Microbiomes Reduce Their Host's Sensitivity to Interspecific Interactions.

Bacteria associated with eukaryotic hosts can affect host fitness and trophic interactions between eukaryotes, but the extent to which bacteria influence the eukaryotic species interactions within trophic levels that modulate biodiversity and species coexistence is mostly unknown. Here, we used phytoplankton, which are a classic model for evaluating interactions between species, grown with and without associated bacteria to test whether the bacteria alter the strength and type of species interactions within a trophic level. We demonstrate that host-associated bacteria alter host growth rates and carrying capacity. This did not change the type but frequently changed the strength of host interspecific interactions by facilitating host growth in the presence of an established species. These findings indicate that microbiomes can regulate their host species' interspecific interactions. As between-species interaction strength impacts their ability to coexist, our findings show that microbiomes have the potential to modulate eukaryotic species diversity and community composition.IMPORTANCE Description of the Earth's microbiota has recently undergone a phenomenal expansion that has challenged basic assumptions in many areas of biology, including hominid evolution, human gastrointestinal and neurodevelopmental disorders, and plant adaptation to climate change. By using the classic model system of freshwater phytoplankton that has been drawn upon for numerous foundational theories in ecology, we show that microbiomes, by facilitating their host population, can also influence between-species interactions among their eukaryotic hosts. Between-species interactions, including competition for resources, has been a central tenet in the field of ecology because of its implications for the diversity and composition of communities and how this in turn shapes ecosystem functioning

Intra- guild predation (IGP) can increase or decrease prey density depending on the strength of IGP

In consumer communities, intra- guild predation (IGP) is a commonly observed interaction that is widely believed to increase resource density. However, some recent theoretical work predicts that resource density should first decrease, and then increase as the strength of IGP increases. This occurs because weak to intermediate IGP increases the IG predator density more than it reduces the IG prey density, so that weak to intermediate IGP leads to the lowest resource density compared to weak or strong IGP. We test this prediction that basal resource density would first decrease and then increase as the strength of IGP increase. We used a well- studied system with two protozoa species engaged in IGP and three bacteria species as the basal resources. We experimentally manipulated the percentage of the IG prey population that was available to an IG predator as a proxy for IGP strength. We found that bacterial density first decreased (by ~25%) and then increased (by ~30%) as the strength of IGP increased. Using a modified version of a published IGP model, we were able to explain ~70% of the variation in protozoa and bacterial density. Agreement of the empirical results with model predictions suggests that IGP first increased the IG predator density by consuming a small proportion of the IG prey population, which in turn increased the summed consumer density and decreased the bacterial resource density. As IGP strength increased further, the IG predator became satiated by the IG prey, which then freed the bacterial resource from predation and thus increased bacterial density. Consequently, our work shows that IGP can indeed decrease or increase basal resource density depending on its strength. Consequently, the impacts of IGP on resource density is potentially more complex than previously thought.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155990/1/ecy3012-sup-0002-AppendixS2.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155990/2/ecy3012-sup-0001-AppendixS1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155990/3/ecy3012.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155990/4/ecy3012_am.pd

Effects of Algal Diversity on the Production of Biomass in Homogeneous and Heterogeneous Nutrient Environments: A Microcosm Experiment

BACKGROUND: One of the most common questions addressed by ecologists over the past decade has been--how does species richness impact the production of community biomass? Recent summaries of experiments have shown that species richness tends to enhance the production of biomass across a wide range of trophic groups and ecosystems; however, the biomass of diverse polycultures only rarely exceeds that of the single most productive species in a community (a phenomenon called 'transgressive overyielding'). Some have hypothesized that the lack of transgressive overyielding is because experiments have generally been performed in overly-simplified, homogeneous environments where species have little opportunity to express the niche differences that lead to 'complementary' use of resources that can enhance biomass production. We tested this hypothesis in a laboratory experiment where we manipulated the richness of freshwater algae in homogeneous and heterogeneous nutrient environments. METHODOLOGY/PRINCIPAL FINDINGS: Experimental units were comprised of patches containing either homogeneous nutrient ratios (16:1 nitrogen to phosphorus (N:P) in all patches) or heterogeneous nutrient ratios (ranging from 4:1 to 64:1 N:P across patches). After allowing 6-10 generations of algal growth, we found that algal species richness had similar impacts on biomass production in both homo- and heterogeneous environments. Although four of the five algal species showed a strong response to nutrient heterogeneity, a single species dominated algal communities in both types of environments. As a result, a 'selection effect'--where diversity maximizes the chance that a competitively superior species will be included in, and dominate the biomass of a community--was the primary mechanism by which richness influenced biomass in both homo- and heterogeneous environments. CONCLUSIONS/SIGNIFICANCE: Our study suggests that spatial heterogeneity, by itself, is not sufficient to generate strong effects of biodiversity on productivity. Rather, heterogeneity must be coupled with variation in the relative fitness of species across patches in order for spatial niche differentiation to generate complementary resource use

9. Ecological Transition

The global climate emergency is the main concern of chapter 9, by D’Maris Coffman, Roberto Cardinale, Jing Meng and Zhifu Mi. Anthropogenic climate change is widely understood to be the greatest existential threat to human societies in the coming centuries. The Intergovernmental Panel on Climate Change (IPCC) was established in 1988 to coordinate a global response to the coming crisis. The IPCC’s publication of the Special Report on Global Warming of 1.5 °C (SR15) in October 2018 has helped to galvanize public opinion and has given rise to unprecedented climate activism. State actors now recognise a need for immediate action. Broadly speaking, possible responses to climate change fall into three categories: mitigation, adaptation and remediation. Mitigation means measures to reduce carbon and methane emissions or to enhance carbon sinks; adaptation means measures that ameliorate the effects of climate change on human populations; and remediation means intentional measures to counteract the effects of greenhouse gas (GHG) emissions, including global warming and ocean acidification. There are inevitable trade-offs between the costs of mitigation and those of adaptation over decadal time horizons. Nevertheless, with all three responses, large-scale infrastructure investment is required, with varying degrees of involvement by state actors, multilateral organizations, other non-governmental organizations (including religious groups) and, most significantly, private capital markets. In the current climate, multilateral development banks (MDBs) have taken a leading role. The EIB particularly is in the process of rebranding itself as a Climate Bank for Europe following Emmanuel Macron’s call. The authors then explore the investment opportunities that arise as a result of the growing urgency of the low carbon transition

Reply to comment by S. P. Ferguson and C. D. Rennie on “A mechanistic model linking insect (Hydropsychidae) silk nets to incipient sediment motion in gravel‐bedded streams”

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/112221/1/jgrf20397.pd

Consistency and sensitivity of stream periphyton community structural and functional responses to nutrient enrichment

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Niche and fitness differences relate the maintenance of diversity to ecosystem function: reply

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Niche and fitness differences relate the maintenance of diversity to ecosystem function

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/116920/1/ecy20119251157.pd