The Population Biology of the Early Spider Orchid, Ophrys Sphegodes Mill. II. Temporal Patterns in Behaviour

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Abstract
(1) Over 70% of Ophrys sphegodes plants flower in the first year of emergence above ground. The proportion of plants which flower increases with age until 4 years after first emergence, when virtually all plants flower whenever they are not in a dormant state. Probability of dormancy was independent of age. (2) Measures of plant performance increase with age to peak in plants between four and seven years after first emergence, and decline again in older plants. (3) Weak support was obtained for the hypothesis that flowering performance in a given year may be limited as a result of flowering having taken place in the previous year. No support was obtained for the hypothesis that a greater investment in flowering in a given year reduces the capacity to flower in the following year. The probability that a plant will flower is significantly higher following a year in which it flowered than following a year in which it was either vegetative or dormant. The probability of dormancy is significantly lower following a year in which a plant flowered than following a year in which it was vegetative or dormant. Death is significantly more likely to follow a year spent in dormancy than a year in which an orchid flowered or was vegetative. Even orchids which flowered in one year had a probability > 0.5 of being dormant the following year. One-third of orchids which flower in any year die without reappearing in the population. (4) The probability of O. sphegodes emerging above ground in any year declines significantly as life-span increases. Probability of flowering shows the same trend, but does not change significantly with life-span. The likelihood that emergence of O. sphegodes will be accompanied by flowering increases significantly with life-span. (5) All but one of the cohorts of O. sphegodes recorded during a ten-year period exhibited statistically similar survivorship curves. Amalgamation of data for all but the one anomalous cohort yields a survivorship curve with a half-life of 2.09 years measured from the date of first emergence. Measures of age-specific mortality risks fall until the sixth year after first emergence to low values, and increase again for older plants. (6) The population of O. sphegodes is estimated to produce 7.3 times its own number of flowers annually: 37% of flower production is by plants in their first year above ground, and 54% is by flowers in their first two years above ground. (7) Only young plants are numerous enough in the population to provide a major contribution to future recruitment. Conservation of O. sphegodes depends on creation of conditions conducive to flowering, seed setting and seedling establishment.