4,127 research outputs found
Estimating the tolerance of species to the effects of global environmental change
Global environmental change is affecting species distribution and their
interactions with other species. In particular, the main drivers of
environmental change strongly affect the strength of interspecific interactions
with considerable consequences to biodiversity. However, extrapolating the
effects observed on pair-wise interactions to entire ecological networks is
challenging. Here we propose a framework to estimate the tolerance to changes
in the strength of mutualistic interaction that species in mutualistic networks
can sustain before becoming extinct. We identify the scenarios where generalist
species can be the least tolerant. We show that the least tolerant species
across different scenarios do not appear to have uniquely common
characteristics. Species tolerance is extremely sensitive to the direction of
change in the strength of mutualistic interaction, as well as to the observed
mutualistic trade-offs between the number of partners and the strength of the
interactions.Comment: Nature Communications 4, Article number: 2350, (2013
How structurally stable are global socioeconomic systems?
The stability analysis of socioeconomic systems has been centered on
answering whether small perturbations when a system is in a given quantitative
state will push the system permanently to a different quantitative state.
However, typically the quantitative state of socioeconomic systems is subject
to constant change. Therefore, a key stability question that has been
under-investigated is how strong the conditions of a system itself can change
before the system moves to a qualitatively different behavior, i.e., how
structurally stable the systems is. Here, we introduce a framework to
investigate the structural stability of socioeconomic systems formed by the
network of interactions among agents competing for resources. We measure the
structural stability of the system as the range of conditions in the
distribution and availability of resources compatible with the qualitative
behavior in which all the constituent agents can be self-sustained across time.
To illustrate our framework, we study an empirical representation of the global
socioeconomic system formed by countries sharing and competing for
multinational companies used as proxy for resources. We demonstrate that the
structural stability of the system is inversely associated with the level of
competition and the level of heterogeneity in the distribution of resources.
Importantly, we show that the qualitative behavior of the observed global
socioeconomic system is highly sensitive to changes in the distribution of
resources. We believe this work provides a methodological basis to develop
sustainable strategies for socioeconomic systems subject to constantly changing
conditions
Nestedness in mutualistic networks
James et al. (2012) presented simulations that apparently falsify the
analytical result by Bastolla et al. (2009), who showed that nested mutualistic
interactions decrease interspecific competition and increase biodiversity in
model ecosystems. This contradiction, however, mainly stems from the incorrect
application of formulas derived for fully connected networks to empirical,
sparse networks.Comment: 2 pages, 1 figur
Not Like Me
This is a poem that looks through a child's lens as the child is desperately trying to find someone with whom she can identify in school, in the books she reads, and in the adults who make decisions about her education
Components of phylogenetic signal in antagonistic and mutualistic networks.
Recent studies have shown a phylogenetic signal in the structure of ecological networks, making the point that evolutionary history is important in explaining network architecture. However, this previous work has focused on either antagonistic (i.e., predator-prey) or mutualistic networks and has used different methodologies. Thus, a comparative assessment of both the frequency and the strength of phylogenetic signal across network types and components of network structure has been precluded. Here, we address this issue using a data set comprising 60 antagonistic and mutualistic networks. By quantifying simultaneously the matching and centrality components of network architecture—capturing the modular and nested structure, respectively—we test the presence and quantify the strength of phylogenetic signal across network types, species sets, and components of network structure. We find contrasting differences across such groups. First, phylogenetic signal is stronger in antagonistic webs than in mutualistic webs. Second, resources are more strongly constrained than consumers in food webs, while animals show more constraints than plants in mutualistic networks. Third, phylogenetic constraints are stronger for the matching component than for the centrality component of network structure. These results can shed light on the contrasting evolutionary constraints shaping network structure across interaction types and species sets
Biological waste gas treatment with a modified rotating biological contactor. Ι. Control of biofilm growth and long-term performance
In this work, we introduce a modified rotating biological contactor (RBC) system and demonstrate its feasibility by applying the newly devised process to the biological treatment of artificial waste gas. In the proposed system, the waste gas is introduced to the bioreactor in the spacings between the rotating discs through a hollow shaft, thus allowing for intimate gas-liquid contact. A 91-l modified RBC containing 20 biofilm support discs 40cm in diameter was used in the experiments. Toluene was used as the model pollutant, and the system was operated under standard operating conditions for more than one year in order to investigate its long-term performance and assess its ability to control the growth of the biofilm. It was demonstrated that the proposed system allows to efficiently control the growth of the biofilm, thus overcoming the clogging problem inherent in most conventional methods for the biological treatment of waste gas. Moreover, the system was shown to exhibit stationary long-term performance for a period of more than one year, hence indicating its feasibility for industrial applicatio
Decay dynamics of quantum dots influenced by the local density of optical states of two-dimensional photonic crystal membranes
We have performed time-resolved spectroscopy on InAs quantum dot ensembles in
photonic crystal membranes. The influence of the photonic crystal is
investigated by varying the lattice constant systematically. We observe a
strong slow down of the quantum dots' spontaneous emission rates as the
two-dimensional bandgap is tuned through their emission frequencies. The
measured band edges are in full agreement with theoretical predictions. We
characterize the multi-exponential decay curves by their mean decay time and
find enhancement of the spontaneous emission at the bandgap edges and strong
inhibition inside the bandgap in good agreement with local density of states
calculations.Comment: 9 pages (preprint), 3 figure
On the structural stability of mutualistic systems
In theoretical ecology, traditional studies based on dynamical stability and numerical simulations have not found a unified answer to the effect of network architecture on community persistence. Here, we introduce a mathematical framework based on the concept of structural stability to explain such a disparity of results. We investigated the range of conditions necessary for the stable coexistence of all species in mutualistic systems. We show that the apparently contradictory conclusions reached by previous studies arise as a consequence of overseeing either the necessary conditions for persistence or its dependence on model parameterization. We show that observed network architectures maximize the range of conditions for species coexistence. We discuss the applicability of structural stability to study other types of interspecific interactions
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