Abstract
In this work, we conducted three comparative studies on arthropods in Central Amazonian forest ecosystems.
(1) The soil faunas from seven forest types were compared using
the soil extraction method of Kempson. Anthropod abundance
varied between 3,500 and 9,000 ind/m2 . Abundance generally
was higher in inundation forests when compared to dryland
forests. Acari and Collembola represented 60-80% of the soil
fauna collected. Dominance of frequent taxa varied significantly
among forest types. For preliminary studies of ecosystems,
particularly orientation projects such as these, we recommend
modern standing crop methods.
(2) Abundance of arthropods and dominance of "key taxa" in different
strata (soil/litter, trunk, and canopy) of riverine inundation
forests, one in the Black Water Region and one in the White
Water Region, were compared with a primary forest in the
Dryland Region during the rainy season. Sampling methods were
Kempson soil extraction, ground and arboreal photo-eclectors,
and canopy fogging. Relative abundance of arthropods (Acari and Collembola disregarded) ranged between 1,000 and 1,500
ind/m2 in the soil and from 1,000 to 7,000 ind/m2 in ground
photo-eclectors. Between 1,000 and 8,000 arthropods occurred
per tree trunk and 30 to 60 ind/m2 were collected from the
canopy. Relative abundance of arthropods was somewhat higher
in the black water inundation forest, intermediate in the
primary dryland forest, and lower in the white water inundation
forest. Dominance of taxa varied significantly among strata
within the forests and among forest types as well. Zoophagous
groups were predominant. On the forest floor, primary decomposers other than Diptera (in particular, larvae) were almost
absent. We recommend a combination of permanent collecting
methods, complemented by standing crop samplings, for future
comparative studies on arthropod populations in neotropical
forest ecosystems.
(3) Population fluctuations of arthropods may correspond somewhat
with altering abiotic conditions. The activity density of
arthropods on trunks was studied during and between seasons
both in a black and a white water inundation forest, as well
as in a primary and a secondary dryland forest. More arthropods
were caught during the rainy season, except in the primary
dryland forest. Formicidae represented the predominant group
with 36-81% of the total catch. Dominance of taxa in samples
varied considerably within and between seasons. Pronounced
trunk ascents of ants were observed during the dry season in
all forest types. A dry, warm climate is believed to stimulate
tree inhabiting, meso-xerophilous ant species to become highly
active and to migrate between canopy, trunk region, and forest
floor. With the beginning of tbe rainy season and a changing
microclimate, their activity density decreased steadily. In
the black water inundation forest, numerous non-flying (terricolous) arthropods migrated into the trunk-canopy region with
the beginning of the rainy season, where they remained throughout
forest inundation (5-6 months duration). Trunk ascents of
hygrophilous species apparently are influenced by rising
wetness on the forest floor and increasing relative humidity
in the lower trunk region. Thus, for the Central Amazonian
forests we studied, we could not confirm the hypothesis that
tropical ecosystems with sufficiently high numbers of species
lack population fluctuations.
We conclude this paper by discussing theories about the diversity of Amazonian arthropods and by posing timely research questions
'for tropical studies. Integrated long term studies are required to
achieve indepth insights into the structure and function of neotropical forest ecosystems. Information obtained by basic research is
the foundation for ecological criteria to be used in biological
management plans for Amazonia.
