Ecology: the biology of interaction. 5.21. Clinal variability and some ecological rules

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5.20. The concept of effective temperatures

D. Shabanov, M. Kravchenko. Ecology: Biology of Interaction Chapter 5. Autecology and Fundamentals of Environmental Science

5.22. Main habitats and their characteristics

{ "title": "5.20. Concept of Effective Temperatures", "summary": "", "body": "Dmytro Shabanov, Maryna Kravchenko. Ecology: Biology of Interaction\nChapter 5. Autecology and Fundamentals of Environmental Science\n\n5.22. Main Habitats and Their Features\n\n5.21. Clinal Variability and Some Ecological Rules\nComparing conditions in different parts of the Earth's surface, we can see that many important ecological factors change gradually, forming a gradient (a smooth sequence of changes). For example, traveling in a certain direction, we can observe how the height above sea level gradually decreases, humidity increases, and temperature changes. At some point, a discrete (abrupt) change in environmental conditions occurs - for example, we move from land to sea. However, as we continue to move, already in the sea, we see that many factors (depth, illumination) change gradiently.\nComparing organisms that inhabit an area with a gradient change of a particular factor, we can observe a regular change in certain characteristics of these organisms. When it comes to intraspecific variability, such a gradual geographical variability is called clinal. Speaking of characteristics, we can say that they form clines. For example, in deciduous forests, forest-steppes, and even in steppe and semi-desert zones, we can find oak forests - oak woods. The transition between these zones is primarily determined by the amount of water available to plants. If in the zone of deciduous forests oaks grow on flat surfaces, not related to riverbeds, then in the steppe and semi-desert they are tied to depressions (ravines) and river valleys - places with increased humidity. Comparing oaks from these oak forests with each other, we will be convinced that they have many changing characteristics: growth, stem diameter, leaf size, and features of the leaf plate structure. These differences are related to the reaction of plants to smoothly changing climatic characteristics.\nThe study of clinal variability is of particular interest for clarifying the features of the relationship between organisms and the environment (Figure 5.21.1). Clinal variability is the result of selection that adapts each population to local environmental conditions and the interaction between neighboring populations (crossing, migration) that smooths out differences between them. In fact, clinal variability \"manifests\" and makes these usually hidden processes from the researcher visible and accessible for study.\n\n[IMG_1]\nFigure 5.21.1. This diagram shows the clinal variability in wing pigmentation of one of the species of butterflies, the cabbage white (Pieris napi), according to a study conducted at the beginning of the 20th century. Isophenes - lines connecting areas of distribution of organisms with the same severity of the studied trait\nUsually, clinal variability of organisms is not considered a basis for the allocation of subspecies. Geographical subspecies (forms within a species with an independent status in the system of organisms) are distinguished in the case of discrete (discontinuous, abrupt) variability. However, sometimes between subspecies or even species that are capable of hybridization, there are transition zones - zones of intergradation.\nIn most cases, the concept of a cline is used to describe intraspecific variability, although similar changes can be recorded by considering the diversity of different species of the same genus or even family, if they lead a similar lifestyle and inhabit an environment with a gradient change of any important factor for these organisms.\nSome rules describing clinal and interspecific geographical variability have been formulated for a long time. For example, Bergmann's and Allen's rules, which apply to both intraspecific variability and differences between close species leading a similar lifestyle, were formulated back in the 19th century.\nBergmann's rule (1847): among related forms of homeothermic animals leading a similar lifestyle, those that live in a colder climate have larger body sizes.\nAllen's rule (1877): among related forms of homeothermic animals leading a similar lifestyle, those that live in a colder climate have relatively smaller protruding parts of the body: ears, legs, tails, etc.\nFor example, the geographical variability of the common fox corresponds to both of these rules. The linear dimensions of the body of southern foxes are about 10-15% smaller than those of northern foxes. In addition, southern foxes have relatively longer ears and tails. If we go beyond the boundaries of this species and consider more northern and more southern relatives of foxes, we will see that they obey the same rule. Arctic foxes have a rather large body, short paws, muzzle, tail, and ears. Desert fennec foxes are rather small foxes with long paws, muzzle, and tail and simply huge ears.\nThe largest tigers are Amur, living in the harshest climate, and the smallest are Sumatran. In the tundra, wolves live, reaching 50 kg in weight, and in the deserts, their sizes are only 35 kg. Bergmann's rule applies to interspecific geographical variability as well. It is perfectly obeyed by bears - from giant polar bears and grizzlies to small Himalayan bears. The largest penguins (Emperor and King) live in Antarctica, and the smallest - on the Galapagos Islands.\nBergmann's and Allen's rules have a similar physiological nature: they reflect the fact that in a cold climate, it is easier to maintain a constant body temperature for animals that have a smaller relative body surface area. Heat loss through the body surface is proportional to its surface area, and heat capacity and heat production are proportional to the body volume. It is possible to reduce the relative surface area by increasing the linear dimensions of the body or by \"rounding\" it, reducing the protruding parts.\nLike any rules, Bergmann's and Allen's rules have many exceptions. For example, they do not apply to burrowing mammals. Their size and proportions are significantly influenced by the peculiarities of movement in the soil environment, which, among other things, protects them from cold air.\nFor example, elephants obey Allen's rule but do not obey Bergmann's rule. African elephants are larger than Indian elephants, although they live in a hotter climate. This is due to the fact that African elephants live mainly in open spaces (in savannas), while Indian elephants are associated with forests. By the way, forest African elephants are smaller than Indian ones! But, as expected, African elephants have greater difficulties with lowering their temperature during overheating, so they have much larger ears than Indian elephants.\nCan we compare animals leading a dissimilar lifestyle with each other? Can we say that Bergmann's rule refutes, for example, tropical bats (flying foxes, flying dogs, etc.), which are much larger than bats of temperate latitudes? Of course, such a conclusion would be incorrect. These animals lead a fundamentally different lifestyle. Bats feed mainly on fruits, while our bats specialize in catching flying nocturnal insects. A different character of nutrition leads to significant differences in the heat balance of these animals, which determines the differences in their size.\nAre Bergmann's and Allen's rules applicable to intraspecific variability of humans? Although all people belong to the same species, our ecological plasticity is so great that in different parts of the range, people lead a different lifestyle. These differences prevent the manifestation of Bergmann's rule. At the same time, when comparing many peoples, it is possible to see manifestations of Allen's rule. So, Eskimos and other indigenous peoples of the Far North have stocky bodies with short arms, legs, and neck. Inhabitants of open spaces of equatorial Africa (for example, the Maasai) are slender and have relatively long and thin legs and arms. Naturally, it is possible to observe manifestations of Allen's rule only in indigenous peoples existing in close interaction with their habitat. Representatives of modern global humanity, many of whom have moved around the world and live in an artificially changed environment, usually do not demonstrate the manifestation of these ecological rules.\nAnother well-known ecological rule describing clinal variability is Gloger's rule, proposed in 1833 by the ornithologist C. Gloger. It consists in the fact that among related forms (subspecies or species) of homeothermic animals, those that live in conditions of a warm and humid climate are more brightly colored than those living in conditions of a cold and dry climate.\nThe probable reasons that lead to such a character of variability may be considerations related to protective coloration - soils (or snow surfaces) in a cold and dry climate are usually lighter than in a warm and humid one. However, this circumstance is not enough to explain Gloger's rule, since it applies even to nocturnal animals. It is possible that a humid and warm climate more favors the synthesis of pigments in animals. To some extent, Gloger's rule is applicable to humans as well.\nAdditional materials:\nEducational model: Bergmann's Rule\nEducational model: Allen's Rule\n\n5.20. Concept of Effective Temperatures\n\nDmytro Shabanov, Maryna Kravchenko. Ecology: Biology of Interaction\nChapter 5. Autecology and Fundamentals of Environmental Science\n\n5.22. Main Habitats and Their Features" }

5.20. The concept of effective temperatures

D. Shabanov, M. Kravchenko. Ecology: Biology of Interaction Chapter 5. Autecology and Fundamentals of Environmental Science

5.22. Main habitats and their characteristics