Behavioral Studies Develop through Animal Observation and Experimentation

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Behavioral Studies Develop through Animal Observation and Experimentation

Overview

Early in the twentieth century, scientists became interested not only in discovering new organisms, but in understanding more about the behavior of known organisms. A group of biologists took special note of social behavior, and learned about the amazingly complex organizations of a wide range of animals from protozoa to bees, and ants to birds. One of the best-known behaviorists of the period was Karl von Frisch (1886-1982), who established how honey bees communicate with one another about the location of a food source. That study has become a staple in biology and behavior textbooks. Other major researchers who made important contributions to the study of animal behavior during this time included Warder Allee (1885-1955), Herbert S. Jennings (1868-1947), Nikolaas Tinbergen (1907-1988), Konrad Lorenz (1903-1989), and William Morton Wheeler (1865-1937).

Background

One of the most famous examples of the research on social behavior during this or any period came from Karl von Frisch, a zoologist from Vienna, and his study of honey bees. Originally, he was interested in how bees detected color and odors, but he soon turned his attention to the method by which a few scout bees were able to inform the hive of a newly found flower patch or other food source, and then give accurate directions to it. Frisch set out in the early 1920s to discover how this communication system worked. At first, he believed that the scout bees were informing the other foragers about the availability of a food source by carrying the food scent back to the hive. The others, then, simply sought out the source of the scent. It was only through additional experiments he conducted nearly two decades later that he discovered a more elaborate communication system involving so-called dances that conferred precise directions to the food.

At the turn of the century, American naturalist Herbert Jennings was studying protozoa, a group of single-celled microorganisms. In some of his most well-known behavioral work, he used heat, light, and other negative stimuli to demonstrate how protozoans respond to environmental changes. In his often-cited 1904 publication, "Contributions to the Study of the Behavior of Lower Organisms," he described how different protozoans respond to stimuli. In this work, he refuted the commonly held "theory of tropisms," which stated that the stimuli affected specific motor organs within an individual organism, and that the responses of those motor organs caused the organism to move away from the negative stimuli. Instead, he reported, "The responses to stimuli are usually reactions of the organisms as wholes, brought about by some physiological change produced by the stimulus; they cannot, on account of the way in which they take place, be interpreted as due to the direct effect of stimuli on the motor organs acting more or less independently. The organism reacts as a unit, not as the sum of a number of independently reacting organs."

Nikolaas Tinbergen's work with the fish called three-spined sticklebacks is another standard in animal-behavior textbooks. This researcher from the Netherlands found a stimulus-response pattern in which females give males cues, and vice versa, and ultimately generate a progressive series of courtship activities. He also found that male-to-male attacks were triggered by the color red. Using artificial models, he showed that the males would attack models as long as they had a red underside. He verified the importance of the color red by offering males different fish models, some of which closely resembled fish and others that looked little like fish.. The males preferentially attacked even the crudely made red-bellied models over much more accurate models that lacked the red bellies. The red, he concluded, was the stimulus—or the "releaser"—that triggers the attack behavior.

William Morton Wheeler, an American entomologist, did his behavioral research primarily on ants and other insects. In his studies, he detailed the complex social structure and division of labor within ants and within bees. Noting how well these groups of invertebrates worked together as a unit, he described the ant or bee colony as a superorganism made up of individuals playing their roles for the benefit of the overall colony.

Warder Allee and T. Schjelderup-Ebbe were the primary researchers in the area of dominance hierarchies, which include the so-called pecking order in animal societies. In such hierarchies, several patterns can emerge. The animals can arrange themselves in a linear fashion so that one member of the group is the most dominant, followed by the second-most dominant, the third-most dominant, and so on, with all those ranking lower in subordinate positions. More complex hierarchies also develop, with patterns where individual A is dominant over B, B over C, yet C over A. These hierarchies affect behavior in a number of ways. Once the hierarchies are formed, for instance, they are relatively firm, eliminating the need for constant infighting to determine dominance.

Allee's contributions to animal behavior extended well beyond his work on dominance, however. He also studied how loose associations between animals were important to their survival. In studies of planarian flatworms and goldfish, for example, he showed that these animals prefer to form aggregations in adverse environmental conditions and actually gain protective benefits from the associations. In perhaps his most important work, Allee summarized much of the known research on societal behavior among animals in his 1951 book Cooperation among Animals.

Impact

The experiments that led Frisch to discover the communication system of honey bees have often been cited as excellent examples of solid behavioral research. In these experiments, he set out a tray of scented food for the scout bees. When the scout found the food and returned to the hive, Frisch quickly set out another tray of the same food, but placed it nearer the hive. If the bees communicated by scent, he reasoned, the other foragers should leave the hive, pick up the stronger food scent, and go to the nearest food tray. Instead, he found that they went to the tray that the scout visited.

Next, he went to the hive to see what communication was occurring there. Using a glass-sided hive, he was able to watch the scout when it returned from the planted food to the hive. Frisch observed the scout engaging in either a "round dance" or a "waggle dance." Through a series of experiments, the researcher was able to determine that the round dance, in which the scout bee traces an approximate circle on a wall of the honey comb, told the other bees to search for food within about 164 feet (50 m) of the hive. As Frisch moved the food sources farther from the hive, the scout performed a more elaborate "waggle" dance. In this dance, the scout walked a figure-eight pattern on the vertical wall of the honeycomb, waggling its body when it reached the middle of the pattern. Frisch deduced that the waggle portion of the dance gave other bees the direction of the food source: a vertical dance meant the food source was located directly toward the sun, 20 degrees to the right of vertical meant the food source was 20 degrees to the right of the sun, and so on. He also learned that a faster dance related that the food was farther away. He described his bee studies in his 1967 book The Language and Orientation of Bees.

When Frisch's findings first became known, they were met with incredulity. Skeptics felt the lowly bee certainly could not have the capacity to engage in such a complicated communication system: Symbolic language was a human characteristic that surely was not shared by insects. Scientists also challenged his experimental design and his results. Despite the initial furor, numerous scientific studies have since confirmed Frisch's findings and conclusions, and opened the door to the realization that complex social behavior, including communication, extends well beyond humans.

Jennings and Wheeler's investigations of protozoans and insects, respectively, provided added evidence that a wide variety of organisms exhibit sometimes elaborate behaviors. Wheeler's work particularly expanded the current understanding of complex social structures. Tinbergen's work on releasers, and his collaborations with Austrian zoologist Konrad Lorenz, helped to develop a theoretical framework for the newly emerging field of ethology, or the systematic study of the function and evolution of behavior. In 1973, Tinbergen, Lorenz, and Frisch shared a Nobel Prize for their contributions to the study of animal behavior.

Through Allee's research, and particularly his book Cooperation among Animals, this researcher had a profound impact on the study of societal behavior. He investigated dominance and competition, as well as altruism and cooperation, and delineated social behaviors into several categories. These categories included the colonial behavior of some invertebrates, such as coelenterates; aggregations, like those he demonstrated with flatworms and goldfish; orientation to stimuli, as seen in the work by Jennings with protozoans; and the more complex social behaviors of some animals, like honey bees and chickens.

These researchers were only a few of the many scientists who helped promote the study of animal social behavior during the first half of the century, and helped to define animal behavior or ethology as a separate field of research.

LESLIE A. MERTZ