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Abstract
Festuca novae‐zelandiae is a New Zealand endemic bunchgrass that occurs from near sea‐level to 1400 m. In a study of seed production at a range of altitudes, flowering plants were found to produce between 0 and 967 seeds. On average, 28.3% of florets were attacked by invertebrate seed predators and a further 46.2% of ovules failed to produce a mature seed for reasons other than predation. The most common, identifiable, predators were Dipterid larvae, including the flightless Diplotoxa moorei. Seed set was most strongly related to the number of florets initiated, but was also significantly related to rates of ovule failure and pre‐dispersal predation. Seed set did not vary systematically with altitude, but ovule failure rate showed a significant increase and predation rate a significant decrease with increasing altitude. Predation rate was also positively related to plant density; altitude and plant density together accounted for 56% of variation in predation rate. Path analysis showed that the near‐zero direct correlation between seed set and altitude was the product of an indirect positive effect, via a strong negative effect on predation rate, being cancelled out by indirect negative effects via reduced floret initiation and increased ovule failure rates with increasing altitude.