
Biogeographic features mediate marine subsidies to island food webs
Author(s) -
Obrist Debora S.,
Hanly Patrick J.,
Brown Norah E. M.,
Ernst Christopher M.,
Wickham Sara B.,
Fitzpatrick Owen T.,
Kennedy Jeremiah C.,
Nijland Wiebe,
Reshitnyk Luba Y.,
Darimont Chris T.,
Starzomski Brian M.,
Reynolds John D.
Publication year - 2022
Publication title -
ecosphere
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.255
H-Index - 57
ISSN - 2150-8925
DOI - 10.1002/ecs2.4171
Subject(s) - food web , ecology , trophic level , detritivore , marine ecosystem , ecosystem , context (archaeology) , biology , geography , environmental science , paleontology
Although marine subsidies often enrich terrestrial ecosystems, their influence is known to be context‐dependent. Additionally, the multitrophic impact of marine subsidies has not been traced through food webs across physically diverse islands. Here, we test predictions about how island characteristics can affect marine enrichment of food web constituents and how nutrients flow through island food webs. To evaluate enrichment and trace marine nutrients across food webs, we used stable isotopes of soil, flora, and fauna ( n = 4752 samples) collected from 97 islands in British Columbia, Canada. Island area was the strongest predictor of enrichment across taxa; we found that samples were more 15 N‐rich on smaller islands. Enrichment declined with distance from shore but less so on small islands, implying a higher per‐unit‐area subsidy effect. These area and distance‐to‐shore effects were taxon‐specific, and nearly twice as strong in basal food web groups. We also found that increases in δ 15 N correlated with increases in %N in basal trophic groups, as well as in songbirds, implying biologically relevant uptake of a potentially limiting nutrient. Path analysis demonstrated that subsidies in soil flow through plants and detritivores, and into upper‐level consumers. Our results reveal an interplay between island biogeography and marine subsidies in shaping island food webs through bottom‐up processes.