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Effects on a Harsh Environment on the Life History Patterns of Two Species of Tropical Aquatic Hemiptera (Family: Naucoridae)

Stout, R. Jean
Ecology 1982 v.63 no.1 pp. 75-83
Hemiptera, Naucoridae, adults, animals, aquatic organisms, dissolved oxygen, dry season, insects, life history, nymphs, population density, rivers, seasonal variation, streams, watersheds, Costa Rica
The relative abundances and distribution patterns for two species of aquatic predaceous creeping water bugs (Family: Naucoridae) were determined for two tropical streams at Finca La Selva, Costa Rica, from July 1975 to August 1977. Seasonal changes in population densities were found to be related to differential recruitment and dispersal patterns for the two populations. Extreme population losses for both species occurred during flood periods in one of the two streams. Heavy rains in the mountainous watershed, which can occur 15—30 times/yr, caused one stream, the Sabalo, to spate, and it was in that stream that populations of both species were negatively affected during spates. The second stream, the Sura, is a low—gradient tropical stream and it is backflooded by a large river, the Puerto Viejo. During backflooding, there are reductions in dissolved oxygen and in velocity, but the changes do not affect these plastron—breathing insects. Although depths in both streams increase up to 9 m during flooding, the Sabalo is a more harsh environment for the bugs, owing to intense substrata redistribution processes during spates. Nymphs and adults of the vestigally—winged bug, Limnocoris insularis Champion, move upstream against the current, both in the wet and dry seasons. Adults can recolonize the two streams by moving in from the Puerto Viejo River (a 6th—order river into which both streams flow). Population densities of the naimals are low in the Sabalo because the animals do not recruit well there and because they are also washed out during spates. Population densities are high in the Sura. The animals can recruit there and they are not washed out during flooding. Individuals of the second species, C. latus Usinger, do not move along stream bottoms against the current. Nymphs and brachypterous adults remain stationary or are passively moved downstream with the current. Populations can recurit and disperse in both streams; however, their dispersal abilities are temporally limited because only the winged morph, uncommon except in the dry seasons, has the ability to colonize upstream sections.