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

5.4.2.3. Position of Mammals in Biocenoses

Inhabiting virtually the entire Earth, mammals occupy ecological niches in terrestrial and marine biocenoses as both primary consumers of plant food (muroid rodents, lagomorphs, ungulates, proboscideans, sirenians, sloths, hyraxes, and a significant portion of primates) and carnivores, which are typically divided into non-aggressive species (insectivores, planktivores) that feed on small animals, and predators that hunt large, active prey. The former group includes shrew-like mammals, bats (excluding nectar-feeders and frugivorous fruit bats), xenarthrans, aardvarks, and baleen whales; the latter includes toothed whales, seals, and caniforms. Omnivory occurs among muroid rodents, caniforms, and primates. Occupying the upper tiers of food chains, mammals, like birds and insects, influence plant evolution. Examples include the color, shape, and taste of fruits, as well as the scent of flowers that attract animals with highly developed Sensory Organs, alongside The Development of thorns and The Emergence of Alkaloids that reduce herbivory. There are also adaptations for attaching seeds and spores to animal dispersers.

The stability of biogeocenoses is closely linked to mammalian activity. The extinction or eradication of burrowing muroid rodents (voles, gerbils) in deserts and steppes is accompanied by the overgrowth of certain plant species (perennial, turf grasses) and the elimination or reduction of dicotyledonous or monocotyledonous ephemerals, which depletes and sometimes devastates pastures. Moderate grazing by ungulates helps maintain high productivity of pasture herbage, whereas the exclusion of grazing, as well as overgrazing, leads to the degradation of steppe vegetation cover. All this points to the close relationships between plants and animals in biogeocenoses. In terms of Abundance and biomass among aquatic vertebrates, mammals are second to fish, but on land, they usually hold first place. During years of population booms, small mammals, especially voles and mice, can reach densities of 100-200 individuals per 1 ha, and in aggregations, their numbers can rise to 1-5 per 1 m². During population crashes, they survive only in refugia, occupying just 1-10% of the suitable area with a density of less than 10-15 individuals per 1 ha. Large ungulates and seals also form massive aggregations in restricted areas during Migrations or at breeding sites. The rest of the time, they stay in small groups of 1-5 individuals per 1 000 ha. The population density of large carnivorans (felids, canids) under favorable conditions does not exceed 1-3 per 1 000 ha. Small carnivorans (mustelids) have a 2-3 times higher density.