arXiv subjects

Axel G. Rossberg

Publications and source records attributed to Axel G. Rossberg.

10 recordsLinked to original sources

arXiv2023

A metric for tradable biodiversity credits linked to the Living Planet Index and global species conservation

Difficulties identifying appropriate biodiversity impact metrics remain a major barrier to inclusion of biodiversity considerations in environmentally responsible investment. We propose and analyse a simple science-based local metric: the sum of proportional changes in local species abundances relative to their global species abundances, with a correction for species close to extinction. As we show, this metric quantifies changes in the mean long-term global survival probability of species. It links mathematically to a widely cited global biodiversity indicator, the Living Planet Index, for which we propose an improved formula that directly addresses the known problem of singularities caused by extinctions. We show that, in an ideal market, trade in our metric would lead to near-optimal allocation of resources to species conservation. We further show that the metric is closely related to several other metrics and indices already in use. Barriers to adoption are therefore low. Used in conjunction with metrics addressing ecosystem functioning and services, potential areas of application include biodiversity related financial disclosures and voluntary or legislated no net biodiversity loss policies.

q-bio.PE↗

arXiv2017

Multi-model ensembles for ecosystem prediction

When making predictions about ecosystems, we often have available a number of different ecosystem models that attempt to represent their dynamics in a detailed mechanistic way. Each of these can be used as simulators of large-scale experiments and make forecasts about the fate of ecosystems under different scenarios in order to support the development of appropriate management strategies. However, structural differences, systematic discrepancies and uncertainties lead to different models giving different predictions under these scenarios. This is further complicated by the fact that the models may not be run with the same species or functional groups, spatial structure or time scale. Rather than simply trying to select a 'best' model, or taking some weighted average, it is important to exploit the strengths of each of the available models, while learning from the differences between them. To achieve this, we construct a flexible statistical model of the relationships between a collection or 'ensemble' of mechanistic models and their biases, allowing for structural and parameter uncertainty and for different ways of representing reality. Using this statistical meta-model, we can combine prior beliefs, model estimates and direct observations using Bayesian methods, and make coherent predictions of future outcomes under different scenarios with robust measures of uncertainty. In this paper we present the modelling framework and discuss results obtained using a diverse ensemble of models in scenarios involving future changes in fishing levels. These examples illustrate the value of our approach in predicting outcomes for possible strategies pertaining to climate and fisheries policy aimed at improving food security and maintaining ecosystem integrity.

q-bio.QM↗

arXiv2017

New univariate characterization of fish community size structure improves precision beyond the Large Fish Indicator

The size structure of fish-communities is an emergent high-level property of marine food webs responsive to changes in structure and function. To measure this food web property using data arising from routine fisheries surveys, a simple metric known as Typical Length has been proposed as more suitable than the Large Fish Indicator, which has been highly engineered to be responsive to fishing pressure. Typical Length avoids the inherent dependence of the Large Fish Indicator on a parameter that requires case-by-case adjustments. Using IBTS survey time series for five spatial subdivisions of the Greater North Sea, we show that the Typical Length can provide information equivalent to the Large Fish Indicator when fishing is likely the strongest driver, but differences can also arise. In this example, Typical Length exhibits smaller random fluctuations ("noise") than the Large Fish Indicator. Typical Length is also more adaptable than the Large Fish Indicator and can be easily applied to monitor pelagic fish in addition to demersal fish, and together with information on the potential growth of the fish community, a proxy of which can be derived from the Mean Maximum Length indicator, it is possible to partition change in community composition from change in size structure. This suggests that Typical Length is an improvement over the Large Fish Indicator as a food web indicator with the potential to offer further insight when considered in conjunction with indicators of community composition.

q-bio.PE↗

arXiv2016

Maximum sustainable yield from interacting fish stocks in an uncertain world: two policy choices and underlying trade-offs

The case of fisheries management illustrates how the inherent structural instability of ecosystems can have deep-running policy implications. We contrast ten types of management plans to achieve maximum sustainable yields (MSY) from multiple stocks and compare their effectiveness based on a management strategy evaluation (MSE) that uses complex food webs in its operating model. Plans that target specific stock sizes ($B_{\text{MSY}}$) consistently led to higher yields than plans targeting specific fishing pressures ($F_{\text{MSY}}$). A new self-optimising control rule, introduced here for its robustness to structural instability, led to intermediate yields. Most plans outperformed single-species management plans with pressure targets set without considering multispecies interactions. However, more refined plans to "maximise the yield from each stock separately", in the sense of a Nash equilibrium, produced total yields comparable to plans aiming to maximise total harvested biomass, and were more robust to structural instability. Our analyses highlight trade-offs between yields, amenability to negotiations, pressures on biodiversity, and continuity with current approaches in the European context. Based on these results, we recommend directions for developments of EU fisheries policy.

q-bio.PE↗

arXiv2012

Spontaneous genetic clustering in populations of competing organisms

We introduce and analyse an individual-based evolutionary model, in which a population of genetically diverse organisms compete with each other for limited resources. Through theoretical analysis and stochastic simulations, we show that the model exhibits a pattern-forming instability which is highly amplified by the effects of demographic noise, leading to the spontaneous formation of genotypic clusters. This mechanism supports the thesis that stochasticity has a central role in the formation and coherence of species.

q-bio.PE↗

arXiv2012

Demographic noise can lead to the spontaneous formation of species

When a collection of phenotypically diverse organisms compete with each other for limited resources, with competition being strongest amongst the most similar, the population can evolve into tightly localised clusters. This process can be thought of as a simple model of the emergence of species. Past studies have neglected the effects of demographic noise and studied the population on a macroscopic scale, where species formation is found to depend upon the shape of the curve describing the decline of competition strength with phenotypic distance. In the following, we will show how including the effects of demographic noise leads to a radically different conclusion. Two situations are identified: a weak-noise regime in which the population exhibits patterns of fluctuation around the macroscopic description, and a strong-noise regime where species appear spontaneously even in the case that all organisms have equal fitness.

q-bio.PE↗

arXiv2005

No need to blur the picture

A formalism specifying efficient, "emergent" descriptions of experimental systems is developed. It does not depend on an a priori assumption of limited available data.

physics.data-an↗

arXiv2003

A generic scheme for choosing models and characterizations of complex systems

It is argued that the two problems of choosing characterizations and models of complex systems should not be considered independently. A particular criterion for these choices, oriented on the potential usefulness of the results, is considered, and a generic formalization applicable to realistic experiments is developed. It is applied to Kuramoto-Sivashinsky chaos.

physics.data-an↗

arXiv2000

Three-dimensional pattern formation, multiple homogeneous soft modes, and nonlinear dielectric electroconvection

Patterns forming spontaneously in extended, three-dimensional, dissipative systems are likely to excite several homogeneous soft modes ($\approx$ hydrodynamic modes) of the underlying physical system, much more than quasi one- and two-dimensional patterns are. The reason is the lack of damping boundaries. This paper compares two analytic techniques to derive the patten dynamics from hydrodynamics, which are usually equivalent but lead to different results when applied to multiple homogeneous soft modes. Dielectric electroconvection in nematic liquid crystals is introduced as a model for three-dimensional pattern formation. The 3D pattern dynamics including soft modes are derived. For slabs of large but finite thickness the description is reduced further to a two-dimensional one. It is argued that the range of validity of 2D descriptions is limited to a very small region above threshold. The transition from 2D to 3D pattern dynamics is discussed. Experimentally testable predictions for the stable range of ideal patterns and the electric Nusselt numbers are made. For most results analytic approximations in terms of material parameters are given.

nlin.PS↗

arXiv1999

Abnormal Rolls and Regular Arrays of Disclinations in Homeotropic Electroconvection

We present the first quantitative verification of an amplitude description for systems with (nearly) spontaneously broken isotropy, in particular for the recently discovered abnormal-roll states. We also obtain a conclusive picture of the 3d director configuration in a spatial period doubling phenomenon involving disclination loops (CRAZY rolls). The first observation of two Lifshitz frequencies in electroconvection is reported.

patt-sol↗