Data from: Individual specialization in a generalist apex predator: The leopard seal

Apex predators are typically considered dietary generalists, often masking
individual variability. However, individual specialization—consistent
differences in diet and foraging strategies among individuals— is common
in apex predators. In some species, only a few specialized individuals can
significantly impact prey populations. Leopard seals (Hydrurga leptonyx)
are apex predators important to the structure and function of the Southern
Ocean ecosystem. Leopard seals are broadly described as generalists, but
little is known about their trophic ecology at the population or
individual level. We analyzed δ13C and δ15N profiles in whiskers
(n=46) from 34 leopard seals from an important aggregation in the Western
Antarctic Peninsula to assess population and individual trophic variation.
We also evaluated individual consistency across years using repeat samples
from 7 seals collected over 2-10 years. We compared population and
individual isotopic niche space and explored drivers of intraspecific
variation in leopard seal trophic ecology. We find that leopard
seals have a broad trophic niche (range: 6.96-15.21‰) and are generalists
at the population level. However, most individuals are specialists (59%
for δ15N and δ13C), with only a few generalists (13% for δ15N, 6% for
δ13C). Furthermore, individual seals specialize at different trophic
levels, resulting in niche partitioning. Most variation in trophic ecology
is driven by individual specialization, but sex and mass also contribute.
We also find that some seals specialize over time, consistently foraging
at the same trophic level, while others switch trophic levels within and
between years. Long-term specialization by only a few leopard
seals has likely contributed to the decline of a significant local
mesopredator colony, the Antarctic fur seal. Our findings show the
importance of examining individual specialization in leopard seals across
their range to understand their impact on other prey populations. More
broadly, this approach should be applied to other apex predator
populations, as a few specialists can significantly impact ecosystems.