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To assess protistan grazing impact and temperature sensitivity on plankton population dynamics, we measured bulk and species-specific phytoplankton growth and herbivorous protist grazing rates in Disko Bay, West Greenland in April-May 2011. Rate estimates were made at three different temperatures in situ (0 °C), +3 °C and +6 °C over ambient. In situ Chlorophyll a (Chl a) doubled during the observation period to ∼12 µg Chl a L−1, with 60–97% of Chl a in the >20 µm size-fraction dominated by the diatom genus Chaetoceros. Herbivorous dinoflagellates comprised 60–80% of microplankton grazer biomass. At in situ temperatures, phytoplankton growth or grazing by herbivorous predators

To assess protistan grazing impact and temperature sensitivity on plankton population dynamics, we measured bulk and species-specific phytoplankton growth and herbivorous protist grazing rates in Disko Bay, West Greenland in April-May 2011. Rate estimates were made at three different temperatures in situ (0 °C), +3 °C and +6 °C over ambient. In situ Chlorophyll a (Chl a) doubled during the observation period to ~12 µg Chl a L-1, with 60-97% of Chl a in the >20 µm size-fraction dominated by the diatom genus Chaetoceros. Herbivorous dinoflagellates comprised 60-80% of microplankton grazer biomass. At in situ temperatures, phytoplankton growth or grazing by herbivorous predators <200 µm was not measurable until 11 days after observations commenced. Thereafter, phytoplankton growth was on average 0.25 d-1. Phytoplankton mortality due to herbivorous grazing was only measured on three occasions but the magnitude was substantial, up to 0.58 d-1. Grazing of this magnitude removed ~100% of primary production. In short-term temperature-shift incubation experiments, phytoplankton growth rate increased significantly (20%) at elevated temperatures. In contrast, herbivorous protist grazing and species-specific growth rates decreased significantly (50%) at +6 °C. This differential response in phytoplankton and herbivores to temperature increases resulted in a decrease of primary production removed with increasing temperature. Phaeocystis spp. abundance was negatively correlated with bulk grazing rate. Growth and grazing rates were variable but showed no evidence of an inherent, low temperature limitation. Herbivorous protist growth rates in this study and in a literature review were comparable to rates from temperate waters. Thus, an inherent physiological inhibition of protistan growth or grazing rates in polar waters is not supported by the data. The large variability between lack of grazing and high rates of primary production removal observed here and confirmed in the literature for polar waters implies larger amplitude fluctuations in phytoplankton biomass than slower, steady grazing losses of primary production. [ABSTRACT FROM AUTHOR]

Fish stocking is used worldwide in conservation and management, but its effects on food-web dynamics and ecosystem stability are poorly known. To better understand these effects and predict the outcomes of stocking, we used an empirically validated network model of a well-studied lake ecosystem. We simulate two stocking scenarios with two native fish species valuable for fishing. In the first scenario, we stock planktivorous fish (whitefish) larvae in the ecosystem. This leads to a 1% increase in adult whitefish biomasses and decreases the biomasses of the top predator (perch). In the second scenario, we also stock perch larvae in the ecosystem. This decreases the planktivorous whitefish and the oldest top predator age class biomasses, and destabilizes the ecosystem. Our results demonstrate that the effects of stocking depend on the species' position in the food web and thus cannot be assessed without considering interacting species. We further show that stocking can lead to undesired outcomes from both management and conservation perspectives. The gains of stocking can remain minor and have adverse effects on the entire ecosystem.

Some parasites move from one host to another via trophic transmission, the consumption of the parasite (inside its current host) by its future host. Feeding links among free-living species can thus be understood as potential transmission routes for parasites. As these links have different dynamic and structural properties, they may also vary in their effectiveness as trophic transmission routes. That is, some links may be better than others in allowing parasites to complete their complex life cycles. However, not all links are accessible to parasites as most are restricted to a small number of host taxa. This restriction means that differences between links involving host and non-host taxa must be considered when assessing whether transmission routes for parasites have different food web properties than other links. Here we use four New Zealand lake food webs to test whether link properties (contribution of a link to the predator's diet, prey abundance, prey biomass, amount of biomass transferred, centrality, and asymmetry) affect trophic transmission of parasites. Critically, we do this using both models that neglect the taxonomy of free-living species and models that explicitly include information about which free-living species are members of suitable host taxa. Although the best-fit model excluding taxonomic information suggested that transmission routes have different properties than other feeding links, when including taxonomy, the best-fit model included only an intercept. This means that the taxonomy of free-living species is a key determinant of parasite transmission routes and that food-web properties of transmission routes are constrained by the properties of host taxa. In particular, many intermediate hosts (prey) attain high biomasses and are involved in highly central links while links connecting intermediate to definitive (predator) hosts tend to be dynamically weak. [ABSTRACT FROM AUTHOR]

Predicting the ability of the biosphere to continue to deliver ecosystem services in the face of biodiversity loss and environmental change is a major challenge. The results of short-term and small-scale experimental studies are both equivocal and difficult to extrapolate from. In this study we use data on benthic palaeocommunities covering 4,000,000 years (in the Late Jurassic when temperate coastal seas in NW Europe experienced fluctuations in oxygenation). The biological traits associated with each species in the palaeocommunities were combined to index the delivery of ecological functions. Five ecosystem functions were examined: food for large mobile predators, biogenic habitat provision, nutrient recycling/regeneration, inorganic carbon sequestration and food-web dynamics. In modern systems these ecological functions underpin ecosystem services that are important for human well-being. Our results show that the supply of food for higher predators was remarkably constant during the 4,000,000 years, suggesting that redundancy amongst species in the assemblage drives the biodiversity-ecosystem function ( BEF) relationship. By contrast, the provision of biogenic habitat varied with the occurrence of a relatively few taxa, a pattern consistent with a rivet type model of BEF. For nutrient regeneration, carbon sequestration and food-web dynamics the patterns were complex and suggestive of an idiosyncratic model of BEF. To our knowledge this is the first study to quantify ecological functioning through deep time and demonstrates the utility of this approach to understanding long-term patterns of BEF in both ancient and contemporary marine ecosystems. The delivery of all five ecological functions studied became increasingly variable as the regional climate became drier, thus modifying the supply of terrigenous nutrient inputs. [ABSTRACT FROM AUTHOR]

The dispersal of organisms in fragmented habitats connects spatially separated local populations at the regional, metapopulation scale, with potential consequences for spatial population dynamics and persistence. As any dispersing organism is engaged in trophic interactions as well, dispersal also connects local food webs at the regional scale, and differential dispersal among taxa of different trophic levels has the potential to strongly influence spatial food-web dynamics., We used a combination of field surveys and experiments to test the significance of passive dispersal via overflowing water for population and food-web dynamics in a system of freshwater rock pools on Appledore Island, Maine, U.S.A. The rock pools contain a three-trophic-level food chain consisting of phytoplankton (primarily chlorophyte algae), grazer zooplankton (two species of Cladocera) and a predatory insect ( Trichocorixa), all of which are passively dispersed between rock pools when the pools overflow during rain events., During the summers of 2010 and 2011, rain events were observed (on average) every two and a half days. Three-quarters of rain events generated overflows, and observed overflow rates varied over four orders of magnitude (0.5-474 mL s−1). A Monte Carlo simulation showed that, on average, a pool is expected to overflow 5.6 times during a summer., Despite all three taxa dispersing in overflows, and dispersing more at higher flow rates, a mesocosm experiment showed that dispersal rates decreased significantly with increasing trophic level, such that Trichocorixa dispersed less than cladocerans, which dispersed less than phytoplankton. Results from a follow-up experiment suggest that this decrease in dispersal is primarily due to organisms at higher trophic levels being more able to avoid currents, rather than an ability to swim more strongly against currents., Finally, we conducted a field experiment to determine the influence of overflows on population and food-web dynamics in situ. Populations in pools that were part of experimental overflows were significantly more variable than nearby populations that were not in the overflow, and taxa at all three trophic levels were influenced similarly by the overflows., This study demonstrates that passive dispersal of aquatic organisms among habitat patches is likely to occur at different rates for different taxa, which may have strong effects on spatial food-web dynamics. [ABSTRACT FROM AUTHOR]

Abstract: Climatic change is recognized as an important factor capable of influencing the structural properties of aquatic ecosystems. Lake ecosystems are particularly sensitive to climate change. Several long time-series studies have shown close coupling between climate, lake thermal properties and individual organism physiology, population abundance, community structure, and food-web structure. Understanding the complex interplay between climate, hydrological variability, and ecosystem structure and functioning is essential to inform water resources risk assessment and fisheries management. The purpose of this paper is to present the current understanding of climate-induced changes on lake ecosystem phenology. We first review the ability of climate to modulate the interactions among lake hydrodynamics, chemical factors, and food-web structure in several north temperate deep lakes (e.g., Lake Washington, Lake Tahoe, Lake Constance, Lake Geneva, Lake Baikal, and Lake Zurich). Our aim is to assess long-term trends in the physical (e.g., temperature, timing of stratification, and duration of ice cover), chemical (e.g., nutrient concentrations), and biological (e.g., timing of the spring bloom, phytoplankton composition, and zooplankton abundance) characteristics of the lakes and to examine the signature of local weather conditions (e.g., air temperature and rainfall) and large-scale climatic variability (e.g., ENSO and PDO) on the lake physics, chemistry and biology. We also conducted modeling experiments to quantify the relative effect of climate change and nutrient loading on lake phenology. These modeling experiments focused on the relative changes to the major causal associations underlying plankton dynamics during the spring bloom and the summer stratified period. To further understand the importance of climate change on lakes, we propose two complementary directions of future research. First, additional research is needed to elucidate the wide array of in-lake processes that are likely to be affected by the climate change. Second, it is essential to examine the heterogeneity in responses among different water bodies. The rationale of this approach and its significance for dealing with the uncertainty that the climate signals cascade through lake ecosystems and shape abiotic variability and/or biotic responses have been recently advocated by several other synthesis papers. [Copyright &y& Elsevier]

Fungi are a highly complex group of organisms of the kingdom Eumycota (i.e. the true-fungi) and other fungus-like organisms traditionally studied by mycologists, such as slime molds (Myxomycota) and oomycota (Straminopiles or Heterokonts). They constitute a significant proportion of the as yet undiscovered biota that is crucial in ecological processes and human well-being, through at least three main trophic modes: saprophytism, parasitism, or symbiosis. In addition to direct benefit (sources of antibiotics) or adverse effects (agents of disease), fungi can impact many environmental processes, particularly those associated with the decomposition of organic matter. They are present in almost all regions and climates, even under extreme conditions. However, studies have focussed mostly on economically interesting species, and knowledge of their diversity and functions is mainly restricted to soil, rhizosphere, mangrove, and lotic ecosystems. In this study, we review the diversity and potential functions of microscopic fungi in aquatic ecosystems, with focus on the pelagic environments where they often are regarded as allochthonous material, of low ecological significance for food-web processes. Recent environmental 18S rDNA surveys of microbial eukaryotes have (1) unveiled a large reservoir of unexpected fungal diversity in pelagic systems, (2) emphasized their ecological potentials for ecosystem functioning, and (3) opened new perspectives in the context of food-web dynamics. In spite of persisting methodological difficulties, we conclude that a better documentation of the diversity and quantitative and functional importance of fungi will improve our understanding of pelagic processes and biogeochemical cycling. [ABSTRACT FROM AUTHOR]

Ecological communities used in biological pest control are usually represented as three-trophic level food chains with top-down control. However, at least two factors complicate this simple way of characterizing agricultural communities. First, agro-ecosystems are composed of several interacting species forming complicated food webs. Second, the structure of agricultural communities may vary in time. Efficient pest management approaches need to integrate these two factors to generate better predictions for pest control. In this work, we identified the food web components of an avocado agro-ecosystem, and unravelled patterns of co-occurrence and interactions between these components through field and laboratory experiments. This allowed us to predict community changes that would improve the performance of the naturally occurring predators and to test these predictions in field population experiments. Field surveys revealed that the food-web structure and species composition of the avocado community changed in time. In spring, the community was characterized by a linear food chain of Euseius stipulatus, an omnivorous mite, feeding on pollen. In the summer, E. stipulatus and a predatory mite, Neoseiulus californicus, shared a herbivorous mite prey. Laboratory experiments confirmed these trophic interactions and revealed that N. californicus can feed inside the prey nests, whereas E. stipulatus cannot, which may further reduce competition among predators. Finally, we artificially increased the coexistence of the two communities via addition of the non-herbivore food source (pollen) for the omnivore. This led to an increase in predator numbers and reduced populations of the herbivore. Therefore, the presence of pollen is expected to improve pest control in this system. [ABSTRACT FROM AUTHOR]

Abstract: Weak trophic interactions have been shown to promote the stability of ecological food webs characterized by perfect mixing. However, their importance at the landscape level and response to enrichment has not been extensively examined. In this paper we examine the food-web model explored by McCann et al. [1998. Weak trophic interactions and the balance of nature. Nature 395, 794–798]. The model is expanded into a metacommunity construct where local communities are coupled through global or local dispersal. We analyze global and local stability, as well as spatial synchrony in relation to trophic interaction strength and dispersal regimes. Results reveal that weak interactions can operate through two scale-dependent mechanisms: (i) under low local dispersal regimes, local stabilization of each community under weak interactions directly scales-up to global stability. (ii) Under high local dispersal, asynchronous local destabilization associated with weak interactions proves the driver behind global stability. In the face of enrichment, weak trophic interactions are shown to be instrumental in promoting global stability when dispersal is local. These results demonstrate how the importance of weak trophic interactions can be generalized at the landscape level despite contrary local predictions. [Copyright &y& Elsevier]

Processes controlling the production of new fish (recruitment) are poorly understood and therefore challenge population ecologists and resource managers. Sprat in the Baltic Sea is no exception: recruitment varies widely between years and is virtually independent of the biomass of mature sprat. Sprat is a key prey and predator species in the Baltic ecosystem and is commercially exploited (1.86 × 108 kg/yr since 1974). The population and fishery must therefore be managed sustainably and if necessary accommodate environmental effects on population dynamics. We demonstrate using 45 years of data that recruitment depends on temperature conditions during the months when sprat gonads, eggs, and larvae are developing. We also show that recruitment can be predicted before adults spawn (and fully 15 months earlier than using present technology) by using linkages between recruitment, large-scale climate variability (North Atlantic Oscillation), Baltic Sea ice coverage, and water temperature. These relationships increase our under- standing of sprat population dynamics and enable a desirable integration of fisheries ecology and management with climatology and oceanography. [ABSTRACT FROM AUTHOR]