Ecology: Biology of Interaction. 5.05. Key Factors in Earth’s Biosphere
Considering Earth’s biosphere, we can identify which factors most strongly affect distribution of organisms across the planet’s surface. Factors whose variation most often coincides with species distribution boundaries are limiting factors. For terrestrial ecosystems these are primarily temperature and moisture; for aquatic ecosystems, light and biogens.
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5.04. Subenvironments and adaptations to them
D. Shabanov, M. Kravchenko. Ecology: Biology of Interaction, Chapter 5. Autecology and Fundamentals of Environmental Science
5.06. Liebig's Law of the Minimum
5.05. The Most Important Factors in the Earth's Biosphere When considering the Earth's biosphere, we can establish which factors have the greatest impact on the distribution of organisms across the planet's surface. Those factors, the change of which is most often associated with the boundaries of organism distribution, will be limiting. The action of these factors was discussed in more detail in the chapter devoted to ecosystems, and here we can note that the main factors for terrestrial ecosystems are temperature and humidity, and for aquatic ecosystems - the availability of light and biogens. The distribution of organisms across the Earth's surface is most clearly related to temperature. Recall how much importance we attach to moving south or north, closer to the equator or the poles, in relation to the distribution of organisms. The main factor that changes during such a movement is temperature. For example, coffee can only be grown in regions of the planet where the average monthly temperature in the coldest month does not drop below 13°C. Sometimes the dependence on temperature is more complex. For example, the Saguaro cactus, which lives in the Sonoran Desert in Arizona (USA), can withstand night frosts in winter only if there is a thaw during the day. Two consecutive nights with negative temperatures without a thaw in between are fatal for the Saguaro, and the northern and eastern boundaries of its distribution almost (but not entirely!) coincide with the boundaries of regions where there are never winter days without a thaw (Fig. 5.5.1). Fig. 5.5.1. The distribution boundaries of the Saguaro (giant cactus) in the Sonoran Desert depend on the climate It is impossible to answer what temperature is optimal for living organisms on Earth, as different organisms prefer different temperatures. It can be said that, in general, the vast majority of life processes on Earth occur in the temperature range from 0°C to +45°C, and even these temperatures are fatally dangerous for most organisms on our planet. Many organisms can tolerate temporary temperature drops below 0°C, as happens in winter in temperate latitudes, but few can tolerate temperature increases significantly above the specified limit. The adverse effect of high temperatures is due to the fact that they lead to a disruption of the natural conformation (spatial 'folding') of enzymes and loss of their activity, while low temperatures lead to a deep inhibition of all reactions associated with the life of organisms. In addition, high temperatures can lead to the death of organisms due to dehydration, and low temperatures - to damage to their cells by ice crystals that form inside them during freezing, or to dehydration due to the fact that intracellular water binds in the composition of these crystals. The lack of available water is an even more acute problem for terrestrial organisms than unfavorable temperature. Water, without exaggeration, is the basis of life, and where there is no liquid water, life becomes impossible. It is the presence of water on the Earth's surface in all three of its forms (liquid, solid, and gaseous) that stabilizes temperature conditions and makes the planet suitable for a multitude of diverse organisms. Another most important characteristic of the Earth is the oxidizing nature of its atmosphere. As you will see later, it is a result of the activity of living organisms. Most of them (including practically all animals, as well as plants and fungi) are aerobes, i.e., they require a sufficient amount of oxygen in the environment for their life activities. The distribution of anaerobes (organisms that live without oxygen) on modern Earth is limited to relatively few habitats. Additional materials: Educational model: Plant water balance
5.04. Other Classifications of Ecological Factors
D. Shabanov, M. Kravchenko. Ecology: Biology of Interaction, Chapter 5. Autecology and Fundamentals of Environmental Science
5.06. Liebig's Law of the Minimum