The examination of the ecology of interacting plants and animals by using an evolutionary, holistic perspective. For example, the chemistry of defensive compounds of a plant species may have been altered by natural-selection pressures resulting from the long-term impacts of herbivores. Also, the physiology of modern herbivores may be modified from that of thousands of years ago as
|Interaction||Effect on species A||Effect on species B|
|*+ = beneficial, - = harmful, 0 = neutral.|
noindent adaptations for the detoxification or avoidance of plant defensive chemicals have arisen.
The application of the theories based on an understanding of plant-animal interactions provides an understanding of problems in modern agricultural ecosystems. In addition, plant-animal interactions have practical applications in medicine. For example, a number of plant chemicals, such as digitalin from the foxglove plant, that evolved as herbivore-defensive compounds have useful therapeutic effects on humans.
The evolutionary consequences of plant-animal interactions vary, depending on the effects on each participant. Interaction types range from mutualisms, that is, relationships which are beneficial to both participating species, to antagonisms, in which the interaction benefits only one of the participating species and negatively impacts the other. Interaction types are defined on the basis of whether the impacts of the interaction are beneficial, harmful, or neutral for each interacting species (see table).
Plants and animals interact in a variety of ways within modern ecosystems. These interactions may range from simple examples of herbivory (animals eating plants) to more complex interactions such as pollination or seed and fruit dispersal. Animals also rely on plants for food and shelter. The complex interactions between these organisms over geologic time not only have resulted in an abundance and diversity of organisms in time and space but also have contributed to many of the evolutionary adaptations found in the biological world.
Paleobiologists have attempted to decipher some of the interrelationships that existed between plants and animals throughout geologic time. The ecological setting in which the organisms lived in the geologic past is being analyzed in association with the fossils. Thus, as paleobiologists have increased their understanding of certain fossil organisms, it has become possible to consider some aspects of the ecosystems in which they lived, and in turn, how various types of organisms interacted.
Perhaps the most widespread interaction between plants and animals is herbivory, in which plants are utilized as food. One method of determining the extent of herbivory in the fossil record is by analyzing the plant material that has passed through the digestive gut of the herbivore.
The stems of some fossil plants show tissue disruption similar to various types of wounds occurring in plant parts that have been pierced by animal feeding structures. As plants developed defense systems in the form of fibrous layers covering inner, succulent tissues, some animals evolved piercing mouthparts that allowed them to penetrate these thick-walled layers. In some fossil plants, it is also possible to see evidence of wound tissue that has grown over these penetration sites. See Herbivory
Another example of the interactions between plants and animals that can be determined from the fossil record is mimicry. Certain fossil insects have wings that are morphologically identical to plant leaves, thus providing camouflage from predators as the insect rested on a seed fern frond.
The transfer of pollen from the pollen sacs to the receptive stigma in angiosperms or to the seed in gymnosperms is an example of an ancient interaction between plants and animals. It has been suggested that pollination in some groups initially occurred as a result of indiscriminate foraging behavior by certain animals, and later evolved specifically as a method to effect pollination. The size, shape, and organization of fossil pollen grains provide insight into potential pollination vectors. See Pollination