The concept and utility of ‘ecological thresholds’ in biodiversity conservation

In the life and natural sciences, the concept of thresholds or points or zones of change from one state to another has been investigated since the late 18th century. Over the past three decades, ecologists and economists around the world have been examining the existence and use of ‘ecological thresholds’ in natural and modified systems, primarily as a conceptual basis for the development of tools to conserve and sustainably manage natural resources. In Australia, there has been a recent renewed interest in the definition and application of ecological thresholds in the conservation of threatened fauna and flora, modelling the impact of habitat loss, modification and fragmentation on terrestrial biota, management of pest plant and animal species, and development of natural resource management policies and plans. This paper reviews the threshold concept from an ecological perspective. It considers the definition, types and behaviour of this phenomenon. The theoretical and empirical evidence for their purported existence is reviewed and their potential utility in biodiversity conservation and natural resource management is discussed, along with key issues relating to their use.     

Typhoon Yolanda and post‐disaster resilience: Problems and challenges

After Typhoon Yolanda devastated the Philippines, ‘resilient’ was a term frequently used by the media, survivors, government officials and various other stakeholders in the city of Tacloban to describe those affected by the disaster. The focus of this article is therefore on how this term was articulated and experienced during this period. The analysis covers how resilience was discursively deployed to describe the condition of residents who were, in fact, often suffering from a double process of dispossession: once by the typhoon and once more by government policy and the inequitable distribution of relief goods and services due to the inadequacies of the disaster response. Despite these inadequacies, Tacloban was presented as ‘an exemplary centre’ of the post‐Typhoon Yolanda relief effort. I argue that the overarching rhetoric and strategies of resilience became rituals aimed at normalising modes of profit‐seeking and recreating the unequal socio‐economic status quo. These rituals occurred at multiple levels; however, the fortunes of Tacloban were indelibly intertwined with the political credibility and status pride of the Marcos/Romualdez family. I argue that ‘resilience’ is a complex, overused, manipulated and contested term and that a more transparent understanding of resilience for disaster relief and rehabilitation is needed.     

Weaknesses in stock assessment modelling and management practices affect fisheries sustainability

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Identification of a spatially efficient portfolio of priority conservation sites in marine and estuarine areas of Florida

• 1. A systematic conservation planning approach using benthic habitat and imperilled species data along with the site prioritization algorithm, MARXAN, was used to identify a spatially efficient portfolio of marine and estuarine sites around Florida with high biodiversity value.
• 2. Ensuring the persistence of an adequate geographic representation of conservation targets in a particular area is a key goal of conservation. In this context, development and testing of different approaches to spatially‐explicit marine conservation planning remains an important priority.
• 3. This detailed case study serves as a test of existing approaches while also demonstrating some novel ways in which current methods can be tailored to fit the complexities of marine planning.
• 4. The paper reports on investigations of the influence of varying several algorithm inputs on resulting portfolio scenarios including the conservation targets (species observations, habitat distribution, etc.) included, conservation target goals, and socio‐economic factors.
• 5. This study concluded that engaging stakeholders in the development of a site prioritization framework is a valuable strategy for identifying broadly accepted selection criteria; universal target representation approaches are more expedient to use as algorithm inputs, but may fall short in capturing the impact of historic exploitation patterns for some conservation targets; socio‐economic factors are best considered subsequent to the identification of priority conservation sites when biodiversity value is the primary driver of site selection; and the influence of surrogate targets on portfolio selection should be thoroughly investigated to ensure unintended effects are avoided.
• 6. The priority sites identified in this analysis can be used to guide allocation of limited conservation and management resources.

Copyright © 2008 John Wiley & Sons, Ltd.     

Conserving the Greater Sage-Grouse: A Social-Ecological Systems Case Study from the California-Nevada Region

The Endangered Species Act (ESA) continues to serve as one of the most powerful and contested federal legislative mandates for conservation. In the midst of heated debates, researchers, policy makers, and conservation practitioners champion the importance of cooperative conservation and social-ecological systems approaches, which forge partnerships at multiple levels and scales to address complex ecosystem challenges. However, few real-world examples exist to demonstrate how multifaceted collaborations among stakeholders who share a common goal of conserving at-risk species may be nested within a systems framework to achieve social and ecological goals. Here, we present a case study of Greater Sage-grouse (Centrocercus urophasianus) conservation efforts in the “Bi-State” region of California and Nevada, United States. Using key-informant interviews, we explored dimensions and drivers of this landscape-scale conservation effort. Three themes emerged from the interviews, including 1) ESA action was transformed into opportunity for system-wide conservation; 2) a diverse, locally based partnership anchored collaboration and engagement across multiple levels and scales; and 3) best-available science combined with local knowledge led to “certainty of effectiveness and implementation”—the criteria used by the US Fish and Wildlife Service to evaluate conservation efforts when making listing decisions. Ultimately, collaborative conservation through multistakeholder engagement at various levels and scales led to proactive planning and implementation of conservation measures and precluded the need for an ESA listing of the Bi-State population of Greater Sage-grouse. This article presents a potent example of how a systems approach integrating policy, management, and learning can be used to successfully overcome the conflict-laden and “wicked” challenges that surround at-risk species conservation.     

镉胁迫对4种草坪草抗逆生理特性的影响

通过盆栽试验研究了不同Cd2+浓度(1,50,100,150mg/kg)胁迫对4种草坪草(草地早熟禾、多年生黑麦草、高羊茅、白三叶)脯氨酸含量、MDA含量和抗氧化酶活性等抗逆生理特性的影响。结果表明,Cd2+胁迫下4种草坪草脯氨酸含量和MDA含量显著高于对照(P0.05),且随着离子浓度的增加而增加;Cd2+对草地早熟禾抗氧化酶活性影响均较大;Cd2+处理对多年生黑麦草、高羊茅和白三叶抗氧化酶系统表现出低浓度影响较小,高浓度影响较大的趋势。     

Urban parks can maintain minimal resilience for Neotropical bird communities

Birds may use urban parks as shelter and refuge, contributing with numerous ecosystem services upon which humans and other organisms depend on. To safeguard these services, it is important that bird communities of urban environments hold some degree of resilience, which refers to the capacity of a system to absorb disturbances and changes, while maintaining its functions and structures. Here we assessed the resilience of the bird community inhabiting an urban park in the Southeast region of Brazil. We classified birds in feeding guilds and identified discontinuities and aggregations of body masses (i.e., scales) using hierarchical cluster analysis. We then calculated five resilience indices for our urban park and for a preserved continuous forest (reference area): the average richness of functions, diversity of functions, evenness of functions, and redundancy of functions within- and cross-scale. The urban park had less species, lower feeding guild richness, and lower within-scale redundancy than the reference area. However, they had similar proportion of species in each function, diversity of functions, evenness of functions, and cross-scale redundancy. The lower species richness and, consequently, the lack of some species performing some ecological functions may be responsible for the overall lower resilience in the urban park. Our results suggest that the bird community of the urban park is in part resilient, as it maintained many biological functions, indicating some environmental quality despite the high anthropogenic impacts of this area. We believe that urban forest remnants with more complex and diverse vegetation are possibly more likely to maintain higher resilience in the landscape than open field parks or parks with suppressed or altered vegetation. We propose that raising resilience in the urban park would possibly involve increasing vegetation complexity and heterogeneity, which could increase biodiversity in a large scale.     

Generalized and Specific State-and-Transition Models to Guide Management and Restoration of Caldenal Forests

Management impacts and natural events can produce ecosystem state changes that are difficult to reverse. In such cases, a detailed understanding of drivers, thresholds, and feedback mechanisms are needed to design restoration interventions. The Caldenal ecoregion in central Argentina has undergone widespread state change, and restoration is urgently needed, but as yet there has been no knowledge synthesis to support restoration actions. In this paper, we provide evidence-based guidelines for ecological restoration of the Caldenal forest derived from a general to local conceptual understanding of ecosystem dynamics. We develop a Caldenal forest state transition model based on a generalized fire-mediated savanna-woodland transition model. The generalized model depicts global similarities in fire-grass feedback loops as a primary factor controlling savanna to woodland transition (thicketization) in semiarid savannas around the world. An open forest is considered to be the reference state of the Caldenal that developed under a historical regime of frequent low-intensity fire. The introduction of large livestock herds in the region disrupted the positive fire-grass feedback loop and increased dispersal and recruitment of Prosopis caldenia, creating conditions for thicketization of the forest. Controlled, low-intensity fire can be used to build the resilience of an open forest state. Restoring open forest states from woodland states requires a large-scale selective thinning and pruning operation. Long-term restoration requires breaking the positive livestock-thicketization ? high-intensity fire feedback and reestablishing the positive grass-low intensity fire feedback to ensure the persistence of a restored open forest state.     

Assessing arbuscular mycorrhizal plant metal uptake and soil metal bioavailability among ‘dwarf’ sunflowers in a stratified compartmental growth environment

Using the micronutrient zinc (Zn) as a metal contaminant, a stratified compartmental pot greenhouse experiment involving ‘dwarf’ sunflowers and an arbuscular mycorrhizal (AM) fungus was designed to assess the role of AM symbiosis toward plant growth and metal uptake, and to differentiate its impact toward edaphic parameters across different soil strata. Consistent with previous hypotheses, AM plants contained up to 40% lower metal concentrations in their shoots than non-AM plants, particularly at the highest soil Zn levels (200 and 400 mg Zn kg^?1 dry soil); this, corresponding with an enhanced growth status among AM plants. Upon assessing the soil Zn concentrations and pH, AM treatments also tended to have higher soil Zn levels and more alkaline conditions compared to non-AM treatments. This was found especially in the topmost soil stratum where AM root colonization was deemed most active as evidenced by a higher frequency of extraradical hyphae, vesicles, and arbuscules. Together, these effects were putatively linked to the AM-induced mechanism of metal biosorption known to modulate soil nutrient bioavailability and even delay the onset of metal toxicity.     

联合收获机拨禾轮谷物回弹问题的仿真试验

对收获机谷物茎秆回弹问题进行定量分析,通过建立数学模型,并利用计算机模拟试验和田间试验的数据对比作进一步地论证。试验证明,谷物回弹是造成拨禾损失的重要因素,因而为进一步优化稻麦联合收割机结构参数提供了设计的基础。