Fauna: Composition and Function

Abstract

Tropical mountain rain forests form biodiversity hotspots for a number of animal and plant taxa (Küper et al. 2004; see Chapter 2 in this volume). Only a few taxa, such as parasitic Hymenoptera, appear not to conform to the general rule of increasing diversity from temperate to tropical regions (Gauld et al. 1992). However, one important component of the animal community, the soil fauna, has rarely been studied in tropical rain forests, especially in mountain regions. The reasons for this presumably are that: (a) soil animals have to be extracted from a 3-dimensional medium by heat or other methodology, (b) there are few keys for determination and (c) a large number of species is still not described. 11.4.2 Methods We investigated the density and diversity of the soil microarthropod community in a tropical mountain rain forest in southern Ecuador. We focused on microar-thropods (mainly oribatid mites and collembolans), since at our study site the density of soil macrofauna, such as earthworms , diplopods and isopods , was low, which may be due to low pH and low resource (litter) quality. Due to the low density of large decomposer animals we expected soil microarthropods to signifi-cantly affect decomposition processes. Changes in density and community struc-ture of the soil mesofauna were investigated along an altitudinal gradient spanning over 2000 m. To evaluate the trophic structure of the soil food web we studied natural variations in stable isotope ratios (15 N/ 14 N; 13 C/ 12 C) of dominant soil fauna taxa. Knowledge on the trophic structure of the decomposer food web is necessary for understanding the limiting factors of soil animal species and the role of decomposer species for decomposition processes. By manipulating carbon and nutrient availability we evaluated limiting factors for soil microorganisms and investigated the role of microorganisms as food resources for animal decompos-ers. Finally, by investigating the decompositon of leaf litter enclosed in litterbags E. Beck et al. (eds.), Gradients in a Tropical Mountain Ecosystem of Ecuador. 181 Ecological Studies 198.