Effects of nitrogen fertilizer and pesticide management on floodwater ecology in a wetland ricefield : 2. Dynamics of microcrustaceans and dipteran larvae

La dynamique des populations de cyanobactéries et de microalgues, du zooplancton et des populations de mollusques a été étudiée au cours d'un cycle cultural dans des rizières expérimentales soumises à différentes méthodes de fertilisation azotée et d'application de pesticides. L'article présente les résultats concernant la dynamique des populations de microcrustacés et des larves aquatiques de diptères. Les différents groupes se développent suivant la succession : larves de moustiques et de chironomides -> ostracodes -> copépodes + cladocères. Les populations d'ostracodes et les larves de moustiques et de chironomides se développent rapidement après l'épandage d'engrais azoté. L'enfouissement de l'engrais azoté évite cette prolifération. A l'exception des larves de chironomides en début de cycle cultural, les populations d'invertébrés aquatiques sont généralement moins abondantes dans les parcelles ou de l'engrais vert a été enfoui. A l'échelle du cycle cultural, les populations d'invertébrés ne sont pas significativement affectées par les applications de pesticides effectuées. (Résumé d'auteur

Density and composition of aquatic oligochaete populations in different farmers' ricefields

La densité et la composition des populations d'oligochetes aquatiques ont été estimées dans 32 rizières des Philippines et mises en relation avec les propriétés physico-chimiques des sols et les quantités d'agrochimiques utilisées. La distribution spatiale des organismes et les stratégies d'échantillonnage ont été déterminées à partir d'un échantillonnage de haute densité effectué dans une rizière de référence. Une faible diversité spécifique des organismes a été mise en évidence. Les espèces dominantes sont #Limnodrilus hoffmeisterii et #Branchiura sowerbii. La distribution spatiale des populations est de type contagieux et les densités varient de 0 à 35000 m-2 (Maximum = 620 kg P.F. ha-1). La densité moyenne des populations montre une corrélation positive avec la teneur en eau du sol, sa teneur en matière organique et la quantité d'engrais azoté épandue. Aucun effet des pesticides n'a pu être mis en évidence. (Résumé d'auteur

The potential of marginal coastal nursery habitats for the conservation of a culturally important Caribbean marine species

Aim: Identifying the potential of marginal habitats for species conservation is of key importance when their core high-quality habitats are under substantial disturbances and threats. However, there is currently a knowledge gap on how useful marine marginal habitats may be for conserving endangered marine species. Here, we investigate the potential of groundwater-fed coastal areas for the conservation of the queen conch, an economically and culturally important marine gastropod. Location: The inlet of Xel-Ha, typical of groundwater-fed coastal areas widely distributed along the Yucatan Peninsula coast in Mexico and partially protected by a network of marine protected areas. Methods: We tracked 66 queen conchs (Lobatus gigas) using acoustic telemetry over a period of 3.5 years. We investigated for ontogenetic niche shift using a network analysis and by modelling their growth. Results: The queen conchs exhibited the same ontogenetic niche shift required to complete their life cycle in this marginal habitat as they do in offshore core habitats. A total of 33 individuals departed the inlet and migrated from shallow groundwater-affected nursery grounds to deeper marine habitats more suitable for breeding aggregation. Main conclusions: As the broad-scale movement behaviour of queen conch in this inlet is similar to that observed on the overfished core habitats, our findings suggest that groundwater-fed coastal areas should be included in conservation planning for an effective management of this species within a network of marine protected areas

Reproductive Strategy of the Giant Electric Ray in the Southern Gulf of California

The objective of the present study was to describe and characterize macroscopic and microscopic aspects of the reproductive biology of the Giant Electric Ray Narcine entemedor, a viviparous elasmobranch targeted by commercial fishers in Mexico. A total of 305 individual rays were captured (260 females, 45 males); all males were sexually mature. The median size at maturity for females was estimated to be 58.5 cm TL, the median size at pregnancy was 63.7 cm TL, and the median size at maternity was 66.2 cm TL. The range of ovarian follicles recorded per female was 1–69; the maximum ovarian fecundity of fully grown vitellogenic oocytes was 17, and uterine fecundity ranged from 1 to 24 embryos per female. The lengths of the oblong ovarian follicles varied significantly among months, and the largest ovarian follicles were found in July, August, and September. Median embryo size was largest in August, and the size at birth was between 12.4 and 14.5 cm TL. Histological evidence of secretions from the glandular tissue of the uterine villi indicate that this species probably has limited histotrophy as a reproductive mode. Vitellogenesis in the ovary occurred synchronously with gestation in the uterus. The Giant Electric Ray has a continuous annual reproductive cycle; a period of ovulation occurs between May and September and two peaks of parturition, one in January and one in August, occur, suggesting that embryonic diapause occurs in some individuals. These results provide useful information for the management of this important commercial species in Bahía de La Paz, Mexico, and will allow possible modification of the current Mexican regulations to enable better protection of this species

Does access to free health insurance crowd-out private transfers? Evidence from Mexico’s Seguro Popular

This study examines whether Seguro Popular, a free-of-charge publicly provided health insurance program for otherwise uninsured households, crowded-out private transfers in Mexico. Using data from the National Household Income and Expenditure Survey, the effects of Seguro Popular are identified using the spatial variation in the program's coverage induced by its sequential roll-out throughout Mexico. The results show that Seguro Popular reduced on average a household's probability of receiving private transfers by 5.55 % points. This finding appears to be driven by domestic private transfers, since the program's effects are only statistically significant for private transfers originating within Mexico. In addition, Seguro Popular had a weak and not statistically significant negative effect on the amount of private transfers received. Failure to take into account possible changes in private behaviour induced by Seguro Popular may overstate the program's potential benefits or distributional impacts

Precipitation regionalization, anomalies and drought occurrence in the Yucatan Peninsula, Mexico

© 2020 The Authors. International Journal of Climatology published by John Wiley & Sons Ltd on behalf of the Royal Meteorological Society. Climate change projections have identified the Yucatan Peninsula as being vulnerable to increasing drought. Understanding spatial and temporal precipitation variability and drought occurrence are therefore important. Drought monitoring in Mexico has been carried out only relatively recently and often without considering the long-term variability in both droughts and precipitation. This research explores the spatio-temporal variability of precipitation and occurrence of droughts at a much finer spatial resolution and over a longer temporal period than previous studies. Using statistical (cluster analysis and standardized precipitation index) and geostatistical (kriging) techniques, maps of precipitation and droughts are generated for the period 1980–2011. These show that whilst many previous studies have regarded the Yucatan Peninsula as a homogenous region with respect to precipitation, there are actually four distinctive clusters of precipitation amount, showing climatic variability across the Peninsula. The analyses also show that droughts in the Peninsula are regionalised. Twelve-month Standardized Precipitation Indices (SPI), calculated for individual stations and for precipitation surfaces, reveal distinct patterns of spatial and temporal variability. SPI surfaces indicate the occurrence of major droughts in 1981, 1986–1987, 1994, 1996, 2003, 2004 and 2009, but these rarely affect the whole Yucatan Peninsula uniformly. Wetter years, such as 1983, 1984, 1988, 1992, 1995, 2002 and 2005 sometimes reflect the impact of individual extreme events, such as hurricane Isidore in 2002. Our results show that drought can be regionalised, thus enhancing the quality of information about droughts in the area and providing evidence and support for future drought mitigation and environmental protection. These methods could usefully be applied elsewhere

Opuntia in México: Identifying Priority Areas for Conserving Biodiversity in a Multi-Use Landscape

BACKGROUND: México is one of the world's centers of species diversity (richness) for Opuntia cacti. Yet, in spite of their economic and ecological importance, Opuntia species remain poorly studied and protected in México. Many of the species are sparsely but widely distributed across the landscape and are subject to a variety of human uses, so devising implementable conservation plans for them presents formidable difficulties. Multi-criteria analysis can be used to design a spatially coherent conservation area network while permitting sustainable human usage. METHODS AND FINDINGS: Species distribution models were created for 60 Opuntia species using MaxEnt. Targets of representation within conservation area networks were assigned at 100% for the geographically rarest species and 10% for the most common ones. Three different conservation plans were developed to represent the species within these networks using total area, shape, and connectivity as relevant criteria. Multi-criteria analysis and a metaheuristic adaptive tabu search algorithm were used to search for optimal solutions. The plans were built on the existing protected areas of México and prioritized additional areas for management for the persistence of Opuntia species. All plans required around one-third of México's total area to be prioritized for attention for Opuntia conservation, underscoring the implausibility of Opuntia conservation through traditional land reservation. Tabu search turned out to be both computationally tractable and easily implementable for search problems of this kind. CONCLUSIONS: Opuntia conservation in México require the management of large areas of land for multiple uses. The multi-criteria analyses identified priority areas and organized them in large contiguous blocks that can be effectively managed. A high level of connectivity was established among the prioritized areas resulting in the enhancement of possible modes of plant dispersal as well as only a small number of blocks that would be recommended for conservation management