Print PageA well known and thoroughly studied case of a mutualistic relationship is the interaction of American swollen‐thorn Acacias and their ant inhabitants (Janzen, 1966). Ants also visit Australian Acacias, attracted principally by extra-floral nectaries. What are they doing there?. This mutualism is still unstudied for most Acacia species, despite being one of the biggest groups of vascular plants on the continent, with over 900 species. We examined fitness-related traits in Acacia myrtifolia at four sites across a 600 km ecological gradient in south-eastern Australia. We sampled the background ant fauna and conducted ant- and pollinator-exclusion experiments for one year at each site. We ask whether the presence of various ant guilds explains variation in herbivory damage, growth rate, pollinator visitation rates, fruit set, seed germination and seedling establishment. Analysing to what extent does the combination of interactions impact the plant’s fitness.
Results/Conclusions
Our data shows differences in ant fauna feeding on extra-floral nectar among sites, but no obvious differences in herbivory damage between plants or among sites. Our observations suggest that there are effects of ant-present and ant-exclusion treatments on increasing branch growth and seed set. Fruit set required pollinator visits (except at one site, where pollinator exclosures may have been breached), but, fruit set rates were low (4–30%). The exclusion of ants had no apparent effect on pollinator visitation rates and did not alter the production of fruits.
The array of guilds plays a significant role in this study system. Our results on fruit set as an index of successful pollination, imply that this plant could be another example where pollination occurs by insects, wind and autonomous pollination. In relating multiple interactions we gain an insight into the evolution of complex net interactions and the result of different trade-off decisions.
