A community-based evaluation of population growth and agro-pastoralist resilience in Sub-Saharan drylands

Human population growth is considered together with climate warming as major driver of change in Sub-Saharan Africa. Research on the implications of increased population densities often utilises community knowledge but without incorporating the view of local stakeholders. In this study, we applied a community-centred approach to assess direct and indirect consequences of population growth in drylands of north-western Kenya. Combined social, agricultural and geo-spatial analyses allowed us to identify major system transitions, determine their linkage to population growth and deduce consequences for local livelihoods and community resilience.Community-members reported positive and negative consequences of fourfold population growth since 1974 but evaluated its overall effect as clearly beneficial. This overall positive effect was based on both, positive developments and the successful mitigation of potential system stressors. First, food security was maintained despite high growth rates because a shift from migratory pastoralism to a more labour-intensive agro-pastoralist system helped to increase agricultural productivity. Additionally, land-use changes were linked to land privatisation and improved erosion protection on private land, decoupling population growth from environmental degradation.We detected, however also early warning signs of reduced community resilience as households were unable to fully recover livestock densities after catastrophic events. A population-growth driven reduction in household land-sizes and the decreased monetary value of agricultural production were identified as drivers of this development. The extrapolation of our results to establish a general relationship between population densities, land-use and household resilience in Sub-Saharan drylands suggest that further system transformations will be required to ensure regional food-security.Swedish Research Counci

Improving the reliability of eDNA data interpretation

Global declines in biodiversity highlight the need to effectively monitor the density and distribution of threatened species. In recent years, molecular survey methods detecting DNA released by target‐species into their environment (eDNA) have been rapidly on the rise. Despite providing new, cost‐effective tools for conservation, eDNA‐based methods are prone to errors. Best field and laboratory practices can mitigate some, but the risks of errors cannot be eliminated and need to be accounted for. Here, we synthesize recent advances in data processing tools that increase the reliability of interpretations drawn from eDNA data. We review advances in occupancy models to consider spatial data‐structures and simultaneously assess rates of false positive and negative results. Further, we introduce process‐based models and the integration of metabarcoding data as complementing approaches to increase the reliability of target‐species assessments. These tools will be most effective when capitalizing on multi‐source data sets collating eDNA with classical survey and citizen‐science approaches, paving the way for more robust decision‐making processes in conservation planning.GCR

The potential of fatty acid isotopes to trace trophic transfer in aquatic food-webs

Compound-specific isotope analyses (CSIA) of fatty acids (FA) constitute a promising tool for tracing energy flows in food-webs. However, past applications of FA-specific carbon isotope analyses have been restricted to a relatively coarse food-source separation and mainly quantified dietary contributions from different habitats. Our aim was to evaluate the potential of FA-CSIA to provide high-resolution data on within-system energy flows using algae and zooplankton as model organisms. First, we investigated the power of FA-CSIA to distinguish among four different algae groups, namely cyanobacteria, chlorophytes, haptophytes and diatoms. We found substantial within-group variation but also demonstrated that δ13C of several FA (e.g. 18:3ω3 or 18:4ω3) differed among taxa, resulting in group-specific isotopic fingerprints. Second, we assessed changes in FA isotope ratios with trophic transfer. Isotope fractionation was highly variable in daphnids and rotifers exposed to different food sources. Only δ13C of nutritionally valuable poly-unsaturated FA remained relatively constant, highlighting their potential as dietary tracers. The variability in fractionation was partly driven by the identity of food sources. Such systematic effects likely reflect the impact of dietary quality on consumers' metabolism and suggest that FA isotopes could be useful nutritional indicators in the field. Overall, our results reveal that the variability of FA isotope ratios provides a substantial challenge, but that FA-CSIA nevertheless have several promising applications in food-web ecology. This article is part of the theme issue ‘The next horizons for lipids as ‘trophic biomarkers’: evidence and significance of consumer modification of dietary fatty acids’.Svenska Forskningsrådet Forma

Integration of SWMM into a Dam Break, Hurricane, and Extreme Flood Modeling and Damage Assessment Framework

SWMM5 has been seamlessly integrated with a Geographic Information System (GIS) for simulation of inundation and analysis of consequences resulting from extreme flood events. The GIS-based environment processes digital elevation models, land use/cover data, stream networks and soils to create stream network, sub-basins, and cross-section shapefiles for river basins selected for analysis. The following readily-available public-domain datasets are utilized: 30-m topographical data from the United States Geological Survey (USGS), 30-m NLCD, Natural Resources Conservation Service (NRCS) (STATSGO), and National Hydrography Dataset (NHD). Rainfall predictions are made by a numerical weather model and ingested in gridded format into the simulation environment. Runoff hydrographs are estimated using Green-Ampt infiltration excess runoff prediction and a onedimensional diffusive wave overland flow routing approach. The hydrographs and the channel morphology are used to generate a SWMM5 compatibl

Impact of food quality on aquatic consumers : Behavioral and physiological adjustments

Food quantity and quality together determine growth rates of consumers and the utilisation efficiencies of available resources in aquatic and terrestrial ecosystems. The effect of food quality on the performance of consumers is dependent on both, its direct influence on ingestion and assimilation rates, and on the behavioural and physiological adjustments of consumers to their food environment. The main target of this thesis was to investigate the nature and scope of behavioural and physiological adjustments in consumers and assess the resulting consequences for consumers’ fitness and ecosystem-wide nutrient flows. In paper I, we investigated the extent of elemental homeostasis across several taxonomic groups of planktonic herbivores. We found that adjustments in elemental ratios (C:N:P) in body tissues are an important physiological response of heterotrophic flagellates, but that in ciliates and multi-cellular organisms C:N:P ratios varied much less than in their algal prey. Hence, alternative regulatory mechanisms determine the reactions of metazoan zooplankton to decreases in food quality. In paper II, we developed a theoretical model to explore regulation in behaviour and digestive physiology of consumers to changes in the food environment. Our results demonstrate that feeding and digestion of consumers are determined by trade-offs between benefits and costs of investments in these processes. We revealed that the flexibility in consumers’ behaviour and physiology had strong influences on assimilation rates and efficiencies and thereby affected growth rates and a wide range of ecosystem functions. In paper III, we investigated the scope and consequences of adjustments in feeding and assimilation rates of copepods exposed to different diets. An important finding was that consumers can use resources, which are available in surplus, to increase the uptake of a limiting nutrient. Such nutrient interconversion led to co-limitation, the simultaneous limitation of copepods by two different nutrients. Finally, in paper IV, we aimed to test the effect of food quality on population dynamics in the field. We investigated zooplankton populations in tropical soda-lakes, an environment with a surplus of planktonic food sources that thus provides an ideal setting for investigations of food quality. However, we found that the hatching of resting eggs from lake sediments was the main driver of zooplankton bloom formation resulting in non-cyclical dynamics that were not related to food quality. These findings contributed to our understanding under which circumstance and by which mechanisms food quality affects the performance of consumers. My results highlight that food quality has not only direct effects on consumers’ growth but also triggers behavioral and physiological responses in consumers to maximize their fitness.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript.</p

Nutrient deficiencies and the restriction of compensatory mechanisms in copepods

The flexible regulation of feeding behaviour and nutrient metabolism is a prerequisite for consumers to grow and survive under variable food conditions. Thus, it is essential to understand the ecological trade-offs that restrict regulatory mechanisms in consumers to evaluate the consequences of nutrient limitations for trophic interactions. Here, we assessed behavioural and physiological adjustments to nutrient deficiencies in copepods and examined whether energy limitation, food digestibility or co-limitation with a second nutrient restricted compensatory mechanisms. A combination of C-13-labelling and compound-specific stable isotope measurements revealed that copepods compensated nitrogen deficiencies by raising retention efficiencies of amino acids (AA). The costs of higher retention efficiencies were reflected in the doubling of structural fatty acids (FA), probably required for morphological adaptations of the gut. A depletion of highly unsaturated FA in storage lipids and their selective retention suggested that these FA became co-limiting and restricted a further increase in AA retention efficiencies. Copepods feeding on phosphorus-limited algae showed a marked increase in ingestion rates but were not fully able to compensate dietary deficiencies. The increase in ingestion rates was thereby not restricted by higher foraging costs because energy storage in copepods increased. Instead, thicker cell walls of nutrient-limited algae indicated that algal digestion resistance restricted the extent of surplus feeding. The strongly nutrient-specific response of copepods had large implications for recycling rates, growth efficiencies and the potential top-down control at the plant-animal interface. Compensatory mechanisms to mitigate nutrient deficiencies are therefore an essential aspect of trophic interactions and have the potential to alter the structure of food web.FORMA

Corals as canaries in the coalmine: Towards the incorporation of marine ecosystems into the ‘One Health’ concept

‘One World – One Health’ is a developing concept which aims to explicitly incorporate linkages between the environment and human society into wildlife and human health care. Past work in the field has concentrated on aspects of disease, particularly emerging zoonoses, and focused on terrestrial systems. Here, we argue that marine environments are crucial components of the ‘One World – One Health’ framework, and that coral reefs are the epitome of its underlying philosophy. That is, they provide vast contributions to a wide range of ecosystem services with strong and direct links to human well-being. Further, the sensitivity of corals to climate change, and the current emergence of a wide range of diseases, make coral reefs ideal study systems to assess links, impacts, and feedback mechanisms that can affect human and ecosystem health. There are well established protocols for monitoring corals, as well as global networks of coral researchers, but there remain substantial challenges to understanding these complex systems, their health and links to provisioning of ecosystem services. We explore these challenges and conclude with a look at how developing technology offers potential ways of addressing them. We argue that a greater integration of coral reef research into the ‘One World – One Health’ framework will enrich our understanding of the many links within, and between, ecosystems and human society. This will ultimately support the development of measures for improving the health of both humans and the environment.N