, absence or insufficiency of management practices on endangered plants may favor loss of their populations. Understanding current management motives and their consequences on the purpose of ensuring availability of plant resources might allow us to understand similar processes occurring in the past. This issue is particularly important to be studied in the Tehuacán Valley, where archaeologists documented possible scenarios motivating origins of plant management by agriculture during prehistory.MethodsThrough ethnobotanical collecting, 55 semi-structured and free listing interviews we inventoried edible plant species used in five villages of Coyomeapan, Mexico. We identified: (1) native plant species whose products are obtained exclusively through simple gathering, (2) native species involving simple gathering and other management types, and (3) non-native species managed by agricultural management. We conducted in depth studies on the 33 native species managed through gathering and other types of practices. We carried out a total of 660 sessions of detailed interviews to 20 households randomly selected. We showed to people voucher specimens and photos of the sample of species chosen and documented their cultural and economic values. Spatial availability of these plant species was evaluated through vegetation sampling. Values for each cultural, economic, and ecological indicator were codified and averaged or summed and weighed according to frequency of interviewees’ responses or ecological conditions per plant species. With the standardized values of these indicators we performed a PCA and scores of the first principal component were considered as a risk index, which summarizes information of thirteen indicators of human use, demand and scarcity of each plant species. Similarly, eleven indicators of energy invested, complexity, tools and management strategies were used for performing PCA and scores of the first principal component were considered as management intensity index for each plant species. A linear regression analysis was performed to analyze the relation between risk and management intensity indexes. Amounts of variation of management data explained by ecological, cultural and economic information, as well as their risk level were analyzed through canonical correspondence analyses (CCA).ResultsA total of 122 edible plant species were recorded, nearly 30% of them were introduced domesticated plants, 51 were wild species obtained exclusively by simple gathering and 33 were native species obtained by simple gathering and other management practices, these latter were the ones more deeply studied. People recognized variants in 21 of these latter 33 species, the variants receiving differential use, management, artificial selection and incipient domestication. The lowest values of management intensity corresponded to species under simple gathering and tolerance, mostly annual abundant plants, occasionally consumed by few people. The highest management intensity values were recorded in species with economic importance, mostly perennial with recognized variants whose management requires using tools, and which are protected by collective regulations. The regression analysis indicated significant value R2 = 0.433 (P < 0.001) between risk and management indexes. CCA explained 65.5% of variation of management intensity, mainly by socio-cultural factors (32.6%), whereas ecological data explained 21.3% and the intersection of all factors 11.6%. Variation of management intensity is 67.6% explained by risk variables. Length-span of life cycle, reproductive system type, distribution, number of parts used, number of management and use forms and type of regulations were statistically significant.ConclusionPeople manage plant resources according to the role these play in households’ subsistence, the quantity available and the quality of their useful products; particularly important is the balance between resources availability and demand. Management responses to risk are also influenced by the ease to propagate or manipulate individual plants and time requiring the construction of manipulation strategies and techniques.

Pollination ecology of Agave macroacantha (Agavaceae) in a Mexican tropical desert. I. Floral biology and pollination mechanisms

In a study of sexual reproduction in long-lived semelparous plants, we observed Agave macroacantha in the tropical desert of Tehuacán-Cuicatlán, Mexico, describing duration of flowering, flower phenology, and nectar production patterns. We also performed two manipulative experiments evaluating (a) the seed production efficiency of different crossing systems (selfing, cross-pollination, apomixis, and control), and (b) the effect of different pollinators (diurnal exposure to pollinators, nocturnal exposure, exclusion, and control) on the seeds produced. Flowering occurred from early May to late July and had a mean duration of 29 days in the individual rosettes. The flowers were protandrous; anthesis occurred in the afternoon of the third day after floral opening, and the pistils matured in the afternoon of the fifth day. The stigmas remained receptive from dusk to the following morning. Pollination was mostly allogamous. Nectar was produced principally during the night, from the first stages of floral aperture until the stigmas wilted and flowering ceased. The flowers were visited during the day by hymenoptera, butterflies, and hummingbirds and during the night by bats and moths. Only the nocturnal visitors, however, were successful pollinators. Agave macroacantha is extremely dependent on nocturnal pollinators for its reproductive success.

Pollination ecology of Agave macroacantha (Agavaceae) in a Mexican tropical desert. II. The role of pollinators

We did a series of observational studies and manipulative experiments on the guild of nocturnal visitors of Agave macroacantha, including (1) a description of the hourly patterns of visits by moths and bats, (2) an evaluation of the relative contribution of bats and moths to flowering success, and (3) an evaluation of the pollination efficiency of the different bat species. Scapes exposed to moths but excluded to bats yielded ∼50% fewer fruits than those exposed to both pollinator groups. Flowers exposed to the bat species Leptonycteris curasoae showed similar fruiting success to those exposed to Choeronycteris mexicana and to those exposed to the whole nocturnal visitor guild. However, the fruits originated from flowers pollinated by Leptonycteris curasoae yielded significantly more seed than those exposed to Choeronycteris mexicana or to the whole pollinator guild. It is concluded that Agave macroacantha is extremely dependent on nocturnal pollinators for its reproductive success and that bats are especially important for successful pollination. Some of these pollinators are migratory and have been reported to be steadily declining. A continuing decline in the populations of pollinators may impede the successful sexual reproduction of the plant host and may put the long-term survival of this agave species under risk.

Influence of traditional markets on plant management in the Tehuacan Valley.

BackgroundThe Tehuacán Valley, Mexico is a region with exceptionally high biocultural richness. Traditional knowledge in this region comprises information on nearly 1,600 plant species used by local peoples to satisfy their subsistence needs. Plant resources with higher cultural value are interchanged in traditional markets. We inventoried the edible plant species interchanged in regional markets documenting economic, cultural and ecological data and about their extraction and management in order to: (1) assess how commercialization and ecological aspects influence plant management, (2) identify which species are more vulnerable, and (3) analyze how local management contributes to decrease their risk. We hypothesized that scarcer plant species with higher economic value would be under higher pressure motivating more management actions than on more abundant plants with lower economic value. However, construction of management techniques is also influenced by the time-span the management responses have taken as well as biological and ecological aspects of the plant species that limit the implementation of management practices. Plant management mitigates risk, but its absence on plant species under high risk may favor local extinction.MethodsSix traditional markets were studied through 332 semi-structured interviews to local vendors about barter, commercialization, and management types of local edible plant species. We retrieved ethnobotanical information on plant management from ten communities in a workshop and sampled regional vegetation in a total of 98 sites to estimate distribution and abundance of plant species commercialized. Through Canonical Correspondence Analysis (CCA) we analyzed the amount of variation of management types that can be explained from socioeconomic and ecological information. A risk index was calculated relating distribution, abundance, economic value and management of plant resources to identify the most vulnerable species.ResultsWe recorded 122 edible plant species interchanged in the main regional markets. CCA explained significantly 24% of management variation, spatial distribution and plant parts used being particularly important in management decisions. The indeterminate 76% of variation suggests that management decisions depend on particular variables that are not explained by the ecological and socioeconomic factors studied and/or their high variation in the context at the regional scale. The risk index indicated that management was the factor that mostly influences decreasing of risk of interchanged plant species. We identified Clinopodium mexicanum, Pachycereus weberi, Dasylirion serratifolium, Disocorea sp., Ceiba aesculifolia, Neobuxbamia tetetzo, Lippia graveolens, Litsea glaucescens, L. neesiana, Jatropha neopauciflora, Agave potatorum and other agave species used for producing mescal among the more endangered plant species due to human pressure, their relative scarcity and limited or inexistent management.ConclusionSpatial distribution and plant parts used are particularly meaningful factors determining risk and influencing management actions on edible plant species interchanged in the region. Limited or inexistent management may favor extinction of local populations under risk. Local management techniques synthesize knowledge and experiences crucial for designing sustainable management programs. Traditional management techniques supported by ecological information and environmental management approaches could make valuable contributions for sustainable use of plant species, particularly those becoming economically important more recently.

Seed-mediated connectivity among fragmented populations of Quercus castanea (Fagaceae) in a Mexican landscape

PREMISE OF STUDY Anthropogenic fragmentation is an ongoing process in many forested areas that may create loss of connectivity among tree populations and constitutes a serious threat to ecological and genetic processes. We tested the central hypothesis that seed dispersal mitigates the impact of fragmentation by comparing connectivity and genetic diversity of adult vs. seedling populations in recently fragmented populations of the Mexican red oak Quercus castanea. METHODS Adult individuals, established before fragmentation, and seedlings, established after fragmentation, were sampled at 33 forest fragments of variable size (0.2 to 294 ha) within the Cuitzeo basin, Michoacán state, and genotyped using seven highly polymorphic chloroplast microsatellite markers (cpSSRs). To test whether seed dispersal retains connectivity among fragmented populations, we compared genetic diversity and connectivity networks between adults and progeny and determined the effect of fragment size on these values. KEY RESULTS Seventy haplotypes were identified, 63 in the adults and 60 in the seedlings, with average within-population diversity (hS) values of 0.624 in the adults and 0.630 in the seedlings. A positive correlation of genetic diversity values with fragment size was found in the seedling populations but not in the adult populations. The network connectivity analysis revealed lower connectivity among seedling populations than among adults. The number of connections (edges) as well as other network properties, such as betweenness centrality, node degree and closeness, were significantly lower in the seedlings network. CONCLUSIONS Habitat fragmentation in this landscape is disrupting seed-dispersal-mediated genetic connectivity among extant populations.

A Suite of Tools for Assessing Thematic Map Accuracy

Although land use/cover maps are widely used to support management and environmental policies, only some studies have reported their accuracy using sound and complete assessments. Thematic map accuracy assessment is typically achieved by comparing reference sites labeled with the “ground-truth” category to the ones depicted in the land use/cover map. A variety of sampling designs are used to select these references sites. The estimators for accuracy indices and the variance of these estimators depend on the sampling design. However, the tools used to assess accuracy available in the main program packages compute the accuracy indices without taking into account the sampling and give inconsistent estimates. As an alternative, we present free user-friendly tools that enable users beyond the Geographic Information Science Community to compute accuracy indices and estimate corrected areas of given categories with their respective confidence intervals. The tool runs in Dinamica EGO, a free platform for environmental spatial modeling as well as a Q-GIS plugin and a R package. Additionally, a practical application example is described using a case study area in central-west Mexico.

Population Dynamics and Sustainable Management of Mescal Agaves in Central Mexico: Agave potatorum in the Tehuacán-Cuicatlán Valley

Population Dynamics and Sustainable Management of Mescal Agaves in Central Mexico:Agave potatorumin the Tehuacán-Cuicatlán Valley. A total of 37 agave species are extracted from forests of Mexico for producing mescal. This activity has caused decline of numerous populations, and their sustainable management is indispensable for preventing species extinctions. Our study analyzed demographic information about Agave potatorum in the Tehuacán Valley with the goal of developing proposals for sustainable use for agaves in general. We studied protected populations in two contrasting environments, and through prospective analyses and real data about extraction and reforestation rates, we simulated different scenarios of actions. Our analyses indicate that the populations’ growth rates (λ) in conserved populations are 0.9903 ± 0.062 and 1.021 ± 0.062, but viability analyses suggest that even those unmanaged populations would decrease 30% to 90% in 30 years. Survival and growth of early agave plant stages contribute most to λ; adult stages and fecundity have low contribution but their conservation is crucial for population recovery. Based on a successful management experience with A. cupreata, we suggest that at least 30% of reproductive plants should be left to ensure seed provision for natural and assisted populations’ recovery. The reintroduction of plants at two early stages of growth is recommended, particularly 1–2-year-old plants, the size categories with the highest contribution to λ. Current efforts by local people to promote cattle exclusion from forest areas, seed collection, and their propagation in nurseries, and actions for recovery and conservation of populations are strategies of high value. Our research contributes to optimizing the effectiveness of such actions and aids in the conservation of other agave species.Dinámica de poblaciones y manejo sustentable de agaves mezcaleros en la región central de México:Agave potatorumen el Valle de Tehuacán-Cuicatlán. En total, 37 especies de agaves se extraen de los bosques de México para producir mezcal, lo que ha determinado la degradación o extinción de numerosas poblaciones. Su manejo sustentable es indispensable para evitar la extinción de poblaciones y aún especies. Nuestro estudio analizó información demográfica de poblaciones de Agave potatorum del Valle de Tehuacán con el fin de desarrollar propuestas generales para el uso sustentable de agaves. Estudiamos poblaciones conservadas de agave en dos ambientes contrastantes y a través de análisis prospectivos e información real sobre tasas de extracción y reforestación simulamos las consecuencias de diferentes escenarios de acciones para la conservación. Nuestros análisis indican que las tasas de crecimiento (λ) en poblaciones conservadas son 0.9903 ± 0.062 y 1.021 ± 0.062, respectivamente, pero los análisis de viabilidad poblacional sugieren que aún tales poblaciones decrecerían de 30 a 90%, respectivamente en 30 años. La sobrevivencia y crecimiento de las etapas tempranas del ciclo de vida contribuyen mayormente al valor de λ. Las etapas adultas y la fecundidad tienen baja contribución, pero el manejo sustentable y el manejo de restauración sustentable de las poblaciones requieren que éstas se mantengan. Con base en una experiencia exitosa de manejo de A. cupreata sugerimos que al menos 30% de las plantas reproductivas sean respetadas para asegurar provisión de semillas para la recuperación natural y asistida de las poblaciones. La reintroducción de plantas de1 a 2 años de edad es necesaria, particularmente porque éstas son las categorías de tamaño con mayor contribución a λ. Los esfuerzos actuales que lleva a cabo la gente de la zona para promover la exclusión del ganado a las áreas forestales, la recolecta de semillas, su propagación en viveros, así como las acciones para la recuperación y conservación de poblaciones constituyen estrategias de alto valor. Nuestra investigación busca contribuir a optimizar la efectividad de tales acciones y ayudar a las que se pueden llevar a cabo con otras especies de agave que se extraen de los bosques.

Differential survival and growth of wild and cultivated seedlings of columnar cacti: Consequences of domestication

PREMISE OF THE STUDY Studies of domestication of cacti in the Tehuacán Valley have identified morphophysiological divergences between wild and cultivated populations. To determine whether such divergences are associated with differential survivorship in xeric and mesic environments characterizing wild and cultivated habitats, respectively, we hypothesized that seedlings from cultivated populations are less tolerant of xeric environments and that differences between wild and cultivated populations are greater in species with higher management intensity. METHODS We compared size, survivorship, and absolute and relative growth rates (AGRs, RGRs) in shade and humidity gradients of seedlings from wild and cultivated populations of Stenocereus pruinosus, S. stellatus, Polaskia chichipe, and Escontria chiotilla. These species represent a range of management intensity, from highest to lowest, respectively. KEY RESULTS Seedlings of cultivated populations were larger than those of wild populations in all species studied. The AGRs were significantly different in P. chichipe and E. chiotilla associated with management, whereas the RGRs and seedling survival were significantly different in S. pruinosus and P. chichipe throughout the shade gradient tested. We also found significant differences in seedling survival among humidity treatments in E. chiotilla and among shade treatments in P. chichipe. CONCLUSIONS Artificial selection favoring larger fruits favors larger seeds and seedlings. Seedling survivorship and growth of managed plants are generally higher in mesic environments apparently because of natural selection associated with habitat conditions. Such differences may contribute to morphophysiological divergences between wild and cultivated populations. Interspecific differences might be associated with adaptations to the natural environments where each species occurs.

The Brahea edulis palm forest in Guadalupe Island: A North American fog oasis?

La niebla es un factor que afecta profundamente la estructura de la vegetacion de los desiertos costeros. Guadalupe es una isla oceanica a 260 km de la costa de Baja California y constituye uno de los pocos lugares de la costa del Desierto Sonorense donde se reunen una topografia escarpada proxima a la costa y una alta frecuencia de nieblas. Con el objeto de identificar el efecto de la niebla sobre la comunidad del palmar de Brahea edulis presente en la ladera norte de la isla: (1) analizamos la diferencia de la riqueza y la composicion de plantas vasculares del palmar respecto del resto de la isla, y (2) analizamos la variacion altitudinal de la abundancia de palmas, plantas acompanantes y musgo para determinar si existe variacion altitudinal de la vegetacion. Encontramos que, aunque la composicion de plantas del palmar no fue diferente del resto de la isla, la riqueza de especies y la cobertura fueron claramente superiores en el palmar. Finalmente, constatamos una clara zonacion altitudinal de la vegetacion en el palmar semejante a la encontrada en las comunidades dependientes de la niebla en Sudamerica, tales como las lomas. Por tanto, la comunidad del palmar de Isla Guadalupe puede considerarse como un oasis de niebla, uno de los pocos existentes en Norteamerica.

Fostering Traditional Yucatec Maya Management of Natural Resources through Microcredits: A Community Case Study

In this research we show the way in which a small Yucatec Mayan community conducts a diversified management strategy of its natural resources, as well as how this strategy is supplemented and financed by microfinance. The local description of the ecological process of succession was used for describing the strategy of nature appropriation. Network analysis was used for studying how productive activities are correlated, depending on households having or not having microcredits. Results show that households carry out a diversified management strategy of natural resource in which 12 productive activities are implemented in 5 different land-use units. Study findings show that the network of productive activities of households with microfinance is more interconnected, and that 59% of the people are devoting their microcredits to finance traditional activities such as crop fields, beekeeping, or home gardens, which are the most socially, economically, and ecologically contextualized productive activities in the region.