The effect of sowing time on the growth of chia (Salvia hispanica L.): What do nonlinear mixed models tell us about it?

Chia (Salvia hispanica L.) is an annual short-day plant whose growth has not been studied extensively in low-altitudes and at temperatures outside of its optimal range. The objective of this study was to describe the growth dynamics of a chia crop from an experimental plantation in south-east Mexico, on three different sowing dates. The chia grew at temperatures (18-37°C) and an altitude (9 m a.s.l.) outside of the recommended conditions (20-30°C, 500-1000 m a.s.l.). Three individual-plant responses were measured weekly, before seed harvest: height, number of leaves and number of inflorescences. Three theoretical nonlinear growth models were fitted to the data, a different model for each response. Mixed-effect model parameters were estimated by maximum likelihood, and the goodness of fit for each model was evaluated using two criteria: Modeling Efficiency and Root Mean Square Error. Chia seed yield was also measured in each treatment. Estimated parameters for plant height confirmed that medium sowing time (MST) and late sowing time (LST) plants had smaller heights than the early sowing time (EST) plants. Moreover, at the end of their life cycle, EST plants had a greater number of leaves and inflorescences, and higher seed yield. All of these differences were associated to the extended time of vegetative growth of EST plants favored by optimal photoperiod and temperature. Growth dynamics of chia during its ontogenic phases was explored, in more detail, with relative growth parameters derived from fitted models: a decrease in photoperiod influences the beginning of the reproductive phase, with the consequent reduction in speed of vegetative growth. In addition, nonlinear mixed-effects models can be useful in understanding the relation between growth parameters, plant maturity, and the suitable time for chia seed harvest. Our results suggest chia crops are adaptable to non-conventional environmental conditions.

Potential impact of neonicotinoid use on Northern bobwhite (Colinus virginianus) in Texas: A historical analysis.

The widespread use of neonicotinoid insecticides in recent years has led to increasing environmental concern, including impacts to avian populations. In Texas and across their range, Northern bobwhite (Colinus virginianus) habitat frequently overlaps cultivated cropland protected by neonicotinoids. To address the effects of neonicotinoid use on bobwhites in Texas, we conducted a historical analysis from 1978-2012 in Texas' ecological regions using quail count data collected from North American Breeding Bird Survey and Texas Parks and Wildlife Department, and neonicotinoid use data from the U.S. Geological Survey. We considered bobwhite abundance, neonicotinoid use, climate, and land-use variables in our analysis. Neonicotinoid use was significantly (p<0.05) negatively associated with bobwhite abundance in the High Plains, Rolling Plains, Gulf Coast Prairies & Marshes, Edwards Plateau, and South Texas Plains ecological regions in the time periods following neonicotinoid introduction (1994-2003) or after their widespread use (2004-2012). Our analyses suggest that the use of neonicotinoid insecticides may negatively affect bobwhite populations in crop-producing regions of Texas.

Validation of models with proportional bias / Validación de modelos con sesgo proporcional

ABSTRACT Objective. This paper presents extensions to Freese's statistical method for model-validation when proportional bias (PB) is present in the predictions. The method is illustrated with data from a model that simulates grassland growth. Materials and methods. The extensions to validate models with PB were: the maximum anticipated error for the original proposal, hypothesis testing, and the maximum anticipated error for the alternative proposal, and the confidence interval for a quantile of error distribution. Results. The tested model had PB, which once removed, and with a confidence level of 95%, the magnitude of error does not surpass 1225.564 kg ha-1. Therefore, the validated model can be used to predict grassland growth. However, it would require a fit of its structure based on the presence of PB. Conclusions. The extensions presented to validate models with PB are applied without modification in the model structure. Once PB is corrected, the confidence interval for the quantile 1-α of the error distribution enables a higher bound for the magnitude of the prediction error and it can be used to evaluate the evolution of the model for a system prediction.

RESUMEN Objetivo. En este trabajo se presentan extensiones al método estadístico de Freese para validar modelos con sesgo proporcional (SP) en sus predicciones y se ilustra el método con datos provenientes de un modelo de simulación de crecimiento de praderas. Materiales y métodos. Las extensiones para validar un modelo con SP fueron: el error máximo anticipado para el planteamiento original, la prueba de hipótesis y error máximo anticipado para el planteamiento alternativo, y el intervalo de confianza para un cuantil de la distribución de los errores. Resultados. El modelo evaluado presentó SP, una vez removido y con un nivel de confianza del 95% la magnitud del error no sobrepasa 1225.564 kg ha-1. Por lo que el modelo validado podría usarse para predecir el crecimiento de praderas, sin embargo, requerirá un ajuste en su estructura con base a la presencia de SP. Conclusiones. Las extensiones presentadas para validar modelos en presencia de SP se aplican sin que el modelo sea modificado en su estructura. El intervalo de confianza para el cuantil 1-α de la distribución de los errores una vez que se corrige el SP, permite determinar una cota superior para la magnitud del error de predicción y usarla para evaluar la evolución del modelo en predicción del sistema.

Dung removal by dung beetles (Coleoptera: Scarabaeidae) and macrocyclic lactone use on cattle ranches of Yucatan, Mexico / Remoción de estiércol por escarabajos estercoleros (Coleoptera: Scarabaeinae) y uso de lactonas macrocíclicas en ranchos ganaderos de Yucatán, México

Abstract:The expanded use of macrocyclic lactones (ML) to treat endo- and ectoparasites in cattle in tropical regions, can reduce dung beetle populations, and thus interrupt the dung removal process in cattle pasture ecosystems. During the reproductive period (the rainy season) of two functional groups of dung beetles (paracoprid and telocoprid Scarabaeinae), we compared dung removal amount in ranches where ML are and are not used in Yucatan, Mexico, through exclusion traps baited with 500 g of ML-free cow dung. On each ranch, two transects (separated by 500 m) with six traps each, were set up for 24 hours. After this time, all the dung remnants in each trap were obtained and weighed in order to record the dung removal. Results showed that dung removal amounts were similar in ranches with and without ML use. Dung beetles removed 40.1 % of all cow dung weighed. Paracoprids removed 87.46 % and telocoprids 12.54 % of all the dung that was removed. Our results indicated that the ecological function of dung beetles in the pastures studied, does not seem to be affected by the ML use, and that paracoprid species removed most of the dung. For both types of ranch, further studies that take into account the population dynamics and movement of the most important dung beetle species in the region are required, coupled with laboratory studies evaluating the effect of ML on their reproductive success. This could give some light on the effect of ML on the ecological function of this important insect group in the sustainability of cattle production systems. Rev. Biol. Trop. 64 (3): 945-954. Epub 2016 September 01.

ResumenLa expansión en el uso de lactonas macrocíclicas (LM) para el tratamiento de endo y ectoparásitos del ganado en las regiones tropicales puede reducir las poblaciones de escarabajos del estiércol, interrumpiendo así el proceso de eliminación de estiércol de ganado en los pastizales. Durante el período reproductivo (época de lluvias) de dos grupos funcionales de escarabajos coprófagos (paracópridos y telecópridos), se comparó la cantidad removida de estiércol usando trampas de exclusión cebadas con 500 g de estiércol de vaca libre de LM en dos ranchos donde se usan y en dos donde no se usan LM, en la península de Yucatán, México. En cada rancho se establecieron dos transectos (separados por 500 m) con seis trampas cada uno, las cuales estuvieron activas durante 24 horas. Después de este tiempo, todos los restos de estiércol en cada trampa se pesaron para registrar la remoción. Los resultados mostraron que las cantidades de remoción fueron similares en ranchos con y sin uso de LM. Los escarabajos estercoleros removieron 40.1 % del peso total del excremento. Los paracópridos removieron 87.46 % y los telecópridos 12.54 % del total de excremento removido. Los resultados indican que la función ecológica de los escarabajos estercoleros en los potreros estudiados no parece verse afectada por el uso de LM y que las especies paracórpidas remueven la mayor parte del excremento. Se requiere hacer más estudios en ambos tipos de ranchos, en los que se tome en cuenta la dinámica poblacional y el movimiento de las especies más importantes de la región, acoplados a estudios de laboratorio que evalúen el efecto de las LM sobre el éxito reproductivo, y de esta manera esclarecer el efecto de las LM sobre la función ecológica de este grupo de insectos tan importante para la sustentabilidad de los sistemas ganaderos.

Performance of growing rabbits fed increasing levels of discarded Salvia hispanica L. (chia) seed.

This experiment was carried out to evaluate the effect of including five levels of discarded chia seed (DCS) on growth, energy, and economic efficiency in rabbits. Fifty crossbred (New Zealand × Californian) weaning rabbits, weighing 798 ± 170 g, were randomly assigned to the following treatments: 0 % (control), 10 % (Ch10), 20 % (Ch20), 30 % (Ch30), and 40 % (Ch40) of DCS. Ten unsexed rabbits were allocated to each treatment and housed individually in cages; the experimental period was 6 weeks. There were no statistically significant differences between treatments in final body weight (2050 g), body weight gain (30 g/rabbit/day), and carcass weight (1010 g); however, feed intake (91 g/rabbit/day in Ch20 vs. 80 g/rabbit/day in Ch40), feed conversion ratio (2.77 in control and Ch40 vs. 2.95 in Ch10, Ch20, and Ch30), energy conversion ratio (32 MJ/kg in Ch20 vs. 29 MJ/kg on average in control, Ch10, Ch20, Ch30, and Ch40), and economic efficiency (358 % in control vs. 433 % in Ch40) showed differences (P < 0.05) between treatments. Discarded chia seed can be included up to 40 % in growing rabbit diets without any adverse effects on growth and carcass weight, and increased economic efficiency.

Dung removal by dung beetles (Coleoptera: Scarabaeidae) and macrocyclic lactone use on cattle ranches of Yucatan, Mexico.

The expanded use of macrocyclic lactones (ML) to treat endo- and ectoparasites in cattle in tropical regions, can reduce dung beetle populations, and thus interrupt the dung removal process in cattle pasture ecosystems. During the reproductive period (the rainy season) of two functional groups of dung beetles (paracoprid and telocoprid Scarabaeinae), we compared dung removal amount in ranches where ML are and are not used in Yucatan, Mexico, through exclusion traps baited with 500 g of ML-free cow dung. On each ranch, two transects (separated by 500 m) with six traps each, were set up for 24 hours. After this time, all the dung remnants in each trap were obtained and weighed in order to record the dung removal. Results showed that dung removal amounts were similar in ranches with and without ML use. Dung beetles removed 40.1 % of all cow dung weighed. Paracoprids removed 87.46 % and telocoprids 12.54 % of all the dung that was removed. Our results indicated that the ecological function of dung beetles in the pastures studied, does not seem to be affected by the ML use, and that paracoprid species removed most of the dung. For both types of ranch, further studies that take into account the population dynamics and movement of the most important dung beetle species in the region are required, coupled with laboratory studies evaluating the effect of ML on their reproductive success. This could give some light on the effect of ML on the ecological function of this important insect group in the sustainability of cattle production systems.

Arbuscular mycorrhizal propagules in soils from a tropical forest and an abandoned cornfield in Quintana Roo, Mexico: visual comparison of most-probable-number estimates.

The present study was aimed at comparing the number of arbuscular mycorrhizal fungi (AMF) propagules found in soil from a mature tropical forest and that found in an abandoned cornfield in Noh-Bec Quintana Roo, Mexico, during three seasons. Agricultural practices can dramatically reduce the availability and viability of AMF propagules, and in this way delay the regeneration of tropical forests in abandoned agricultural areas. In addition, rainfall seasonality, which characterizes deciduous tropical forests, may strongly influence AMF propagules density. To compare AMF propagule numbers between sites and seasons (summer rainy, winter rainy and dry season), a "most probable number" (MPN) bioassay was conducted under greenhouse conditions employing Sorgum vulgare L. as host plant. Results showed an average value of 3.5 ± 0.41 propagules in 50 ml of soil for the mature forest while the abandoned cornfield had 15.4 ± 5.03 propagules in 50 ml of soil. Likelihood analysis showed no statistical differences in MPN of propagules between seasons within each site, or between sites, except for the summer rainy season for which soil from the abandoned cornfield had eight times as many propagules compared to soil from the mature forest site for this season. Propagules of arbuscular mycorrhizal fungi remained viable throughout the sampling seasons at both sites. Abandoned areas resulting from traditional slash and burn agriculture practices involving maize did not show a lower number of AMF propagules, which should allow the establishment of mycotrophic plants thus maintaining the AMF inoculum potential in these soils.

Genetic variation in the response of the weed Ruellia nudiflora (Acanthaceae) to arbuscular mycorrhizal fungi.

The main goal of this work was to test for plant genetic variation in the phenotypic plasticity response of the weed Ruellia nudiflora to arbuscular mycorrhizal (AM) fungi inoculation. We collected plants in the field, kept them under homogeneous conditions inside a nursery, and then collected seeds from these parent plants to generate five inbred lines (i.e., genetic families). Half of the plants of each inbred line were inoculated with AM fungi while the other half were not (controls); a fully crossed experimental design was then used to test for the effects of treatment (with or without AM fungi inoculation) and inbred line (genetic family). For each plant, we recorded the number of leaves produced and the number of days it survived during a 2-month period. Results showed a strong positive treatment effect (plastic response to AM fungi inoculation) for leaf production and survival. Moreover, in terms of survival, the treatment effect differed between genetic families (significant genetic family by treatment interaction). These findings indicate that the positive effect of AM fungi on plant survival (and potentially also growth) differs across plant genotypes and that such condition may contribute to R. nudiflora's capacity to colonize new environments.

Spatial and temporal variation of fish assemblages in a coastal lagoon of the Biosphere Reserve La Encrucijada, Chiapas, Mexico

Composition and abundance of the ichthyofauna in estuarine and coastal lagoon systems of the South Pacific in Mexico have been scarcely studied. In particular, there is a lack of information on how environmental variables determine the spatio-temporal structure of fish assemblages in those habitats. In this study, fishes were sampled by drop net during twelve months (May 2004 -April 2005) in 22 sites distributed along the Carretas-Pereyra lagoon, located in the Biosphere Reserve La Encrucijada, Chiapas, Mexico. We recorded 11 797 individuals (40 species, in 30 genera and 21 families). Dormitator latifrons was the most dominant species in terms of the Importance Value index, IV (23.05 %), followed by Lile gracilis (10.31 %), Poecilia sphenops (8.60 %) and Poecilia butleri (7.30 %). D. latifrons also accounted for more than one half of the total biomass (50.14 %). Species richness and Shannon-Wiener’s diversity indexes showed similar temporal fluctuations, reaching their highest values during the dry season. The system evidenced temporal variations in salinity, having observed four different regimes: freshwater, oligohaline, mesohaline and polyhaline. Mean richness and diversity indexes achieved their highest values during the mesohaline period. On the other hand, mean abundances (CPUE) were highest during the freshwater period. Canonical correspondence analysis (CCA) indicated that salinity and temperature were the most important environmental parameters affecting associations of fishes in terms of their abundances. Correlation analyses revealed that among the environmental variables measured in this study, transparency showed the most significant negative correlation with fish richness and Shannon-Wiener’s diversity index. At a local scale, results suggest that spatial and temporal distribution of fish assemblages are determined by differences in the regimes of salinity and transparency, primarily driven by freshwater input from rivers. Rev. Biol. Trop. 56 (2): 557-574. Epub 2008 June 30.

Se evaluó la influencia de los factores ambientales sobre la variación espacio-temporal de los ensamblajes de peces, en el sistema lagunar Carretas-Pereyra, Chiapas, México. Entre mayo de 2004 y abril de 2005, se realizaron 12 muestreos mensuales en 22 sitios. Se recolectaron 11 797 organismos, pertenecientes a 40 especies, representando a 30 géneros y 21 familias. Dormitator latifrons fue la especie dominante en Índice de Valor de importancia, IV (23.05 %), seguida por Lile gracilis (10.31 %), Poecilia sphenops (8.60 %) y Poecilia butleri (7.30 %). D. latifrons, contribuyó con 50.14 % de la biomasa total. Los valores de riqueza y diversidad de especies (H’) mostraron variaciones temporales similares, siendo más altos en la época de secas que de lluvias. El sistema lagunar presentó variaciones importantes en los valores de salinidad con los siguientes regimenes: agua dulce, oligohalino, mesohalino y polihalino. La riqueza media de especies y la diversidad alcanzaron sus valores más altos durante el periodo mesohalino. Contrario a los valores de riqueza y diversidad, la abundancia promedio (CPUE) presentó los valores más altos durante el régimen de agua dulce.

Spatial and temporal variation of fish assemblages in a coastal lagoon of the Biosphere Reserve La Encrucijada, Chiapas, Mexico.

Composition and abundance of the ichthyofauna in estuarine and coastal lagoon systems of the South Pacific in Mexico have been scarcely studied. In particular, there is a lack of information on how environmental variables determine the spatio-temporal structure of fish assemblages in those habitats. In this study, fishes were sampled by drop net during twelve months (May 2004 - April 2005) in 22 sites distributed along the Carretas-Pereyra lagoon, located in the Biosphere Reserve La Encrucijada, Chiapas, Mexico. We recorded 11,797 individuals (40 species, in 30 genera and 21 families). Dormitator latifrons was the most dominant species in terms of the Importance Value index, IV (23.05%), followed by Lile gracilis (10.31%), Poecilia sphenops (8.60%) and Poecilia butleri (7.30%). D. latifrons also accounted for more than one half of the total biomass (50.14%). Species richness and Shannon-Wiener's diversity indexes showed similar temporal fluctuations, reaching their highest values during the dry season. The system evidenced temporal variations in salinity, having observed four different regimes: freshwater, oligohaline, mesohaline and polyhaline. Mean richness and diversity indexes achieved their highest values during the mesohaline period. On the other hand, mean abundances (CPUE) were highest during the freshwater period. Canonical correspondence analysis (CCA) indicated that salinity and temperature were the most important environmental parameters affecting associations of fishes in terms of their abundances. Correlation analyses revealed that among the environmental variables measured in this study, transparency showed the most significant negative correlation with fish richness and Shannon-Wiener's diversity index. At a local scale, results suggest that spatial and temporal distribution of fish assemblages are determined by differences in the regimes of salinity and transparency, primarily driven by freshwater input from rivers.