Exploitation competition between seed predators and dispersers introduced to Hawaiian forests.

Exploitation competition occurs when one group of organisms reduces the availability of a resource for another group of organisms. For instance, plants produce a certain number of fruits for seed dispersal by fruit-eating animals (hereafter frugivores), and fruit consumption by one group of frugivores can reduce the number of fruits available for other frugivores. However, it is uncertain whether exploitation competition is common among frugivores, particularly in novel ecosystems, where food resources are generally thought to be abundant and invasive species are dietary generalists.

Mechanisms underlying interaction frequencies and robustness in a novel seed dispersal network: lessons for restoration.

As human-caused extinctions and invasions accumulate across the planet, understanding the processes governing ecological functions mediated by species interactions, and anticipating the effect of species loss on such functions become increasingly urgent. In seed dispersal networks, the mechanisms that influence interaction frequencies may also influence the capacity of a species to switch to alternative partners (rewiring), influencing network robustness. Studying seed dispersal interactions in novel ecosystems on O'ahu island, Hawai'i, we test whether the same mechanisms defining interaction frequencies can regulate rewiring and increase network robustness to simulated species extinctions.

Ecological correlates of species' roles in highly invaded seed dispersal networks.

Ecosystems with a mix of native and introduced species are increasing globally as extinction and introduction rates rise, resulting in novel species interactions. While species interactions are highly vulnerable to disturbance, little is known about the roles that introduced species play in novel interaction networks and what processes underlie such roles. Studying one of the most extreme cases of human-modified ecosystems, the island of O'ahu, Hawaii, we show that introduced species there shape the structure of seed dispersal networks to a greater extent than native species.

Age and performance at fledging are a cause and consequence of juvenile mortality between life stages.

Should they stay or should they leave? The age at which young transition between life stages, such as living in a nest versus leaving it, differs among species and the reasons why are unclear. We show that offspring of songbird species that leave the nest at a younger age have less developed wings that cause poorer flight performance and greater mortality after fledging. Experimentally delayed fledging verified that older age and better developed wings provide benefits of reduced juvenile mortality.