Peter Cuneo

History of the invasive African olive tree in Australia and Hawaii: evidence for sequential bottlenecks and hybridization with the Mediterranean olive.

Humans have introduced plants and animals into new continents and islands with negative effects on local species. This has been the case of the olive that was introduced in Australia, New Zealand and Pacific islands where it became invasive. Two subspecies were introduced in Australia, and each successfully invaded a specific area: the African olive in New South Wales (NSW) and the Mediterranean olive in South Australia. Here, we examine their origins and spread and analyse a large sample of native and invasive accessions with chloroplast and nuclear microsatellites. African olive populations from the invaded range exhibit two South African chlorotypes hence supporting an introduction from South Africa, while populations from South Australia exhibit chlorotypes of Mediterranean cultivars. Congruently, nuclear markers support the occurrence of two lineages in Australia but demonstrate that admixture took place, attesting that they hybridized early after introduction. Furthermore, using an approximate Bayesian computation framework, we found strong support for the serial introduction of the African olive from South Africa to NSW and then from NSW to Hawaii. The taxon experienced successive bottlenecks that did not preclude invasion, meaning that rapid decisions need to be taken to avoid naturalization where it has not established a large population yet.

Seed ecology of the invasive woody plant African Olive (Olea europaea subsp. cuspidata): implications for management and restoration

Knowledege of the seed ecology of invasive exotic species, including soil seedbank dynamics, is essential to understanding key factors in successful invasion and in identifying management opportunities. African Olive, Olea europaea L. subsp. cuspidata, is an exotic invasive woody plant in Hawaii, Norfolk Island and eastern Australia, and is now well established in the Cumberland Plain region of western Sydney, Australia. In the present study, the key aspects of the seed ecology of African Olive were determined for populations in western Sydney. Extracted seed germinated at a wide range of temperatures, consistent with tolerance of a wide range of climatic conditions. A seed-burial experiment indicated a slow decrease in viability down to 70.3% during the first year, followed by a rapid decline down to 14.7% in the second year. Probit analysis indicated that under field conditions, seed persistence in the soil was ~29 months (2.4 years). In situ germination was low (3.3%) and did not occur until the mechanical constriction of the endocarp was released through decomposition. The woody seed endocarp was found to be permeable to water, indicating that physical dormancy was not imposed by providing a barrier to water uptake. Within its invasive range, African Olive produces abundant seed. However, the rapid loss of viability of soil-stored seed results in a narrow window of opportunity for germination. The short persistence of seed in the soil may provide an opportunity for managers to achieve control of African Olive once mature plants are removed.

An ecological and evolutionary perspective on the parallel invasion of two cross-compatible trees

The cultivated olive is an iconic Mediterranean crop that has been spread over the world in all regions with a Mediterranean climate. The species is however able to escape from cultivation, and can invade new ranges with negative impacts on native vegetation. The parallel invasion of two olive subspecies in different climatic zones of Australia provides an interesting case study of invasion, characterised by early genetic admixture between domesticated and wild taxa. In this synthesis, we provide an overview of the history and ecology of invasive olives, and identify further research needed to guide future management and invasion risk.