60 research outputs found
Revisiting the stability of spatially heterogeneous predator-prey systems under eutrophication
We employ partial integro-differential equations to model trophic interaction
in a spatially extended heterogeneous environment. Compared to classical
reaction-diffusion models, this framework allows us to more realistically
describe the situation where movement of individuals occurs on a faster time
scale than the demographic (population) time scale, and we cannot determine
population growth based on local density. However, most of the results reported
so far for such systems have only been verified numerically and for a
particular choice of model functions, which obviously casts doubts about these
findings. In this paper, we analyse a class of integro-differential
predator-prey models with a highly mobile predator in a heterogeneous
environment, and we reveal the main factors stabilizing such systems. In
particular, we explore an ecologically relevant case of interactions in a
highly eutrophic environment, where the prey carrying capacity can be formally
set to 'infinity'. We investigate two main scenarios: (i) the spatial gradient
of the growth rate is due to abiotic factors only, and (ii) the local growth
rate depends on the global density distribution across the environment (e.g.
due to non-local self-shading). For an arbitrary spatial gradient of the prey
growth rate, we analytically investigate the possibility of the predator-prey
equilibrium in such systems and we explore the conditions of stability of this
equilibrium. In particular, we demonstrate that for a Holling type I (linear)
functional response, the predator can stabilize the system at low prey density
even for an 'unlimited' carrying capacity. We conclude that the interplay
between spatial heterogeneity in the prey growth and fast displacement of the
predator across the habitat works as an efficient stabilizing mechanism.Comment: 2 figures; appendices available on request. To appear in the Bulletin
of Mathematical Biolog
Intercomparison of five nets used for mesozooplankton sampling
Intercomparison of nets commonly used for mesozooplankton sampling in the Black and Mediterranean seas was attempted within SESAME (Southern European Seas: Assessing and Modelling Ecosystem Changes) project. Five nets were compared: three Juday nets equipped with 150 μm, 180 μm and 200 μm mesh size, Nansen net (100 μm mesh size) and WP2 (200 μm mesh size). Replicated samples were collected at one station in the western Black Sea offshore waters in April 2009. Collected samples were analyzed at species level (except for meroplankton), stages (for copepods) and size length. A decrease of total abundance values was observed with increasing mesh size, due to the significantly higher numbers of animals smaller than 1 mm in the samples obtained by fine mesh size than with coarser nets. Few comparisons were revealed significant for the abundance of animals with 1-2 mm length, while no significance was detected for specimens larger than 2 mm. The above differences resulted in discripancies between nets regarding species and stages composition. Biomass values did not differ significantly between nets, due to the strong contribution to total biomass of the large animals fraction (Calanus euxinus). The smallest and the largest animals revealed high variability between replicates collected by Nansen, Juday- 200 μm and WP2 nets. Correction factors were calculated for the conversion of abundance values between each couple of nets. The detected differences between nets regarding the abundance and biomass, the community taxonomic composition and size structure, as well as the estimated correction factors, provide useful information for the harmonization of data obtained by the above nets in the Black Sea
Comparative Assessment of Climate Change Scenarios Based on Aquatic Food Web Modeling
In the years 2004 and 2005, we collected samples of phytoplankton, zooplankton, and macroinvertebrates in an artificial small pond in Budapest (Hungary). We set up a simulation model predicting the abundances of the cyclopoids, Eudiaptomus zachariasi, and Ischnura pumilio by considering only temperature and the abundance of population of the previous day. Phytoplankton abundance was simulated by considering not only temperature but the abundances of the three mentioned groups. When we ran the model with the data series of internationally accepted climate change scenarios, the different outcomes were discussed. Comparative assessment of the alternative climate change scenarios was also carried out with statistical methods
A MSFD complementary approach for the assessment of pressures, knowledge and data gaps in Southern European Seas : the PERSEUS experience
PERSEUS project aims to identify the most relevant pressures exerted on the ecosystems of the Southern
European Seas (SES), highlighting knowledge and data gaps that endanger the achievement of SES Good
Environmental Status (GES) as mandated by the Marine Strategy Framework Directive (MSFD). A complementary
approach has been adopted, by a meta-analysis of existing literature on pressure/impact/knowledge
gaps summarized in tables related to the MSFD descriptors, discriminating open waters from coastal
areas. A comparative assessment of the Initial Assessments (IAs) for five SES countries has been also
independently performed. The comparison between meta-analysis results and IAs shows similarities
for coastal areas only. Major knowledge gaps have been detected for the biodiversity, marine food
web, marine litter and underwater noise descriptors. The meta-analysis also allowed the identification
of additional research themes targeting research topics that are requested to the achievement of GES.
2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license.peer-reviewe
Patterns of Zooplankton Functional Response in Communities with Vertical Heterogeneity: a Model Study
Parameterization of zooplankton functional response is crucial for constructing plankton models. Theoretical
studies predict enhancing of system stability in case the response is of sigmoid type. Experiments on feeding in laboratories tell us in
favor of non-sigmoid types for most herbivorous zooplankton species. However, recent field observations show that the overall functional
response of zooplankton in the whole euphotic zone can exhibit a sigmoid behavior even when the response for the same species in laboratory
mesocosms is non-sigmoid. Here we propose a simple model explaining the observed alterations of functional response. We divide the euphotic
zone into a number of layers and take into account the food-dependent migration of zooplankton. In each layer, the functional response (local
response) is suggested to be non-sigmoid. We show that the overall response of zooplankton exhibits different behavior compared to the
patterns of the local response. In particular, the model predicts emergence of a sigmoid type as a result of zooplankton accumulation and
feeding in layers with high phytoplankton density. We show the importance of light attenuation by phytoplankton on the alteration of
functional response. The modelling results allow us to hypothesize that the sigmoid functional response in real communities should emerge
more often than it was suggested earlier based only on experimental studies on zooplankton feeding
Biomass of upper-interzonal copepod filter feeders in the Kurile-Kamchatka region
Vertical distribution of abundance and biomass of upper interzonal copepods Calanus cristatus, C. plumchrus, Eucalanus bungii, Metridia ochotensis and M. pacifica have been studied in the whole depth range of their occurrence. These species comprise 55 per cent of total plankton biomass in the 0-4000 m layer. The major part (90% of the population) of C. cristatus inhabit depths are above 3000 m, and of the other species - above 750-1000 m. Feeding of juveniles proceeds in the surface euphotic zone, and then adolescent animals descend to deep water. At depth 1000-2000 m they make up >40%, and at 2000-3000 m, about 20% of total biomass of plankton inhabiting these depths. Interzonal species serve as a food reserve for predatory deep-sea animals and as a close connection between the surface and deep-water communities that makes it possible to regard these communities as parts of a single biocoenosis
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