Abstract
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 offsets 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.
Highlights
Individuals within a population can vary considerably in their patterns of resource use, even when accounting for Variation in resource use is thought to occur because individuals differ in their rank preferences, the criteria by which they rank resources, and/or their ability to obtain their preferred resource, for example, if they are socially dominant versus subordinate (Ekman and Askenmo 1984; Svanbäck and Bolnick 2005; Tinker et al 2009; Araújo et al 2011)
We examined the link between intraspecific variation in metabolic rate and microhabitat use among juvenile Atlantic salmon (Salmo salar) in natural streams subjected to manipulated levels of nutrients and subsequent per capita food availability
Links between metabolic rate and microhabitat use depended on nutrient levels and subsequent per capita food availability
Summary
Individuals within a population can vary considerably in their patterns of resource use, even when accounting for Variation in resource use is thought to occur because individuals differ in their rank preferences, the criteria by which they rank resources, and/or their ability to obtain their preferred resource, for example, if they are socially dominant versus subordinate (Ekman and Askenmo 1984; Svanbäck and Bolnick 2005; Tinker et al 2009; Araújo et al 2011). The baseline energetic cost of living (defined as standard metabolic rate [SMR] in ectotherms and basal metabolic rate in endotherms; Hulbert and Else 2000) can differ up to threefold among individuals in a population (Burton et al 2011) These intraspecific differences in metabolism are repeatable within individuals (Auer et al 2016, 2018b) and consistent within families (Pough and Andrews 1984; Docker et al 1986; Steyermark and Spotila 2000; Pakkasmaa et al 2006; Robertsen et al 2014) across a wide variety of taxa. Individuals with a faster baseline metabolic rate tend to have a higher meal-processing capacity (Millidine et al 2009), activity levels (Careau et al 2008), daily energy expenditure (Auer et al 2017), boldness, competitive dominance, and territorial aggression (Biro and Stamps 2010)
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