ecology of phasmids - KLUEDO - Universität Kaiserslautern
ecology of phasmids - KLUEDO - Universität Kaiserslautern
ecology of phasmids - KLUEDO - Universität Kaiserslautern
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Predation mediated mortality & migratory behavior <strong>of</strong> nymphs 80<br />
leaves (P. marginatum saplings were grown in the greenhouse to keep them free from herbivores). The<br />
diameter <strong>of</strong> the exclosures was sufficiently large so that leaves <strong>of</strong> the enclosed plant did not touch the<br />
mesh sides. Control plants were positioned 1 m next to an exclosure.<br />
The experiment was repeated four times (run 1 to 4) during three months in 2001 (September 18 to<br />
October 2, October 3 to October 17, October 25 to November 6, November 23 to December 5), each<br />
time with a new set <strong>of</strong> plants. Before starting an experimental runexclosures and the plants therein were<br />
checked for herbivores and predators such as frogs, ants, spiders and bugs, which were then removed. I<br />
also checked the surrounding vegetation <strong>of</strong> each control plant (in a circle <strong>of</strong> 1 m radius, 2 m height) to<br />
ensure that no individuals <strong>of</strong> M. diocles were present (no M. diocles specimens were found).<br />
First instar nymphs <strong>of</strong> M. diocles were set in the experimental plots (one nymph per plant). In average<br />
nymphs weighed 14.82 mg (StDev 7.10 mg, N = 219) and were 12 to 15 mm long. The nymphs were<br />
reared from eggs collected in a laboratory colony. All individuals had hatched at least three days before<br />
the beginning <strong>of</strong> the experiment. After three days the cuticle and mandibles have hardened and the<br />
intestines are fully functional. All individuals were only used once.<br />
In each run I recorded survival and migratory activity <strong>of</strong> the nymphs for 14 days. At the beginning <strong>of</strong> an<br />
experiment in the morning (before 10 am) <strong>of</strong> day 1, I set one nymph on each plant in exclosures and<br />
controls. I then checked each plant whether the nymph was still present: daily in the morning and the<br />
evening for run 1 to 3 and daily in the morning for run 4 (by then the difference between nocturnal and<br />
daytime events was supported by sufficient data).<br />
Nymphs in the exclosures that were not found on the host plant either fell dead to the ground, or moved<br />
(i.e., ‘migrated’) up to the mesh <strong>of</strong> the exclosures.<br />
I thoroughly searched for nymphs that disappeared from control plants in the surrounding vegetation (in<br />
a circle <strong>of</strong> 1 m radius, 2 m height, see above). Nymphs found alive <strong>of</strong>f their host were recorded as<br />
migrating (only two dead nymphs were found <strong>of</strong>f-host). The location was marked and the distance<br />
traveled measured. Migrating nymphs were followed during the experiment to record remigration to<br />
their hosts, further emigration or loss. If a nymph could not be found, it was recorded as disappeared. In<br />
total, I obtained data for 238 nymphs in both exclosures and controls.<br />
To allow for an analysis <strong>of</strong> potential bottom-up effects triggering nymph migration, I estimated the size<br />
and condition <strong>of</strong> the host plant by counting healthy young and mature leaves at the beginning <strong>of</strong> a trial<br />
and after a nymph had disappeared or left the plant. I discarded senescent leaves. Plant size was then<br />
expressed as the total number <strong>of</strong> healthy leaves per host plant individual.<br />
5.2.3 Greenhouse experiment<br />
To account for intrinsic mortality and migratory potential that is not predation related, I<br />
documented migratory activity and residence (survival) <strong>of</strong> nymphs for 14 days in seven<br />
greenhouse experimental plots (these open greenhouses are protected against intruders by