59 research outputs found
Estimates of new and total productivity in central Long Island Sound from in situ measurements of nitrate and dissolved oxygen
Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Estuaries and Coasts 36 (2013): 74-97, doi:10.1007/s12237-012-9560-5.Biogeochemical cycles in estuaries are regulated by a diverse set of physical and
biological variables that operate over a variety of time scales. Using in situ optical sensors, we
conducted a high-frequency time-series study of several biogeochemical parameters at a mooring
in central Long Island Sound from May to August 2010. During this period, we documented
well-defined diel cycles in nitrate concentration that were correlated to dissolved oxygen, wind
stress, tidal mixing, and irradiance. By filtering the data to separate the nitrate time series into
various signal components, we estimated the amount of variation that could be ascribed to each
process. Primary production and surface wind stress explained 59% and 19%, respectively, of the
variation in nitrate concentrations. Less frequent physical forcings, including large-magnitude wind events and spring tides, served to decouple the relationship between oxygen, nitrate, and
sunlight on about one-quarter of study days. Daytime nitrate minima and dissolved oxygen
maxima occurred nearly simultaneously on the majority (> 80%) of days during the study period;
both were strongly correlated with the daily peak in irradiance. Nighttime nitrate maxima
reflected a pattern in which surface-layer stocks were depleted each afternoon and recharged the
following night. Changes in nitrate concentrations were used to generate daily estimates of new
primary production (182 ± 37 mg C m-2 d-1) and the f-ratio (0.25), i.e., the ratio of production
based on nitrate to total production. These estimates, the first of their kind in Long Island Sound,
were compared to values of community respiration, primary productivity, and net ecosystem
metabolism, which were derived from in situ measurements of oxygen concentration. Daily
averages of the three metabolic parameters were 1660 ± 431, 2080 ± 419, and 429 ± 203 mg C
m-2 d-1, respectively. While the system remained weakly autotrophic over the duration of the
study period, we observed very large day-to-day differences in the f-ratio and in the various
metabolic parameters.This work was supported by the Yale
Institute for Biospheric Studies, the Sounds Conservancy of the Quebec-Labrador Foundation,
and the Yale School of Forestry and Environmental Studies Carpenter-Sperry Fund.2014-01-0
Persistence Increases with Diversity and Connectance in Trophic Metacommunities
We are interested in understanding if metacommunity dynamics contribute to the persistence of complex spatial food webs subject to colonization-extinction dynamics. We study persistence as a measure of stability of communities within discrete patches, and ask how do species diversity, connectance, and topology influence it in spatially structured food webs.We answer this question first by identifying two general mechanisms linking topology of simple food web modules and persistence at the regional scale. We then assess the robustness of these mechanisms to more complex food webs with simulations based on randomly created and empirical webs found in the literature. We find that linkage proximity to primary producers and food web diversity generate a positive relationship between complexity and persistence in spatial food webs. The comparison between empirical and randomly created food webs reveal that the most important element for food web persistence under spatial colonization-extinction dynamics is the degree distribution: the number of prey species per consumer is more important than their identity.With a simple set of rules governing patch colonization and extinction, we have predicted that diversity and connectance promote persistence at the regional scale. The strength of our approach is that it reconciles the effect of complexity on stability at the local and the regional scale. Even if complex food webs are locally prone to extinction, we have shown their complexity could also promote their persistence through regional dynamics. The framework we presented here offers a novel and simple approach to understand the complexity of spatial food webs
Functional Effects of Parasites on Food Web Properties during the Spring Diatom Bloom in Lake Pavin: A Linear Inverse Modeling Analysis
This study is the first assessment of the quantitative impact of parasitic chytrids on a planktonic food web. We used a carbon-based food web model of Lake Pavin (Massif Central, France) to investigate the effects of chytrids during the spring diatom bloom by developing models with and without chytrids. Linear inverse modelling procedures were employed to estimate undetermined flows in the lake. The Monte Carlo Markov chain linear inverse modelling procedure provided estimates of the ranges of model-derived fluxes. Model results support recent theories on the probable impact of parasites on food web function. In the lake, during spring, when ‘inedible’ algae (unexploited by planktonic herbivores) were the dominant primary producers, the epidemic growth of chytrids significantly reduced the sedimentation loss of algal carbon to the detritus pool through the production of grazer-exploitable zoospores. We also review some theories about the potential influence of parasites on ecological network properties and argue that parasitism contributes to longer carbon path lengths, higher levels of activity and specialization, and lower recycling. Considering the “structural asymmetry” hypothesis as a stabilizing pattern, chytrids should contribute to the stability of aquatic food webs
Biodiversity and the Functioning of Ecosystems in the Age of Global Change: Integrating Knowledge Across Scales
The dramatic decline of biodiversity worldwide has raised a general concern on the impacts this process could have for the well-being of humanity. Human societies strongly depend on the benefits provided by natural ecosystems, which are the result of biogeochemical processes governed by species activities and their interaction with abiotic compartments. After decades of experimental research on the biodiversity-functioning relationship, a relative agreement has been reached on the mechanisms underlying the impacts that biodiversity loss can have on ecosystem processes. However, a general consensus is still missing. We suggest that the reason preventing an integration of existing knowledge is the scale discrepancy between observations on global change impacts and biodiversity-functioning experiments. The present chapter provides an overview of global change impacts on biodiversity across various ecological scales and its consequences for ecosystem functioning, highlighting what is known and where knowledge gaps still persist. Furthermore, the reader will be introduced to a set of tools that allow a multi-scale analysis of how global change drivers impact ecosystem functioning
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