Complex ecological models with simple dynamics: From individuals to populations

The aim of this work is to study complex ecological models exhibiting simple dynamics. We consider large scale systems which can be decomposed into weakly coupled subsystems. Perturbation Theory is used in order to get a reduced set of differential equations governing slow time varying global variables. As examples, we study the influence of the individual behaviour of animals in competition and predator-prey models. The animals are assumed to do many activities all day long such as searching for food of different types. The degree of competition as well as the predation pressure are dependent upon these activities. Preys are more vulnerable when doing some activities during which they are very exposed to predators attacks rather than for others during which they are hidden. We study the effect of a change in the average individual behaviour of the animals on interspecific relationships. Computer simulations of the whole sets of equations are compared to simulations of the reduced sets of equations.     

Arable acronyms analysed – a review of integrated arable farming systems research in Western Europe

Arable production has come under increasing economic and environmental pressures, especially in the last decade. These have derived from over-production, decreased farm incomes and a concern with the possible environmental effects of intensive pesticide use associated with such intensive cultivation. A number of long-term research programmes on integrated farming systems and their sustainability have recently been completed or are currently under way. In the UK, these include the ‘Boxworth’ project, ‘SCARAB’, TALISMAN’, RISC, ‘LINK Integrated Farming Systems’, ‘LIFE’ and the demonstration-only programme ‘LEAF’. These projects are reviewed in terms of their objectives, designs and results to date, and are compared with some parallel programmes in Germany, the Netherlands, Switzerland and France.     

Root movements: Towards an understanding through attempts to model the processes involved

Roots have the ability to change the direction of their forward growth. Sometimes these directional changes are rapid, as in mutations, or they are slower, as in tropisms. The gravitational force is always present and roots have an efficient graviperception mechanism which enables them to initiate gravitropic movements. In trying to model and simulate the course of gravitropic root movements with a view to analyse the component processes, the following aspects of the plant's interaction with gravity have been considered: (1) The level of organization (organism, organ, cell) at which the movement process is expressed; (2) whether the gravity stimulation event is dynamic or static (i.e. whether or not physiologically significant displacements take place with respect to the gravity vector); (3) the sub-systems involved in movement and the processes which they regulate; (4) the mathematical characterization of the relevant sub-systems. A further allied topic is the nature of nutational movements and whether they are linked with gravitropic movements in some way. In considering how they can best be modelled, two types of nutational movements are proponed: stochastic nutation and circumnutation. Most, if not all, natural movements developed in response to static gravistimulation can be viewed as gravimorphisms. This applies at the levels of cell, organ and organism. However, when a system at any one of these levels experiences dynamic gravistimulation, because of its inherent homeostatic properties, it is induced to regenerate a state similar to that previously held. Thus, gravitropism is a regenerative gravimorphic process at the level of the organ.     

Cultural responsibility in the preservation of local economic plant resources

Understanding the relationships between indigenous people and their threatened economic plants can aid the conservation effort on many levels. Understanding ethnic perceptions of the taxon is critical toin situ andex situ conservation projects and enhances the accompanying educational effort. Examples are discussed from the experience of a grassroots conservation group in southwestern United States, Native Seed/SEARCH. Four levels of economic plant vulnerability are examined among 1) wild-harvested plants, 2) husbanded wild plants, 3) domesticates, and 4) wild relatives of domesticates. Legal interpretations of endangered husbanded and domestic plants are discussed, and further documentation encouraged. Genetic dynamism of threatened indigenous crops is examined and the concept of Systems Conservation (i.e. the plant/human interactive systems) is introduced. Guidelines are offered for incorporating better cultural responsibility intoex situ conservation strategies. The concept of Biocultural Restoration is introduced with an example from an O'odham community. Examples are given of ways indigenous peoples and their knowledge can assist in the conservation effort.     

Interactions between nitrate and ammonium during uptake by carob seedlings and the effect of the form of earlier nitrogen nutrition

Seedlings of carob ( Ceratonia siliqua L. cv. Mulata) were used in two sets of experiments in order to evaluate; (1) the reciprocal effects of each nitrogen form on net uptake of nitrate and ammonium, and (2) the effect of earlier nitrogen nutrition on ammonium versus nitrate uptake. In the former group of experiments we studied the kinetics of nitrate and ammonium uptake as well as the interference of each of the two forms with net uptake of ammonium and nitrate by both nitrogen depleted and nitrogen fed carob seedlings. On the whole, nitrogen depletion led to increase in both affinity and V_max of the system for both forms of nitrogen, at the same time as the effects of nitrate on uptake of ammonium and vice versa were concentration dependent. In the second group of experiments the effects of earlier nitrogen nutrition on nitrate and ammonium uptake were characterized, and in this case we observed that: (a) if only one form of N was supplied, ammonium was taken up in greater amounts than nitrate; (b) the presence of ammonium enhanced nitrate uptake; (c) ammonium uptake was inhibited by nitrate; (d) there was a significant effect of the earlier nitrogen nutrition on the response of the plants to a different nitrogen source. The latter was evident mainly as regards ammonium uptake by plants grown in ammonium nitrate. The interactions between nitrate and ammonium uptake systems are discussed on the basis of the adaptation to the nitrogen source during early growth.     

PEAK SHIFTS AND POLYMORPHISM DURING PHASE THREE OF WRIGHT'S SHIFTING-BALANCE PROCESS

The third phase of Wright's shifting-balance theory involves the export of adaptive gene combinations from one subpopulation to another. Previous results have demonstrated that this can occur at very low migration rates, but it has been argued that this simply reflects the ability of migration to overcome selection and fix any (even deleterious) alleles. Here, previous analyses are extended by concentrating on the critical balance between forward and reverse migration rates that still allows phase III to proceed. It is shown that selective advantage, dominance, recombination rate, and the number of loci all affect the ability of a genotype to invade and become fixed in a new subpopulation, but it is unlikely that phase III will occur in the absence of differential migration unless the invading genotype consists of a few dominant loci with a large selection advantage, spreading into a few populations of lower fitness. Therefore, as was envisioned by Wright, differential migration from more to less fit populations will be necessary for phase III to occur under most circumstances.     

Diffuse serotoninergic neurohemal systems associated with cerebral and suboesophageal nerves in the head of the Colorado potato beetle Leptinotarsa decemlineata

We analyzed the anatomy of two diffuse neurohemal systems for serotonin in the head of the Colorado potato beetle Leptinotarsa decemlineata by means of immunohistochemistry. One system is formed by axons from two bilateral pairs of neurons in the frontal margin of the suboesophageal ganglion that enter the ipsilateral mandibular nerve, emerge from this nerve at some distance from the suboesophageal ganglion, and cover all branches of the mandibular nerve with a dense plexus of immunoreactive axon swellings. The other system is formed by axons from two large neurons in the frontal ganglion that enter the ipsilateral frontal connectives, emerge from these connectives, and form a network of axon swellings on the labroforntal, pharyngeal, and antennal nerves and on the surface of the frontal ganglion. Immunohistochemical electron microscopy demonstrated that the axon swellings are located outside the neural sheaths of the nerves and hence in close contact with the hemolymph. We therefore suggest that these plexuses represent extensive neurohemal systems for serotonin. Most immunoreactive terminals are in direct contact with the hemolymph, and other terminals are closely associated with the muscles of the mandibles, labrum, and anterior pharynx, as well as with the salivary glands, indicating that these organs are under serotoninergic control.     

A matter of timing: System requirements for repair and their temporal dimensions

Research into repair within the circular economy (CE) typically focuses on technical aspects of design, policy, and markets, and often assumes simplified conditions for the user/owner and the product system to explain the barriers to scaling repair activities. However, factors occurring at pre-use stages of the product's life cycle can significantly influence whether, and to what extent, repair is viable or possible, that is, warranty duration, after-sale service provision, and access to necessities. The passing of time can directly and indirectly affect the ability, difficulty, and thus, the likelihood of repair activities being performed at each stage of the product's life cycle. Drawing from the literature and applying inductive systems-thinking tools, we propose a framework for considering the “System of Repairability.” We delineate how the passing of time (temporal dimensions) affects one's ‘‘ability to repair,’’ as a product progresses through different life cycle phases (i.e., breakdown vs. repair vs. disposal), and the point(s) at which the repair is considered or attempted (i.e., year of usage). By integrating life cycle and temporal (time-based) dimensions into a broad System of Repairability framework, we clarify relevant interconnections, iterations, sequences, and timing of decision points, stakeholders, and necessary conditions to facilitate an outcome of successful repair at the individual level, and thus intervention strategies for scaling repair within CE. We discuss how a policy mix can address the life cycle of products and the repair system more holistically. We conclude with a future outlook on how temporal dimensions can inform policy strategies and future research.     

Phototropism in hypocotyls of radish. VI. No exchange of endogenous indole-3-acetic acid between peripheral and central cell layers during first and second positive phototropic curvatures

Using a physicochemical method, the distribution of endogenous indole-3-acetic acid (IAA) was measured in the peripheral and central cell layers, as well as in the illuminated and shaded sides of phototropically stimulated radish hypocotyls (Raphanus sativus var. hortensis f. gigantissimus Makino). The IAA was evenly distributed over the illuminated and shaded sides in the first and second positive phototropic curvatures induced by a pulse or a continuous unilateral illumination with blue light. Also, no net exchange of the IAA between the peripheral and central cell layers was observed during these curvatures. These results suggest that phototropism of radish hypocotyls cannot be described by the Cholodny-Went theory.