Comparison of Hearing Organs Jawless fishes: These primitive vertebrates have only two semicircular canals within the inner ear. In jawless fishes, the structures of the inner ear are more associated with equilibrium than hearing. Gnathostome fishes: All fishes possess membranous labyrinths embedded in the auditory region of the skull. The labyrinths consist of the utriculus and sacculus and three semicircular canals. The inner ear serves primarily as an organ of equilibrium in fishes, but a few species have developed an accessory function of detecting sound transmissions. Amphibians: The hearing organ of amphibians is considerably advanced over that of the fishes. In frogs and toads, the outer ear consists of a tympanic membrane in the adults that lies flat on the head. The middle ear is an air-filled chamber with a small movable bone. The inner ear consists of a utriculus, a sacculus, a lagena, and three semicircular canals filled with endolymph and perilymph. The hair cells are located at the base of each canal. Reptiles and birds: Hearing is well developed in reptiles and especially birds. There is a tympanic membrane, a well-developed middle ear, and a straight-tubed cochlea and spiral organ. Some birds can hear ultralow frequencies that may be important in navigating. Mammals: The membranous labyrinth and the sense of hearing are highly developed in mammals. Mammal ears consist of all of the components discussed in the text. Mammals are keenly adapted to hearing. Humans can hear in a range of sixteen to twenty thousand hertz, but bats can detect frequencies up to one hundred thousand hertz.
Territoriality in the Field Territoriality is typically investigated in the field using an observational approach. Initial information collected includes assessing the amount of area used by each individual, how much of that area is defended from conspecifics, and exactly what is being defended. It is relatively easy to discern the spatial utilization of animals. For many species, all that is required is capturing each individual, marking it for field identification, and watching its movements. For species that range long distances, such as hawks or large mammals, and species that are nocturnal, radio telemetry is frequently used. This methodology requires putting radio transmitters on the individuals to be followed and using hand-held antennas, or antennas attached to cars or airplanes, to monitor movements. For fossorial species (animals that are adapted for digging), animal movements are often determined by repeated trapping. This method involves placing numerous baited live traps above the ground in a predetermined grid. Knowing the spatial utilization of an animal does not document territoriality. Many types of animals repeatedly use the same regions in the habitat but do not defend these areas from conspecifics. Such "home ranges" may or may not contain areas that are defended (that is, territories). Territorial defense can be readily documented for some animals by simply observing individual interactions. These data often need to be supplemented by experiments. Behavioral interactions might only occur in part of the organism's living space because neighbors do not surround it. For these individuals, researchers play taperecorded territorial vocalizations or place taxidermy mounts of conspecifics in different locations and note the response of the territory holder. For other species, such as fossorial rodents, direct estimates of territory size cannot be obtained because aggressive interactions cannot be observed; as a result, territory boundaries must be inferred fromtrapping information. Regions in which only the same individual is repeatedly trapped are likely to be areas that the individual defends. This is an indirect method, however, and can be likened to watching the shadow of an organism and guessing what it is doing. It is often difficult to determine exactly what an animal is defending in an all-purpose territory where organisms use many different types of resources. Which resource, that is, constitutes the "reason" for territorial defense? On the other hand, several resources may contribute in some complex way. For many species these things simply are not known. This uncertainty also complicates estimates of territory quality. For example, red-winged blackbirds in North America have been particularly well studied for several decades by different investigators in various parts of the species range. Males defend areas in marshes (or sometimes fields), and some males obtain significantly more mates than others. Biologists think that males defend resources that are crucial for female reproduction. Some males may be more successful at mating than others because of variation in territory quality.Yet the large number of studies done on this species has not yielded a consensus on what the important resources are, whether food, nest sites, or something else. Theoretical investigations of territorial behavior often employ optimality theory and game theory approaches. Optimality theory considers the benefits and costs of territorial defense for an individual. Benefits and costs might be measured simply as the number of calories gained and lost, respectively. Alternatively, benefits might be measured as the number of young produced during any one season; costs might be measured as the reduction in number of future young attributable to current energy expenditures and risks of injury. For territorial behavior to evolve by means of natural selection, the benefits of territorial behavior to the individual must exceed its costs. Game theory analyses compare the relative success of individuals using alternative behaviors (or "strategies"). For example, two opposing strategies might be "defend resources from intruders" and "steal resources as they are encountered." In the simplest case, if some individuals only defend and other individuals only steal resources, the question would be which type of individual would leave the most offspring. Yet defenders interact with other defenders as well as with thieves, and the converse holds for thieves. By considering the results of interactions within and between these two types of individuals, a game theory analysis can predict the conditions under which one strategy would "win" or "lose" and how the success of each type of individual would vary as the frequency of the other increases in the population. A complete understanding of territoriality involves not only empirical approaches in the field but also the development of testable theoretical models. Considerable advances have been made recently merging these two methodologies. Future investigations will no doubt include experimental control over resource levels that will allow definitive tests of predictions of alternative theoretical models.
