We are aware of only two papers that investigate the relationship between seed predation and latitude. Garcia et al. (2000) found no correlation between pre-dispersal seed predation and latitude across 31 populations of Juniperus communis. Moles and Westoby (2003a) compiled the global seed predation literature and found no relationship between pre-dispersal seed predation and latitude across 122 species, and no relationship between post-dispersal seed removal and latitude across 205 species. However, data compiled from the literature are necessarily from studies with a wide range of methods, over widely differing time scales. The main purpose of this section of the study is to assess whether a greater proportion of seeds are killed by seed predators near the equator, using simple but consistent methods across a broad range of species at the same sites as used for the herbivory study. We will also ask:

a) How much of the variation in seed predation can be explained by latitude?

b) Are seeds better defended in environments close to the equator?

Levels of pre- and post-dispersal seed predation will be measured for the five species at each site estimated to be producing the greatest biomass of seeds in each season, and for global standard “seeds” such as cracked wheat. Predation trials will be carried out using the same methods as deployed in Moles et al. (in press). That is, pre-dispersal seed predation will be assessed by collecting 100 ripe seeds of each species (from at least five individual plants), and using dissections and/or visual observation to determine the proportion of seeds that have been subject to pre-dispersal seed predation. Seeds will be considered inviable when enough of the embryo has been damaged to make germination unlikely. In order to assess post-dispersal seed removal, at least 100 seeds of each species will be set out in naturally formed depressions in the ground, and removal quantified after 24 hours of exposure to post-dispersal seed predators. This method quantifies post-dispersal seed removal, but not post-dispersal seed predation per se. Most studies of “post-dispersal seed predation” actually measure post-dispersal seed removal in this way. Techniques for following seed fate are available (most commonly used are radio tracking and thread following), but these techniques are too labour intensive for use in a study of this size. Trials using standard seed will be run four times during the year, in order to encompass variability in seed predator activity. Trials on local seed will be run only at the times of year at which such seed is normally available to seed predators.