Ecology: biology of interactions. 5.23. Adaptations of organisms

Ukrainian language (latest version) / Russian language (update discontinued) 5.22. Main habitats and their characteristics D. Shabanov, M. Kravchenko. Ecology: the biology of interaction Chapter 5. Autecology and the basics of habitat studies 5.24. Life forms of organisms 5.23. Adaptations of organisms For living beings whose organization is deeply permeated by correlations and interdependencies, the compromise between conflicting requirements for optimizing various adaptive functions must be especially tense. Therefore, a stable epigenotype (a reliable system for ensuring individual development under a certain range of conditions) must be organized on the principle of a deeply worked‑out compromise between conflicting needs for maximal optimization of all adaptive functions. A.P. Rasnitsyn Many living organisms achieve perfection with respect to a particular parameter. Let us consider only the widely known examples. You know how perfect eagle vision, dog smell, turtle longevity, swiftlet speed, and camel endurance are. Why do these remarkable traits occur separately rather than combined in a single organism? Apparently because they are poorly compatible with each other. As sad as it is, improving adaptations for one parameter means a reduction in fitness for others. Winning in one aspect inevitably forces organisms to lose in another… You probably know that organisms that care for their offspring produce far fewer offspring than those that leave the next generation unattended. The smaller the eggs of fish, the larger the number (ceteris paribus) of eggs each female will lay. To understand why this happens, one can assess the amount of energy each species spends on reproduction. In this case we will see that the energetic costs of offspring production are roughly comparable among different species. This energy can be spent on producing a small number of energy‑intensive eggs or a multitude of small ones; besides egg production, energy can be spent on caring for the eggs and larvae (nest building, protection, feeding). In each case the reproductive traits of a given species represent a compromise between the need to leave offspring and the need to conserve energy. Given certain reproductive expenditures, each species’ strategy is a compromise among different forms of such costs. Are the conditions in which organisms live always optimal for them? Naturally, not always. Unfavorable conditions may characterize a habitat permanently, or they may occur intermittently, periodically (over a day, a year, or a solar cycle) or irregularly (e.g., weather anomalies). How do organisms respond to an unfavorable environment? They develop various adaptations to it. Adaptations are adjustments to specific environmental conditions that manifest in morphological, physiological, and behavioral traits of an organism’s way of life under those conditions. Adaptations are observed as a result that can be studied through the teleology of living organisms and other biosystems (according to Aristotle, teleology is the central problem of biology). The same term is sometimes used for the process of generating adaptations, which can cause terminological confusion. Pre‑adaptations are traits that originated as adaptations to one factor but prove useful for overcoming another factor. The lungs of the first tetrapods arose as an organ for breathing air from organic‑rich water, and limbs with digits as a means of moving in shallow water. Together they became a pre‑adaptation for colonizing land. If environmental conditions are extremely adverse, coping with them becomes impossible. For example, there are no amphibians or reptiles in either the Arctic or the Antarctic—overcoming cold is impossible for these poikilothermic animals. In less severe conditions three groups of organismal adaptations to adverse environments can be distinguished: overcoming, avoidance, and tolerance. We will consider them in turn. Overcoming. We noted that there are no amphibians or reptiles in the polar fauna. However, mammals and birds are abundant there. Their main strategy for coping with severe cold is the active maintenance of a constant body temperature. Let the majority of food energy be spent on thermoregulation; if the remainder suffices for basic life needs, survival is possible even amid perpetual ice. Besides cold, one of the main factors limiting Arctic fauna diversity is the near‑total lack of terrestrial plant food. Higher plants require prolonged positive temperatures for growth; where such temperatures are absent, all terrestrial photosynthesis is performed by algae and cyanobacteria living on stone and ice surfaces. In contrast, polar waters are rich in life, especially animals. Because of water’s exceptionally high heat capacity, it prevents both aquatic animals and algae from freezing. The good solubility of gases in cold water provides favorable conditions for their functioning. Thus many terrestrial mammals and birds of polar regions live thanks to marine production. One striking example of an extraordinary adaptation to an extremely inhospitable environment is the polar bear. Among the order Carnivora, members of the family Ursidae are characterized by the highest proportion of plant food in their diet. The only exception is the polar bear, an exclusively carnivorous animal. Some bear species (e.g., the brown bear) can supplement their diet with fish they catch in rivers (such as salmon during spawning), but they mainly feed on land. The polar bear’s diet is largely marine, and this predator has mastered swimming and diving in icy water. Sea ice floating on the surface of the Arctic Ocean serves as a “land” for the polar bear (unfortunately, the reduction of ice area due to global warming is turning into a catastrophe for polar bears). Large body size, a thick fat layer, and a high metabolic rate enable the bear to maintain a constantly high body temperature in the harshest cold. Even the bear’s white fur is an adaptive marvel: its colour camouflages the animal on ice and snow, and its permeability to solar radiation allows light to reach the dark, well‑heated skin underneath. As you see, the case we have examined is far from the only example of overcoming adverse conditions. And what about human behavior and way of life, if not a continual overcoming of countless environmental constraints? Avoidance of adverse conditions. Forms of avoidance are diverse. One may consider a ground squirrel hiding from rain in its burrow, or a desert lizard moving around a sagebrush shrub while tracking its shifting shadow, as avoiding unfavorable conditions. On the other hand, such behaviors are better viewed as the selection of favorable, preferred conditions. In fact, within a given animal’s permanent habitat, local conditions change, and the animal selects those that are most suitable. What if the entire habitat becomes unsuitable? A common “solution” is migration. Migrations are regular movements of animals between different habitats that are separated by considerable (for those animals) distances. The note about distance significance is intentional. Migratory birds can travel to the opposite side of the globe, while migrating soil invertebrates may move from the leaf‑litter layer down to depths of several tens of centimeters. Both phenomena can be regarded as migrations proportional to the locomotor capacities of the taxa involved. As the examples show, migrations can be horizontal (geographic) or vertical. Depending on whether the trigger is regularly acting or irregular, migrations can be divided into periodic and non‑periodic. The most famous category of migrations is bird migration. For most of our migratory birds, the trigger that sets them on the journey is the winter food shortage (with the photoperiod shortening as the proximate cue). Among the longest migrations are those of the Arctic skua—a bird that breeds in the Arctic and winters in Antarctica (where, during the Northern Hemisphere’s winter, it is “summer”). The one‑way distance of this migration exceeds 30 000 km! When environmental changes are not extremely abrupt, birds may perform not true migrations but nomadic movements, staying within a single region and shifting according to weather or food availability. Seasonal migrations are also characteristic of many African or Central Asian ungulates. Their trigger is changes in humidity and food availability. Vertical migrations are typical for mountain, soil, and especially aquatic inhabitants. For zooplankton, daily movements to the surface at night and to depths of tens or hundreds of meters by day are common. The reason is that zooplankton feed on phytoplankton, which is confined to near‑surface layers where light for photosynthesis is available. To feed, zooplankton must stay close to phytoplankton. However, at the surface during daylight they are easy prey for visually hunting fish. Consequently, many planktonic animals, especially crustaceans, hide in darkness at depth by day and rise to the surface at night to feed. These movements also contribute substantially to the mixing of marine water layers, influencing the cycling of many biogenic elements. It should be noted that migrations are not always a form of avoidance. For example, anadromous fish perform spawning migrations from marine to freshwater waters (e.g., salmon), and catadromous fish migrate from freshwater to marine waters (e.g., eels). One could view these as avoidance of unfavorable conditions (marine water is unsuitable for salmon eggs and larvae, freshwater is unsuitable for early eel stages), but overall these migrations reflect the evolutionary history of the species and its habitat‑adaptation strategy. Such migrations are called ontogenetic. Ontogenetic migrations of marine turtles, which can circumnavigate the globe, rival the length of polar skua migrations. Tolerance of adverse conditions. We have already mentioned how difficult it is for poikilothermic tetrapods to live in a harsh cold climate. Nevertheless, some amphibians and reptiles have adapted to life beyond the Arctic Circle. Antarctica is surrounded by ocean, and both Eurasia and North America approach the Arctic. For instance, the ranges of the common adder and a viviparous lizard extend beyond the Arctic Circle. Yet the most northerly amphibians and reptiles (up to 72° N) are the Siberian coal‑tooth (a small—about 15 cm with tail—tailed amphibian) that crosses the Arctic Circle in the Northern Urals, Magadan region, and Yakutia. Coal‑tooth salamanders even inhabit the vicinity of the “pole of cold,” the Yakutian town of Oymyakon! What traits help them survive there? First, the ability to tolerate cold. These animals endure freezing in permafrost (the recorded record for frozen survival is 90 years) and remain active at 0 °C. Cold tolerance is linked to low metabolic rate, cold‑stable enzymes, and the presence of cryoprotective substances in tissues that prevent the formation of damaging ice crystals. When environmental conditions are unsuitable for active life, many organisms can enter physiological states that enhance their ability to withstand adverse factors. Such states include anabiosis (or cryptobiosis)—a condition in which life processes are slowed so much that they proceed without external manifestations. Anabiosis is an adaptation to cold, desiccation, and other stresses; after conditions improve, the organism returns to normal physiology. Thus, when moist, mosses and lichens become active, tardigrades—eight‑legged invertebrates belonging to the phylum Tardigrada, a sister group to arthropods—also become active. These animals are usually measured in fractions of a millimeter. Moving slowly over moss, tardigrades feed on plant cells, bacteria, or other invertebrates. Tardigrades are renowned for extreme resistance to adverse environmental factors in a dormant stage. When moss humidity drops, the tardigrade contracts, opens its mouth, retracts its limbs, and enters the “tun” stage—anabiosis. In this state it can endure prolonged desiccation, low temperatures, toxic substances, vacuum, high radiation doses, and many other stresses. In the tun stage tardigrades could probably survive a journey through outer space! In this stage they may spend most of their lives. In rarely moist habitats, the lifespan of a single individual (less than a millimeter long!) may exceed 100 years! When re‑hydrated, the tardigrade exits dormancy and becomes highly sensitive to many environmental stresses. Some animals, such as heterothermic mammals and birds, can enter hibernation—a slowing of life processes accompanied by a marked drop in body temperature and heart rate. Unlike anabiosis, however, physiological activity remains detectable during hibernation. Hibernation may be seasonal (ground squirrels, hedgehogs, etc.), daily (bats, hummingbirds), or irregular, triggered by sudden adverse conditions (swifts, raccoon dogs). Paradoxically, bears are often cited as examples of animals entering anabiosis or hibernation, although these states are not characteristic for them. Bears (as well as badgers) endure cold in a state of winter sleep (simply a deeper sleep than ordinary), not anabiosis. These animals are large enough (recall Bergmann’s rule) to maintain a constant body temperature for extended periods without food‑derived energy. A hunter falling into a bear’s den would quickly awaken the animal. Female bears give birth and nurse cubs while in this state! In contrast, a true hibernator such as a ground squirrel has a markedly reduced body temperature, a dramatically slowed heart rate, and can “wake up” only after lengthy, energy‑intensive physiological processes (heat production by brown fat cells). The term hibernation (and also torpor) is also applied to the overwintering state of amphibians and reptiles of temperate latitudes. For example, the marsh turtle in autumn (October–November) dives to the bottom of a pond and remains there until spring (April). Its physiological processes slow sharply, and gas exchange through the oral cavity, pharynx, and cloaca suffices for survival. The turtle may still show limited activity (e.g., moving along the pond bottom). The Central Asian tortoise in the deserts of Turkmenistan emerges from winter hibernation (hibernation) in February and remains active until the end of May. When desert vegetation dries, the tortoises enter summer aestivation. In late September–early October, autumn rains may stimulate a brief emergence. If rains are scarce, aestivation turns into hibernation (a low‑activity mode at high body temperature switches to one at low temperature). Under especially severe conditions, the total active period of the Central Asian tortoise is less than three months! Human normal life cycle does not include hibernation, but our distant ancestors were probably capable of it. Today some mammals that do not naturally hibernate can be induced into it artificially. For instance, by making laboratory mice inhale a hydrogen sulfide gas mixture, they can be driven into a hibernation‑like state (and later revived by ventilating their lungs with an oxygen‑enriched mixture and warming their bodies). A number of unfortunate cases have shown that a person can be revived if the body is cooled under conditions where the central thermoregulatory center does not attempt to maintain normal body temperature. This may occur during rapid cooling (a child falling through ice), in a carbon‑dioxide atmosphere (a refrigerated‑truck driver accidentally sealing himself in a chamber with solid CO₂ “dry ice”), or under other, still insufficiently studied conditions. Frozen (but not sub‑zero) individuals in such a state can be rescued and returned to life even after several hours, provided proper resuscitation measures are applied. The potential human ability to remain in a physiologically inactive state has inspired proposals to place astronauts in such states during long‑duration space flights. While not dismissing the idea outright, it must be noted that it currently remains in the realm of pure speculation. In the West, a service called cryonics offers post‑mortem freezing of wealthy clients. Immediately after death, the body is subjected to deep cooling and immersed in liquid nitrogen (–196 °C).{ "translated_text": "Then it is placed in a Dewar vessel (simply—a thermos), where it is stored in nitrogen, replenishing fresh nitrogen to replace the evaporated portion. Usually this activity is performed on a percentage of the capital that the frozen client left with the firm responsible for storing his body. The bodies of clients fossilized by cold are kept in special storage units in a vertical position upside‑down, so that in case of a drop in nitrogen level the feet, not the head, would be damaged. It is to be taken on faith that when in the future people learn to treat the diseases from which the frozen clients of such firms died, they will thaw their bodies, cure the consequences of the fatal diseases and provide an opportunity for a new life in a happy future. Not to mention that forecasting the capabilities and actions of our descendants is extremely difficult; apparently, the freezing technology used in such firms leads to irreversible destruction of the cells of people whose fear of death manifested in such a strange form.\nFinally, dormant stages of the life cycle can help survive unfavorable periods. These include cysts of protozoa, spores of bacteria, fungi and some plants, plant seeds, dormant animal eggs and much more. In addition to surviving adverse conditions, dormant stages can perform other functions, for example, dispersal. For instance, dormant eggs of shield‑tails (crustaceans of the order Listronogues, which, among other things, include the more widely known daphnia) serve both for surviving the dry season and for distribution by wind‑carried dust.\nFor many plants it is characteristic that when favorable conditions arise their seeds do not germinate simultaneously, forming a dormant soil seed bank. Even if a catastrophe destroys a forest, as long as forest soil remains somewhere, the seeds of most of the populations of flowering plants that formed that forest (as well as spores characteristic of that forest’s bacterial flora—the assemblage of bacteria, and the mycobiota—the assemblage of fungi) will await the appropriate moment.\nConcluding the review of detailed examples, we note that the ability of organisms to endure unfavorable conditions is extremely important for maintaining the state of the biosphere that we observe.\nAdditional materials:\nColumn: On skin colour: a discussion of a human adaptation with justification of far‑reaching conclusions about the specificity of ecological factor action\nColumn: And also on skin colour: why we are white and why we tan\n\n5.22. Main habitats and their features\n\nD. Shabanov, M. Kravchenko. Ecology: biology of interaction\nChapter 5. Autecology and fundamentals of environmental science\n\n5.24. Life forms of organisms" }

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{ "title": "D. Shabanov, M. Kravchenko. Ecology: Biology of Interaction", "summary": "", "body": "Chapter 5. Autecology and Fundamentals of Environmental Science
\n5.24. Life Forms of Organisms
\nBATRIMG1>BATR BATRIMG2>BATR" } { "title": "5.24. Life Forms of Organisms", "summary": "The concept of life forms in biology and ecology", "body": "The diversity of living organisms on Earth is manifested in various life forms or biological forms. A life form is an external morphological feature of an organism that allows it to adapt to certain environmental conditions. BATR Different life forms can be observed within the same species, for example, in Pelophylax esculentus, or between different species, such as in Anura and Chondrichthyes. The classification of life forms helps to better understand the ecological strategies of organisms and their adaptations to different ecosystems." }

Concluding the review of detailed examples, we note that the ability of organisms to withstand unfavorable conditions is extremely important for maintaining the state of the biosphere observed by us.

Additional materials: Column: About skin color: experience of discussing one human adaptation with justification of far-reaching conclusions about the specifics of ecological factors' action Column: And about skin color again: why we are white and why we tan

5.22. Main habitats and their characteristics

D. Shabanov, M. Kravchenko. Ekolohiia: biolohiia vzaiemodii
Rozdil 5. Avtoekolohiia ta osnovy seredoviedinnia

5.24. Life forms of organisms