Ecological implications of climate change will include surprises

In addition to assessing the impacts of CO₂ doubling on environment and society, more consideration is needed to estimate extreme events or surprises. This is particularly important at the intersection of disciplines like climate and ecology because the potential for large discontinuities is high given all the possible climate/biota interactions. The vast disparities in scales encountered by those working in traditional ecology (typically 20 m) and climatology (typically 200 km) make diagnoses of such interactions difficult, but these can be addressed by an emerging research paradigm we call strategic cyclical scaling (SCS). The need to anticipate outlier events and assign them subjective probabilities suggests emphasis on interdisciplinary research associations. The desire to reduce societal vulnerability to such events suggests the need to build adaptive management and diverse economic activities into social organizations. The effectiveness of adaptation responses to anticipated climatic changes is complicated when consideration of transient changes, regional disturbances, large unforseeable natural fluctuations and surprises are considered. Slowing down the rate of disturbances and decreasing vulnerability are advocated as the most prudent responses to the prospect of human-induced climatic changes.     

Non-linearities, synergisms and plant extinctions in South African fynbos and Australian kwongan

This paper explores the determinants of extinction of endemic plant taxa in mediterranean-climate regions in South Africa and southwestern Australia. Major threats to biodiversity in these areas include agriculture, deforestation, fragmentation, invasive alien organisms and urbanization. Case studies from the two regions show that synergisms between factors can lead to discontinuous, or non-linear, responses that have increased extinction rates (or threaten to) beyond predictions based on simple deterministic processes.     

Lessons from a kill

During their colonization by Polynesians and later by Europeans, the Hawaiian islands suffered a massive loss of species. All the extinctions are indirectly attributable to human impact. Nonetheless, it has proved extremely difficult to specify which of several possible mechanisms caused each particular extinction. This seems to admit defeat in the battle to understand past extinctions. Such understanding could guide our efforts to protect species that are now threatened with extinction. Will it be easier to understand the causes of future extinctions? Surveys of future extinctions stress habitat destruction as the simple and dominant mechanism. This contrasts to its secondary (and generally confused) role in past extinctions. I argue that this contrast between the complexity of the past and the apparent simplicity of the future arises because extinction mechanisms are inherently synergistic. Once extensive species losses begin, it may be impossible to separate the mechanisms and thus manage an individual species as if its decline had a single cause.     

An Amazonian rainforest and its fragments as a laboratory of global change

We synthesize findings from one of the world's largest and longest‐running experimental investigations, the Biological Dynamics of Forest Fragments Project (BDFFP). Spanning an area of ∼ 1000 km² in central Amazonia, the BDFFP was initially designed to evaluate the effects of fragment area on rainforest biodiversity and ecological processes. However, over its 38‐year history to date the project has far transcended its original mission, and now focuses more broadly on landscape dynamics, forest regeneration, regional‐ and global‐change phenomena, and their potential interactions and implications for Amazonian forest conservation. The project has yielded a wealth of insights into the ecological and environmental changes in fragmented forests. For instance, many rainforest species are naturally rare and hence are either missing entirely from many fragments or so sparsely represented as to have little chance of long‐term survival. Additionally, edge effects are a prominent driver of fragment dynamics, strongly affecting forest microclimate, tree mortality, carbon storage and a diversity of fauna. Even within our controlled study area, the landscape has been highly dynamic: for example, the matrix of vegetation surrounding fragments has changed markedly over time, succeeding from large cattle pastures or forest clearcuts to secondary regrowth forest. This, in turn, has influenced the dynamics of plant and animal communities and their trajectories of change over time. In general, fauna and flora have responded differently to fragmentation: the most locally extinction‐prone animal species are those that have both large area requirements and low tolerance of the modified habitats surrounding fragments, whereas the most vulnerable plants are those that respond poorly to edge effects or chronic forest disturbances, and that rely on vulnerable animals for seed dispersal or pollination. Relative to intact forests, most fragments are hyperdynamic, with unstable or fluctuating populations of species in response to a variety of external vicissitudes. Rare weather events such as droughts, windstorms and floods have had strong impacts on fragments and left lasting legacies of change. Both forest fragments and the intact forests in our study area appear to be influenced by larger‐scale environmental drivers operating at regional or global scales. These drivers are apparently increasing forest productivity and have led to concerted, widespread increases in forest dynamics and plant growth, shifts in tree‐community composition, and increases in liana (woody vine) abundance. Such large‐scale drivers are likely to interact synergistically with habitat fragmentation, exacerbating its effects for some species and ecological phenomena. Hence, the impacts of fragmentation on Amazonian biodiversity and ecosystem processes appear to be a consequence not only of local site features but also of broader changes occurring at landscape, regional and even global scales.     

Interactive and cumulative effects of multiple human stressors in marine systems

Humans impact natural systems in a multitude of ways, yet the cumulative effect of multiple stressors on ecological communities remains largely unknown. Here we synthesized 171 studies that manipulated two or more stressors in marine and coastal systems and found that cumulative effects in individual studies were additive (26%), synergistic (36%), and antagonistic (38%). The overall interaction effect across all studies was synergistic, but interaction type varied by response level (community: antagonistic, population: synergistic), trophic level (autotrophs: antagonistic, heterotrophs: synergistic), and specific stressor pair (seven pairs additive, three pairs each synergistic and antagonistic). Addition of a third stressor changed interaction effects significantly in two‐thirds of all cases and doubled the number of synergistic interactions. Given that most studies were performed in laboratories where stressor effects can be carefully isolated, these three‐stressor results suggest that synergies may be quite common in nature where more than two stressors almost always coexist. While significant gaps exist in multiple stressor research, our results suggest an immediate need to account for stressor interactions in ecological studies and conservation planning.     

Ancient Maya Agroforestry Echoing Through Spatial Relationships in the Extant Forest of NW Belize

Previous research has shown that ancient Maya ‘forest gardens’—tree‐dominated home gardens containing a diversity of tree species used for daily household needs—still resonate in the species composition of the modern forest. Centuries of positive interspecies interactions may enhance the reproductive and survival success of garden species selected and encouraged by experienced Maya forest gardeners. We hypothesized that such interaction may result in aggregated spatial patterns between 32 pre‐selected, commonly utilized forest garden species. In this paper, we developed a novel randomization (Monte Carlo) method designed to measure and test if the spatial relationships among pairs of Maya ‘forest garden’ trees species differ between areas that experienced high and low ancient settlement density in northwestern Belize. A total of 28 high ancient settlement density and 27 low ancient settlement density plots containing a total of 2772 and 3134 trees, respectively, were used for this study. The analysis revealed that 58 pairs of forest garden species tended to ‘cluster’ together significantly more often in the high settlement density areas than would be expected in a random distribution. In low settlement density plots, only 12 pairs of species exhibited a significant clustered spatial relationship. The effect was not species specific, suggesting that some synergistic relationships, mediated by third‐party agents such as dispersers, may occur at the community level. The impacts of ancient human land use, echoing across centuries of dispersal, colonization, disturbance, and biotic and abiotic interactions, can have important implications for understanding the current biodiversity patterns and processes.     

Integrating theory into disturbance interaction experiments to better inform ecosystem management

Managing multiple, interacting disturbances is a key challenge to biodiversity conservation, and one that will only increase as global change drivers continue to alter disturbance regimes. Theoretical studies have highlighted the importance of a mechanistic understanding of stressor interactions for improving the prediction and management of interactive effects. However, many conservation studies are not designed or interpreted in the context of theory and instead focus on case‐specific management questions. This is a problem as it means that few studies test the relationships highlighted in theoretical models as being important for ecological management. We explore the extent of this problem among studies of interacting disturbances by reviewing recent experimental studies of the interaction between fire and grazing in terrestrial ecosystems. Interactions between fire and grazing can occur via a number of pathways; one disturbance can modify the other's likelihood, intensity or spatial distribution, or one disturbance can alter the other's impacts on individual organisms. The strength of such interactions will vary depending on disturbance attributes (e.g. size or intensity), and this variation is likely to be nonlinear. We show that few experiments testing fire–grazing interactions are able to identify the mechanistic pathway driving an observed interaction, and most are unable to detect nonlinear effects. We demonstrate how these limitations compromise the ability of experimental studies to effectively inform ecological management. We propose a series of adjustments to the design of disturbance interaction experiments that would enable tests of key theoretical pathways and provide the deeper ecological understanding necessary for effective management. Such considerations are relevant to studies of a broad range of ecological interactions and are critical to informing the management of disturbance regimes in the context of accelerating global change.     

牛心朴子与苦豆子两种提取物复配对小菜蛾幼虫的联合毒力作用

以牛心朴子和苦豆子为供试植物,小菜蛾幼虫为供试试虫,采用浸渍法测定了两种植物提取物复配后对小菜蛾幼虫的联合毒力。结果表明:牛心朴子与苦豆子提取物复配后具有增效作用,其中以干粉质量比为2∶1时增效作用最显著,其共毒系数(CTC)为248.30。复配物对小菜蛾幼虫具有显著的触杀活性,质量浓度为20.00 mg/mL时,72 h校正死亡率可以达到100%,致死中浓度LC50=2.0747 mg/mL。     

Two key challenges for biodiversity: discontinuities and synergisms

The survival outlook for biodiversity is being profoundly and adversely influenced by the twin phenomena of discontinuities and synergisms. So potent are their impacts that they may well cause the mass extinction to overtake us more swiftly and extensively than is often expected. Despite their importance, however, we know all too little about these phenomena. They remain almost entirely a black hole of research. This paper, being an introduction to the special issue, presents a short selection of both phenomena, with an evaluation of their impacts on biodiversity. It concludes with an overview of the human enterprise and its probable future repercussions for biodiversity.