Chordate Zoology - textbook - Y. V. Tsaryk - 2013

Chapter 5. SUPERCLASS TETRAPODS (LAND VERTEBRATES) TETRAPODA, seu QUADRIPEDA.

ANAMNIOTES (ANAMNIA) AND AMNIOTES (AMNIOTA)

5.4. CLASS MAMMALS, OR BEASTS, MAMMALIA, seu THERIA

5.4.2. Behavior and Lifestyle

5.4.2.1. Population Organization and Lifestyle

The Increasing complexity of intraspecific relationships is accompanied by The formation of temporary or stable groupings of individuals based on communication and behavioral coordination. This gave rise to the ethological Structure of populations, which corresponds to the species' lifestyle and reproductive strategy. Mammals that live in burrows or use permanent shelters usually lead a solitary or family lifestyle, occupy specific home ranges, and defend them against intruders (many mouse-like rodents, shrews, and canids). The advantage of such behavior lies in reducing competition for food and shelter, and in a relatively even utilization of the territory. Large, mobile animals, especially ungulates, form nomadic herds or packs. Nomadic movements reduce the risk of depleting pastures, while grouping increases protection against canids. In cetaceans and seals, grouping enhances The ability to locate food concentrations.

An intermediate position between solitary and herd lifestyles is occupied by colonial settlements of mouse-like rodents (marmots, ground squirrels, etc.) or lagomorphs (pikas). They live in areas with abundant food, which provides better opportunities for detecting canids as well as birds. Under conditions of close coexistence and constant communication among neighbors, these animals maintain their individual or family territories within the settlement. Other species that lead a solitary lifestyle are also frequently attracted to settle here by the favorable conditions (food, shelter) of such colonies.

In animal groups with a nomadic lifestyle and in settlements of species leading a solitary or family lifestyle, subgroups of individuals form that maintain more frequent contact and often act together. Such parcel groups, large families, or clans, ensure more effective reproduction while organizing food utilization and facilitating the creation of shelters, refuges, and trails in their habitats. Contacts and frequent interactions among animals in such groups provide a broader basis for raising the young and enriching them with the experience of previous generations. Population structure emerges through animal communication, reflecting their species-specific and individual characteristics. The foundation of population structure is the ranking of individuals, which reflects the different status of individuals in a group: dominant, subdominants, and subordinates. The rank system in a population is usually complex and always dynamic. In mammals, especially herd-dwelling ones, it becomes exceptionally complex. Circular systems of subordination occur, and there are parallel, non-overlapping systems of subordination that serve different aspects of the group's life (Fig. 5.73).

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Fig. 5.73. Ranking (subordination) systems in different population groups.

Letters indicate individual specimens, numbers indicate the number of dominance cases

The acquired position in a group is usually related to hereditary traits, the individual's condition, and its experience. A dominant individual loses its rank due to a mistake, illness, or the appearance of a stronger rival. This flexibility of the rank system ensures high adaptability of the group to changing environmental conditions. Ranking is usually accompanied by clashes between contenders, which are particularly fierce in herd animals that form harems during the breeding season. Emotionally intense male duels during this period could often be fatal to the rivals if, in the course of natural Selection, the weapons of attack had not acquired a ritualized, relatively safe nature, or if protective adaptations had not evolved, such as the shield (kalkan) of wild boars—a thick, resilient Connective Tissue and fat pad on the shoulders that protects against the opponent's tusks.

In some groups, a division of labor is observed. For example, in lion prides, males primarily defend hunting territories from the intrusion of outsiders (members of neighboring prides), while females hunt for food and care for the young. In wolf packs (large families), when attacking large prey, some members pursue it, while others try to cut off its path or ambush it.

The complex intrapopulation structure alters the action of natural selection: alongside individual selection, group selection of better-organized groups also occurs. A population divided into parcel groups does not lose its integrity, which is maintained by a general system of intrapopulation connections (chemical, visual, acoustic), and the creation of shared burrows, trails, nests, etc. Within the territory occupied by the population, a signaling field emerges, linking the parcels into a single population. Studying signaling systems and signaling fields is of practical importance, as it opens up possibilities for managing the distribution, Abundance, and behavior of beneficial and pest wild animals through the technical reproduction of signals or their systems. Individual exchange occurs between populations, primarily during juvenile dispersal. As young animals mature, their physiological state changes (the level and Variability of their METABOLISM increase, and nervous excitability rises). During this period, they leave their familiar territory in search of mates and new habitats. As tagging studies have shown, during dispersal, juveniles usually make non-directional movements that exceed the mobility of adults by tens or hundreds of times.

Biological (annual) cycles vary among mammals with different lifestyles. The timing of birth always coincides with the most favorable period for their GROWTH AND DEVELOPMENT, in most cases in spring or early summer. The mating season is determined by the duration of Pregnancy (sometimes extended by embryonic diapause) and can occur in different seasons: in spring (in mouse-like rodents and shrews), in winter (in canids), in autumn (in cervids), in summer (in martens), or immediately after giving birth (in seals). In mammals with several litters per year (small mouse-like rodents), breeding can continue year-round under favorable conditions (mice, voles, lemmings).

Once the young grow up, in animals with a solitary lifestyle, families break up and juvenile dispersal occurs. In herd-dwelling species, the young either stay with the females or form separate groups. In autumn, mammals prepare for wintering; during this time, animals accumulate fat reserves, molt from summer to winter coats, and some species store food for the winter. Simultaneously, a restructuring of the population Organization takes place; before winter, small groups of animals often merge into larger ones. In the burrows of mouse-like rodents (mice, voles), which live in separate families during summer, up to 20-30 animals have been found sharing a single shelter. Many ungulates gather into large herds before winter, which facilitates migration and survival in feeding areas. Grouping allows predators (wolves, etc.) to hunt large prey. Only small carnivores (mustelids), winter-active shrews, some mouse-like rodents, and hares continue their solitary existence.

Many mammals undergo hibernation or winter torpor, but The Nature of these phenomena varies across different orders. Hibernation does not occur in cervids, seals, and cetaceans, which are characterized by nomadic lifestyles. In squirrels, activity merely decreases during severe winter cold spells. In some caniforms (bears, badgers, etc.), winter Sleep manifests as a suppression of locomotor activity, while a High Metabolic Rate and body Temperature are maintained. A deeper sleep is characteristic of some mouse-like rodents (hamsters) and bats. True hibernation with complete torpor and a sharp drop in body temperature is characteristic of some insectivores, terrestrial sciurids (marmots and ground squirrels), dormice, and jerboas. It is typical not only for the winter period but also for summer droughts.

Migrations are characteristic of a wide range of mammals. Caniforms change their habitats in different seasons in search of prey, moving over relatively short distances. Limited seasonal movements are made by many mouse-like rodents. Significant migrations are characteristic of most herd species. Some ungulates (reindeer), seals, and cetaceans, as well as some bats, migrate over hundreds or even thousands of kilometers. Seasonal migrations, like bird migrations, are repeated annually and follow specific migration routes. Seasonal migrations should be distinguished from juvenile dispersal, which in years of population booms often takes the form of mass emigration. Such are primarily the migrations of squirrels and the invasions of lemmings; during such seasonal movements, Arctic foxes penetrate into the southern taiga.