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 29<br />
On the species level, <strong>phasmids</strong> used different resources reflected by the comparison <strong>of</strong> both realized or<br />
absolute niche dimensions. Niche differentiation among species occupying the same habitat is <strong>of</strong>ten an<br />
effect <strong>of</strong> competition (Begon et al. 1996). One simple prediction arising from the assumption that the<br />
observed niche differentiation resulted from interspecific competition would be: while phasmid species<br />
use resources differentially in the field they should not discriminate among resources when they are<br />
released from competition, like in feeding trials. Thus, interspecific overlap in realized niches should be<br />
smaller than overlap <strong>of</strong> absolute niches. This prediction was not confirmed for <strong>phasmids</strong> on BCI.<br />
Principally overlap <strong>of</strong> realized niches between phasmid species was marginal with overlap indices from<br />
3 to 20% (Pianka’s niche overlap). This cannot be generalized as being opposed by an almost complete<br />
niche overlap between O. martini and I. dentipes.<br />
Results from feeding trials revealed that absolute niches <strong>of</strong> phasmid species were even more distinct<br />
(note that I. dentipes was not included in feeding trials). Overlap in absolute niches <strong>of</strong> four phasmid<br />
species was restricted to B. ploiaria sharing one host family each with O. martini and Otocrania sp..<br />
There was no overlap <strong>of</strong> the absolute food niche <strong>of</strong> M. diocles and any <strong>of</strong> the other three species.<br />
This can be partially explained by the fact that many plants in the diet <strong>of</strong> M. diocles (Araceae and<br />
Piperaceae) mirror the understory-habitat, the use <strong>of</strong> which was negligible for all the other species.<br />
Nevertheless, many Piper species are gap adapted (Croat 1978), and hence also available to other<br />
phasmid species. Possibly these <strong>phasmids</strong> are not able to handle particular chemical compounds <strong>of</strong><br />
Piperaceae and Araceae. The phylogenetic separation <strong>of</strong> the Piperaceae from other dicots may involve<br />
differences in phytochemistry (Judd et al. 2002). In fact, Piper species are characterized by a wide array<br />
<strong>of</strong> aromatic compounds (Sengupta & Ray 1987; Baldwin & Schultz 1988; Parmar et al. 1997; Dyer et<br />
al. in press) many <strong>of</strong> them deterring insect herbivores (Parmar et al. 1997 and references therein).<br />
Likewise the Araceae as monocots are distinct from dicots in many features. Araceae contain calcium<br />
oxalate crystals, cyanogenic compounds, and sometimes alkaloids, all known to deter herbivores (Judd<br />
et al. 2002 and references therein). M. diocles seems to be able to detoxify such toxic or deterrent plant<br />
chemicals suggesting that its evolutionary history is closely linked to these plants. However, a<br />
coevolutionary scenario (sensu Ehrlich & Raven 1964) would demand that Araceae and Piperaceae<br />
were closely related. Recent phylogenetic analyses cannot support this imperative (Judd et al. 2002).<br />
While this approach so far lacks an explanation for niche differentiation among O. martini, B. ploiaria<br />
and Otocrania sp., I suggest that their host ranges may reflect their evolution with less defended fast<br />
growing pioneer plants <strong>of</strong> high nutritious quality (Coley 1983; Coley et al. 1985). Both evolutionary<br />
hypotheses are supported by the refusal <strong>of</strong> foliage <strong>of</strong> late successional plant species in feeding trials.<br />
The presented pattern in host range corresponded with the mobility <strong>of</strong> three <strong>of</strong> the focal phasmid<br />
species. Limits to the rate at which a suitable host can be found (like mobility) are clearly related to host<br />
range (Jaenike 1990). Small organisms perceive their environment in a coarse grained fashion (Levins<br />
1968). For specialist herbivores, the resolution becomes worse because with decreasing host range, a