Project 2: Interactions between global change, biodiversity, and feedback mechanisms

Project Team

Owen Petchey
Jakob Pernthaler
Samuel Abiven
Thomas Posch
Yana Yankova
Aurélie Garnier

Research aims - This project will investigate the relations between global change as driver of biodiversity change and feedback effects of biodiversity change on ecosystem functions using aquatic ecosystems. It will include both small- and large-scale research, with a long-term aim of explicitly scaling between these.

Small-scale experiments with aquatic microcosms – Microcosm (small-world) ecosystems based in the laboratory provide a unique opportunity to simulate environmental change and observe effects on biodiversity and ecosystem processes. Aquatic microcosms can contain considerable biodiversity including decomposers, autotrophs, herbivores, and predators. This biodiversity influences ecosystem processes such as decomposition, respiration, and nutrient cycling (Petchey et al., 1999). Furthermore, experimental communities can include locally important species, for example the quantitative dominant primary producer of Lake Zurich, the cyanobacterium Planktothrix rubescens (Van den Wyngaert et al., 2011). This species is important not only as a dominant producer, but also due to the toxic secondary metabolites it stores. The scale and tractability of these model ecosystems has contributed to many fundamental advances in environmental change-biodiversity research.

Experiment Set 1. Combinatorial effects of the ‘big five’ environmental changes. As far as we are aware, no experiments have investigated simultaneously the combinatorial effects of the ‘big five’ types of global change. There are 21 different combinations of these five, which makes for a large replicated experiment. Five replicates of each combination yield 105 experimental units. An experiment of this scale is feasible using small artificial ecosystems (microcosms) housed in the laboratory. Furthermore, the organisms (microbes) in these ecosystems have very short generation times, so that an experiment that would take tens to hundreds of years with larger organisms can be performed in just a few months. We will employ the same types of statistical analyses as those carried out for large combinatorial manipulations of biodiversity (e.g., Bell et al. 2009). These analyses partition the effects of environmental change into those caused by additive and interactive effects. We would repeat this general experiment several times, with different sets of species comprising the communities.

Experiment Set 2. Biodiversity–environment feedbacks. A powerful mechanism for understanding the importance and consequences of biodiversity–environment feedbacks is to experimentally manipulate them. For example, manipulation of whether the CO2 produced by respiration causes an increase in atmospheric CO2 concentration. This kind of manipulation of the strength of the biodiversity to environment effect is quite unique, and would reveal the importance of environmental change-biodiversity feedback. We would repeat this general experiment several times, again with different sets of species. In both sets of experiments, population dynamics and community structure will be recorded by a combination of direct counts and flow cytometry in experimental communities or samples thereof. Ecosystem processes, such as gas fluxes and decomposition rates, will be measured by analysing gas concentrations in the liquid and headspace, and by measuring weight loss by dead organic matter (Petchey et al., 1999).

Large-scale observations at Lake Zurich – Climate warming could affect the seasonal dynamics of important organisms in Lake Zurich, such as the previously mentioned toxic cyanobacterium Planktothrix rubescens. There is anecdotal evidence that spring phytoplankton blooms will become shorter, with knock-on consequences for system-wide biogeochemical processes, e.g. sedimentation rates and lake net heterotrophy. Moreover, changes in environmental conditions might alter competitive relations, allow increased dominance of P. rubescens, and further alter ecosystem processes. The goal of this subproject is to predict system- (i.e., Lake-) wide changes in biodiversity patterns and associated ecosystem processes, by novel coupling of remote and in-situ sensing.

Remote sensing of chlorophyll a (chl a) is a powerful means of determining global primary production in marine surface waters (Platt et al., 2008). This approach has been modified to also assess the concentrations and spatiotemporal distribution patterns of phytoplankton in inland waters (Bresciani et al., 2011; Odermatt et al., 2012). Lake Zurich was one model system in this research (Odermatt et al., 2010). However, the available 30-year time series of chl a concentration in Lake Zurich has not been used for more accurate matching of remotely sensed and locally recorded conditions. Depth-resolved chlorophyll a distribution data will be used to establish a conversion of chl a values in the surface layers of the lake — as determined by optical remote sensing — to the magnitude of bloom events (that typically feature their maxima in several m depth) throughout the photic zone. Finally, a combination of remote sensing with high-resolution spatial sampling (using an autonomous robotic platform) will shed light on the magnitude and system-wide ecological significance of horizontal variability of primary production in the lake.

Expected contributions to research theme – This project includes research at small and large scales, experimental and comparative approaches, and novel collaborations at the UZH. Mathematical models will provide a framework for integration of results across these scales, as well as for prediction. Focus on aquatic ecosystems provides complementary with other projects in the URPP GCB. The proposed research will contribute towards increased fundamental understanding of how environmental changes interact to affect biodiversity and ecosystem processes, and the importance of feedback mechanisms between biodiversity and environmental changes. Fundamental research of this nature is timely, novel, and policy relevant. The research also concerns a locally important ecosystem — Lake Zurich — and some of the dominant organisms within it, including one that is toxic to humans. The research concerning the Lake Zurich ecosystem includes the development and validation of novel and timely remote sensing methods that are needed to predict the timing and location of phytoplankton blooms in the context of global change.