Impact of Holocene environmental change on the evolutionary ecology of an Arctic top predator

Abstract

The Arctic is among the most climatically sensitive environments on Earth, and the disappearance of multiyear sea-ice in the Arctic Ocean is predicted within decades. As apex predators, polar bears are sentinel species for addressing the impact of environmental variability on Arctic marine ecosystems. By integrating genomics, isotopic analysis, morphometrics, and ecological modelling, we investigate how Holocene environmental changes affected the evolutionary ecology of polar bears around Greenland. We show that throughout the last ~11,000 years, Greenlandic polar bears have been heavily influenced by changes in sea-surface temperature (SST) and sea-ice cover. Most notable are major reductions in effective population size at the beginning of the Holocene and during the Holocene Thermal Maximum ~6 kya, which coincide with increases in annual mean SST, reduction in sea-ice covers, declines in suitable habitat, and shifts in suitable habitat northwards. Furthermore, we show how individuals sampled from west and east Greenland are genetically, morphologically, and ecologically distinct. We find bears sampled in west Greenland to be larger, more genetically diverse and have diets dominated by ringed seals, whereas bears from east Greenland are smaller and less diverse with more varied diets, putatively driven by regional biotic differences. Taken together, we provide novel insights into the vulnerability of polar bears to environmental change, and how the Arctic marine ecosystem plays a vital role in shaping the evolutionary and ecological trajectories of its inhabitants.

Four centuries of commercial whaling eroded 11,000 years of population stability in bowhead whales

“…The clear differentiation in δ 15 N between the Canadian Arctic Archipelago and the Svalbard Archipelago is likely due to regional variability in δ 15 N at the base of the food web, as has been reported in other marine predators [37][38][39] . During the second half of the Holocene, δ 15 N in bowhead whales around both the Canadian Arctic Archipelago and the Svalbard Archipelago decreased gradually (Fig 2F ), suggesting a slow change in nutrient dynamics, possibly decreasing rates of sedimentary denitrification, a process which results in 15 Nenrichment in water column organic matter in Arctic and subArctic continental shelf environments 40 .…”

“…The clear differentiation in δ 15 N between the Canadian Arctic Archipelago and the Svalbard Archipelago is likely due to regional variability in δ 15 N at the base of the food web, as has been reported in other marine predators 37–39 . During the second half of the Holocene, δ 15 N in bowhead whales around both the Canadian Arctic Archipelago and the Svalbard…”

“…Nevertheless, the remarkable long-term stability observed in bowhead genetic diversity across the Holocene, despite significant environmental perturbations, is in stark contrast with other Arctic marine mammals for which Holocene demographic reconstructions are available. For example, Greenlandic polar bears ( Ursus maritimus ) experienced marked declines in area of suitable habitat and in population size in the Atlantic Arctic during the Holocene, in response to increasing SST and decreasing sea-ice cover 32 .…”