Abstract

LONGO-SANCHEZ, Magnolia C.; GOMEZ-AGUIRRE, Ana M.; BLANCO, Juan F.  and  ZAMORA-GONZALEZ, Hilldier. MULTI-ANNUAL AND SPATIAL CHANGES IN COMPOSITION AND STRUCTURE OF AQUATIC INSECTS ASSEMBLE AT PERENNIAL STREAMS OF GORGONA ISLAND, COLOMBIA. Actu Biol [online]. 2009, vol.31, n.91, pp.141-160. ISSN 0304-3584.

This study shows an analysis of multi-annual (1986, 1993, and 2008) change of composition and structure of aquatic insect assembles at five streams at the Eastern (Ilú, Iguapoga, and Pizarro) and Western drainage (Cocal Norte and La Camaronera or Cocal Sur) at Gorgona Island. Were used data of Cala from 1986 and Zamora et al. from 1993, and the GIS-BIO project from 2008, in order to make comparisons at three spatial scales: island (γ diversity), drainages (β), and streams (α). The number of orders in 1986, 1993, and 2008 was 8, 7, and 9, respectively. Between 1993 and 2008, the number of families increased from 17 to 29, while the number of genera increasing from 5 to 24. Because of that increase in the number of taxa, the similarity index (Sorensen) between 1993 and 2008 was 57.8% based on the family composition and 32.0% based on genus composition. The Shannon-Wiener's diversity index (H') also increased with time, in 1993 the island's average was 1.92 (range: 1.67-2.12 nats/ind.) and in 2008 was 2.54 (2.30-2.82). Both, dominance (D) (< 0.19) and evenness (J') (> 0.68), were similar in both periods. The Eastern drainage streams showed higher numbers of families and genera during both periods. The similarity of the compositions among drainages was higher for the year 2008 (74%) than for 1993 (50%), then genera turnover (β diversity) between drainages was inverse. The relationship between local and regional diversities followed the type I (unsaturated) during 1993 and 2008. The temporal and spatial patterns may be explained by the extensive deforestation at El Poblado area during the operation of the penitentiary between 1960 and 1984. Native riparian forests were replaced by subsistence crops or were exploited for fire wood. Additionally, a small hydropower central was constructed at a stream. Therefore, the impacted basins have naturally recovered since Gorgona Island was designated as a National Natural Park in 1984. Then, the samplings in 1993 and 2008, represent succession trajectories of at least 10 and 24 years, respectively. However, we do not overlook that the differences in sampling effort between years, and the limited availability of taxonomic keys for South America during the years 90 may have biased the temporal trends. This is supported by a higher rate of new families and genera records at the Western drainage, where the landscape was minimally impacted by human intervention.

Keywords : alpha, beta and gamma diversity; aquatic insects; hierarchical fluvial landscape; Gorgona Island; local and regional diversity.

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