A trade‐off in vital rates for a large carnivore inhabiting an anthropogenic landscape and a protected island ecosystem

Abstract

Anthropogenic landscapes generally provide abundant human foods but increase mortality risk, which can alter vital rates for some species. Some species exhibit altered survival in anthropogenic landscapes, whereas others exhibit changes in reproduction. While changes in vital rates have been previously documented, the role of human food subsidies in vital rate trade‐offs is often overlooked, especially for large carnivores. Here, we explored how human food subsidies affect American black bear ( Ursus americanus , Makwa [Ojibwe]) apparent survival, recruitment, and population growth rate. We compared bears in a protected island ecosystem featuring minimal risk of human‐caused mortality and little human food to a neighboring mainland population featuring relatively high human‐induced mortality from hunting but abundant human food subsidies. We estimated proportional diets of 105 bears using stable isotope analysis (δ ¹³ C and δ ¹⁵ N), assessed how landcover types in bear use areas influence diet, and explored how these variables affected bear vital rates. Island bears consumed almost entirely natural foods, principally hard mast, with virtually no human foods. Mainland bears consumed a diversity of items with nearly 1/3rd of their diet coming from human foods. Bear survival on protected islands increased with the amount of hard mast consumed, while survival on the mainland was not correlated with either diet or landcover. These populations also exhibited notable differences in vital rates: bears on the islands were characterized by high survival (>0.8 annual survival) but low recruitment (<0.2 annual recruitment), whereas bears on the mainland exhibited 37% lower survival (0.44 annual survival) but 35% (0.54 annual recruitment) higher recruitment. Our work suggests that anthropogenic landscapes, and notably food subsidies they provide, can lead to a trade‐off in vital rates by changing the risk‐reward landscape. Conversely, refugia that maintain natural trophic pathways can maintain intact food webs and ecosystem processes.