ecology of phasmids - KLUEDO - Universität Kaiserslautern
ecology of phasmids - KLUEDO - Universität Kaiserslautern
ecology of phasmids - KLUEDO - Universität Kaiserslautern
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Community structure & host range 30<br />
decreasing availability <strong>of</strong> patches with suitable hosts is inherent (particularly in high diverse tropical<br />
rainforests). This may explain why both sexes <strong>of</strong> M. diocles dispose <strong>of</strong> cost intensive wings. Higher<br />
mobility as compared to wingless <strong>phasmids</strong> may allow them to search for scattered resources more<br />
efficiently. But finding suitable resource patches also represents a critical challenge for nonvolant<br />
<strong>phasmids</strong> like the generalistic O. martini and B. ploiaria. In B. ploiaria only the male is winged and<br />
able to fly short distances (personal observation) while in O. martini both sexes are wingless. Their<br />
restricted host range consisting <strong>of</strong> characteristic gap plant species involves the risk <strong>of</strong> depleting host<br />
plants when a light gap closes. Then the detection <strong>of</strong> a new gap becomes crucial; the more as nonvolant<br />
<strong>phasmids</strong> were shown to move at low velocities (a maximum <strong>of</strong> 6 m per day; Willig et al. 1986). I<br />
suggest that gap phasmid species may escape from being doomed because their diet contains liana<br />
species. I argue that the wingless habitus <strong>of</strong> the Otocrania species does not contradict its specialization,<br />
because Otocrania specialized on Sapindaceae, a plant family that contains many lianas such as<br />
Paullinia spp. and Serjania spp. (Croat 1978). Lianas may contribute up to 14 % <strong>of</strong> above ground<br />
biomass in tropical forests (Gerwing & Farias 2000). They are characteristic components <strong>of</strong> early<br />
successional habitats such as gaps, but they are also present all over the canopy (Putz 1984, DeWalt<br />
et.al. 2000; Schnitzer & Bongers 2002). Thus, <strong>phasmids</strong> that include lianas into their diet may find<br />
sufficient food in upper canopy. The generalistic O. martini and B. ploiaria that were abundant in forest<br />
edges may on their search for new light gaps be able to traverse the forest canopy and rely on lianas. In<br />
contrast, the forest canopy may represent the preferred habitat <strong>of</strong> the specialist Otocrania sp. and<br />
thereby explain its low abundance in my study.<br />
2.4.4 Conclusions<br />
Broadening the meaning <strong>of</strong> specialization, I presented evidence that <strong>phasmids</strong> are specialized to habitat<br />
specific food resources and that their distribution was clearly connected to the distribution <strong>of</strong> their host<br />
plants (as reflected by their successional status). The higher density and species richness <strong>of</strong> phasmid<br />
species in forest edges as compared to the understory may reflect their evolution with less defended fast<br />
growing pioneer plants <strong>of</strong> high nutritious quality (Coley 1983; Coley et al. 1985). The refusal <strong>of</strong> foliage<br />
<strong>of</strong> persistent late successional tree species gives support to this view.<br />
Other than by resources, the distribution <strong>of</strong> an herbivore can be influenced by its natural enemies.<br />
Contagiousness could then be due to differential predation, i.e. an herbivore species suffers less<br />
predation related mortality on a particular host plant species (Sandoval 1994; Price et al. 1980; Bernays<br />
& Graham 1988). Such mechanisms could have led to narrow host range including unrelated plant<br />
species <strong>of</strong> M. diocles. Low abundances <strong>of</strong> M. diocles in the understory then would result from high<br />
predation pressure rather than from nutritious limitations through the host plants.