Diel vertical migration promotes zooplankton horizontal patchiness

Spatial patchiness of plankton enhances fishery production and carbon export in the ocean. While diel vertical migration (DVM) has been identified as an important factor contributing to vertical patchiness, its effect on horizontal patchiness has never been investigated. We use a simple individual-based zooplankton model to examine the effect of DVM on the horizontal patchiness of four zooplankton groups with differing DVM patterns in a two-dimensional ocean circulation model. We find that zooplankton horizontal patchiness can be induced by two mechanisms: (1) in stratified waters, DVM can synchronize zooplankton vertical positions with the horizontal current velocities that drive them, resulting in horizontal patchiness; and (2) migrating zooplankton tend to aggregate in deep waters when they encounter sea bottom. Due to these mechanisms, zooplankton horizontal patchiness may be ubiquitous in the ocean, enhancing secondary production and fisheries.

Methane consumption by proteobacterial methanotrophs in boreal spruce phyllosphere activated with methane

<p>Current knowledge on methane (CH<sub>4</sub>) sinks is limited to chemical processes in the atmosphere, and to methanotrophy in forest soils and peatlands. Recent discoveries have indicated that also tree branches, i.e. phyllosphere, may consume atmospheric CH<sub>4</sub>, thus functioning as a novel CH<sub>4</sub> sink. However,  the process is not yet confirmed and the mechanism not resolved.</p><p>Here, we confirm that leaves and needles of boreal trees have the capacity to consume CH<sub>4</sub> with stable isotope enrichment studies in field and laboratory experiments, and that the consumption is a biological process. With molecular analyses, we confirmed that the activity of needle-associated proteobacterial methanotrophs increased sporadically under CH<sub>4</sub> and acetate enrichment. Our results indicate that CH<sub>4</sub> consumption can exist in the tree canopy, which is characterized by interspecies variation, spatial patchiness and small but significant microbial activity.</p><p>This is a novel symbiotic connection between microbes and plant cells, which can enhance overall carbon sequestration in the boreal forests.</p>

Habitat loss-induced tipping points in metapopulations with facilitation

Habitat loss is known to pervade extinction thresholds in metapopulations. Such thresholds result from a loss of stability that can eventually lead to collapse. Several models have been developed to understand the nature of these transitions and how are they affected by the locality of interactions, fluctuations, or external drivers. Most models consider the impact of grazing or aridity as a control parameter that can trigger sudden shifts, once critical values are reached. Others explore instead the role played by habitat loss and fragmentation. Here we consider a minimal model incorporating facilitation along with habitat destruction, with the aim of understanding how local cooperation and habitat loss interact with each other. An explicit mathematical model is derived, along with a spatially explicit simulation model. It is found that a catastrophic shift is expected for increasing levels of habitat loss, but the breakpoint dynamics becomes continuous when dispersal is local. Under these conditions, spatial patchiness is found and the qualitative change from discontinuous to continuous results from a universal behaviour found in a broad class of nonlinear ecological systems (Weissmann and Shnerb, 2014; Martin et al. PNAS (2015) E1828-E1836). Our results suggest that species exhibiting facilitation and displaying short-range dispersal will be markedly more capable of dealing with habitat destruction, also avoiding catastrophic tipping points.

Using citizen-science data to identify local hotspots of species occurrence

Seabirds have been identified and used as indicators of ecosystem processes such as climate change, and anthropogenic activity in nearshore ecosystems around the globe. Temporal and spatial trends have been documented at large spatial scales, but few studies have examined fine scale spatial patterns, by species or functional group, because . In this paper, we apply spatial occupancy models to assess the spatial patchiness and interannual trends of 18 seabird species in the Puget Sound region (Washington state, USA). Our dataset, the Puget Sound Seabird Survey, is unique in that represents a seven year study, collected in winter months (October – April), and is collected at an extremely fine spatial scale (62 sites in the current analysis). Despite historic declines of seabirds in the region over the last 50 years, results from our study are optimistic, suggesting increases in probabilities of occurrence for 14 of the 18 species included. We found support for declines in occurrence for white-winged scoters, brants, and 2 species of grebes. The declines of Western grebes in particular are troubling, but in agreement with other recent studies that have shown support for a range shift south in recent years, to the California Current.

Using citizen-science data to identify local hotspots of species occurrence

Seabirds have been identified and used as indicators of ecosystem processes such as climate change, and anthropogenic activity in nearshore ecosystems around the globe. Temporal and spatial trends have been documented at large spatial scales, but few studies have examined fine scale spatial patterns, by species or functional group, because . In this paper, we apply spatial occupancy models to assess the spatial patchiness and interannual trends of 18 seabird species in the Puget Sound region (Washington state, USA). Our dataset, the Puget Sound Seabird Survey, is unique in that represents a seven year study, collected in winter months (October – April), and is collected at an extremely fine spatial scale (62 sites in the current analysis). Despite historic declines of seabirds in the region over the last 50 years, results from our study are optimistic, suggesting increases in probabilities of occurrence for 14 of the 18 species included. We found support for declines in occurrence for white-winged scoters, brants, and 2 species of grebes. The declines of Western grebes in particular are troubling, but in agreement with other recent studies that have shown support for a range shift south in recent years, to the California Current.

Optical community index to assess spatial patchiness during the 2008 North Atlantic Bloom

The ratio of two in situ optical measurements, chlorophyll fluorescence (Chl F) and optical particulate backscattering (bbp), varied with changes in phytoplankton community composition during the North Atlantic Bloom experiment in the Iceland Basin in 2008. Using ship-based measurements of Chl F, bp, chlorophyll a (Chl), HPLC pigments, phytoplankton composition and carbon biomass, we found that oscillations in the ratio varied with changes in plankton community composition; hence we refer to Chl F/bp as an "optical community index". The index varied by more than a factor of two, with low values associated with pico- and nanophytoplankton and high values associated with diatom dominated phytoplankton communities. A Lagrangian mixed-layer float and four Seagliders, operating continuously for two months, made similar measurements of the optical community index and followed the evolution and later demise of the diatom spring bloom. Temporal changes in optical community index and, by implication the transition in community composition from diatom to post-diatom bloom communities, were not simultaneous over the spatial domain surveyed by the ship, float and gliders. Not only phytoplankton biomass, but also community composition was patchy at the submesoscale. The ratio of simple optical properties measured from autonomous platforms, when carefully validated, provides a tool for studying phytoplankton patchiness on extended temporal scales and ecological relevant spatial scales, and should offer new insights into the processes regulating patchiness.

Theoretical Modeling Suggests that Synergy May Result from Combined Use of Two Biocontrol Agents for Controlling Foliar Pathogens Under Spatial Heterogeneous Conditions

There has been a trend for combined use of several biocontrol agents (BCAs) with an expectation of synergistic interactions among BCAs. However, previous modeling studies suggested that, under homogeneous and temporal-fluctuating conditions, combined use of two BCAs, in most cases, only results in efficacies similar to the more efficacious one used alone; a result consistent with published experimental data. The present modeling study investigated whether combined use of two mycoparasitic BCAs, two competitive BCAs, or a mycoparasitic and a competitive BCA leads to synergistic interactions under spatially heterogeneous conditions. In the model, there were two patches with varying relative sizes and two BCAs differentially adapted to the two patches. Within the range of model parameter values considered, combined use of two BCAs is more effective than the more efficacious BCA used alone in 72% of the simulated cases. There was also a considerable proportion (≈21%) of model simulations in which combined use of two BCAs led to synergy (i.e., efficacy was greater than expected under the assumption of Bliss independence, especially when each of the two BCAs can only survive in one [different] patch). Combined use of a mycoparasitic BCA with a competitive one is more likely to result in synergy than the other two BCA combinations. When biocontrol activities of individual BCAs are low or moderate, biocontrol efficacy arising from combined use of two BCAs does not depend greatly on biocontrol mechanisms. However, for high BCA activities, combined use with at least one competitive BCA resulted in better control than combined use of two mycoparasitic BCAs. The present modeling study emphasized the need for understanding the degree of spatial patchiness and quantitative relationships between biocontrol activities and external conditions in order to apply commercial BCAs effectively.