Jacqueline McGlade

Modelling complex human systems: A fisheries example

Abstract The basis of current models used in Fishery Management is briefly examined, and various shortcomings are discussed. Alternative, dynamic models are described which are based on the data available for the Nova Scotia Groundfish Fisheries. It is shown that human responses can amplify relatively small annual environmental fluctuations, leading to large, quasi- cyclic changes in catch and profit. In a detailed spatial model it is shown that stochastic behaviour on the part of some fishermen is necessary for the survival of the fishery, and that the efficiency and size of the industry depends very much on the information flows concerning catch. A very general discussion is given which shows how these ideas are important in our understanding of innovation and discovery in general terms.

Ecology, thermodynamics and H.T. Odum's conjectures

The central rôle of energy in all life processes has led to the development of numerous hypotheses, conjectures and theories on the relationships between thermodynamics and ecological processes. In this paper we examine the theoretical and empirical support for these developments, and in particular for the widely published set of thermodynamic conjectures developed by H.T. Odum, in which the maximum power principle is put forward as a generic feature of evolution in ecosystems. Although they are widely used, we argue that many of the ecological studies that have adopted the ideas encapsulated in Odums work have done so without being aware of some of the fundamental problems underlying this approach. We discuss alternative ways in which a general available-work concept could be constructed for use as a numeraire in an energy-centered ecological theory or paradigm. In so doing, we examine what is meant by material accessibility and energy stocks and flows with respect to traditional food web and food chain theories, and relate these to results from the evolutionary dynamics of ecosystems. We conclude that the various forms and uses of energy bound up in essential ecosystem processes present a formidable obstacle to obtaining an operational definition of a general, aggregated available-work concept, a prerequisite for the systems approach of Odum and others. We also show that the prototypical derivations of the maximum power principle, and its interpretation, are contradicted on many scales both by empirical data and models, thereby invalidating the maximum power principle as a general principle of ecological evolution. The conclusions point to the fundamental problem of trying to describe ecosystems in a framework which has a one-dimensional currency.

Clupeoid population variability, the environment and satellite imagery in coastal upwelling systems

Sardine, pilchard and anchovy stocks form the basis of commercially important purse seine fisheries in eastern boundary upwelling regions. High levels of environmentally driven recruitment variability have, however, made them especially difficult to manage. Reliable forecasts of recruitment success would greatly help with the setting of catch quotas prior to each fishing season. Theories of how environmental conditions influence recruitment success, according to survival/mortality of the early life-history stages, can be divided into mechanistic and sythesis theories. Mechanistic theories are concerned with specific physical processes, whereas synthesis theories attempt to unite the various mechanistic processes within a single conceptual framework. Despite the successful testing of some theories, there has been little success in reliably predicting recruitment success from a knowledge of environmental conditions. Possible reasons include the following: non-linearity in the relationship between environmental parameters and recruitment; the poor spatial and temporal resolution of much oceanographic data; the wide range of different factors involved in determining recruitment success; and the choice of environmental index. The recent compilation of time series of satellite images for these regions offers a solution to some of these problems, and in doing so reopens the possibility of finding sufficiently good relationships between environmental conditions and recruitment success for management purposes. In particular, the high resolution of these time series allows for the construction of environmental indices across many different spatial and temporal scales. These time series also open up the possibility of quantifying the behaviour of upwelling systems according to the evolution of their spatial structure through time, using pattern analysis techniques.

Evolutionary Drive: The Effect of Microscopic Diversity, Error Making, and Noise

In order to model any macroscopic system, it is necessary to aggregate both spatially and taxonomically. If average processes are assumed, then kinetic equations of “population dynamics” can be derived. Much effort has gone into showing the important effects introduced by non-average effects (fluctuations) in generating symmetry-breaking transitions and creating structure and form. However, the effects of microscopic diversity have been largely neglected. We show that evolution will select for populations which retain “variability,” even though this is, at any given time, loss-making, predicting that we shall not observe populations with “optimal behavior,” but populations which can “learn.” This lesser short-term efficiency may be why natural diversity is so great. Evolution is seen to be “driven” by the noise to which it leads.

The Stability of Ecosystems

Stability criteria and phase boundaries for complex ecosystems are obtained and contrasted with previously studied scenarios. The stability of such systems is determined by the behaviour of the largest eigenvalue of matrices governing the response of the system to small perturbations. As a result we show that ecosystems with unstructured cooperative interactions between arbitrary species can be less stable than had been previously determined. We also examine hierarchical ecologies, and demonstrate their increased stability under certain conditions.

The Role of Memory in Ecological Systems

A cellular automaton model of a middle European beech forest mosaic cycle is used to demonstrate the essential role played by memory in a spatially extended artificial ecology. The emergent spatial structure is shown to be fundamentally dependent on the amplification of local interactions by the mechanism of memory.

A coupled map lattice model of the growth of plant monocultures

Abstract A coupled map lattice (CML) model is used to analyse the role of neighbourhood effects and competition on spatial patterns and size hierarchies in annual plant monocultures. The results are compared with those from a traditional model of circular zones, and show that the CML results are highly robust over a range of densities. Asymmetric competition is observed to give rise to increased size variability compared to symmetric competition. Spatial effects are concluded to be secondary to the degree of competitive asymmetry.

Seasonal and interannual variability of oceanographic processes in the Gulf of Guinea: an investigation using AVHRR sea surface temperature data

The Gulf of Guinea is situated in a critical position for understanding Atlantic equatorial dynamics. This study investigates seasonal and interannual variability in sea surface temperature (SST) throughout this region, focusing on dynamical ocean processes. A 10.5-year time series of remotely sensed SST data with 4 km spatial resolution from the Advanced Very High Resolution Radiometer (AVHRR) were used for this investigation, as they are sufficient to resolve shelf processes. Firstly, patterns of cloud cover were assessed, then spatio-temporal variability in SST patterns was investigated. Features identified in climatological SST images were the Senegalese upwelling influence, coastal upwelling, tropical surface water, river run-off and fronts. Of particular interest is a shelf-edge cooling along the coast of Liberia and Sierra Leone in February. Interannual variability, assessed using annual mean images, time series decomposition and spectral analysis, showed a quasi-cyclic pattern of warm and cool years, perhaps related to El Niño-type forcing. The results of this study show the usefulness of infrared remote sensing for tropical oceanography, despite high levels of cloud cover and atmospheric water vapour contamination, and they provide evidence for theories of westward movement of the upwelling against the Guinea current and remote forcing of the upwelling.

A two-dimensional individual-based model of territorial behaviour: possible population consequences of kinship in red grouse

Abstract A two-dimensional simulation model of territory establishment and maintenance by individual male red grouse investigated whether differences in aggressive behaviour between kin and non-kin might cause population cycles or other demographic instability. Two behavioural phenotypes were envisaged. Intolerant cocks were equally aggressive to all neighbours, while kin-tolerant cocks were less aggressive to their close kin. The models dynamics showed that: (i) pure populations of intolerants reached low but quite stable densities; whereas (ii) pure populations of kin-tolerant cocks attained higher densities with larger fluctuations; while (iii) populations of kin-tolerant cocks able to disperse showed even wider fluctuations. Mixed populations of intolerants and kin-tolerants co-existed at intermediate frequencies, with marked fluctuations. Thus kin-tolerant behaviour destabilised the model, giving it the potential to bifurcate to a cycle, but cycles were not observed. Two variants of the model altered grouse behaviour in response to changes in density, by changing either their kin tolerance or their number of dispersal attempts. Sensitivity tests showed these variants often produced density cycles, with periods around 6–15 years. We concluded that: differential aggressive behaviour between kin and non-kin during territorial disputes can destabilise a two-dimensional model population that has a life history similar to red grouse; dispersal may have a big effect on the stability of such model populations; some realistic variant models produced density cycles with periods and amplitudes comparable to those observed in some studies of wild red grouse.

Climatic trends in continental shelf waters off Ghana and in the Gulf of Guinea, 1963-1992

Using time series analyses, some physical parameters of the continental shelf waters of the Gulf of Guinea were examined. Analysis of coastal sea surface temperatures from Ghana and Ivory Coast, and offshore sea surface temperatures from the Gulf of Guinea clearly shows spatial and inter-annual patterns of cooling in coastal waters of West Africa. The behaviour of the decomposed trend of coastal and offshore sea surface temperatures, sub-surface: temperature measured at 100 m depth off Ghana and salinity showed that the observational period (1963-1992) could be divided into three climatic periods: the period before 1972, from 1972 to 1982, and the period after 1982. In the first period, sea surface temperature at both coastal and offshore areas and bottom temperature declined and coastal salinity was relatively low. The second period was a cold one with less than average sea surface and sea bottom temperatures. The mixed layer was narrow with the thermocline remaining shallower than its: long-term average position. Coastal and bottom salinity (measured at the 100 m depth) were relatively high but the seasonal variation was minimal. This period of significant change in the physical components of the ecosystem of the Ghanaian shelf waters has hitherto not been documented in the literature. In the final phase, temperatures were high, and salinity was low and erratic. The observed localised environmental changes are consistent with global changes in the Gulf of Guinea and possibly in the tropical Atlantic basin