ecology of phasmids - KLUEDO - Universität Kaiserslautern

Life history & potential population growth 41
Size differences among females may reflect the effects of differing intensities of multiple control factors
like food quality and availability, competition and predation pressure in the natural setting of an
organism (Price 1984). Hence, in M. diocles control factors like food quality and predation pressure
(addressed to in Chapters 4 and 5) most likely will influence female fecundity.
However, larger body size and higher weight can also be at the expense of mobility. Bedford (1978)
reported that in most phasmid species females become gravid with eggs and cannot fly, although the
wings may be large as in M. diocles. This may decrease female searching efficiency for new food
patches. One deriving possible scenario for M. diocles would be that fertile females show a high fidelity
to food patches resulting in clustered distributions as described in Chapter 2.
Generally, the variability in developmental times of phasmid eggs is enormous; hatching times range
from 13 days up to three years. Species in temperate regions take longer times of egg development often
linked to diapauses. For tropical phasmid species Bedford (1978) reported hatching times from 13 to
114 days, with the main hatching spreading over a time span of 20 to 30 days and only small numbers
taking longer. By comparison M. diocles is situated in the middle of embryonic development time.
Developmental time of M. diocles nymphs and adult lifetime were consistent with other species, but
mean female adult lifetime ranged on the lower end of published data on phasmids. Phasmid males in
general have shorter larval development than females and are shorter lived as adults. Both was
confirmed for M. diocles, although the difference in adult longevity was small compared to other
phasmid species. M. diocles females in average lived 13 days longer than males. For example, adult
females may live two (9 weeks, Phyllium bioculatum Gray) to eight times longer than males (8 months,
Phasma gigas Amboine). Nonetheless, maximum lifetime of M. diocles adults almost reached 6 months
for females and 4 months for males.
In terms of egg production M. diocles remained below the lowest values reported with 60 to 80 eggs per
female for Timema californica Scudder. P. bioculatum produced in a comparable lifespan 80 to 100
eggs per female. In other species females can lay up to 1000 eggs.
3.4.2 The biotic potential of Metriophasma diocles
Both, low egg production and short-lived adult females converted into low reproductive potential of
M. diocles, especially facing a relatively long generation time of approximately eight months. Prominent
tropical herbivore groups, such as Lepidopterans and Coleopterans exhibit much shorter generation
times and much higher reproductive potential (e.g., Braker & Greene 1994, Caldas 1994, Chi & Yang
2003, Atluri et al. 2004). To give an example, Braker & Greene (1994) provide data on eight tropical
butterfly species at La Selva, Costa Rica, with lifetime fecundity ranging from 217 to 521 eggs and
maximum generation times of 74 to 227 days. While generation times of single species may be
comparable to M. diocles (239 days for females) these species all possess much higher individual
fecundities (40 eggs for M. diocles females). The low biotic potential of M. diocles becomes apparent
compared to the intrinsic rate of increase of a predatory coccinelid beetle including stage specific