Impact of Insect Predation on Ovule Survivorship in Eucalyptus Baxteri

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Abstract
(1) Limitations of resources and pollen are often highlighted as factors regulating ovule survivorship, and the importance of ovule predation has received compartively little attention. The results presented here demonstrate that insect predation is a major factor influencing ovule survivorship throughout ovule development in Eucalyptus baxteri in south-eastern Australia. (2) The potential life of an ovule was considered to begin with the first appearance of floral buds, and to end as a dispersed seed available for germination. Buds of E. baxteri are produced over summer, and flowering occurs two summers later. One cohort of buds was heavily galled, and less than 20% flowered. Galling appeared to have adverse effects on the proportion of surviving buds flowering and on the proportion of flowers maturing fruit. Mortality of the previous cohort of buds, which was not galled, was also high, but was apparently caused by low water availability. The proportion of flowers maturing fruit was about 30% in both cohorts. At this stage total ovule mortality was at least 95%. (3) The woody fruits mature late in the year following flowering and many persist unopened for several years. Pre-dispersal insect seed predators reduced seed production by at least 70% due primarily to their effects on seed/ovule ratios and on seed viability, and seed harvesting ants destroyed about 90% of dispersed seeds. The proportion of ovules that became viable seeds available for germination was less than 0.2%. (4) Predation by insects appeared to have potentially important effects on flowering intensity, flowering success, premature fruit abscission, seed/ovule ratios, seed viability, and directly on the supply of dispersed seeds. (5) The importance of predation demonstrated here suggests that the traditional pollen vs resource limitation debate has seriously neglected another major source of ovule mortality.