Past work

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Pollinator Contribution Synthesis

 

Although 87% of plant species are pollinated by animals, we don't know exactly how important pollinators are for their reproduction because many plant species have some ability to self-fertilise without insects. To understand the potential impacts of pollinator declines on plant reproduction, we obtained data on the contribution of pollinators to plant reproduction from 1528 separate pollinator exclusion experiments, representing 1392 plant populations and 1174 species from 143 plant families across the world. We showed that the majority of flowering plants are highly dependent on pollination by insects, even though some species are pollinated by wind or can self-pollinate.

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Joint evolution of self-fertilisation and dispersal 

 

One might expect that plants (or even animals) with colonising lifestyles would evolve to be both good at dispersal, to reach new habitat and good at self-fertilisation to ensure reproduction after arriving there. In a study of self-fertilisation and dispersal in annual daises with Allan Ellis and Caroli de Waal, we found that some species do have both high self-fertilisation and high dispersal abilities. A previous model predicted that self-fertilisation and dispersal should have a negative relationship (Cheptou & Massol 2009. Am. Nat. 174: 44-55) but it did not incorporate the benefit of self-fertilisation for mitigating low density of colonising individuals (ie an Allee effect).  In a study with Pietro Landi and Cang Hui, we showed that the Good Coloniser Syndrome can evolve in metapopulations with Allee effects.

 

The evolutionary role of pollen limitation and self-pollination in the Greater Cape Floristic Region

 

I synthesised information on pollination in The Greater Cape Floristic Region (GCFR) of South Africa while during a postdoc with Allan Ellis at Stellenbosch University, South Africa. The GCFR consists of two biodiversity hotspots with a total of around 11 400 plant species, over half of which come from only 33 evolutionary radiations. This makes the GCFR an important model system for the study of speciation. Limitation of the reproduction by the pollination process is a potent evolutionary force and it has been believed that this pollen limitation is higher in the GCFR than other parts of the world. As speciation in the GCFR often coincides with shifts in pollination system, it has been suggested that exceptionally high pollen limitation in the region has contributed to diversification by favouring pollination shifts and pollinator driven speciation. However, it hadn't been assessed if pollen limitation in the GCFR was actually higher than in other parts of the world. I synthesised data from the GCFR and the rest of South Africa to do this. I found no evidence for higher pollen limitation in South Africa as a whole or the GCFR in particular compared to pollen limitation globally.  Interestingly, pollinator-dependent self-compatible species had even higher pollen limitation than self-incompatible species.

 

 

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Consequences of self-fertilisation for fecundity and progeny performance in invasive plants

During my PhD with Steve Johnson at the UKZN in Pietermariburg I worked on the ecological consequences of self-fertilisation for invasive plants, using detailed case studies. I  focused on an idea called Baker’s Law, which states that plants that can self-fertilise should be better colonisers than those that can’t because self-fertilisation allows small groups of plants or single individuals, isolated after long distance dispersal, to reproduce despite shortages of pollinators or mates. I showed that in Lilium formosanum, a Taiwanese species that is invasive in South Africa, plants relied on self-fertilisation for two thirds of their seed production because of inadequate cross-pollination by their hawkmoth pollinators. Single isolated plants depended even more on self-pollination, not because they got visited any less by pollinators but because pollinators were less likely to already be carrying pollen from another plant when they visited isolated individuals. One of my current projects is a continuation of this work.