Predators and prey

In addition to reproductive effects, fish exposed to endocrine disrupters may have a decreased response to stress or decreased growth and metabolism which can affect their ability to survive, or to defend themselves against predators. All of these factors can affect the ability of the species to survive and to reproduce itself in sufficient numbers to maintain the stocks on which our commercial and sport fisheries are based. Not all fish species will be equally susceptible to the effects of endocrine disrupters. Selective sensitivity to such effects, especially those affecting reproduction, may well lead to major changes in the flora and fauna of some of our major aquatic ecosystems as the balance between fish, mammals, invertebrates and plants, and between predators and prey, is destabilised... 

Turning now to indirect effects of neurotoxic pollutants, the status of predators and parasites can be affected by reductions in numbers of the species that they feed upon. Thus, the reduction in numbers of a prey species due to a behavioral effect can, if severe enough, cause a reduction in numbers of a predator. Also, as mentioned earlier, behavioral effects upon a prey species may lead to selective bioaccumulation of persistent neurotoxic pollutants such as DDT and dieldrin by predators thus, a behavioral effect may be hazardous for predator and prey alike ... 

A predator and prey simulation. The population of gazelles (the higher line) has been scaled down since, in reality, it would be many times that of the lions. 

K.H. Krause, Professional phagocytes predators and prey of microorganisms. Schweizerische Medizinische Wochenschrift 130, 97-100 (2000). 

Leonards, P.E.G., S. Broekhuizen, P. de Vogt, N.M. Van Straalen, U.A.T. Brinkman, W.P. Cofino, and B. van Hattum. 1998. Studies of bioaccumulation and biotransformation of PCBs in mustelids based on concentration and congener patterns in predators and preys. Arch. Environ. Contam. Toxicol. 35 654-665. 

Figure 3-34. Lotka-Volterra s predator and prey kinetics .

As indicated above, theoretical models for biological rhythms were first used in ecology to study the oscillations resulting from interactions between populations of predators and preys [6]. Neural rhythms represent another field where such models were used at an early stage The formalism developed by Hodgkin and Huxley [7] stiU forms the core of most models for oscillations of the membrane potential in nerve and cardiac cells [33-35]. Models were subsequently proposed for oscillations that arise at the cellular level from regulation of enzyme, receptor, or gene activity (see Ref. 31 for a detailed fist of references). 

In their predator avoidance, salamanders use complex odors that combine chemicals from both predator and prey. In the laboratory, red-backed salamanders, P. cinereus, avoid filter papers soaked with water extracts from garter snakes that had been preying on salamanders, while earthworm-fed snakes lacked this effect. Exudations from unfed snakes and extracts from homogenized salamanders had no such alarming effect (Madison etal, 2002). 

Disappearance of predators may also imbalance the equilibrium, and the problem scales up, such as the disappearance of foxes, predators of the deer mouse, which has allowed spreading of the hantavirus in the US, carried by mice (Levins 1993). Similarly, Sabia virus has emerged in Brazil, Guaranito virus in Venezuela (Lisieux 1994), machupo virus in Bolivia, and Junin fever in Argentine (Garrett 1994). In contrast, in a robust ecosystem, elimination of a predator provides space for another predator, such as in the disappearance of the coyote, which has opened the control of field mice to snakes and owls. When both predator and prey are endangered, it may occur that the prey develops resistance. This is taken into account in Volterra s equation (Ehrlich 1986). 

When a more detailed analysis of microbial systems is undertaken, the limitations of unstructured models become increasingly apparent. The most common area of failure is that where the growth is not exponential as, for example, during the so-called lag phase of a batch culture. Mathematically, the analysis is similar to that of the interaction of predator and prey, involving a material balance for each component being considered. 

Chemical Ecology of Mobile Benthic Invertebrates Predators and Prey,... 

This example is not chemically relevant, but is all the more exciting. It models the dynamics of a population of predators and preys in a closed system. Consider an island with a population of sheep and wolves. In the first reaction, the sheep are breeding. Note that there is an unlimited supply of grass and that this reaction could go on forever. But there is the second reaction, where wolves eat sheep and breed themselves. To complete the system, wolves have to die a natural death. 

From the 1970s onwards, Cesare Marchetti and other system analysts have studied thousands of artifacts, and have discovered that their behaviour is described by the same equations that Lotka and Volterra found for the behaviour of predators and prey. The growth pattern of cars, for example, is a logistic curve. Cars spread in a market exactly as bacteria in a broth or rabbits in a prairie. Cultural novelties diffuse into a society as mutant genes in a population, and markets behave as their ecological niches. But why ... 

Food chain for The physiology of the species involved (both predator and prey) strongly... 

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