Assessing Chaco Serrano Woodland area effects on diversity of ground-dwelling insects at different taxonomic levels

MOLINA, S. I.; VALLADARES, G. R.; CAGNOLO, L.; SALVO, A.

San Carlos de Bariloche

Workshop; Workshop on Forest Fragmentation in South America; 2006

International Association of Landscape Ecology (IALE).

The advance of agricultural frontier and urbanization have transformed the Chaco Serrano Woodland into a fragmented lanscaped where remmants of vegetation of different area are immersed in a mainly agricultural matrix. Area reduction may have negative effects on species richness although the different components of an ecosystem may respond in different ways. We analyzed taxonomic composition of the ground-dwelling Coleoptera community in Chaco Serrano remnants of different size, in Central Argentina. Taxonomic composition, at Family level, of the whole ground-dwelling insect community was also analyzed. Using this taxonomic level has been suggested as an alternative way to estimate species richness with less cost and time investment (Oliver and Beattie, 1996 ), which is important in view of the fast rate of habitat destruction. Previous studies showed the usefulness of this approach for other areas of Chaco Woodland. Nine woodland fragments were selected, covering an area gradient (0.57 ha to over 1000ha) and isolated 100 m, on average. Insects were sampled using pitfall traps placed in linear parallel transects at the border and in the interior of each fragment. Collected specimens were determined to Family (insects) and species (Coleoptera) taxonomic level. Species richness, abundance and diversity (Shannon) were estimated for each taxonomic level. Data were analyzed by Multivariate Classificacion methods, X2, Wilcoxon test and Spearman correlation. Remnants showed low similitude in their insect community composition at both taxonomic levels, with many taxa being represented by just one indivivual. The largest (continuum) woodland clearly differed in its composition from all other remnants, supporting fewer species than remnants smaller than 1 ha. Edges were on average richer than the interior of remnants, although differences were (marginally) significant only for Coleoptera species. Contrary to expectations, richness and diversity of insects at the remnant interior was negatively correlated with woodland area. This relationship was noticeably stronger for Coleoptera species than for insect families, and probably reflected the expansion of the border effect to the interior of the smaller remnants. According to these results, using family taxonomic level allowed the detection of change tendencies, possibly related to habitat fragmentation, in the composition of ground-dwelling insect communities. However, stronger evidence of such changes was observed at species level. Within a conservation framework, our results suggest that the maintenance of remnants of various sizes would be necessary in order to better preserve diverse ground-dwelling insect and beetle assemblages in this system