Role of functionally dominant species in varying environmental regimes: evidence for the performance-enhancing effect of biodiversity

Background Theory suggests that biodiversity can act as a buffer against disturbances and environmental variability via two major mechanisms: Firstly, a stabilising effect by decreasing the temporal variance in ecosystem functioning due to compensatory processes; and secondly, a performance enhancing effect by raising the level of community response through the selection of better performing species. Empirical evidence for the stabilizing effect of biodiversity is readily available, whereas experimental confirmation of the performance-enhancing effect of biodiversity is sparse. Results Here, we test the effect of different environmental regimes (constant versus fluctuating temperature) on bacterial biodiversity-ecosystem functioning relations. We show that positive effects of species richness on ecosystem functioning are enhanced by stronger temperature fluctuations due to the increased performance of individual species. Conclusions Our results provide evidence for the performance enhancing effect and suggest that selection towards functionally dominant species is likely to benefit the maintenance of ecosystem functioning under more variable conditions

Biodiversity, community structure and function of biofilms in stream ecosystems

Multi-species, surface-attached biofilms often dominate microbial life in streams and rivers, where they contribute substantially to biogeochemical processes. The microbial diversity of natural biofilms is huge, and may have important implications for the functioning of aquatic environments and the ecosystem services they provide. Yet the causes and consequences of biofilm biodiversity remain insufficiently understood. This review aims to give an overview of current knowledge on the distribution of stream biofilm biodiversity, the mechanisms generating biodiversity patterns and the relationship between biofilm biodiversity and ecosystem functioning

Natural vs. financial insurance in the management of public-good ecosystems

In the face of uncertainty, ecosystems can provide natural insurance to risk averse users of ecosystem services. We employ a conceptual ecological-economic model to analyze the allocation of (endogenous) risk and ecosystem quality by risk averse ecosystem managers who have access to financial insurances, and study the implications for individually and socially optimal ecosystem management, and policy design. We show that while an improved access to financial insurance leads to lower ecosystem quality, the effect on the free-rider problem and on welfare is determined by ecosystem properties. We derive conditions on ecosystem functioning under which, if financial insurance becomes more accessible, (i) the extent of optimal regulation increases or decreases; and (ii) welfare, in the absence of environmental regulation, increases or decreases.ecosystem quality, ecosystem services, ecosystem management, endogenous environmental risk, insurance, risk-aversion, uncertainty

Biodiversity and Ecosystem Functioning - What Diversity? Which Functioning?

We share our planet with an estimated 8.7 million eukaryotic species and an uncountable number of bacteria and archaea. But that amazing diversity is under threat from overexploitation, habitat destruction and climate change. This realization has lead ecologists to study the consequences of species loss. The consensus after 30 years of research is that biodiversity can have many benefits. More diverse communities tend to be more productive and more stable. But the research has mostly focused on diversity at the level of species, in relatively species-poor ecosystems, and often measured diversity as the number of species - independent of their identity or relative abundance. In this thesis I leverage the advancements of modern sequencing technology to use mega-diverse bacterial communities as a model system. The thesis includes four chapters. Chapter I shows that bacterial freshwater communities sustain ecosystem functioning despite extensive reductions in diversity. A literature review corroborates the results - only 25 % of the reported experimental manipulations show a positive effect of bacterial diversity on ecosystem functioning. In Chapter II, we investigate the effects of habitat diversity on ecosystem functioning. We use experimental landscapes of shallow bay sediment habitats. Depending on the season, both greater habitat diversity and greater bacterial diversity increased landscape ecosystem functioning. Chapter III, in which we related the diversity of microbial denitrifiers to nitrogen fixation rates in natural marine sediments, shows no connection between diversity and functioning. Nor can other microbial community metrics be related to nitrogen fixation rates, including the diversity of the general bacterial community and the abundance of certain species. In a previous study, nitrogen fixation was correlated to the abundance of the genes that encode the protein involved in the process (nifH genes). Yet, that model fails to predict nitrogen fixation rates in our study. Chapter IV is about the “functioning” part in biodiversity and ecosystem functioning research. It has been suggested that while biodiversity is only weakly important for single functions, its importance increases when multiple functions are considered simultaneously. The logic is intuitively appealing: if species perform different functions, more species are needed to perform more functions simultaneously. Nonetheless, it is wrong. We show that considering multiple functions does not per se change the biodiversity ecosystem functioning relationship. In concert, the four chapters included in this thesis call into question some of the broad claims that have been made in the field of biodiversity and ecosystem functioning. The number of species as such is unlikely to be generally related to ecosystem functioning, especially in highly diverse systems. Claims that any species loss will result in loss of ecosystem functioning cannot be justified. Jointly considering multiple functions does not change that conclusion. Nevertheless, protecting diversity is a moral imperative, and inflicting irreversible changes to nature without understanding the consequences is careless and shortsighted. As human impact is unavoidable, we need the best possible knowledge base to make evidence- based and informed decisions. Research in ecology is crucial to provide this knowledge. To be reliable it must be as rigorous as possible. This thesis hopes to provide some small steps in the right direction

Microbes in the Anthropocene: spillover of agriculturally selected bacteria and their impact on natural ecosystems

Soil microbial communities are enormously diverse, with at least millions of species and trillions of genes unknown to science or poorly described. Soil microbial communities are key components of agriculture, for example in provisioning nitrogen and protecting crops from pathogens, providing overall ecosystem services in excess of $1000bn per year. It is important to know how humans are affecting this hidden diversity. Much is known about the negative consequences of agricultural intensification on higher-organisms, but almost nothing is known about how alterations to landscapes affect microbial diversity, distributions and processes. We review what is known about spatial flows of microbes and their response to land use change, and outline nine hypotheses to adva nce research of microbiomes across landscapes. We hypothesise that intensified agriculture selects for certain taxa and genes, which then “spill over” into adjacent unmodified areas and generate a halo of genetic differentiation around agricultural fields. Consequently, the spatial configuration and management intensity of different habitats combines with the dispersal ability of individual taxa to determine the extent of spillover, which can impact the functioning of adjacent unmodified habitats. When land scapes are heterogeneous and dispersal rates are high, this will select for large genomes that allow exploitation of multiple habitats , a process that may be accelerated through horizontal gene transfer. Continued expansion of agriculture will increase genotypic similarity, making microbial community functioning increasingly variable in human - dominated landscapes , potentially also impacting the consistent provisioning of ecosystem services . While the resulting economic costs have not been calculated, it is clear that dispersal dynamics of microbes should be taken into consideration to ensure that ecosystem functioning and services are maintained in agri - ecosystem mosaics

Valuing ecosystem resilience

The concept of ecosystem resilience is being increasingly discussed as a driver of biodiversity values. It implies that marginal deteriorations in ecosystem conditions can abruptly result in non-marginal and irreversible changes in ecosystem functioning and the economic values that the ecosystem generates. This challenges the traditional approach to the valuation of biodiversity, which has focused on quantifying values attached to individual species or other elements of ecosystems. As yet, little is known about the value society attaches to changes in ecosystem resilience. This paper investigates this value. A discrete choice experiment is used to estimate implicit prices for attributes used to describe ecosystem resilience using the Border Ranges rainforests in Australia as an example. We find evidence that implicit prices for the attributes describing ecosystem resilience are positive and statistically significantly different from zero.ecosystem resilience, discrete choice experiments, implicit prices, willingness to pay space, Environmental Economics and Policy,

The relationship between biodiversity and ecosystem functioning across space and time

Recent empirical studies conducted in disparate ecosystems have shown that greater species diversity has positive effects on ecosystem functioning; however, other studies have found neutral or sometimes negative results. It is still unclear why the relationship between biodiversity and functioning varies among studies, but perhaps, investigating this relationship across spatial and temporal scales will lead to further understanding. One theory predicts that local niche complementarity among species (the partitioning of species based upon niche differentiation) is predicted to positively affect local ecosystem functioning at the local spatial scale. However, more recent theory predicts that greater local diversity may hinder local ecosystem functioning when diversity is enhanced through regional processes. I suggest community assembly as a way to incorporate both the local and regional processes that determine biodiversity and its consequent effects on ecosystem functioning. From this, I propose a hump-shaped relationship between diversity and ecosystem functioning at local spatial scales, but a linear increase of functioning with diversity at regional spatial scales. Thus, species diversity may have different effects on ecosystem functioning across different spatial scales. Species diversity may affect ecosystem functioning differently across time as environmental conditions shift. Through integrating recent theoretical models in ecosystem ecology and empirical examples of food-webs in community ecology, the effects of herbivore diversity on ecosystem functioning (grazing of primary producers) were examined under unchanged (no nutrients added) and changed (nutrients added) environmental conditions. I found that communities with higher species richness and diversity did not significantly differ from lower diversity communities in grazing intensity in the unchanged environments. However, higher diversity communities did have a significant effect on the biomass of primary producers in the nutrient enriched environments, while lower diversity communities did not. This empirical study showed that the functioning of local communities is dependent on the environmental conditions present in the habitat. Overall, this investigation found that the relationship between species diversity and ecosystem functioning may be dependent on spatial scale and environmental changes over time