Aspects of the population ecology of Goniosoma sp. (Arachnida Opiliones Gonyleptidae) in limestone caves in southeastern Brazil

R.L. FERREIRA, R.P. MARTINS, S.F. MACHADO

Abstract


The new species of Goniosoma found in the city of Pains, Brazil, is well
distributed in the caves of the region, occurring in 55 out of 62 visited caves.
The species is still being described. This study aimed to evaluate oscillations in
population sizes and to show possible allometric variations between individuals.
The caves presented more constant temperature and relative humidity than the
external environment. In Dona Rita cave the population of Goniosoma sp. varied
between 48 and 140 individuals; in São Lourenço cave, between 45 and 346 individuals;
in Isaias cave, between 93 and 509 individuals, and in Sorvetão cave,
between 27 and 125 individuals. Despite the different sizes, the populations presented
similar oscillations, reaching maximum values in June and July and then
decreasing until October. No migration events were observed between the nearest
caves, about 250 m apart. The species is trogloxen, leaving the cave regularly
to feed on the nearest trees and rocky walls and returning in the morning. A
Principal Components Analysis (PCA) revealed a sexual dimorphism in the size
of the second leg and its femur, the males with average leg length of 16 cm and
femur length of 4.5 cm and the females with average leg length of 9 cm and
femur length of 2.5 cm.
KEY WORDS: Brazil, caves, Goniosoma sp., population ecology.

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