A significant proportion of the mortality of rainforest trees occurs during early life stages (seeds and seedlings), but mortality agents are often elusive. Our study investigated the role of herbivorous insects and pathogens in the early regeneration dynamics of Guazumaulmifolia (Malvaceae), an important tree species in agroforestry in Central America. We reared pre-dispersal insect seed predators from G.ulmifolia seeds in Panama. We also carried out an experiment, controlling insects and pathogens using insecticide and/or fungicide treatments, as well as seed density, and compared survivorship of G.ulmifolia seeds and seedlings among treatments and relative to untreated control plots. We observed (1) high pre-dispersal attack (92%) of the fruits of G.ulmifolia, mostly by anobiine and bruchine beetles; (2) negligible post-dispersal attack of isolated seeds by insects and pathogens; (3) slow growth and high mortality (> 95%) of seedlings after 14 weeks; (4) low insect damage on seedlings; and (5) a strong positive correlation between seedling mortality and rainfall. We conclude that for G.ulmifolia at our study site the pre-dispersal seed stage is by far the most sensitive stage to insects and that their influence on seedling mortality appears to be slight as compared to that of inclement weather. Thus, the regeneration of this important tree species may depend on effective primary dispersal of seeds by vertebrates (before most of the seed crop is lost to insects), conditioned by suitable conditions in which the seedlings can grow.

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Plants use many strategies to defend themselves against animals that eat plants, also called herbivores. One clever way that some plants, called myrmecophytes, do this is by teaming up with ants. Myrmecophytes are plants that have evolved close relationships with ants. In return for protection from herbivores, myrmecophytes provide ants with food and/or shelter. Sounds like a great deal, right? Yes, but sometimes working with ants can be tricky for a plant. Because myrmecophytes cannot choose the ant bodyguards that they get, they must balance their needs with the needs of their ant defenders. In this article, we introduce a classic example of plants that have beneficial relationships with ants, describe how ants and plants in these relationships depend on each other, and investigate how these ant-dependent plants interact with various ant species.

Myrmecophytes may adjust the investment on ant rewards, depending on tree size and ant defence level. In swollen-thorn acacias (Vachellia collinsii), we tested whether the level of protection provided by the resident ants (defending vs. non-defending) influenced the relation between tree size and ant rewards, or between types of ant rewards (housing and food). We quantified ant rewards in trees occupied by defending and by non-defending ants. We predicted: (1) a positive relation between plant diameter and ant reward investment, with a steeper slope for defending than for non-defending ant species; and (2) that if there is any tradeoff between ant rewards, it should be aggravated (steeper slope) when inhabited by non-defending ants. We found that most structures for ants grew according to plant diameter, but contrary to our first prediction it was independent of the level of ant defence. Most ant rewards did not show a tradeoff between them, besides a weak negative relation between spine length and number of pinnules, which contrary to the prediction occurred when occupied by defending ants. The evidence shows that the interacting ants had a weaker influence on the scaling of defence structures in myrmecophytes than the habitat (location).