Environmental variability and allocation trade-offs maintain species diversity in a process-based model of succulent plant communities

Ecological theory suggests that environmental variability can promote coexistence, provided that species occupy differential niches. In this study, we focus on two questions: (1) Do allocation trade-offs provide a sufficient basis for niche differentiation in succulent plant communities? (2) What is the relative importance of different forms of environmental variability on species diversity and community composition? We approach these questions with a generic, individual-based simulation model. In our model, plants compete for water in a spatially explicit environment. Species differ in their size at maturity and in the allocation of carbon to roots, leaves and storage tissue. The model was fully specified with independent literature data. Model output was compared to characteristics of a species-rich community in the semi-arid Richtersveld (South Africa). The model reproduced the coexistence of plants with different sizes at maturity, the dominance of succulent shrubs, and the level of vegetation cover. We analyzed the effects of three forms of environmental variability: (a) temporal fluctuations in precipitation (rain and fog), (b) spatial heterogeneity of water supply due to run-on and run-off processes and (c) ‘rock pockets’ that limit root competition in space. The three types of variability had differential effects on diversity: diversity exhibited a strong hump-shaped response to temporal variation. Spatial variability increased diversity, with the strongest increase occurring at intermediate levels of temporal variability. Finally, rock pockets had the weakest effect, but contributed to diversity by providing refuges for small species, particularly at low temporal variability. The model thus shows that spatio-temporal variation of resource supply can maintain diversity over long time scales even in small systems, as is the case in the Richtersveld succulent communities. Trade-offs in allocation provide the basis for necessary niche differentiation. By describing resource competition between individual plants, our model provides a mechanistic basis for the link from species traits to community composition at given environmental conditions. It thereby contributes to an understanding of the forces shaping plant communities. Such an understanding is critical to reduce the threats environmental change poses to biodiversity and ecosystem services.     

A Typology of Collaboration Efforts in Environmental Management

Collaboration involves stakeholders and the public in a process of consensus building to address some of the most difficult environmental management problems facing society today. Collaborative groups vary widely, ranging from small watershed councils to regional ecosystem collaboratives to groups addressing large-scale policy issues. While these collaboratives all match the common principles of collaboration, a closer examination reveals many differences. Using institutional theories about levels of decision making provides a way of classifying collaboratives along a spectrum from action level to organizational level to policy level. This typology is applied to thirty-six collaboration case studies in Australia and the United States that were investigated over a series of years through interviews, observation, document analysis, and surveys. The application reveals different tendencies among the case types in terms of population, size, problem significance, institutional setting, and focus of activities. The typology also reveals functional differences in the types of stakeholders involved, the management arrangements for implementation, and the approaches to implementing change. This typology can help practitioners better understand the challenges and appropriate types of collaborations for different settings. It helps highlight differences in the role of government and decentralization of power. It distinguishes the different theoretical foundations for different types of collaboratives. Finally, it elucidates the different evaluation approaches for different types of collaboratives.     

Mining taxation issues for the future

During the 1970s and 1980s the main concern of mining policies was to attract investment whilst at the same time balancing the interests of governments and companies. By the turn of the century a new spectrum of challenges faces governments and companies in the mining sector. The need for fiscal regimes to adapt to price cyclicity is to some extent superseded by the requirement that they adapt to a long-term decline of metal prices. The growing importance of environmental and community affairs in the mining sector will force governments to design coherent and comprehensive tax regulations to complement the wide range of initiatives being taken in these fields. Finally, the age-old problem of tax collection continues to raise its head in transition and developing economies.     

Volunteer Environmental Monitoring and the Role of the Universities: The Case of Citizens' Environment Watch

Universities can provide a stable home for launching collaborative community research projects. Citizens' Environment Watch (CEW), an environmental monitoring initiative based at the University of Toronto, has made significant contributions to environmental education and stewardship in Ontario, Canada. Following dramatic cuts in provincial monitoring programs, citizens and youth have used chemical parameters and biological indicators to gauge water and air quality, and to identify areas requiring remediation and pollution prevention efforts. The relationship of Citizens' Environment Watch to government agencies, funders and other grassroots environmental groups has evolved over the past 5 years as CEW attempts to remain effective without taking on the investigative and enforcement roles to support the regulatory enforcement that has been largely abandoned by government. We explore the challenges inherent in developing and maintaining a volunteer organization that carries out rigorous and useful scientific work and we outline the ability of a university to help overcome these critical challenges. Finally, we present lessons learned for the benefit of other citizen and youth monitoring projects.     

Natural history of crop-related wild species: Uses in pest habitat management

The natural histories of crop-related wild species in their native habitats can be used to develop novel pest management strategies. Traditionally, such information has provided insights for biological control, plant breeding, crop management, and applied ecology Further insights can be garnered.     

Is recycled water use risky? An Urban Australian community’s perspective

The emergence of a global water crisis has seen the necessity for a sustainable approach to water management. Policies directed towards water recycling have been implemented in many regions of the world. In Australia, prolonged drought conditions in most major cities during the past decade have led to serious national calls for less drinking water to be used (Prime Minister’s Science Engineering and Innovation Council, 2003), and a strategic policy response from many State Governments, including bold targets for water recycling. A key consideration to the realisation of these policies is greater understanding of community attitudes to recycled water use, without which, a number of recycled water projects have failed (Hurlimann and McKay, 2004). Despite the critical nature of community attitudes, little research has been conducted, especially in relation to perception of risk, which has been found to be critical in the adoption of new technologies (Cvetkovich and Lofstedt, 1999). This paper investigates an urban Australian community’s perception of risk involved with using recycled water. Key findings include: perception of risk increased as the use of recycled water became increasingly personal. Perception of risk was significantly negatively related to trust, perception of fairness and information. Trust in the Water Authority to manage risk was significantly related to perception of trust, communication and integrity of the Authority.     

Interactions betweenLythrum salicaria and native organisms: A critical review

Seventy-one articles concerningLythrum salicaria (purple loosestrife), a European herb introduced to North America, were reviewed for evidence of utilization by North American fauna and the effect of loosestrife on native plant species. In contrast to popular claims, 29 species of organisms were found to utilize this plant, and no evidence of species declines due to purple loosestrife were found. Evidence that loosestrife out-competes cattails and other plant species was found to be lacking or contradictory. Thus detailed, quantitative data are needed to understand loosestrife's natural history, population dynamics, and impacts on native ecosystems if we are to effectively manage this plant.     

Home beyond the house: Experiences of place in an evolving retirement community

This research presents the results of a qualitative study of a small sample of older adults (n = 25), age 55+ who have recently moved to an area that is rapidly changing from a tourist community into a retirement community. The study has two main research objectives: (a) to use Oswald and Wahl's heuristic meaning of home framework to explore the relationships between older adults and their homes and communities, integrating theories from environmental psychology, environmental gerontology and human geography, and (b) to discuss the empirical findings focussing on the core concepts of meaning of home and sense of belonging for new retirees to an area. Findings: For new retirees, there exists a zone between the home and community, that can be viewed as a geographic space comprised of overlapping and interwoven personal, social and physical domains. This zone between the physical house and the surrounding community can be construed as having certain elastic qualities and permeable boundaries that blur the distinctions between home and community. A focus on the micro-environment of the home dwelling and the macro-environment of the neighbourhood and community then appears relevant for understanding place attachment for these persons. This idea of the ‘home beyond the house’ – is one of the most important contributions of this research. Our results view the heuristic framework of Oswald and Wahl as a valuable tool for building understanding about the meaning of home for older adults by drawing attention to the domains themselves, and more importantly, to the interrelationships between them. Consequently, for younger in-migrants, the boundary between home and community blurs into one larger, symbolic entity experienced as ‘home’.     

沉湖底栖动物群落结构及其与表层沉积物营养盐的关系

为了解沉湖底栖动物群落的状况,于2022—2023年对武汉市沉湖底栖动物和表层沉积物营养盐含量进行了4次季节性调查,探讨了它们之间的关系,并对底层沉积物的环境质量进行了评价。调查期间共鉴定出底栖动物2门3纲14种,霍甫水丝蚓（Limnodrilus hoffmeisteri）、长跗摇蚊（Tanytarsus sp.）、羽摇蚊幼虫（Chironomus plumosus）、刺铗长足摇蚊（Tanypus punctipennis）、前突摇蚊（Procladius sp.）为优势种。底栖动物密度、生物量及其香农-维纳（Shannon-Wiener）多样性指数（H′）、Margalef指数（D）表现出明显的季节差异（P <005）。沉湖表层沉积物中总氮（TN）、总磷（TP）、有机质（OM）的质量分数平均值分别为2.96,0.94,64.00 mg/g,沉积物TN和TP呈显著正相关（P <0.05）。在不同的采样点位中,H′、皮耶罗（Pielou）均匀度指数（J）和D这3种多样性指数与TN、TP差异明显（P <005）。相关分析结果显示,多样性指数（H′和D）与OM呈显著负相关（P<0.05）。利用多样性指数（H′和D）、生物学污染指数（BPI）、有机污染指数（OI）和污染指数（PI）等对沉湖表层沉积物现状进行评价,结果表明,该湖处于中—重度污染状态。沉湖底栖动物以寡毛类和水生昆虫（摇蚊类）占优势的结构特征与该湖沉积物有机质含量较高有关。