Metabolic rate interacts with resource availability to determine individual variation in microhabitat use in the wild

Ecological pressures such as competition can lead individuals within a
population to partition resources or habitats, but the underlying
intrinsic mechanisms that determine an individual’s resource use are not
well understood. Here we show that an individual’s own energy demand and
associated competitive ability influence its resource use, but only when
food is more limiting. We tested whether intraspecific variation in
metabolic rate leads to microhabitat partitioning among juvenile Atlantic
salmon (Salmo salar) in natural streams subjected to manipulated nutrient
levels and subsequent per capita food availability. We found that
individual salmon from families with a higher baseline (standard)
metabolic rate (which is associated with greater competitive ability)
tended to occupy faster flowing water, but only in streams with lower per
capita food availability. Faster flowing microhabitats yield more food,
but high metabolic rate fish only benefited from faster growth in streams
with high food levels, presumably because in low food environments the
cost of a high metabolism offset the benefits of acquiring a productive
microhabitat. The benefits of a given metabolic rate were thus
context-dependent. These results demonstrate that intraspecific variation
in metabolic rate can interact with resource availability to determine the
spatial structuring of wild populations.