Predator‐mediated effects of severe drought associated with poor reproductive success of a seabird in a cross‐ecosystem cascade

Thomsen, Sarah; Green, David

Despite the profound impacts of drought on terrestrial productivity in coastal aridecosystems, only a few studies have addressed how drought can influence ecologicalcascades across ecosystem boundaries. In this study, we examine the consequencesof rainfall pulses and drought that subsequently impact the breeding success of athreatened nocturnal seabird, the Scripps's Murrelet (Synthliboramphus scrippsi). Onan island off the coast of southern California, the main cause of reduced nest successfor one of their largest breeding colonies is egg predation by an endemic deer mouse(Peromyscus maniculatus elusus). Mice on the island have an opportunistic diet of pri‐marily terrestrial sources, but drastic declines in terrestrial productivity from droughtmight be expected to increase their reliance on marine resources, including murreleteggs. We compiled data on terrestrial and marine productivity between 1983 and2013 to determine how conditions in these ecosystems influence murrelet nest suc‐cess. We found that the severity of drought had the strongest negative impact onmurrelet nest success. We calculated that the reduction in fecundity during droughtyears due to increased egg predation by mice was substantial enough to produce adeclining population growth rate. Nest success was much higher under normal orhigh rainfall conditions, depending on whether oceanic conditions were favorable tomurrelets. Therefore, the more frequent and severe drought that is projected for thisregion could lead to an increased risk of murrelet population decline on this island.Our study highlights the need for understanding how species interactions will changethrough the effects of increasing drought and altered rainfall regimes under globalchange