Ecology of plant breeding systems

Breeding sytem impacts on the ecology and evolution of coexisting plant species. Perhaps the best example of such impacts is exemplified by dioecious plant species (those with separate male and female individuals), populations of which suffer a fitness cost because of a lower number of seed-bearing stems relative to ecologically similar hermaphrodite species. To maintain per capita growth rates that are equal to their hermaphroditic counterparts, female individuals in dioecious populations must exhibit one or more fitness advantages, which might include: higher fecundity, higher rates of offspring recruitment, earlier ages of reproduction, or higher offspring quality. The fitness advantages predicted to have evolved in dioecious species have remained elusive because of inadequate data and a failure to fully integrate phylogeny and dynamic demographic and distribution data with other species functional traits.

I have developed a database of plant reproductive functional traits, which when combined with demographic data for many species from some of the world's best monitored plant populations, and analysed accounting for the phylogenetic autocorrelation between species, is leading to insights into the impact of dioecy on plant ecology and evolution.


Sex ratios and reproductive investment in the Myristicaceae

Dioecious species often exhibit male-biased sex ratios, even though the overall population sex ratio is close to 1:1. Investment in reproduction is often greater by females in any one reproductive event, and this means that males can reproduce more frequently, mature earlier, and survive longer than females.

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Seed size in woody tropical species

From data on >1,200 species from Yasuni (Ecuador) and Manu (Peru), I have investigated differences in seed size between dioecious and hermaphrodite species. Seed size is highly phylogenetically dependent and differs greatly between life forms. The influence of breeding system on seed size at Yasuni appears to be small.

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Tropical tree breeding systems

A survey of the breeding systems of a series of large forest plots has confirmed the high proportion of dioecy in both species and individuals in tropical forests in the Americas, Africa and Asia.

Factors influencing the distribution of breeding systems

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The factors affecting the distribution of dioecious species have received surprisingly little attention and, as a consequence, are poorly understood. For example, there is a well-documented negative association between dioecy and latitude, for which we have no candidate mechanisms. Conversely, it has been suggested that the relative proportion of dioecious species should be positively correlated with changes in elevation

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Anyone with population demographic or seed size data on a large number of species wishing to collaborate on these questions, please contact me!