Julia Reiss

Emerging horizons in biodiversity and ecosystem functioning research

Two decades of intensive research have provided compelling evidence for a link between biodiversity and ecosystem functioning (B-EF). Whereas early B-EF research concentrated on species richness and single processes, recent studies have investigated different measures of both biodiversity and ecosystem functioning, such as functional diversity and joint metrics of multiple processes. There is also a shift from viewing assemblages in terms of their contribution to particular processes toward placing them within a wider food web context. We review how the responses and predictors in B-EF experiments are quantified and how biodiversity effects are shaped by multitrophic interactions. Further, we discuss how B-EF metrics and food web relations could be addressed simultaneously. We conclude that addressing traits, multiple processes and food web interactions is needed to capture the mechanisms that underlie B-EF relations in natural assemblages.

Global change and food webs in running waters

Riverine habitats are vulnerable to a host of environmental stressors, many of which are increasing in frequency and intensity across the globe. Climate change is arguably the greatest threat on the horizon, with serious implications for freshwater food webs via alterations in thermal regimes, resource quality and availability, and hydrology. This will induce radical restructuring of many food webs, by altering the identity of nodes, the strength and patterning of interactions and consequently the dynamics and architecture of the trophic network as a whole. Although such effects are likely to be apparent globally, they are predicted to be especially rapid and dramatic in high altitude and latitude ecosystems, which represent ‘sentinel systems’. The complex and subtle connections between members of a food web and potential synergistic interactions with other environmental stressors can lead to seemingly counterintuitive responses to perturbations that cannot be predicted from the traditional focus of studying individual species in isolation. In this review, we highlight the need for developing new network-based approaches to understand and predict the consequences of global change in running waters.

Chapter 5 – Environmental Warming and Biodiversity–Ecosystem Functioning in Freshwater Microcosms

Predicting the effects of global warming on biodiversity–ecosystem functioning (B–EF) relationships is complicated by potential interactions among abiotic and biotic variables at multiple levels of organisation, including adaptation within regional species populations and changes in community composition and species richness. We investigated the capacity for assemblages of three freshwater invertebrate consumer species (Asellus aquaticus, Nemoura cinerea and Sericostoma personatum) from temperate (southern England) and boreal (northern Sweden) regions to respond to expected shifts in temperature and basal resources, and quantified rates of a key ecosystem process (leaf-litter decomposition). Predictions of assemblage metabolism, derived from allometric-body size and temperature scaling relationships, accounted for approximately 40% of the variance in decomposition rates. Assemblage species composition accounted for further variance, but species richness per se had no discernible effect. Regional differences were evident in rates of leaf decomposition across temperature and resource manipulations, and in terms of the processing efficiency of temperate and boreal consumers of the same species (i.e. after correcting for body size and metabolic capacity), suggesting that intraspecific variation among local populations could modulate B–EF effects. These differences have implications for extrapolating how environmental warming and other aspects of climate change (e.g. species range shifts) might affect important drivers of ecosystem functioning over large biogeographical scales

Chapter 4 - Assessing the Contribution of Micro-Organisms and Macrofauna to Biodiversity–Ecosystem Functioning Relationships in Freshwater Microcosms

Summary A large body of research has revealed (often) positive biodiversity–ecosystem functioning (B–EF) relationships in manipulative experiments. The vast majority of such studies have focused on either micro- or macro-organisms, and none we are aware of have manipulated the diversity of both simultaneously under controlled laboratory conditions. We performed a microcosm experiment in which we manipulated species richness of aquatic fungi and invertebrates, two taxonomically distant sets of consumers that contribute to the same key ecosystem process in freshwaters, the decomposition of terrestrial leaf litter. We used a novel statistical design to maximize parsimony and analytical power in an experiment with three levels of species richness (seven mono-culture, 21 di-culture, and seven tri-culture treatments). Litter decomposition was measured as both leaf mass loss and the production of fine particulate organic matter (FPOM). We tested whether species richness affected these two processes or whether polycultures performed as predicted from their component mono-cultures. Further, we calculated assemblage metabolism in each microcosm to test whether the processes were driven by the metabolic demands of fungi and invertebrates. In general, across the 35 treatments, most species combinations performed in an additive fashion and we found no effect of species richness on either process. There was evidence of assemblage identity effects (i.e. certain species combinations not performing as expected), with instances of significant differences for species combinations that contained both caddis larvae and fungi. These assemblages performed worse than expected, which might have been due to dual vertical and horizontal interactions, with the possibility that although both consumed litter directly the former may also have grazed on the latter. Apart from these particular species combinations, overall performance of a species in polyculture was effectively the same as in mono-culture and reflected its metabolic demands. This suggests that even taxonomically distant consumers might exhibit a degree of functional redundancy for certain processes provided the remaining species can attain sufficient population biomass (and hence metabolic capacity) to compensate for the loss of other species, although whether such compensatory mechanisms operate in the field remains unknown. Further species contribute to a multitude of ecosystem processes and progressively more species are needed to sustain the sum of them. Our experiment highlights how, by taking metabolic demands into account, future B–EF studies could help to disentangle how species contribute to ecosystem processes both separately and in combination, and to help partition the effects of taxonomic and functional diversity.

Higher biodiversity is required to sustain multiple ecosystem processes across temperature regimes

Biodiversity loss is occurring rapidly worldwide, yet it is uncertain whether few or many species are required to sustain ecosystem functioning in the face of environmental change. The importance of biodiversity might be enhanced when multiple ecosystem processes (termed multifunctionality) and environmental contexts are considered, yet no studies have quantified this explicitly to date. We measured five key processes and their combined multifunctionality at three temperatures (5, 10 and 15 °C) in freshwater aquaria containing different animal assemblages (1–4 benthic macroinvertebrate species). For single processes, biodiversity effects were weak and were best predicted by additive-based models, i.e. polyculture performances represented the sum of their monoculture parts. There were, however, significant effects of biodiversity on multifunctionality at the low and the high (but not the intermediate) temperature. Variation in the contribution of species to processes across temperatures meant that greater biodiversity was required to sustain multifunctionality across different temperatures than was the case for single processes. This suggests that previous studies might have underestimated the importance of biodiversity in sustaining ecosystem functioning in a changing environment.

Life history allometries and production of small fauna

The production of heterotrophic biomass is an important aspect of overall ecosystem functioning. However, single-celled organisms or microscopic metazoans are often ignored in studies of secondary production, despite being very abundant and possessing high mass-specific population growth rates, relative to the more widely studied larger taxa. Here, we focused on how life history parameters scale with body size of ciliates and meiofauna (body mass range from approximately 0.001 to 90 mg C/individual) and integrated experimental and survey data to calculate secondary production of these groups. First, we derived a single allometric scaling relationship between the intrinsic rate of population increase and body mass in a laboratory experiment. We then used this relationship to calculate secondary production for over 260 of these small species in the field, using survey data from two contrasting streams; one of which was nutrient rich, the other nutrient poor. Results from laboratory cultures showed that the scaling relationship between body mass and both daily intrinsic rate of population increase and generation time followed a power law. The relationship between body mass and annual secondary production was consistent in both streams, but the number of taxa was greater in the more productive site. Both ciliates and meiofauna had high rates of biomass production, with annual P/B ratios (production divided by biomass) for the whole assemblage exceeding 11 in both streams. We conclude that a large fraction of benthic production is overlooked when protozoans and microscopic metazoans are excluded from estimates of biomass turnover.

Interplay of hydrology, community ecology and pollutant attenuation in the hyporheic zone

Abstract 1) We describe the hierarchical interplay of hydrology, hyporheic ecology and transformation of nutrients and pollutants in the hyporheic zone (HZ). The exchange of water between the surface-subsurface generates the hyporheic exchange flow: the engine that drives the ecological functioning of the HZ. The magnitude and direction of hydrological fluxes in the HZ follow complex spatial patterns, strongly influenced by the temporal dynamics of surface flow in rivers. 2) The direction and magnitude of hydrological fluxes also shapes the structure of hyporheic communities (hyporheos). During surface disturbances such as flooding or drought, benthic organisms may also use the HZ as a refuge, although the importance of this role is debated. 3) Streambed organisms differ in their ability to colonize the HZ depending on the biological traits they possess. The reduction in oxygen concentration and pore size with increasing sediment depth imposes a limit on the distribution of macroinvertebrates, which are replaced by a suite of smaller organisms (meiofauna and protists) at deeper sediment layers. Therefore, a concomitant reduction in net biomass and productivity might be expected through depth. However, only a few studies have assessed the contribution of the hyporheos to whole system production, and they have focused only on the fraction of relatively large organisms. 4) The bioreactor ability of the HZ to transform nutrients and pollutants is an important ecosystem service sustained by the life activities of hyporheos. Biofilms have the key role in this process due to their capacity to metabolize a wide range of dissolved compounds, including emerging pollutants. However, the residence time of water in pore sediments (resulting from hyporheic exchange flow) and the rest of the community (constantly reworking the sediments and grazing biofilms) are indirectly involved.

Defining geo-habitats for groundwater ecosystem assessments: an example from England and Wales (UK)

Groundwater ecosystems comprising micro-organisms and metazoans provide an important contribution to global biodiversity. Their complexity depends on geology, which determines the physical habitat available, and the chemical conditions within it. Despite this, methods of classifying groundwater habitats using geological data are not well established and researchers have called for higher resolution habitat frameworks. A novel habitat typology for England and Wales (UK) is proposed, which distinguishes 11 geological habitats (geo-habitats) on hydrogeological principles and maps their distribution. Hydrogeological and hydrochemical data are used to determine the characteristics of each geo-habitat, and demonstrate their differences. Using these abiotic parameters, a new method to determine abiotic habitat quality is then developed. The geo-habitats had significantly different characteristics, validating the classification system. All geo-habitats were highly heterogeneous, containing both high quality habitat patches that are likely to be suitable for fauna, and areas of low quality that may limit faunal distributions. Karstic and porous habitats generally were higher quality than fractured habitats. Overall, 70% of England and Wales are covered by lower quality fractured habitats, with only 13% covered by higher quality habitats. The main areas of high quality habitats occur in central England as north–south trending belts, possibly facilitating dispersal along this axis. They are separated by low quality geo-habitats that may prevent east-west dispersal of fauna. In south-west England and Wales suitable geo-habitats occur as small isolated patches. Overall, this paper provides a new national-scale typology that is adaptable for studies in other geographic areas.RésuméLes écosystèmes des eaux souterraines comportant des micro-organismes et des métazoaires contribuent fortement à la biodiversité globale. Leur complexité dépend de la géologie, qui détermine l’habitat physique disponible et son état chimique. Malgré cela, les méthodes de classification des habitats des eaux souterraines à l’aide de données géologiques ne sont pas bien établies et les chercheurs appellent à des cadres pour une détermination de plus haute résolution des habitats. Une typologie innovante pour l’Angleterre et le Pays de Galles (Royaume-Unis) est proposée, distinguant 11 habitats géologiques (géo-habitats) basés sur des principes hydrogéologiques. La distribution de ces habitats est également cartographiée. Des données hydrogéologiques et hydrochimiques sont utilisées pour déterminer les caractéristiques de chacun des géo-habitats, et démontrer les différences entre habitats. En utilisant ces paramètres abiotiques, une nouvelle méthode pour déterminer la qualité abiotique de l’habitat a ainsi été développée. Les géo-habitats ont des caractéristiques suffisamment différentes pour permettre la validation du système de classification. Tous les géo-habitats sont fortement hétérogènes, contenant à la fois des îlots d’habitats de très bonne qualité pour la faune et des secteurs de faible qualité pouvant limiter le développement de la faune. Les habitats karstiques et poreux sont généralement de meilleure qualité que les habitats fracturés. En tout, 70% de l’Angleterre et du Pays de Galles sont couverts par des habitats fracturés de faible qualité, avec seulement 13% couverts par des habitats de haute qualité. Les principaux secteurs d’habitats de haute qualité se situent au centre de l’Angleterre s’étendant du nord au sud, facilitant sans doute une certaine dispersion le long de cet axe. Ces secteurs sont séparés par des géo-habitats de faible qualité qui limitent sans doute la dispersion de la faune selon un axe est-ouest. Au sud-ouest de l’Angleterre et du Pays de Galles les géo-habitat adéquats se retrouvent en petits îlots isolés. D’une manière générale, ce papier propose une nouvelle typologie à l’échelle nationale qui peut être adaptée à des études dans d’autres secteurs géographiques.ResumenLos ecosistemas de aguas subterráneas que comprenden microorganismos y metazoos proporcionan una contribución importante a la biodiversidad global. Su complejidad depende de la geología, que determina el hábitat físico disponible, y las condiciones químicas dentro de él. A pesar de ello, los métodos de clasificación de los hábitats de aguas subterráneas utilizando datos geológicos no están bien establecidos y los investigadores han demandado marcos de hábitat de mayor resolución. Se propone una nueva tipología de hábitat para Inglaterra y Gales (Reino Unido), que distingue 11 hábitats geológicos (geo-hábitats) sobre los principios hidrogeológicos y se mapea su distribución. Se utilizan datos hidrogeológicos e hidroquímicos para determinar las características de cada geo-hábitat y demostrar sus diferencias. Utilizando estos parámetros abióticos, se desarrolla un nuevo método para determinar la calidad del hábitat abiótico. Los geo-hábitats tenían características significativamente diferentes, validando el sistema de clasificación. Todos los geo-hábitats eran altamente heterogéneos, conteniendo tanto áreas de hábitat de alta calidad que probablemente sean adecuados para la fauna, como áreas de baja calidad que pueden limitar las distribuciones faunísticas. Los hábitats cársticos y porosos generalmente eran de mayor calidad que los hábitats fracturados. En general, el 70% de Inglaterra y Gales están cubiertos por hábitats fracturados de menor calidad, con sólo el 13% cubierto por hábitats de mayor calidad. Las principales áreas de hábitat de alta calidad se producen en el centro de Inglaterra como fajas de tendencia norte-sur, lo que posiblemente facilita la dispersión a lo largo de este eje. Están separados por geo-hábitats de baja calidad que pueden impedir la dispersión este-oeste de la fauna. En el suroeste de Inglaterra y Gales, los geo-hábitats adecuados se presentan como pequeñas áreas aisladas. En general, este documento proporciona una nueva tipología a escala nacional que es adaptable para estudios en otras áreas geográficas.摘要包含微生物和后生动物的地下水生态系统为全球的生物多样性做出了重要的贡献。其复杂性取决于地质状况,因为地质状况决定现有的栖息地以及栖息地内的化学条件。尽管如此,利用地质数据对地下水栖息地的方法还没有建立,研究人员需要更高分辨率的栖息地框架。这里提出了(英国)英格兰和威尔士一种新的栖息地类型学,这种类型学根据水文地质原则区分出11个地质上的栖息地(地质栖息地)及绘制出其分布图。利用水文地质和水化学数据确定每一个地质栖息地的特征,论证其差异。利用这些非生物参数,提出了一种新的确定非生物栖息地品质的方法。地质栖息地具有显著不同的特征,验证了分类系统。所有的地质栖息地高度异质,包含很可能适宜动物种群的高品质的栖息地地块以及可能限制动物种群分布的低品质区域。岩溶和多孔渗水的栖息地通常比断裂的栖息地品质要高。总的来说,70%的英格兰和威尔士被低品质断裂的栖息地所覆盖,只有13%的面积被高品质的栖息地所覆盖。高品质栖息地的主要区域位于英格兰中部,呈北-南走向带,可能促进沿这个轴散布。这些区域被可能阻止东-西向动物群分布的低品质地质栖息地所分隔。在英格兰和威尔士西南地区,有适宜的地质栖息地,以小的岛状地块分布。总的来说,本文提供了一种新的全国尺度的类型学,这种类型学也适合在其它地理区的研究。ResumoEcossistemas em águas subterrâneas incluindo microrganismos e metazoários fornecem uma importante contribuição para a biodiversidade global. Sua complexidade depende da geologia, que determina o habitat físico disponível, e as condições químicas dentro dele. Apesar disso, métodos para classificação de habitats em águas subterrâneas usando dados geológicos não são bem estabelecidos e pesquisadores tem requerido por arcabouços para habitats de maior resolução. Uma nova tipologia de habitat para Inglaterra e País de Gales (Reino Unido) é proposta, que distingue 11 habitats geológicos (geohabitats) em princípios hidrogeológicos e mapeia sua distribuição. Os dados hidrogeológicos e hidroquímicos são usados ​​para determinar as características de cada geohabitat e demonstrar suas diferenças. Usando esses parâmetros abióticos, um novo método para determinar a qualidade do habitat abiótico é então desenvolvido. Os geohabitats apresentaram características significativamente diferentes, validando o sistema de classificação. Todos os geohabitats foram altamente heterogêneos, contendo os dois fragmentos de habitat de alta qualidade que provavelmente serão adequados para a fauna e áreas de baixa qualidade que podem limitar as distribuições faunísticas. Os habitats cársticos e porosos geralmente eram de maior qualidade do que os habitats fraturados. No geral, 70% da Inglaterra e do País de Gales são cobertos por habitats fraturados de menor qualidade, com apenas 13% cobertos por habitats de maior qualidade. As principais áreas de habitats de alta qualidade ocorrem no centro da Inglaterra como cinturões de tendência norte-sul, possivelmente facilitando a dispersão ao longo deste eixo. Eles são separados por geohabitats de baixa qualidade que podem impedir a dispersão leste-oeste da fauna. No sudoeste da Inglaterra e do País de Gales, os geohabitats adequados ocorrem como pequenos fragmentos isolados. Em geral, este artigo fornece uma nova tipologia de escala nacional adaptável para estudos em outras áreas geográficas.

Preface: Editorial Commentary: Body Size and the (Re)unification of Ecology

Publisher Summary This section provides the preface of Volume 45 of the book Advances in Ecological Research . The seven papers in this volume are the product of collaborations resulting from the activities of Sizemic, and the evolution of the ideas that are presented in the chapters. Sizemic has been an important venue for this initial stage of cross-fertilization to occur, and its inception may be seen in hindsight as one of the decisive moments when fisheries science and other branches of ecology became engaged anew.

Environmental filtering and community delineation in the streambed ecotone

A current controversy in ecology is whether biological communities are discrete biological entities or simply study units created for convenience; a debate that becomes even more heated when delimiting communities along ecotones. Here, we report an interdisciplinary study designed to address the interplay between environmental drivers and community ecology in a typical ecotone ecosystem: the streambed. Environmental filtering at a micro-scale determined how diversity, productivity and composition of the whole streambed assemblage varied with depth and with the direction of vertical water exchange. Biomass and production decreased with increasing depth, and were lower under upwelling than downwelling conditions. However, the rate at which biomass and production decreased with increasing depth differed significantly for different taxonomic groups. Using quantitative biocenosis analysis, we also showed that benthic and hyporheic zone assemblages (assemblages in close juxtaposition) could be clearly distinguished as discrete communities with individual integrity. Vertical hydrodynamic conditions also influenced the demarcation between both communities; the benthic community reached greater depths in downwelling than in upwelling zones.