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Ba Na Nature Reserve 1996
Table 5. Summary of Pitfall trap samples for five sites.
Site No. Individuals No. RTUs α d
FT1 522 65 19.58 0.44
FT2 296 62 23.90 0.36
FT3 298 66 26.26 0.29
FT4 203 49 20.52 0.27
FT 5 (with ants) 5233 64 10.28 0.81
FT5
(without ants)
123 58 42.88 0.15
The pitfall assemblage at FT5 was heavily dominated by ants, and the diversity and dominance
indices were calculated both with and without the ants considered (the number of ants trapped can
vary greatly for stochastic reasons). When the ants were ignored, the diversity was highest at FT5,
the least disturbed transect. Diversity was lowest in the most disturbed transects (FT1 and FT4).
Diversity was also high in the high altitude transect FT3, possibly due to the addition of highaltitude
invertebrates to the secondary forest floor faunas caught at the other sites.
Figures 4 and 5 show the composition of the assemblages from each Forest Transect, in terms of
the number of species in each of the major groups, and the number of individuals trapped
(excluding ants).
The most diverse invertebrate groups (those having the greatest number of species) in all transects
are the flies (Diptera), beetles (Coleoptera), and spiders (Araneae). There is some apparent
variation in the relative importance of each of these groups, with Diptera being especially diverse
in transects FT4 and FT1 (the early successional transects), but insufficient data was collected to
test any patterns statistically.
The high diversity of the Coleoptera is expected, as this is the most species-rich order of animals
on earth.
In terms of numbers of individuals (Figure 5), the springtails (Collembola), a group showing
relatively little species diversity in these samples, forms a large proportion of each assemblage.
The Collembola are an ancient order of small, wingless insects, generally inhabiting soil and leaf
litter, which are ideally sampled by pitfall trapping, but their dominance of the pitfall fauna in this
case probably reflects the true importance of the insects in the terrestrial invertebrate fauna of the
Ba Na forests. The Diptera are again important, perhaps surprisingly as the majority of the flies
caught were fully winged adults, which would seem able to avoid passive pitfall trapping. The
spiders, although showing high species diversity, were usually present in small numbers (many
species were represented by only one or two individuals), and so make up a small proportion of
the total catch.
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