Climate and Medium

Each climatic factor exerts its critical effects in a variety of ways: temperature as freezing point, highs, lows, means, ranges, heat, cold, daily fluctuations; moisture as rainfall, dew, fog, clouds (and, of course, by determining the fundamental life-supporting media, aquatic versus terrestrial); sunlight as day and night, shade, illumination, radiation, and photoperiod. All act over long time periods as weather

Figure 2.1 MAJOR PHYSIOGRAPHIC AREAS OF LATIN AMERICA (from Sauer 1950 and Sick 1969). MIDDLE AMERICA: 1. Mexican Highlands; 2. Isthmian America (lowland Mexico, Central America); 3. West Indies (Greater and Lesser Antillean Islands); 4. Bahamas; SOUTH AMERICA: 5. Pacific Coastal plain; 6. Andes (including Caribbean Borderlands and Bolivian Altiplano); 7. Amazon Basin; 8. Orinoco Basin; 9. Guiana Highlands; 10. Brazilian Highlands (including Brazilian Coastal Mountains) and Mato Grosso, Plateau of Paraná; 11. Llanos de Mamoré; 12. Paraná-Paraguay Depression; 13. Gran Chaco; 14. Pampas; 15. Patagonia; INSULAR AMERICA: 16. Oceanic islands (Pacific: Galapagos and Revillagigedo Archipelagos, Cocos Island, Easter Island, Juan Fernandez etc. Atlantic: Fernando de Noronha Archipelago, Ascensión Island); 17. Continental islands (Falklands-Malvinas, Tres Marias, Isla de Coiba, Pearl Islands, Magellanic Archipelago).

Figure 2.1 MAJOR PHYSIOGRAPHIC AREAS OF LATIN AMERICA (from Sauer 1950 and Sick 1969). MIDDLE AMERICA: 1. Mexican Highlands; 2. Isthmian America (lowland Mexico, Central America); 3. West Indies (Greater and Lesser Antillean Islands); 4. Bahamas; SOUTH AMERICA: 5. Pacific Coastal plain; 6. Andes (including Caribbean Borderlands and Bolivian Altiplano); 7. Amazon Basin; 8. Orinoco Basin; 9. Guiana Highlands; 10. Brazilian Highlands (including Brazilian Coastal Mountains) and Mato Grosso, Plateau of Paraná; 11. Llanos de Mamoré; 12. Paraná-Paraguay Depression; 13. Gran Chaco; 14. Pampas; 15. Patagonia; INSULAR AMERICA: 16. Oceanic islands (Pacific: Galapagos and Revillagigedo Archipelagos, Cocos Island, Easter Island, Juan Fernandez etc. Atlantic: Fernando de Noronha Archipelago, Ascensión Island); 17. Continental islands (Falklands-Malvinas, Tres Marias, Isla de Coiba, Pearl Islands, Magellanic Archipelago).

climate, and seasonality and, of course, interact with physiography. The interplay of physical agents in the atmosphere creates a multitude of environments that are also circumscribable and can even be mapped. Many schemes have been devised to classify these directly as climatic areas (Kóppen and Geiger 1931-1934).

Major shifts in the earth's climatic pattern occur at irregular intervals, changing the rainfall, temperature, and other aspects of the weather, sometimes drastically over wide areas. In Latin America, the best-known manifestation of such planetary-scale atmospheric fluctuations is the El Niño phenomenon, itself part of the so-called, larger Southern Oscillation that involves much of the Pacific and Indian Ocean basins of the Southern Hemisphere (Philander 1990). At roughly seven- to ten-year intervals, the warm equatorial counter-current in the Panama bight shifts strongly to the south, unduly heating and displacing the normally cool, northward-flowing Humboldt Current. As a result, heavy rains come to the Peruvian coastal deserts, and vegetation flourishes (especially on the lomas; see Special Habitats, below). The effects of El Niño on coastal insect populations have been found to be significant in some cases (Beingolea 1987a, 19876). Associated weather anomalies may be felt even far inland on the continent, for example, prolonged dryness in the western Amazonian rain forest or cold snaps in sub-Andean valleys.

Brief but severe periods of cold weather fronts, originating in Antarctica, pass across the Amazon Basin in odd years, usually during early July (Días Frios de San Juan, friagern) (Ratisbona 1976: 226, 237). Daily minimum temperature may drop from a normal 20° to 8° C. The sky becomes heavily clouded, a strong wind blows, and it fails to rain.

Responses of insects to these stresses may be dramatic or subtle but are as yet virtually unstudied in Latin America. The impact of such sudden weather changes on these small, ectothermic creatures surely must be intense, especially on temperature-sensitive species. Interference with reproduction and population "die-offs" should be expected.

The effects of climate are felt most immediately in the atmosphere. They are manifest equally but more slowly in the aquatic medium, in standing (lentic) waters (ponds, lakes, etc.), in moving (lotic) waters (streams, rivers) (Fittkau 1964; Macan 1962, 1974), and in the soil (Kühnelt 1961).

References

Beingolea, O. D. 1987a. El fenómeno "El Niño" 1982—83 y algunos insectos-plaga en la costa peruana. Rev. Peruana Entomol. 28: 55-57.

Beingolea, O. D. 19876. La langosta Schislocerca interrita en la costa norte del Perú, durante 1983. Rev. Peruana Entomol. 28: 35-40. Kóppen, W., and R. Geiger. 1931-1934. Hand-buch der Klimatologie. Vols. 1 —4. Born-traeger, Berlin. Kühnelt, W. 1961. Soil biology with special reference to the animal kingdom. Faber 8c Faber, London. Fittkau, E. J. 1964. Remarks on limnology of central-Amazon rain-forest streams. Int. Verh. Limnol., Verh. 15: 1092-1096. Macan, T. T. 1962. The ecology of aquatic insects. Ann. Rev. Entomol. 7: 261-288. Macan, T. T. 1974. Freshwater ecology. 2d ect.

Wiley, New York. Philander, S. G. H. 1990. El Niño, La Niña and the Southern Oscillation. Academic, San Diego.

Ratisbona, L. R. 1976. The climate of Brazil, hi W. Schwerdtfeger, ed., Climates of Central and South America, world survey of climatology. 12: 219-293. Elsevier, Amsterdam.

Vegetation Zones

Physicochemical environmental factors not only act directly on insect life forms but influence them indirectly through the kinds of plant growth they allow (biotic factors). Groupings of plants adapted to a particular set of soil and climatic conditions delimit broad environments for insects.

Many types of vegetation are present in Latin America, and these are classified according to various systems (e.g., Beard 1944, Graham 1973, Hueck and Seibert 1972! Sauer 1950, Weber 1969). These systems are only regionally applicable because they often define units in terms of specific plant taxa present. A universal scheme, globally applicable, is Holdridge's (1967, 1982), which combines the effects of elevation, latitude, rainfall, and temperature to define vegetational formations, independent of floristic elements.

It is very apparent that the nature of vegetation plays a primary role in determining the Neotropical insect fauna in each physiographic area. The special richness of the Amazon Basin is a good case in point. Contrary to former ideas, the region's vegetation has not existed continuously unchanged for tens of millions of years but has varied considerably from near desert to lush forest in recent geologic periods, particularly during the Pleistocene Age, during alternating arid and humid conditions. In the drier phases, moisture-requiring vegetation shrunk greatly and fragmented into forest patches where rainfall persisted which was adequate for their survival ("refuge theory," Haffer 1982; but see Endler 1982).

This disjunction into forest islands isolated from each other by grassland or even desertlike plant cover divided many formerly continuous populations and led to their evolution into new species. Wet phases, such as the world is now experiencing, allowed the patches to expand again and the gaps between them to close. But evidences of the former islands, or refugia, are still present as concentrations of endemics. Among insects, this is shown especially well by butterflies (Brown 1982) and among arachnids by scorpions (Louren^o 1986).

This heterogeneity in Amazonian forest and wet forests in other areas partly explains the latest and one of the most extreme forces shaping the modern en-tomofauna of the basin (Simpson and Haffer 1978).

References

Beard, J. S. 1944. Climax vegetation in tropical

America. Ecology 25: 127-158. Brown, Jr., K. S. 1982. Paleoecology and regional patterns of evolution in Neotropical forest butterflies. In G. T. Prance, ed., Biological diversification in the tropics. Columbia Univ. Press, New York. Pp. 255-308. Endler, J. A. 1982. Pleistocene forest refuges: Fact or fancy. In G. T. Prance, ed., Biological diversification in the tropics. Columbia Univ. Press, New York. Pp. 641-657. Graham, A., ed. 1973. Vegetation and vegetational history of northern Latin America. Elsevier, Amsterdam. Haffer, J. 1982. General aspects of the Refuge Theory. In G. T. Prance, ed., Biological diversification in the tropics. Columbia Univ. Press, New York. Pp. 6-24. Holdridge, L. R. 1967. Life Zone ecology.

Trop. Sei. Ctr., San José, Costa Rica. Holdridge, L. R. 1982. Ecología basada en zonas de vida. Insto. Interamer. Coop. Agrie. San José, Costa Rica. Hueck, K., and P. Seibert. 1972. Vegetationskarte von Südamerika (Mapa de la vegetación de America del sur). Fischer, Stuttgart.

Lourenço, W. R. 1986. Diversité de la faune scorpionique de la région amazonienne; centres d'endémisme; nouvel appui à la théorie des refuges forestiers du Pléistocène. Amazo-niana 9: 559-580. Sauer, C. O. 1950. Geography of South America. Handbk. So. Amer. Indians 6: 319-344. Simpson, B. B., and J. Haffer. 1978. Speciation patterns in the Amazonian forest biota. Ann. Rev. Ecol. Syst. 9: 497-518. Weber, H. 1969. Zur natürlichen Vegetationsgliederung von Südamerika. In E. J. Fittkau, J. lilies, H. Klinge, G. H. Schwabe, and H. Sioli, eds., Biogeography and ecology in South America. 2:475-518. Junk, The Hague.

Artificial Environments

The foregoing discussion has been concerned with natural or original conditions and patterns of native flora and fauna. Since coming to the southern lands of the

New World 20,000 to 50,000 years ago, humans have modified the original life zones to varying degrees (Kiinkel 1963), even creating large tracts of essentially new, "artificial life zones." Such are the cities, farms, and vast grasslands for cattle grazing that have come into being since the Conquest. Even before Columbus, the indigenous population cut and burned sizable tracts of forest to support shifting agriculture, turning them into plots of cultivated species that only slowly returned to climax status through successional stages of different vegetation. The Incan civilization fashioned a new Andean landscape by their extensive terracing, grazing, irrigation, and road building.

In addition to changes contrived for living space and agriculture, there have also been impacts on natural populations of animals and plants through hunting and gathering, unintentional pollution, and erosion. Such modifications force adjustments by the insect inhabitants. This is most intense in the urban setting where new complexes of species adapted to civilization come into being. The entomology of cultivated fields of single or mixed crops also departs widely from the norm in natural environments.

Reference

Kunkel, G. 1963. Vegetationszerstorung und Bodenerosion in Lateinamerika. Arch. Natur-schutz Landschaft. 3(1): 59-80.

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