The effects of seabirds, rats and ecosystem restoration on invertebrate food webs
Dr Joshua Thoresen, will present the Department of Biological Science's seminar with a talk entitled, "The effects of seabirds, rats and ecosystem restoration on invertebrate food webs".
Seabirds are ecosystem engineers: they shape the islands that they nest on in dramatic ways including through the transfer of nutrients from the sea to land. This creates highly fertile ecosystems and nutritious plants, which then support abundant and diverse invertebrates, reptiles and birds. However, seabirds are in decline worldwide, as are their community- and ecosystem-level impacts, primarily due to invasive predatory mammals. If seabirds return to a previously degraded nesting island the ecosystem can recover quickly, returning to a pre-disturbance state within as little as 20 years. However, legacy effects of the invasive mammals may occur meaning ecosystems may revert to alternate stable states. Attempting to study entire ecosystems is often prohibitive in cost and effort. I therefore studied a subset of these ecosystems: invertebrate communities. Invertebrate communities are complex and can reflect the functionality of ecosystems, thus they can be used as indicators of ecosystem cohesiveness. I employed network analysis of invertebrate food webs, as a means of simplifying ecological complexity, to better understand the effects seabirds, their loss, and recolonization, may have on island invertebrate communities. I found that on rat-invaded islands the invertebrate food webs were smaller and less complex than on their seabird-dominated counterparts, likely due to the suppression of seabird derived nutrients and consequent effects on trophic cascades. I then used this knowledge to compare a recovering island with one never disturbed to attempt to predict patterns of restoration. I found that while the communities looked similar, there were important groups missing from the recovering island.