The more the merrier? Multi-species grazing of small herbivores mediates plant community impacts

Small herbivores play keystone functional roles in grassland ecosystems. Recognising the combined effects where herbivores co-exist is important for guiding grassland restoration and biodiversity conservation. On the Tibetan Plateau, both plateau pikas and Himalayan marmots are regarded as pests by Tibetan people and local government, but little is known about their combined effects. We conducted a field study to determine the combined effects of pikas and marmots on plant biodiversity and vegetation structure. Plateau pikas alone consistently reduced the plant height and diversity and increased the vegetation cover of physically unpalatable plants. However, the co-existence of marmots with pikas decreased the vegetation cover of physically unpalatable plants, while increasing the cover of palatable plants and plant diversity, ultimately changing the impact of pikas alone and modulating aspects of the plant community. These results illustrate that increasing the abundance and richness of small herbivores in grassland ecosystems may promote plant diversity and benefit vegetation restoration rather than aggravate the degradation of grasslands.     

The value of biodiversity experiments

Recent biodiversity experiments have investigated the relationship between diversity and ecosystem functioning by synthesizing plant communities from pools of species that have been experimentally manipulated to vary numbers and types of species present while holding abiotic factors constant. Biodiversity experiments therefore focus on a previously under-explored aspect of global change: the feedback from diversity to environment. Consequences of random manipulation of species communities may not correspond well to those of specific extinction sequences observed in the past in response to extinction drivers that cause highly non-random loss. However, random manipulation provides a good starting point given that existing communities could undergo many alternative orders of species loss in the future in response to a variety of different potential extinction drivers. Further, the effects of some extinction drivers are currently poorly understood and therefore difficult to predict (e.g. climate change) and it may be premature to dismiss the predictions of random scenarios as irrelevant to all real examples of species loss. The first generations of biodiversity experiments have provided valuable, and sometimes unexpected, discoveries about the general nature of the relationship between diversity and ecosystem functioning. These discoveries could not have been made using observational studies. We propose that different examples of extinction loss in the real or a potential future world form a continuum from situations where the results of the first-generation biodiversity experiments will be highly relevant to less relevant. At the one extreme are examples where the effects of biodiversity on ecosystem functioning will be overwhelmed by direct effects of the extinction driver on processes (e.g. chronic eutrophication). At the other extreme are situations where ecosystem processes are not strongly affected by direct effects of the extinction driver and where the effects of species loss on functioning may be more important (e.g. habitat fragmentation). Given the unprecedented uncertainty about the future of biodiversity and the functioning of ecosystems, a general approach with randomly varying species pools was the right place to start in order to provide a general foundation. The new challenge is to test for effects of biodiversity on functioning in real-world examples of species loss.

Zusammenfassung

Biodiversitätsversuche zeichnen sich dadurch aus, dass natürliche Artenpools experimentell reduziert werden und anschließend der Zusammenhang zwischen der Artenzahl und Ökosystemfunktionen unter konstanten abiotischen Umweltbedingungen untersucht wird. Dadurch unterscheiden sich Biodiversitätsexperimente grundsätzlich von anderen Versuchen, die die Biodiversität als Zielvariable behandeln und stattdessen die abiotische Umwelt manipulieren. Die Auswahl der Arten für die reduzierten Artenpools in Biodiversitätsexperimenten erfolgte bisher meist zufällig, während natürliche Aussterbefaktoren wie Eutrophierung nicht alle Arten gleichermassen gefährden. Für verschiedene Aussterbefaktoren ist aber so wenig bekannt, dass ein zufälliges Aussterbeszenario die beste gegenwärtig verfügbare Option ist. Dies trifft insbesondere für mögliche zukünftige Aussterbeprozesse zu, die durch globale Umweltveränderungen (Klima, biologische Invasionen) oder Habitatsfragmentierung ausgelöst werden könnten. Die erste Generation von Biodiversitätsexperimenten mit zufälligen Aussterbeszenarien hat wertvolle, teilweise unerwartete, generelle Zusammenhänge zwischen Artenzahl und Ökosystemfunktionen aufgedeckt. Diese Zusammenhänge ließen sich durch vergleichende Studien nicht erkennen. In Zukunft sollten Biodiversitätsexperimente dennoch vermehrt Aussterbeszenarien simulieren, die in der realen Umwelt mit größter Wahrscheinlichkeit auftreten.     

The more,the merrier: heterotroph richness stimulates methanotrophic activity

Although microorganisms coexist in the same environment, it is still unclear how their interaction regulates ecosystem functioning. Using a methanotroph as a model microorganism, we determined how methane oxidation responds to heterotroph diversity. Artificial communities comprising of a methanotroph and increasing heterotroph richness, while holding equal starting cell numbers were assembled. We considered methane oxidation rate as a functional response variable. Our results showed a significant increase of methane oxidation with increasing heterotroph richness, suggesting a complex interaction in the cocultures leading to a stimulation of methanotrophic activity. Therefore, not only is the methanotroph diversity directly correlated to methanotrophic activity for some methanotroph groups as shown before, but also the richness of heterotroph interacting partners is relevant to enhance methane oxidation too. In this unprecedented study, we provide direct evidence showing how heterotroph richness exerts a response in methanotroph–heterotroph interaction, resulting in increased methanotrophic activity. Our study has broad implications in how methanotroph and heterotroph interact to regulate methane oxidation, and is particularly relevant in methane-driven ecosystems.     

The more the merrier: how homo-oligomerization alters the interactome and function of ribonucleotide reductase

Stereotyped as a nexus of dNTP synthesis, the dual-subunit enzyme — ribonucleotide reductase (RNR) — is coming into view as a paradigm of oligomerization and moonlighting behavior. In the present issue of ‘omics’, we discuss what makes the larger subunit of this enzyme (RNR-α) so interesting, highlighting its emerging cellular interactome based on its unique oligomeric dynamism that dictates its compartment-specific occupations. Linking the history of the field with the multivariable nature of this exceedingly sophisticated enzyme, we further discuss implications of new data pertaining to DNA-damage response, S-phase checkpoints, and ultimately tumor suppression. We hereby hope to provide ideas for those interested in these fields and exemplify conceptual frameworks and tools that are useful to study RNR's broader roles in biology.     

Ethical consideration in invasion ecology: A marine perspective

Biological introductions of species to regions outside their known natural distribution are considered a major threat to native marine biodiversity and a key consideration for ecological management. For most invasive species in marine systems, however, little is known about potential impacts. If we are to increase our knowledge of the processes and mechanisms behind the spread of nonindigenous species or determine economic or ecological impacts, manipulative ecological field experiments are the best way to unambiguously ascribe causal relationships. For studies of invasions, such research may result in species spread and the establishment of new viable populations. Is it ethical then, to take the risk of potentially modifying or endangering other species, populations or ecosystems? Is it possible to mitigate the risks? Or should invasion ecologists work under restrictions that limit their ability to fully assess the impact of invaders? Consideration of the ethics of experimentation is rarely carried out. As a consequence, we propose a decision model that includes possible risk of escape/establishment versus the value of the research to allow researchers and/or managers to critically evaluate what type of experimental approach is appropriate.     

Loop extrusion: theory meets single-molecule experiments

Chromosomes are organized as chromatin loops that promote segregation, enhancer-promoter interactions, and other genomic functions. Loops were hypothesized to form by ‘loop extrusion,’ by which structural maintenance of chromosomes (SMC) complexes, such as condensin and cohesin, bind to chromatin, reel it in, and extrude it as a loop. However, such exotic motor activity had never been observed. Following an explosion of indirect evidence, recent single-molecule experiments directly imaged DNA loop extrusion by condensin and cohesin in vitro. These experiments observe rapid (kb/s) extrusion that requires ATP hydrolysis and stalls under pN forces. Surprisingly, condensin extrudes loops asymmetrically, challenging previous models. Extrusion by cohesin is symmetric but requires the protein Nipbl. We discuss how SMC complexes may perform their functions on chromatin in vivo.     

Raccoon ecology database: A resource for population dynamics modelling and meta-analysis

The value of scientific studies increases and is extended when their data are stored in a manageable and accessible format. This is demonstrated through development of a raccoon ecology database (REDB) to store, manage and disseminate available peer-reviewed and unpublished data on raccoon (Procyon lotor) biology, ecology and raccoon rabies, including citations for data sources. Over 800 documents were identified and citations for them entered into the database as literature references. Approximately 1000 trait values were entered from almost 200 of these sources. These data included estimates of population density, survival rates, rabies incubation period, litter size, body weight, dispersal distance and home-range size, often by age or sex class. Each datum is linked to a citation for its source, and to information about location and land use in the study area, time of year the study was undertaken, sample size, and variance. The relational database design enables querying and easy updating and manipulation of data.

The relational data model is presented, as is its application in further developing an individual-based, spatially-explicit population model of raccoon rabies. Using information queried from the REDB benefits model development by: i) assessing the appropriateness of input parameter values, ii) providing sources for citing input values, iii) parameterising the model to different geographic regions, iv) enabling meta-analyses for evaluating model structure, as well as further contributing to parameterisation at specific locations, and v) providing biologically appropriate parameter input values for model sensitivity testing. The REDB is a useful research resource that will increase in value with ongoing inclusion of data from future raccoon and raccoon rabies studies and serves as a model for database design and research applications to other species. The database and an empty database for use with other species are available online (http://redb.nrdpfc.ca).     

Optimal Investment in Multi-species Protection: Interacting Species and Ecosystem Health

This article uses an ecological-economic approach to study optimal investment in multi-species protection when species interact in an ecosystem. The analysis is based on a model of stochastic species extinction in which survival probabilities are interdependent. Individual species protection plans can increase a species survival probability within certain limits and contingent upon the existence or absence of other species. Protection plans are costly and the conservation budget is fixed. It is assumed that human well-being depends solely on the services provided by one particular species, but other species contribute to overall ecosystem functioning and thus influence the first species survival probability. One result is that it may be optimal to invest in the protection of those species that do not directly contribute to human well-being, even if biological conservation decisions are exclusively derived from such a utilitarian framework. Another result is that the rank ordering of spending priorities among different species protection plans, as obtained under the assumption of independent species, may be completely reversed by taking species interaction into account. The conclusion is that effective species protection should go beyond targeting individual species, and consider species relations within whole ecosystems as well as overall ecosystem functioning. Ecosystem health is identified as a necessary prerequisite for successful species protection in situ.     

Reproductive ecology of Scalesia cordata (Asteraceae), an endangered species from the Galápagos Islands

The genus Scalesia is endemic to the Galápagos Islands. Scalesia cordata is a tree occurring only in the southern part of Isabela as small, remnant populations of larger forests. We studied the reproductive ecology of a population protected in an enclosure in order to reveal the extent to which the reproductive system limits the recruitment of young individuals. Pollinator observations revealed that each capitulum received, on average, 2.5 visits per hour and exposed receptive stigmas received many pollen grains. Even so, the seed set and recruitment of trees was poor. Crossing experiments showed that S. cordata produced about twice as many fertile seeds after outcrossing than after selfing. In addition, self‐pollinated capitula flowered for a longer time than outcrossed capitula (3.8 ± 1.1 days vs. 2.1 ± 0.8 days). These results may suggest that the species is partly self‐incompatible, as other species of the genus. The small population size, with its potential derived consequences, is most certainly a prominent threat to S. cordata. The pressure from introduced plant species found in the enclosure also contributes to the seemingly poor condition of the population. To recover S. cordata, we suggest enlarging the enclosure, removing the introduced plant species and continuing to cultivate plants as a genetic reserve. Introducing new genetic material is likely to increase the seed set of the population. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 162 , 496–503.     

The more the merrier: Conspecific density improves performance of gregarious larvae and reduces susceptibility to a pupal parasitoid

Aggregation can confer advantages in animal foraging, defense, and thermoregulation. There is a tight connection between the evolution of insect sociality and a highly effective immune system, presumably to inhibit rapid disease spread in a crowded environment. This connection is less evident for animals that spend only part of their life cycle in a social environment, such as noneusocial gregarious insects. Our aim was to elucidate the effects of group living by the gregarious larvae of the Glanville fritillary butterfly with respect to individual performance, immunity, and susceptibility to a parasitoid. We were also interested in the role of family relative to common postdiapause environment in shaping life‐history traits. Larvae were reared at high or low density and then exposed to the pupal parasitoid wasp Pteromalus apum, either in presence or absence of a previous immune challenge that was used to measure the encapsulation immune response. Surviving adult butterflies were further tested for immunity. The wasp offspring from successfully parasitized butterfly pupae were counted and their brood sex ratios assessed. Larvae reared at high density grew larger and faster than those at low density. Despite high mortality due to parasitism, survival was greater among individuals with high pupal immunity in both density treatments. Moreover, butterfly pupae reared at high density were able to kill a larger fraction of individuals in the parasitoid broods, although this did not increase survival of the host. Finally, a larger proportion of variation observed in most of the traits was explained by butterfly family than by common postdiapause rearing environment, except for adult survival and immunity, for which this pattern was reversed. This gregarious butterfly clearly benefits from high conspecific density in terms of developmental performance and its ability to fight a parasitoid. These positive effects may be driven by cooperative interactions during feeding.     

The biogeochemistry of toluene in coastal seawater: radiotracer experiments in controlled ecosystems

The fate of toluene in coastal seawater was investigated in controlled ecosystems using¹⁴C- and³H-toluene as tracers. Under winter-like conditions, 80% of the toluene volatilized from the water column in 2 months. Microbial degradation was less important than volatilization and sorption onto particulate matter with resultant loss to the sediments was minor. During summer most of the toluene was degraded by microbes. Nearly 80% of the toluene was converted to CO₂ within 1 week and the label remained in the water column as dissolved CO₂. The experimental results were applied to estimate the removal rates and the residence time of toluene in adjacent Narragansett Bay, Rhode Island. In winter volatilization would dominate the loss of toluene and a residence time of 6 d would be predicted. However, rapid biodegradation in summer would result in a residence time of < 1 d.     

可持续生态学

可持续生态学系用生态学原理和方法解决自然与社会经济协调发展问题,或者说生态学不断将人类及其社会经济活动纳入研究范畴而形成的自然科学与社会科学的交叉学科。40年来,我国在可持续生态学研究和实践领域取得了丰硕的成果,一是提出了"社会-经济-自然"复合生态系统理论;二是构建了适应中国国情的可持续发展评价指标体系;三是推进实施了国家可持续发展战略,并在不同时空尺度进行了试点示范;四是将可持续发展的区域生态安全格局和生态风险管理理论与方法应用于城市与区域发展规划中,并利用生态补偿机制推进跨域的生态安全格局建设;五是为国家生态文明建设规划纲要的出台提供了重要的科学支撑,有力地推进了生态文明建设战略的实施;六是系统地研究了全球气候变化对中国生态系统的影响,科学评估了气候变化的现状、趋势及其影响,提出了气候变化的生态适应对策;七是不断推进国家和地方层面的生态省、生态市、生态县建设,创建了不同层次和规模的可持续发展实验区、国家可持续发展议程创新示范区、生态农业试点示范县、生态工业示范园区等。本文从宏观生态学与可持续发展、生态城市与可持续发展、生态产业与可持续发展三个方面评述可持续性生态学的研究进展。可持续生态学的重点研究内容随着时代发展而不断更新,生态文明建设、生态安全格局构建、落实联合国2030可持续发展目标、应对全球环境变化、新型城市化和工业化对生态系统的影响等是当前和未来一段时间的研究热点。     

Experimental and physiological ecology of ammonia fungi: studies using natural substrates and artificial media

Experiments using natural substrates and artificial media were categorized into three groups. Using experiments in these three categories, we investigated dispersion, invasion sequence, and decomposing ability of ammonia fungi in the field on natural substrates. Spore germination and vegetative and reproductive growth of ammonia fungi derived from monocultures and five-species cultures were assessed on natural substrates and on artificial media. These features assist understanding of the colonization and successive occurrence of ammonia fungi in the field based on estimation of interactions among the fungi and the physiological characteristics of each ammonia fungus. The sequential colonization and fruiting of ammonia fungi in the field can be explained primarily by the preference or tolerance of a species to high concentrations of ammonium-N under alkaline to neutral conditions. Succession of ammonia fungi results from their sequential colonization associated with the time needed for each fungus to produce reproductive structures. Colonization likely initiates from mycelia and/or spores preinhabiting the soil and from newly invading airborne propagules. Duration of occurrence of ammonia fungi in the field is shortened by the interactions among them. Saprobic ammonia fungi are the principal agents of litter decomposition under alkaline to neutral conditions. Parts of this review were presented as the presidential address of the Mycological Society of Japan (MSJ) at the Mycological Society of America (MSA) and MSJ Joint Meeting 2005 held in Hawaii in August 2005