451 research outputs found

    Studying biodiversity-ecosystem function relationships in experimental microcosms among islands

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    Ecological studies on islands have provided fundamental insights into the mechanisms underlying biodiversity of larger organisms, but we know little about the factors affecting island microbial biodiversity and ecosystem function. We conducted a field experiment on five Baltic Sea islands where we placed aquatic microcosms with different levels of salinity mimicking environmental stress and allowed diatoms to colonize the microcosms via the air. Using structural equation models (SEM), we investigated the interconnections among environmental and dispersal-related factors, diatom biodiversity, and ecosystem productivity (represented by chlorophyll a concentration). We also tested whether the body size structure of the community influences productivity together with biodiversity. In SEMs, we found no relationship between species richness or evenness and productivity. However, productivity increased with increasing mean body size of species in the communities. The effects of environmental stress on both biodiversity and ecosystem productivity were highlighted as species richness and evenness declined, whereas productivity increased at the highest salinity levels. In addition to salinity, wind exposure affected both biodiversity metrics and productivity. This study provides new insights into microbial community assembly in a field experimental setting and the relationship between biodiversity and ecosystem function. Our results indicate that salinity presents a strong abiotic filter, leading to communities that may be species poor, yet comprise salinity-tolerant and relatively productive species at high salinity. Our findings also emphasize the importance of mean community body size in mediating the effects of environmental conditions on productivity and suggest that this trait should be considered more broadly in biodiversity-ecosystem function studies.Peer reviewe

    Can the physiological tolerance hypothesis explain herb richness patterns along an elevational gradient? A trait-based analysis

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    Many taxa show their highest species richness at intermediate elevations, but the underlying reasons for this remain unclear. Here, we suggest that the physiological tolerance hypothesis can explain species richness patterns along elevational gradients, and we used functional diversity to test this hypothesis. We analyzed herb species richness, functional diversity, and environmental conditions along a 1300 m elevational gradient in a temperate forest, Beijing, China. We found that herb richness exhibited a “hump-shaped” relationship with elevation, with peak richness at approximately 1800 m. Functional diversity showed a significant unimodal relationship with elevation. The duration of high temperatures (≥ 300C: DHT) was the best predictor for herb richness and functional diversity along the gradient from 1020 to 1800 m, which suggest richness is limited by high temperature at low elevations. While along the gradient from 1800 to 2300 m, the duration of low temperatures (≤ 0°C: DLT) was the most powerful explanatory variable, which indicated at high elevations, richness reduced due to low temperature. Our analyses showed that the functional diversity of traits related to drought-tolerance (leaf mass per area, leaf area, and leaf hardiness) exhibited negative relationships with DHT, while functional diversity of traits related to freezing-tolerance (leaf thickness and hair density) exhibited negative relationships with DLT. Taken together, our results demonstrated that the richness-elevation relationship is consistent with the physiological tolerance hypothesis: at low elevations, richness is limited by high temperatures, and at high elevations, richness is reduced due to low temperatures. We concluded that our results provide trait-based support for the physiological tolerance hypothesis, suggesting that mid-elevations offer the most suitable environmental conditions, thus higher numbers of species are able to persist

    The role of epibenthic predators in structuring marine soft-bottom communities along an estuarine gradient

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    A unifying theory of community regulation in soft-bottom systems remains elusive, despite extensive field studies on factors controlling community structure. Here, I have (1) reviewed models of community regulation, (2) examined the role of predation in controlling benthic diversity along a salinity gradient, (3) examined effects of predation upon an abundant bivalve, Macoma balthica, and (4) revised a model of community regulation in an estuarine soft-bottom system. The Menge and Sutherland (MS) consumer stress model posits that consumers feed ineffectively in harsh environments, and the importance of physical disturbance, competition and predation varies with recruitment, environmental conditions, and trophic position. In this model, competition for resources depends directly upon the level of recruitment. I have revised the model to fit soft-bottom systems by changing the recruitment axis to a recruitment: resource ratio. Hence, the impact of a given level of recruitment depends upon resource availability. According to the MS model, predation is most important in determining community structure when environmental conditions are not severe. I investigated the applicability of the MS model in a soft-bottom estuarine community. I quantified predator abundance, prey abundance and diversity, and the differential effect of predation on species diversity and survival of an abundant prey species, Macoma balthica, along an estuarine gradient in two tributaries of Chesapeake Bay. Benthic diversity was lower in upriver high-stress habitats than downriver low-stress habitats, in agreement with predictions of the MS model. However, the following findings are inconsistent with model predictions: (1) predator abundance was greater upriver, (2) predation intensity and its impact on benthic diversity were greater upriver, and (3) predation-induced mortality of transplanted Macoma balthica clams, and natural mortality of clams were higher upriver. An alternative community regulation model applies to this system because higher predator abundance and predation intensity in higher environmental stress is contrary to the MS model predictions. Predators aggregated upriver where carbon production was increased, and prey were abundant. Hence, a more suitable model for this soft-bottom system is one that incorporates the effects of production and predation along with recruitment, competition and environmental stress

    Diversity and mean specific leaf area of Mediterranean woody vegetation changes in response to summer drought across a double stress gradient: The role of phenotypic plasticity

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    Aim: Many aspects of vegetation response to increased drought remain uncertain but it is expected that phenotypic plasticity may be key to early adaptation of plants to environmental stress. In this work we observe the response of specific leaf area (SLA) of woody shrub vegetation to the summer drought typical of the Mediterranean climate. In addition, to observe the possible interaction between the impact of drought and the environmental characteristics of the ecosystems, communities from different edaphic and structural contexts distributed along the double stress gradient of the Mediterranean mountains (high temperature and low precipitation at low elevation; low temperature and high irradiation at high elevation) have been analysed. Location: Central Mountain range of the Iberian Peninsula. Methods: Along the entire altitudinal gradient, 33 shrub communities belonging to different habitat typologies (shrublands, rocky areas, hedgerows, understorey) were sampled before and after the passage of summer, both in 2017 and 2019. A total of 1724 individuals and 15,516 leaves were collected and measured to estimate the mean values and diversity of SLA of each community. Results: The community-weighted mean and functional divergence have inverse quadratic relationships with the environmental gradient. Shrub communities at both ends of the gradient have low mean SLA values and high functional divergence of this trait. Summer drought implies a generalised decrease in the mean SLA of the communities throughout the gradient, as well as an alteration in functional richness and uniformity. However, the effect of summer drought on the plant community is mediated by the microenvironmental characteristics of its habitat. Conclusions: Drought acclimatisation of shrub communities through phenotypic plasticity leads to rapid changes in their functional leaf structure. In the long term, our results point to an increase in plant conservative strategies, reduced ecosystem productivity, slower nutrient recycling and the reduction of communities of specific habitats as drought increasesAdministrative and financial support was received from the Autonomous Community of Madrid (Project REMEDINAL TECM S2018/EMT-4338) and Sierra de Guadarrama National Park, which provided the permits for the sampling within the park (ref 10/097831.9/18). Alejandro Carrascosa was supported by a grant for the Promotion of Research in UAM Master studies (UAM 2018– 2019), and Mariola Silvestre by an FPI grant from MINEC

    Environmental dependency of biodiversity-ecosystem functioning relationships

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    The Effects of Enhanced Flows on Community Structure and Ecosystem Functioning in a Montane Utah River System

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    Due to growing human demands for freshwater within the last century, manmade flow alterations are now a common characteristic of rivers worldwide. Alterations to the volume and timing of flows in rivers are known to negatively impact aquatic biodiversity, biological productivity and ecosystem functions such as nutrient cycling. While previous research has focused on the effects of flow reductions and spates, there is a lack of knowledge on how high flows across longer timespans (i.e. ‘enhanced flows’) impact the structure of river communities and the integrity of ecosystem functions. The Utah Reclamation, Mitigation and Conservation Commission has expressed interest in reducing enhanced flows in a central Utah river so as to benefit aquatic habitat and native game fish. With their funding support, I collected aquatic invertebrate and ecosystem function data under natural and enhanced flow conditions throughout Sixth Water Creek and Diamond Fork River. These data were supplemented with historical invertebrate data collected by BIO-West, Incorporated. For each river segment, I tested whether flow volume and variation had relationships with the density and health of streambed invertebrate communities. I also sought to determine how these flow metrics affected leaf litter breakdown, primary production and stream metabolism (i.e. the production and respiration of organic matter). Here, I demonstrate that enhanced flows impact streambed invertebrate communities differently in each river segment, in addition to suppressing stream metabolism system-wide. While streambed communities were mostly unaffected by enhanced flows in Sixth Water Creek, density and community health exhibited negative relationships with flow metrics in Diamond Fork River. In the Lower Diamond Fork mainstem, proportions of pollution-tolerant taxa increased as peak flows increased, while streambed invertebrate density decreased as mean monthly flows increased. Moreover, enhanced flows appeared to severely impact the production of organic matter in Sixth Water Creek and Lower Diamond Fork River. This disproportionate suppression of production over respiration shifted the river towards greater reliance on out-of-stream energy sources. These results demonstrate the importance of considering spatial gradients when investigating community responses to flow alterations, and also reveal how river ecosystems are threatened with losses of in-stream energy supplies under enhanced flows

    An experimental test of the intermediate disturbance hypothesis: influence of two disturbance types on the structure of etablished Western Baltic fouling communities

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    The intermediate disturbance hypothesis (IDH) is a widely accepted concept in community ecology. It assumes disturbance to be a potent agent to override the competitive exclusion principle and to facilitate the long-term coexistence of competitively inequal species. The IDH states that diversity is maximal at intermediate levels of disturbance. The aim of this study is to verify the predictions of the concept in a eutrophic, species-poor system - as it is represented by the Western Baltic Sea - in an in situ experimental approach. In two discrete experimental series, established hard-bottom communities of two successional stages were submitted to various levels of emersion (exposure to the air) and exposure to enhanced UVB radiation. For the communities that experienced emersion treatments, the IDH was confirmed in the first year when diversity was found to peak at intermediate disturbances. However, for communities of both successional stages, diversity-disturbance relationships were U-shaped or non-significant in the second year. This ambiguous picture basically confirms the validity of the mechanisms proposed by the IDH, but shows that their forcing can be masked or reversed by fluctuations in environmental parameters, such as climatic conditions. An extension of the concept, that considers diversity enhancement under extreme conditions due to a disturbance induced change in community structure, is proposed. UVBR treatment effects were transient and did not generate a unimodal disturbance-diversity pattern. Though treatment effects were not persistent, a general tendency for green algae to increase and for red algae to decrease with increasing daily UVBR exposure length was observed

    The Shifting Importance of Competition and Facilitation Along Diversity, Environmental Severity, and Plant Ontogenetic Gradients

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    Ecological theory and empirical studies have focused heavily on the importance of competition in plant communities. Competition can help explain species coexistence, the maintenance of species diversity, and biological invasions. Competition for resources appears to be ubiquitous among coexisting organisms. This overwhelming focus on competition over the past one hundred years may have overshadowed the importance of positive interactions (facilitation). Growing near your neighbors involves competition for resources, but it also involves alteration of a shared microclimate. Neighboring plants have the capacity to increase shade, decrease air temperatures, increase humidity, and increase shallow soil moisture in their local environment. In severe environments - tundra, deserts, salt marshes - facilitation can outweigh the effects of competition. In periods of environmental severity, these benefits can prove essential. In this dissertation, I explore the importance of both competitive and facilitative interactions across gradients of environment severity, plant ontogeny, and productivity. I use an experimental manipulation of herbaceous plant diversity to manipulate the magnitude of competition and facilitation in a series of experiments in central Minnesota. I show that woody encroachment into grasslands is influenced by both competitive and facilitative interactions related to decreasing local species diversity and increasing atmospheric CO2 (Chapter 1). I show that diversity can ameliorate the microclimate to create local conditions that are cooler and more humid, and these effects can facilitate seedling growth and survival. I show that competition appears to increase as seedlings grow in size, but this size-structured change may be due more to decreasing facilitation rather than increasing competition (Chapter 2). Finally, plants may compete strongly for resources much of the time, but this can be outweighed by strong facilitation, and the interaction between the two processes can change on a day-to-day basis (Chapter 3). Finally, I use a modified Lotka-Volterra model to show how competition and facilitation may change as a function of environmental severity and productivity, and the implications of these relationships on individual plant performance and long-term community dynamics (Chapter 4). Nutrient availability, CO2 concentrations, seasonal temperatures and precipitation will likely change independently in future climate change scenarios. It is therefore essential that we have a comprehensive understanding of the positive and negative components that underlie plant interactions, to better predict how plant communities will change in the future

    Aspects of the ecology of Namib Desert ants

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    Includes bibliographial references (leaves 222-234).Thirty-six species of ants were collected in the central Namib Desert, Namibia during the period 1981 to 1985. The ant fauna was dominated by the Myrmicinae, comprising 29 species, followed by the Formicinae, comprising six species and the Pseudomyrmecinae with one species. The dominance of the ant fauna by these subfamilies was in part attributed to the abilities of certain members of these ant groups to store food. The majority of ant species occurred on the gravel plains where species richness was strongly correlated with mean annual rainfall, an index of primary productivity. Certain species were strongly associated with perennial vegetation reflecting the ants' requirements for honeydew, nectar and/or nesting sites. The vast majority of ant species were not dependent on perennial vegetation and relied primarily on seeds, insects or both for food

    Old-field recolonization by animal - dispersed keystoneplants: combining field work, genetics and apatially-explicit modelling

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    Doutoramento em Biologia / Instituto Superior de Agronomia. Universidade de LisboaThe transformation and destruction of natural areas for their exploitation as agricultural lands is a typical example of land-use change that generates high ecosystem degradation worldwide. However, during the last decades, many agricultural lands are being abandoned due to multiple socio-economic factors. Currently, there is a trend that sees the farmland abandonment as an opportunity to restore the functioning of these human-altered ecosystems. To take advantage of this opportunity, it is central to understand the ecological processes that drive and limit the natural regeneration of plant communities in these old-fields. This doctoral dissertation addresses the understanding of two central stages that determine the natural (re)colonization of old-fields where interspecific interactions are central: seed arrival and seedling recruitment and establishment. To do this, a multidisciplinary framework that combines intensive field work, molecular techniques and spatially explicit modelling was used in three old-fields located in southwestern Iberian Peninsula. Specifically, it was applied to the system comprised of the dwarf palm (Chamaerops humilis L.), a pioneer palm endemic to the Mediterranean, and its interspecific interactions with frugivorous mammals (ungulates and carnivores) and woody plant species. The results showed that carnivores promoted a considerable seed arrival. The fecal marking behavior of dispersers, especially badgers, impacted the spatial and genetic structure of dispersed seeds and seedlings. Several nurse shrub species were quantitatively compared, being identified the dwarf palm as a ‘keystone’ species. Indeed, for the first time, it was experimentally demonstrated the role of the dwarf palm as nurse plant of several woody species. However, the strong variation among individual palms confirmed the presence of the facilitation-competition continuum and therefore, that these plant-plant interactions are not always positive. Besides, spatial evidences of the role of the dwarf palm as ‘perche’ for frugivorous birds were found. In conclusion, using the system ‘dwarf palm-mammals-woody plants’ as a model, it was revealed how the natural (re)colonization of old-fields can promote their self-recovery, although active restoration interventions can be highly recommendable to increase the regeneration of some plant communities.N/
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