Historical Biogeography

The historical perspective in zoogeography provides insights into the origins of species and faunas and their changes through time relative to geologic events (Fittkau et al. 1969). Insects make excellent material for such studies because of the very long history of many taxa and the variety of types available to test hypotheses of all kinds (Gressitt 1974, Munroe 1965). A group may be found which will fulfill almost any given set of conditions for any geologic period. For example, upland, sedentary types with limited vagility (such as narrowly adapted, torrenticolous Diptera) are particularly useful for tracing past mountainous land connections as far back as the late Paleozoic.

The existence of two, contrasting means of population disruption, that is, dispersal to isolated areas versus frag-mention in place, is the basis for the "dispersalist" and "vicariance" schools of biogeographic thought (Ferris 1980) to explain the speciation process in evolving organisms. Actually, both mechanisms may cause the branching of phyletic lines and are part of a modern, unified theory of biogeography (Pielou 1979, Brown and Gibson 1983).

Because insects have been on earth for a very long time, at least since the middle of the Paleozoic era, continental connections and disjunctions (tectonics) (Dietz and Holden 1970, Marvin 1973, Smith et al. 1981) are major vicariant events that have affected their evolution and dispersal (Car-bonell 1977: 155-161). In Latin America, the tectonic development of the Caribbean and isthmian regions seems to be much more complicated (Bonini et al. 1984, Durham 1985, Rosen 1985) than that of the South American portions (Jenks 1956, Harrington 1962) with consequent problems in explaining the origins of organisms there (Liebherr 1988, Woods 1989).

The origin of many groups on Gond-wanaland, the great southern continent that was composed of what is now South America, Africa, Antarctica, Australia, and India, is still evident in the restricted occurrences of their descendants in those areas and in the southernmost portions of South America today (e.g., water midges [Brun-din 1966, 1967]; see Keast 1973 for other insect examples of these so-called amphinotic or austral disjunctive distributions). Close affinities of some eastern Brazilian insects with West African species, such as among Schistocerca grasshoppers (Carbonell 1977:169), the amblypygid genus Phrynus (= Tarantula) (Quintero 1983), the psocid genera Belaphapsocus and Notiopsocus (New 1987), and the termite genus Mimeutermes (Emerson 1955), are current evidence of past union of the two continents at midlatitudes.

The formation of the Amazon Basin is a direct result of events brought into play by the break in the South America-Africa connection about 90 million years ago. According to one theory (Putzer 1984), the Amazon River system was probably continuous during the early Mesozoic with the Niger River, and the main flow was westward to the Pacific Ocean. But with the relatively recent (Miocene) uplift of the Andes, the flow was dammed and an enormous lake formed at their foot. As the plates separated, the western portion of the river reversed its flow and came to empty into the Atlantic. An extensive coastal plain was also created along the west side of the Cordillera from ejection of volcanic material and pluvial outwash. These vast physiographic changes have created a mixed heritage for the basin's present-day insect populations. Some are derived from the Old World, others are derived from highlands to the south and north, and still others have evolved in situ after long periods of isolation by river and climatic barriers. This variety of causes is one reason for the basin's incredible species richness.

On a much more limited scale, local natural disasters, such as volcanic eruptions and hurricanes, take a toll on insect life and may actually cause the extinction of small populations or even very regional species and constitute vicariant events, although such consequences have yet to be documented, especially those of low-density forest species (Elton 1975). Changes in the course of rivers, an especially common occurrence in meandering lowland drainages, such as the Amazon, can break up continuous populations and halt gene flow sufficiently to create new entities.

Dispersalist examples of the effects of geology on the history of insect life come from the oceanic islands scattered on the

Survival Treasure

Survival Treasure

This is a collection of 3 guides all about survival. Within this collection you find the following titles: Outdoor Survival Skills, Survival Basics and The Wilderness Survival Guide.

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