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The fitness effects due to initial flowering date in Phlox drummondii were determined for three populations in central Texas (USA) over 3 yr (1990-1992). Mean fitness (seed set) always decreased with the later initiation of flowering. The likelihood of a plant fruiting differed with flowering date in five of the six instances (population by year combinations). Though plants that initiated flowering later tended to have spent more time in the vegetative stage and tended to die later in the year than did earlier flowering plants, this was not sufficient to overcome the reproductive penalties of flowering late. Plants that initiated flowering later in the season spent less time in the adult phase and were smaller. The mean number of flowers, fruits, and seeds per flowering plant always decreased with later flowering. Fruit set was negatively correlated with flowering date in four of the six population by year combinations. Nonparametric fitness functions were used to summarize predicted fitness among different initial flowering dates for each population on a yearly basis. Predicted mean fitness always declined nonlinearly with later flowering; the earliest flowering plants always had the highest predicted fitness. These fitness functions describe directional selection for the early initiation of flowering.

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In this paper, we demonstrate that rapid cycling Brassica rapa (Wisconsin Fast Plants) can be used in inquiry-based, student ecological fieldwork. We are the first to describe age-specific survival for field-grown Fast Plants and identify life history traits associated with individual survival. This experiment can be adapted by educators as a method to teach age-specific demography or ecology with Fast Plants. Four genotypes of Fast Plants (dwarf, elongated internode, standard, and rosette) were used. Fast Plants were grown in a "common garden" experiment. The site was surveyed every day to monitor emergence, and every 2 days to record mortality. Seven life-history traits were measured: days to emergence, emergence date, death date, life span, flowering date, juvenile days, and adult days. Most seedlings emerged 5 to 6 days after sowing and plants lived an average of 30 days. Flowering began about 17 days after seedling emergence. Life table analysis showed that Fast Plants have Type I age-specific survivorship. Analysis of variance showed that these four genotypes did not differ for any of the life-history traits measured. However, correlation analysis revealed that life span was negatively related to emergence date, and flowering date was positively related with emergence date. We suggest that ecologists extend the use of Fast Plants to include student fieldwork. Through inquiry based work, students can construct a personal understanding about the process, practice, and outcomes of science. Students will also gain understanding about the limits of numerical data, their analysis, and their interpretation.