Cerastoderma edule and Mya arenaria are two common bivalve species in European waters. Longevity and maximum size are much greater in the latter species. Because comparison of species life-history strategies states that a long life span (i.e. high annual survival) generally goes with lower fecundity, we hypothesise that reproductive output would be lower in M. arenaria than in C. edule. In the present paper, we studied the reproductive strategies of these two species in an intertidal and a subtidal area of the western Dutch Wadden Sea, by following seasonal changes in absolute and relative weights of somatic and gonadal tissues in these bivalves. Starting of spawning was similar in the two species, around May, except for intertidal M. arenaria, which initiated spawning in August. Individual energy investment in reproduction was similar for the two species but, unlike M. arenaria, C. edule spawned completely, releasing all energy of gonadal mass in the form of gametes. Mya arenaria used the gonad not only for reproduction but also for storage. In the intertidal area, we found a trade-off between longevity and reproduction, i.e. maximum reproductive output (expressed as a proportion of body mass) was higher in C. edule than in M. arenaria. However, since body size is larger and life span longer in M. arenaria than in C. edule, mean lifetime reproductive output per individual must be higher in the first than in the latter. Based on the differences in reproductive strategies of these two species, we hypothesise that the negative effects of warming climate on bivalve population dynamics in the Wadden Sea will be stronger in C. edule than in M. arenaria. 相似文献
Abstract. In situ investigations of growth and production in a stand of Posidonia oceanica (L.) DELILE at a depth of 4 m at Ischia (Gulf of Naples) were carried out over two growing seasons. Posidonia starts to grow in August and an average bundle produces ten leaves in increasing time intervals until May. Growth curves for the leaves are given. Maximum leaf standing crop is in May with 1300 g dry weight per m-2, leaf area index at this time reaches 22 m2 m-2. Leaf net productivity is highest in March with 12 g dry weight per m2 per day. Annual leaf production is estimated as 3110 g dry weight per m2, “underground” production as 115 g dry weight per m2. About half the leaf production is exported from the system. Adaptive strategies of the growth and production pattern are discussed. 相似文献
Famines are often linked to drought in semi-arid areas of Sub-Saharan Africa where not only pastoralists, but also increasingly agro-pastoralists are affected. This study addresses the interplay between drought and famine in the rural semi-arid areas of Makueni district, Kenya, by examining whether, and how crop production conditions and agro-pastoral strategies predispose smallholder households to drought-triggered food insecurity. If this hypothesis holds, then approaches to deal with drought and famine have to target factors causing household food insecurity during non-drought periods. Data from a longitudinal survey of 127 households, interviews, workshops, and daily rainfall records (1961–2003) were analysed using quantitative and qualitative methods. This integrated approach confirms the above hypothesis and reveals that factors other than rainfall, like asset and labour constraints, inadequate policy enforcement, as well as the poverty-driven inability to adopt risk-averse production systems play a key role. When linking these factors to the high rainfall variability, farmer-relevant definitions and forecasts of drought have to be applied. 相似文献
Since the Paris Agreement was adopted in 2015, both national and subnational governments have been encouraged to submit Mid-Century Strategies, outlining how they would reach their deep decarbonization goals. However, research on the design and potential of these strategies has been very limited. To address this shortcoming, here we assess 13 such strategies – six national, seven subnational – in a comparative fashion. We find that the energy-economy-climate models underpinning these strategies are generally of high quality, though national jurisdictions generally performed better. However, most strategies are not plausible without significant changes to policy, and the industrial sector in particular presents a major limitation. The strategies are helpful in revealing this gap, but much works remains to be done for plausible mid-century decarbonization trajectories to become a reality. We also find that public input and societal participation in strategy building were a double-edged sword depending on the constellation of domestic preferences.
Governmental Mid-Century Strategies for deep decarbonization are underpinned by high-quality energy-economy-climate models
Governments’ proposed strategies require significant new policies, as even among jurisdictions that have an MCS, extant policies are insufficient to achieve deep decarbonization
No jurisdiction studied has yet put forward a plausible decarbonization policy for the industrial sector.
Public input and societal participation can be a double-edged sword: they can increase durability of the strategy but also enable opposing forces to mobilize against ambitious changes.
Abstract A Southern Poverty Law Center grant enabled purchasing dolls representing children of different races, ethnicity, and condition of disability. The teacher used these with other materials to sensitize kindergarten children to human differences. She directed them to cut pictures from National Geographic Magazine showing people who are “somehow different/' Responses from children were classified. Nine commented on adornment, three on household setting, two on occupation, and one on race. Little research exists on teaching geography to kindergarteners except on the ability to read maps. The authors contend that kindergarteners are quite ready to learn about regional differences among human populations. 相似文献
Landslides are an increasing problem in Nepal’s Middle Hills due to both natural and human phenomena: mainly increasingly intense monsoon rains and a boom in rural road construction. This problem has largely been neglected due to underreporting of losses and the dispersed nature of landslides. Understanding how populations cope with landslides is a first step toward developing more effective landslide risk management programs. The present research focuses on two villages in Central-Eastern Nepal, both affected by active landslides but with different coping strategies. Research methods are interdisciplinary, based on a geological assessment of landslide risk and a socio-economic study of the villages using household questionnaires, focus group discussions and transect walks. Community risk maps are compared with geological landslide risk maps to better understand and communicate community risk perceptions, priorities and coping strategies. A modified typology of coping strategies is presented, based on previous work by Burton, Kates, and White (1993) that is useful for decision-makers for designing more effective programs for landslide mitigation. Main findings underscore that coping strategies, mainly seeking external assistance and outmigration, are closely linked to access to resources, ethnicity/social status and levels of community organization. Conclusions include the importance of investing in organizational skills, while building on local knowledge about landslide mitigation for reducing landslide risk. There is great potential to increase coping strategies by incorporating skills training on landslide mitigation in existing agricultural outreach and community forest user group training. 相似文献