ecology of phasmids - KLUEDO - Universität Kaiserslautern

Community structure & host range 16
c = Number of plant families only accepted in feeding-trials but not recorded in line-transects
Sørensen’s similarity coefficient is a qualitative measure usually used for matches in species
composition between samples. As feeding-trials result in qualitative data (edible vs. inedible) this
coefficient is also applicable to measure qualitative overlap between realized and absolute food niche.
Sørensen’s similarity coefficient weighs matches more heavily than mismatches and thereby accounts
for the fact that mismatches were over represented both 1) in line-transect data, as all recorded plant
species were considered as potential host plants and 2) in feeding trials, as not all tested plant species
that were edible occurred in line-transects.
2.3 Results
2.3.1 Phasmid diversity and density
In 15 months of line-transect monitoring I recorded 307 specimens representing 11 phasmid species
(Table 2-1). The species accumulation curve from line-transect records reached an asymptote after four
months (Figure 2-1) suggesting that the phasmid fauna of forest edge and understory habitats was
sampled adequately. This was supported by the fact that in field records other than along line-transects
only one additional phasmid species was found (Pseudophasma menius; Table 2-1). One species
(Otocrania sp.) has not been previously reported for Panamá (compare to Appendix 1).
The local phasmid fauna was dominated by four common species comprising more than 89 % of the
sampled specimens (Figure 2-2). Seven phasmid species were found in low numbers of 10 or less
individuals. One of these species was represented by a singleton (Stratocles multilineatus).
Line-transect data uncovered a clear spatial separation in the community structure. Diversity in phasmid
species was higher in forest edges compared to the forest understory (Table 2-1). This higher diversity
resulted from higher species richness and higher eveness along forest edges. The data indicate that
phasmids were mainly restricted to forest edge habitats; ten out of eleven species and 93 % of the
recorded individuals occurred here. In the forest understory phasmids were rare and singletons
represented three out of four species. Only Metriophasma diocles was found regularly and comprised
86 % of the recorded specimens in the understory. As this habitat was poor in species and in individuals,
similarity of phasmid communities between forest understory and forest edge was low (demonstrated by
Morisita’s similarity index Cλ = 0.25; Table 2-1). Phasmid density was 35 times higher in forest edge
habitats than in the understory (Table 2-1). Analogous population density for M. diocles was lower in
the understory than at forest edges. While absolute abundances doubled population density trebled from
6.7 ind.*ha -1 in the understory to 21.6 ind.*ha -1 at forest edges after adjusting for size of the sampled
area (with a respective total area searched of 0.096 and 0.048 ha).