Symbiosis Understanding the ways in which different species of animals interact in nature is one of the fundamental goals of biology. Predator-prey relationships, competition between species for limited resources, and symbiosis are the major forms of species interactions, and these have profoundly influenced the diversity and ecology of all forms of life. Significant advances have been made in understanding how organisms interact, but in studies of symbiosis (which literally means "living together") one finds the most complex, interesting, and important examples of both cooperation and exploitationknownin the living world. Symbiosis involves many types of dependent or interdependent associations between species. In contrast to predator-prey interactions, however, symbioses are seldom rapidly fatal to either of the associating species (symbiotes) and are often of long duration. With the exception of grazing animals that do not often entirely consume or destroy their plant "prey," most predators quickly kill and consume their prey. While a predator may share its prey with other individuals of the same species (clearly an example of "living together"), such intraspecific behavior is not considered to be a type of symbiosis. Fleas, some ticks, mites, mosquitoes, and other bloodsucking flies are viewed as micropredators rather than parasites. All organisms are involved in some form of competition. The abundance and availability of environmental resources are finite, and competition for resources occurs both between members of the same species and between individuals and populations of different species. When the number of individuals in a population increases, the intensity of competition for limited food, water, shelter, space, and other resources necessary for survival and reproduction also increases. Thus, competition plays a major role in populations of free-living animals (those not inhabiting the body of other organisms) and in populations living on or in other animals. For example, both tapeworms and whales must compete for resources, and both have evolved habitat-specific adaptations to accomplish this goal. Whales compete with whales, fishes, and other predators for food; tapeworms compete with tapeworms and other symbiotes (such as roundworms) for food and space; and tapeworms and whales compete with each other for food in the whale's gut. "Symbiosis" is a term used to describe nonaccidental, nonpredatory associations between species. When used by itself, the term "symbiosis" does not provide information on how or why species live together, or the biological consequences of their interactions. Recognizably different forms of symbioses all have one or more characteristics in common. All involve "living together"; most involve food sharing; many involve shelter; and some involve damage to one or both symbiotes.
Uses of Paleoecological Research Paleoecological data are applicable to other, related paleo-fields of the earth and life sciences. The study of fossils, paleontology, is enhanced by the inclusion of information about the fossil organisms' environments and relationships with other organisms. Paleontologists should attempt to reconstruct ancient environments because organisms did not exist alone or in vacuums: They lived in dynamic biological communities. Paleogeography relies heavily on paleoecological information to discern the locations, directions, and time intervals of glaciation, deposition of sediments, temperature, and other environmental variables. This information has been used to determine the past positions of continents and has been a valuable contribution to scientists' knowledge of continental drift. Paleoclimatologists, who study ancient regional and planetwide conditions, must make use of local bits of paleoecological information to see the big picture of climate. One of the major concerns of paleoclimatology is the recognition of planetary climatic cycles and associated environmental and biological cycles. If there is a repeated recurrence of global environmental change, then predictions about future climatic change become more accurate and probable.
