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991.
The effects of agricultural intensification on vertebrate populations could vary depending on whether species are habitat specialists or habitat generalists. Organic farming practices are generally considered to be less intensive and more environmental friendly than conventional farming practices and, as a result, these two managements may impact on habitat specialists and habitat generalists in different ways. The effect of environmental and/or genetic stress on populations can be assessed using fluctuating asymmetry (FA) and body condition of animals. We predicted that populations of a specialist species, the Pampean grassland mouse (Akodon azarae) would have higher levels of FA and poorer body condition on conventional farms compared to populations of A. azarae on organic farms. In contrast, we predicted that populations of generalist species, the corn mouse (Calomys musculinus) and the small vesper mouse (Calomys laucha) would not show differences in FA or body condition between conventional and organic farms. We examined the expression of FA in the hind foot and used the scaled mass index as a surrogate for body condition. As predicted, we found higher FA in the habitat specialist (A. azarae) on conventional farms compared to organic farms, and found no differences in FA among the two generalist species (C. musculinus and C. laucha). However, we found no differences in body condition for the three studied species between the two managements. Our results suggest that the effect of farming practices on small mammals varies between habitat specialists and habitat generalists. The results of this study provide important insights for the study of asymmetries, both from biological and methodological perspectives. Our results support the idea that the level of FA may be used as an index to assess the effects of farming practices on vertebrate populations. 相似文献
992.
During adolescence, interactions with peers influence a teen’s attitudes and behaviors. Adolescents seek for peer approval and acceptance, which may bring them to engage in health-risky behaviors such as smoking and drinking. In this study, we estimate the impact of peers on the drug use of Spanish students aged 14 to 18. We focus on the consumption of alcohol and tobacco, the most prevalent substances used at those ages. We estimate the effect of the average classmates’ consumption—the measure of peers’ use—on individual consumption. Since peers’ use affects individual use and vice versa, we correct for this bias using instrumental variables. Results show that peers’ consumption increases substantially the probability of using alcohol, while it does not significantly affect tobacco consumption. Our results are not sensitive to using different time spans of consumption. This study shows also novel evidence indicating that the higher the proportion of grade-retained students in the class, the stronger the peer effects, especially for alcohol. This suggests that future reforms of the grade retention policy should also consider the negative effects on non-academic outcomes, such as substance use. 相似文献
993.
Elisabeth Jimnez‐Carmona Janine Herrera‐Rangel Luis Miguel Renjifo Inge Armbrecht 《Insect Conservation and Diversity》2020,13(4):384-392
- Ecological restoration of riparian forest corridors at the landscape scale can facilitate recruitment of certain flora and fauna, thus possibly helping to maintain viable wildlife populations.
- We evaluated ecological restoration of three corridors between two protected Andean forests. Soil ants and eight environmental variables focused on edaphic conditions were monitored for 8 years following restoration activity. Soil ants were collected in pitfall traps and by leaf litter extraction on 21 plots classified into five types of habitat: large forest patches, riparian forests, two types of restoration corridors on former timber and pasture land (R‐Forestry and R‐Pasture, respectively), and Pasture.
- A total of 132 ant species belonging to 40 genera were found. Among these, 112 species were found in Forests, 105 in Riparian, 80 in R‐Forestry, 79 in R‐Pasture and 63 in Pasture. Composition analyses (canonical correspondence analysis and NMDS) showed that the ant community in restoration corridors and pastures is far from resembling that of the forests. Yet, there is biological progress with respect to the Pasture.
- Gnamptogenys bisulca and Pheidole pygmaea were indicator species for advanced restoration progress because of their close association to forests, while Linepithema piliferum indicated a reversal of restoration progress due to its preference for open habitats.
- Since both ant richness and composition in restored areas do not yet resemble the reference forest ecosystem, we suggest that other interventions such as restoring wider corridors and changing to wild‐friendly agriculture around the reserves might improve restoration efforts in Andean landscapes.
994.
O. Navratil M.A. Boukerb F. Perret P. Breil C. Caurel L. Schmitt J. Lejot S. Petit L. Marjolet B. Cournoyer 《Ecohydrology》2020,13(4)
Faecal indicator bacteria (FIB) and bacterial pathogens from combined sewer overflow (CSO) in peri‐urban streams represent a major public health concern worldwide. In this study, the relationships between the hydrological regime and the loads and persistence of CSO‐borne bacterial contaminants among benthic sediments of a small peri‐urban stream were explored. Combined sewer overflow events and their impact on benthic sediment layers at a short distance from a CSO were monitored. Concentrations of Escherichia coli (EC) and intestinal enterococci (IE) and of two bacterial pathogens, Pseudomonas aeruginosa (PA) and Aeromonas caviae (AC), were assessed. Relations with hydraulic, hydromorphic and physicochemical factors were analysed. PA cells in benthic sediments increased exponentially with time (0.15 log PA per day), as long as the river discharge remained below the sediment transport. Cycles of erosive floods and low‐flow periods were found to play a critical role in PA settling and growth among benthic riverbed sediments. These hydrological and hydraulic shear forces did not correlate with changing IE, EC, and AC concentrations in the benthic sediments. Their dynamics were rather related to changing physicochemical conditions (total N, phosphate, and organic carbon). AC population size decreases most rapidly with a mean rate of 0.04 log per day according to the duration of the low‐flow period, indicating a poor tropism of AC for river systems. River sediments were found significant biotopes for PA outdoor development. These analyses demonstrate the significance of PA and AC as long‐ and short‐term indicators, respectively, of a river microbiological quality. 相似文献
995.
Ester Holcman Paulo Cesar Sentelhas Marcel Bellato Spsito Marco Antnio Fonseca Conceio Hilton Thadeu Zarate Couto 《Journal of Phytopathology》2019,167(3):185-195
Viticulture has been expanding in tropical regions. However, the climate in these areas is generally favourable to the incidence of plant diseases, especially downy mildew. Plastic covers and warning systems have shown very positive results in disease control, but they are tools that have never been used simultaneously in a tropical area. The Vitis vinifera cv. BRS Morena table grape was evaluated as regards yield and quality under different downy mildew control strategies as carried out on vineyards trained on an overhead trellis system, covered by a black shading screen (BSS) or a braided polypropylene film (BPF), over a 3‐year period. Different grapevine downy mildew management approaches defined the treatments: Co) Control (no spraying); Ca) Conventional control (calendar); Ba) “Rule 3–10” (Atti Istituto Botanico, 8, 1947, 45); Ma25) Low‐infection efficiency—i0>25%; and Ma75) High‐infection efficiency—i0>75% (Plant Disease, 84, 2000, 549). The occurrence of downy mildew and the amount of damage inflicted on vine yield and grape quality are directly related to the period of the crop cycle when there is rainfall. The use of the Ma75 warning system (Plant Disease, 84, 2000, 549) under braided polypropylene film resulted, for the most part, in similar vineyard productivity compared to Ca, but did not influence the number of branches and its fertility. The other warning systems decreased productivity by 31.9% compared to Ca. It was not possible to establish a relationship between the occurrence of downy mildew and its influence on grape sweetness and acidity. The use of warning systems led to a substantial reduction in fungicide sprays, approximately 66.7 to 71.3%, compared to the calendar system commonly used by the vine growers, with the Ba (Atti Istituto Botanico, 8, 1947, 45) and Ma75 controls (Plant Disease, 84, 2000, 549) leading to the highest fungicide saving. 相似文献
996.
997.
QuestionsDoes the vegetation composition of the forests of Nandiar Valley correlate with climatic, topographic and edaphic variables? Is it possible to identify plant communities through indicator species in relation to environmental gradients? Can this approach of classification and ordination will be helpful for conservation planning?LocationForests of Nandiar Valley, Moist temperate Western Himalayas Pakistan.MethodsEighty stands were selected for quantitative and qualitative characteristic of vegetation between an elevations of 525–3817 m. Species composition was recorded by using 400 m long transects. GPS, climatic, edaphic and topographic data were recorded for each sampling site. The relationship between habitat types, species composition and distribution along with climatic, edaphic and topographic variables were analyzed using TWINSPAN, Cluster analysis and DCA ordination.ResultsSum 325 vascular plants species belonging to 97 families were recorded. Diversity index and species richness was maximum in the moist temperate zone. Classification and ordination showed that the variance in species data was 7.07. Two-ways indicator species analysis classified the vegetation into eight plant communities. Indicator species analysis revealed that slope aspect, wind speed, temperature, dew point, wet bulb, pH, organic matter and phosphorous were the strongest parameters (p ≤ 0.05) determining plant community composition and indicator species in each habitat. The results also show the strength of the environment – species relationship using Monte Carlo procedures. DCA ordination grouped different species having similar habitat and habitats having common species.ConclusionsThe multivariate analysis of the vegetation along with environmental variables of Nandiar valley confirmed the indicators of each sort of vegetation communities/microclimatic zones which could further be used in conservation planning and management not only in studied area but also in the adjacent regions as well as in the areas exhibit similar sort of climatic, edaphic and topographic conditions. 相似文献
998.
- The quantification of periphyton growth in situ poses numerous difficulties.
- The RNA/DNA ratio is widely used as a growth indicator in marine ecology. We tested its applicability as a growth indicator of periphyton in streams of different sizes.
- Periphyton‐covered stones sampled from two different watercourses during two seasons were exposed in laboratory flumes to different light levels to induce different growth rates. The relationship between rate of biomass accrual and RNA/DNA ratio was analysed by measuring the chlorophyll‐a content and the RNA and DNA content of total nucleic acid extract of the periphyton respectively.
- The RNA/DNA ratios showed a linear relationship with the biomass accrual at all sampling times. The slopes of these relationships varied significantly between the two watercourses, but not between seasons within the same watercourse.
- These results indicate that the RNA/DNA ratio can be used as a growth indicator for the periphyton studied here. We recommend that it be used to detect differences in growth rate of the same periphyton community either over time or between different treatments in ecological or ecotoxicological experiments. However, for long‐term monitoring studies, we recommend taxonomic analyses of the assemblages because the observed differences in the relationship between the RNA/DNA ratio and growth rate might be attributed to community structure differences in the assemblages.
999.
This paper uses national longitudinal data to analyze the effects of having a teen mother on child health outcomes from birth to young adulthood. We use an empirical strategy that relies on miscarriages to put bounds on the causal effects of teen childbearing. Results show that having a teen mother does not have negative health consequences for children. In addition, children of teen mothers report fewer diagnosed disorders and conditions requiring medical attention. The results suggest that policies focused on delaying teen childbearing will not improve child health outcomes. 相似文献
1000.
The soil vapor to indoor air exposure pathway is considered in a wide number of risk-based site management programs. In screening-level assessments of this exposure pathway, models are typically used to estimate the transport of vapors from either subsurface soils or groundwater to indoor air. Published studies indicate that the simple models used to evaluate this exposure pathway often over estimate the impact for aromatic hydrocarbons (e.g., benzene, toluene, ethylbenzene, and xy-lene or BTEX), while showing reasonable agreement for estimates of chlorinated hydrocarbon impacts (e.g., PCE, TCE, DCE). Aerobic biodegradation of the petroleum hydrocarbons is most often attributed as the source of this disparity in the model/ data comparisons. This paper looks at the significance of aerobic biodegradation of aromatic hydrocarbons as part of the assessment of chemical vapor intrusion from soil or groundwater to indoor air. A review of relevant literature summarizing the available field data as well as various modeling approaches that include biodegradation is presented. This is followed by a simple modeling analysis that demonstrates the potential importance of biodegradation in the assessment of the soil vapor to indoor air exposure pathway. The paper concludes with brief discussions of other model considerations that are often not included in simple models but may have a significant impact on the intrusion of vapors into indoor air. 相似文献