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corresponds to 44 setigers using Equation 2. Several individuals with a 5th setiger
width of 0.37mm were randomly selected and their number of segments were found to
be approximately 40. This agrees with the results of Gudmundsson (1985) and
Morgan (1997) who suggested, based on the size which gametes first appear, that P.
elegans become sexually mature when they reach 40 setigers. This agreement
supports the contention that the relatively simple method of sex determination used in
this study is a reliable one.
Figures 3.2(i-ix) displays the P. elegans population size distribution throughout the
sampling period. New recruits (individuals with a 5th setiger width of 0.13-0.17mm)
were present throughout the study period. However, intense recruitment was confined
to two relatively short periods, one during April/May and the second during
November/December. Only two cohorts could be clearly defined at any one time
during the sampling period. This was because newly settled individuals reached the
size of the adult population before the next cohort appeared. In March 1997 (Figure
3.2(i)), when the abundance of P. elegans was relatively low, the population structure
followed an asymmetric distribution, skewed towards adults. In April, the population
structure followed a bell-shaped distribution, although the majority of the individuals
fell into the adult size categories. In May, there was a sudden increase in new recruits
which resulted in a rapid increase in total abundance and a bimodal appearance of the
population size distribution. One month later, in June, the population size structure
was much the same except the modal size class for the smallest individuals had
slightly increased. In July and August (Figures 3.2(v) and (vi) respectively), the
structure of the population was still slightly bimodal and it was still possible to
distinguish the April/May cohort from the parental population. During October, the
April/May cohort became indistinguishable from the parental population. The
population structure was distinctly bimodal in December due to another sudden
increase in new recruits. Since the modal size class of this cohort approximately
corresponded to that of the cohort observed in May (i.e., 0.17mm 5th setiger width)
when sampling was monthly, it is likely that these new recruits had settled no more
than one month before the sampling date for December (sampling at this time was on
alternate months). This caused the marked increase in total abundance between
October and December. In February 1998 (Figure 3.2(ix)), abundance was relatively
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