How Abiotic Factors Affect the Distribution of Two Species of Tropical Predaceous Aquatic Bugs (Family: Naucoridae)

Abstract

Heavy runoff from watersheds affects lowland streams in two general ways. Either a stream experiences spates (increased forward velocity and scouring of stream bottoms) or it becomes inundated by water from larger rivers, causing the stream to be backflooded. This study shows how these features affect the abundances and distributions of two Costa Rican species of stream—inhabiting predaceous waterbugs, Limnocoris insularis Champion and Cryphocricos latus Usinger (Naucoridae). Backflooding in the Sura was found to have no subsequent effect on the abundances or distribution of either species. But in the Sabalo, which spates, nymphal populations of L. insularis significantly decrease after a spate because of loss of numbers and loss of previous habitat. During severe spates, adults of both species can be washed out, causing abundances to remain low for several months to periods > 1 yr. Abundances of nymphs and adults of C. latus are associated with fast current speeds, large rocks, and coarse—grained pebbles. These sorts of habitats are found in both streams. Even though C. latus is more common in the Sablo than is L. insularis, abundances of adults of the former species fluctuate more in the stream that spates than in the stream that does not, owing both to a high washout rate and to a slow recolonization rate. The basic pattern of distribution is explained by the difference between the flooding characteristics of the two streams.