Toleranzkurve [abiotische Umweltfaktoren, stenök, euryök] - [Biologie, Oberstufe, Teil 7]

In this video, we'll look at tolerance curves and clarify important terms such as physiological and ecological potential. Tolerance curves play a crucial role in the field of ecology – they allow us to characterize the influence of an ecological factor on the activity of an organism. For example, the influence of the abiotic factor temperature on the number of individuals of a particular species can be analyzed. At what temperatures do how many animals exist? Another example: How does hunting activity, measured by the number of prey caught, change with temperature? As mentioned, tolerance curves are an extremely useful tool for analyzing the influence of an abiotic, non-living environmental factor, such as temperature (very common), but also light conditions, soil moisture, and others, on the activity of an animal. All organisms on Earth interact with highly variable abiotic environmental conditions – (temperature differs globally and locally, water is not equally available everywhere, soil moisture varies depending on location, etc.). Therefore, over the course of evolution, they have adapted to their respective environmental conditions. A polar bear, due to its morphological—physical—adaptations, can live very well in the cold Arctic region, while camels inhabit the dry and hot deserts of North Africa, among other places. However well both species are adapted to their respective habitats, they would not be able to survive in the other's habitat in the long run. The physiological and genetic adaptations that allow an organism to thrive under certain environmental conditions are simultaneously a limiting factor for its success under other environmental conditions. Let's take a closer look at the structure of a tolerance curve: The range in a tolerance curve in which an organism (in this case, with regard to temperature) can survive and thus exist in the long term is called the tolerance range—it extends from the so-called minimum to the maximum. Minimum and maximum, in turn, describe the minimum and maximum temperature values ​​that the organism can have for it to survive. The extreme ranges just before the minimum and maximum are defined as the pessima and pessimum, respectively (singular): Here, an organism can survive, but generally cannot reproduce. The preferred range, in which an organism would reside, is defined as the preferendum – this is also where the optimum is found. A tolerance curve can also be used to determine the extent to which an organism tolerates broad fluctuations of an environmental factor or can only be active within a narrow range. In this context, the technical terms stenoecious and euryecious play an important role: Stenoecious means that a species can only tolerate a narrow tolerance range for one of several environmental factors; a species can be characterized as euryecious if it exhibits a broad tolerance range for one or more environmental factors – as is the case, for example, with the polar bear or the camel. Both animals are warm-blooded – also known as homeothermic. Because homeothermic organisms are able to maintain a constant body temperature independent of the ambient temperature, they can usually be active within a fairly wide temperature range and are thus even more specific than eurythermic with regard to the ecological factor of temperature. Their preference range—the temperature range in which an organism prefers to stay—is correspondingly quite broad. Of course, even for homeothermic animals, the ambient temperature cannot be arbitrary—if it falls below or rises above a certain temperature, the animal will experience hypothermia or hyperthermia, which in very extreme cases can even lead to death from exposure or heatstroke. The situation is quite different for cold-blooded—or poikilothermic—organisms. Because their body temperature adapts to the ambient temperature, temperatures that deviate from the optimum temperature quickly lead to reduced activity in the cold-blooded animal. Therefore, their temperature preference is significantly narrower than that of warm-blooded animals – they generally tolerate relatively small temperature fluctuations and are characterized as stenothermic. Many tropical animals fall into this category. While the tolerance range of cold-blooded animals can be similarly large, they enter a state of torpor at ambient temperatures near their minimum or maximum – this is their pessimum or pessima, where they can still survive but are generally no longer able to reproduce.