ecology of phasmids - KLUEDO - Universität Kaiserslautern

Life history & potential population growth 39
3.3.2 Potential population growth and effects of limited hatching success
As generations in M. diocles were shown not to overlap potential population growth was calculated by
the model of discrete stepwise growth described by Equation 3-1.
The fundamental net per capita rate of increase R (Equation 3-2) for M. diocles was 19.79 (intrinsic rate
of natural increase per generation r = 2.98 and per day for females r = 0.0125). In other words: each
individual of a generation contributed with a progeny of 20 individuals to the next generation.
The model resulted in exponential population growth (Figure 3-3). Starting with a hypothetical
population of two individuals representing the founder generation T0 (male and female) the population
comprised 40 individuals in the first generation (2 * 19.79 = 39.58), multiplying to 783 individuals in
the second, and 15494 individuals in the third generation (population size T4 ~ 306572; T5 > 6*10 6 ).
About 90 % of the eggs hatched; 2% of embryos were killed by fungal infestations and another 8%
failed to hatch for unknown reasons. The reduction in hatching success of 10 % resulted in a lowered
net per capita rate of increase of R = 17.81 (r = 2.88 per generation and r = 0.0121 for females per day).
Accordingly population growth was decelerated with T1 ~ 36, T2 ~ 634, T3 ~ 11299 and T4 ~ 201227
individuals (Figure 3-3).
Population size [ind.]
16000
14000
12000
10000
500
0
potential population increase, R = 19.79
population increase
including hatching success, R = 17.81
0 1 2 3
Generation T
Figure 3-3: Model of discrete stepwise population growth (Equation 3-1) of M. diocles for potential population
growth (filled dots) and population growth decreased by reduced hatching success (white dots). Models start from
a hypothetical founder generation T0 of two individuals. Net per capita rates of increase (R) are depicted in the
figure legend.
4