The Cold-Blooded Vertebrates PDF

The Cold- Blooded Vertebrates Dr. Jazi alenezi  The Cold-Blooded Vertebrates ▪ The fishes, amphibians, and reptiles are sophisticated in some of the elements of social organization but not in the ways the elements are assembled. ▪ In territor...

The Cold- Blooded Vertebrates Dr. Jazi alenezi  The Cold-Blooded Vertebrates ▪ The fishes, amphibians, and reptiles are sophisticated in some of the elements of social organization but not in the ways the elements are assembled. ▪ In territoriality, courtship, and parental care, these cold- blooded vertebrates are the equal of mammals and birds, and various of their species have served as key paradigms in field and laboratory investigations.  The Cold-Blooded Vertebrates But for some reason, possibly lack of intelligence, they have not evolved cooperative nursery groups of the kind that constitute the building blocks of mammalian societies. For other reasons, possibly the lack of haplodiploid sex determination or the presence of the right ecological imperatives , they have not become altruistic enough to generate insect-like societies.  Fish Schools In 1927 Albert E. Parr published an article that opened the subject of schooling to objective biological research. Rejecting vague earlier notions of a "social instinct," he postulated that fish schools result from the balance struck between the programmed mutual attraction and repulsion of individual fish based on the visual perception of one another. Species differ in the degree to which they are committed to schooling and in the form of the groupings.  Fish Schools Parr identified schooling by implication as an adaptive biological phenomenon, to be analyzed like any other at both the physiological and the evolutionary level. The past 50 years have seen the accumulation of a very large amount of information on the behavioral basis of schooling and its ecological significance that confirms the validity of Parr's approach. The best recent reviews are those of Shaw (1970), who covers the large English and German literature well, and Radakov (1973) , who deals with the equally large Russian literature. A fish school, to cite Radakov, is "a temporary group of individuals, usually of the same species, all or most of which are in the same phase of the life cycle, actively maintain mutual contact, and manifest, or may manifest at any moment, organized actions which are as a rule biologically useful for all the members of the group. “  Fish Schools A t a distance a fish school resembles a large organism. Its members, numbering anywhere from two or three into the millions, swim in tight formations, wheeling and reversing in near unison. Either dominance systems do not exist or they are so weak as to have little or no influence on the dynamics of the school as a whole. There is, moreover, no consistent leadership. When the school turns to the right or left, individuals formerly on the flank assume the lead.  Fish Schools Why do fishes school in the first place? They are obviously able to do so only when they are not bound to a permanent territory. Species that spend part or all of their lives feeding in open water, moving opportunistically from one site to another, are the ones with the potential to evolve schooling behavior.  Fish Schools What is the advantages of fish schooling? 1. Protection from predators: The strongest and most distinctive changes in schooling behavior occur when the fish are confronted by a predator. 2. Improved feeding ability: In theory at least, individual members of the school can profit from the discoveries and previous experience of all other members of the school during the search for food. This advantage can become decisive, outweighing the disadvantages of competition for food items, whenever the resource is unpredictably distributed in patches.  Fish Schools 3. Energy conservation : Schooling fish can ride the edges of vortices made by other school members in front of them, thus utilizing energy that would otherwise be lost while conserving their own. It is also possible that heat is retained by the crowding, an important consideration for cold-water species. 4. Reproductive facilitation: Membership in schools almost certainly makes it easier for individuals to find mates or to spawn near others.  The Social Behavior of Reptiles The behavior of reptiles has been poorly explored in comparison with that of birds and mammals, largely because reptilian behavior tends to be reduced markedly in captivity. Yet a picture of reptilian social life is beginning to emerge that indicates considerable diversity among species, with a few flashes of sophistication. The average complexity of social behavior is probably below that of the birds and mammals.  The Social Iguanidae Agamidae Behavior of Reptiles Home range and territoriality: Most members of the families Agamidae, Chamaeleontidae, Gekkonidae, and Iguanidae sit and wait for their prey, often in Chamaeleontidae exposed situations, and they rely Gekkonidae heavily on optical cues. They also tend to be territorial, watching their domain constantly and warning off invaders of the same species with visual signals.  The Social Behavior of Reptiles Lacertidae Varanidae In contrast, members of the Lacertidae, Scincidae, Teiidae, and Varanidae typically search for their food Scincidae Teiidae in places where vision is obstructed.  The Social Behavior of Reptiles Most reptilian dominance systems appear to be little more than transmuted forms of territorial hegemony, with a tyrant permitting a few subordinates to exist within his domain. The subordinates themselves are seldom organized. One exception exists in Anolis aeneus. Multiple females live within the territories of single males and are themselves arrayed into hierarchies consisting of at least three levels (Stamps, 1973 ). The Social Behavior of Reptiles Parental care is generally poorly developed in reptiles. It has been observed in both wild and captive king cobras (Ophiophagus hannah ) by Oliver (1956). The females build nests and defend them against all intruders-making these large snakes especially dangerous to man. Since snakes are otherwise the least social of all the reptiles, this unique behavior pattern is quite remarkable and makes the king cobra one of the most promising reptile species for future field investigations.  The Social Behavior of Reptiles It may also be surprising to learn that the most advanced forms of parental care are practiced by the crocodilians - the alligators, crocodiles, caimans, and related forms. The females of all of the 21 living species lay their eggs in nests and defend them against intruders (Greer, 1971). The more primitive behavior is hole nesting, employed by the gharial and 7 species of crocodiles.  The Social Behavior of Reptiles The remaining crocodilians, including alligators, caimans, the tomistoma, and the other crocodile species, build mound nests of leaves, sticks, and other debris. The mounds serve to raise the eggs above rising water, and they probably also generate extra heat by decomposition.  The Social Behavior of Reptiles Just before they hatch, the young emit high-pitched croaks, particularly when disturbed by nearby movements. The response of the mother is to start tearing material off the top of the nest. Her assistance is essential for the escape of the young in many cases, since the outer shell of the nest is baked into a hard crust by the sun after the eggs are buried. In some species at least, the mother also leads the young to the edge of the water and protects them for varying periods afterward.