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Abstract:
"Reactions" of animal populations in Central Amazonian inundation-forests to annual flooding have been poorly investigated.
The terrestrial arthropod-fauna was studied in 1976 in a Várzea-forest (white-water region) and in 1976/77 in an Igapó-forest (black-water region) near Manaus. As capture devices ground photo-eclectors, pitfall traps and arboreal photo-eclectors were used. All captured animals have been registered
and separated to order, family and in some cases to species, except Collembola, Acari, Thysanoptera and part of the Diptera.
Igapó
1. In the trunk region about 127.000 arthropods were caught (46 % lnsecta - mainly Holometabola -, 32 % Arachnida, 22 % lsopda and Myriapoda). Formicoidea dominated (71 species), as well as Pseudoscorpiones, Araneae and Diplopoda. On the forest floor about 80,000 arthropods were captured (90 % lnsecta - mostly Holometabola -, 9 % Arachnida, 1 % lsopoda and Myriapoda).
2. Activity density and emergence abundance of arthropods change throughout the year. In the dry season holometabole insects dominate, in the rainy season Arachnida, Myriapoda and Isopoda dominate on forest-floor and trunk.
3. Numerous arthropods, particularly non-flying ones obviously survive the submersion phase (March/April - Aug./Sept.) in the trunk and canopy region. However, a great part of them perish during the actual inundation, many become prey to predaceous arthropods, paticularly of Formicoidea. With the
beginning of the rainy season (in Dec.) upward migration on the trunk increases as well as downward migration near the end of the submersion phase, particularly of Arachnida and Myriapoda. Trunk migration (upwards/downwards) and flight activity to trunks (=trunk approach) are regulated in a high degree by abiotical factors (soil wetness, rel. humidity) changing with the climate (dry season/rainy season)
4. Development of many arthropods is well synchronized with the annual water-fluctuations.This is exemplarily shown for Pseudoscorpiones (18 species in 8 families, litter and bark inhabitants and Meinertellidae (2 species).
5. The non-flying and limited-flying arthropod fauna of the Igapó is classified into terricole and arboricole groups ("nonmigrants", "migrants").
Várzea
1. About 45.000 arthropods were captured in the trunk region (94 % lnsecta - mainly Formicoidea as well as Coleoptera -, 5,7 % Arachnida, 0,3 % lsopoda and Myriapoda). About 2.000 animals were caught on the forest floor (91,1 % lnsecta - mostly Holometabola -, 9,3 % Araneae, 0,6 % Myriapoda).
2. Arthropods of the Várzea presumably are mostly trunk and canopy inhabitants. Many of them also come on to the forest floor during the emersion phase for oviposition (esp. Diptera) or nutrition (esp. Formicoidea).
3. Non-flying arthropods which emigrate to the trunk and canopy region do not occur.
Conditions for a rich soil life are unfavorable, Pseudoscorpiones e.g. (11 species in 8 families) are almost exclusively represented by bark inhabitants.
