Ecology: Biology of Interaction. 5.09. “Interaction of Factors” and the Hutchinson Niche
The result of factor interaction depends on factor specifics and on mechanisms of adaptation to their adverse effects, but one general rule can still be stated: unfavorable values of one factor narrow tolerance ranges to other factors.
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5.08. Terms describing organism tolerance
D. Shabanov, M. Kravchenko. Ecology: Biology of Interaction Chapter 5. Autecology and Foundations of Environmental Science
5.10. Selye's concept of stress
5.10. Selye’s stress concept 5.09. “Interaction of factors” and the Hutchinson niche As noted, ecological environment is an integrated whole, and the full set of factors acts simultaneously on any organism. Similarly, organism response to environment is also an integrated whole. Naturally, more and less important components can be distinguished. For example, a cold person will spend a substantial part of energy on warming the body (shivering, intense movement, seeking a warm place), while a hungry person will seek food. The factor currently most unfavorable will trigger the most pronounced organism response. What if a person simultaneously experiences cold and food shortage? It becomes much harder to cope with each factor. With sufficient high-calorie food, resisting cold is easier; a freezing person weakens from hunger much faster than one in comfortable temperature conditions. Thus, organism responses to these two factors influence each other. This is called interaction of two factors. Note that in this example we are not talking about interaction of factors in a purely physical sense, but interaction of organism responses to their effects. At language level, this again confirms that ecology is concerned not with factors by themselves outside organism context, but with their action on the being from whose “point of view” ecological environment is assessed. Did you know that in a dry-air sauna (Finnish sauna), a person can tolerate higher temperatures than in a humid Russian bath? This is because in dry air, skin, respiratory mucosa, and lungs are cooled by water evaporation from their surfaces. When characterizing severe frost in northern and Far Eastern Russia, people consider not only negative temperature. Frost severity is assessed by accounting for temperature, humidity, and wind strength. Even without such extreme examples, interaction of factors such as temperature and humidity is evident (Fig. 5.9.1). [IMG_1] Fig. 5.9.1. Response of a lightly clothed person to different values of temperature and air humidity indoors Interacting factors may be very different in biological nature. In botanical gardens, plants from other climatic zones are often grown in open ground. This means local climate may be suitable for foreign species. However, in wild conditions the same species may fail to establish. The reason is that gardeners remove competing plants by weeding. Thus, ability to withstand competitors depends on climate. Result of factor interaction depends on their specificity and on adaptation mechanisms to adverse effects (Fig. 5.9.2), but one general rule can still be stated. Unfavorable values of one factor narrow tolerance ranges to other factors. [IMG_2] Fig. 5.9.2. Influence of soil-solution pH (acidity) on availability of different mineral nutrients for plants Responses to interacting factors may be linked in one or another physiological balance of an organism: water, thermal, energy, etc. Factor interaction can be represented via the Hutchinson niche concept proposed in 1957. By that time, the concept of ecological niche introduced by J. Grinnell and C. Elton was interpreted as belonging to community ecology. American ecologist and hydrobiologist George Hutchinson reinterpreted this concept. Hutchinson’s logic was as follows: as a first step, plot on a linear axis the tolerance range of a given species for one factor. Second, add another axis corresponding to another important factor and plot its tolerance range. After characterizing tolerance limits for two factors, add a third, fourth, and so on — as many as needed to characterize major requirements of the species. As a result, we obtain a hypervolume (multidimensional volume) in factor space that includes combinations of values at which the species can exist. Let us call this the Hutchinson niche (Fig. 5.9.3). A two-dimensional niche can be represented as a rectangle on a plane of two traits, a three-dimensional one as a rectangular prism. But an organism is unlikely to tolerate simultaneous adverse action of all three factors (the prism corner case). Most favorable conditions lie somewhere inside the niche, unfavorable ones near edges (Fig. 5.9.4). If factors (more precisely, responses to them) interact, the real Hutchinson niche shape will differ. The statement that unfavorable value of one factor narrows tolerance to others is reflected in “rounding” of multidimensional niche corners. [IMG_3] Fig. 5.9.3. Hutchinson ecological niche defined by three factors (temperature, oxygen concentration, and salinity) for lobster [IMG_4] Fig. 5.9.4. Space inside the niche is heterogeneous. Here, differences in fitness levels are shown for a two-dimensional Hutchinson niche Additional materials: Learning model: Interaction of factors (photosynthesis control in a greenhouse) 5.08. Terms describing organism tolerance
D. Shabanov, M. Kravchenko. Ecology: Biology of Interaction Chapter 5. Autecology and Foundations of Environmental Science
D. Shabanov, M. Kravchenko. Ecology: Biology of Interaction, Chapter 5. Autecology and Fundamentals of Environmental Science
5.10. Selye’s stress concept