Ecological opportunities and intraspecific competition alter trophic niche specialization in an opportunistic stream predator

Abstract

Many generalist populations are composed of specialized individuals that use a narrow part of the population's niche. Ecological theories predict that individual specialization and population trophic niche are determined by biotic interactions and resource diversity emerging from environmental variations (i.e. ecological opportunities). However, due to the paucity of empirical and experimental demonstrations, the genuine importance of each of these drivers in determining trophic niche attributes is not fully appreciated. The present study aimed at determining the population level and individual responses of brown trout (Salmo trutta) to variations in ecological opportunities (terrestrial prey inputs) and autochthonous prey communities among 10 stream reaches along a riparian condition gradient using individual longitudinal monitoring and stable isotope analyses. Our results suggested that trophic niche diversity varied along the environmental gradient, while individual trophic specialization was indirectly driven by ecological opportunities through strengthened intraspecific competition. Individual diet was repeatable over the study period, and the growth rate of juvenile brown trout increased with their specialization for aquatic predatory invertebrates. Our findings highlight the dual influences of intraspecific competition and ecological opportunities on individual trophic specialization and population trophic niche.

Drivers of intrapopulation variation in resource use in a generalist predator, the macaroni penguin

“…In contrast, extrinsic drivers of opportunity reflect conditions that directly affect local prey biomass or availability, e.g. patch size, climate and topo graphy (Herrera et al 2008, Evangelista et al 2014. Thus, ecological opportunity can vary on multiple spatial and temporal scales and can also fluctuate independently of the abundance or number of individuals in a population, i.e.…”

“…The majority of these studies examined ecological opportunity by comparing allopatric or sub-populations that inhabit systems with different extrinsic conditions, such as levels of prey diversity (e.g. Layman et al 2007, Darimont et al 2009, Evangelista et al 2014. However, alternative approaches include a comparison of sympatric species that have different intrinsic constraints restricting foraging range and resource accessibility (Kernaléguen et al 2015).…”

The evolution and ecology of individual specializations amongst a group of dietary generalists.

“…Increased intraspecific competition and ecological opportunity generally increase IS, while increased interspecific competition is thought to decrease IS Bolnick 2005, 2007;Darimont et al 2009;Frédérich et al 2010). However, as mentioned above, there seem to be fairly frequent exceptions to these patterns (Jones and Post 2013;Evangelista et al 2014;Parent et al 2014). A possible explanation is that individuals of different species respond differently to these ecological conditions.…”

“…The best understood of these is intraspecific competition, whose effects on IS have been well studied in both the field and the laboratory Bolnick 2005, 2007;Darimont et al 2009;Bolnick et al 2010;Frédérich et al 2010;Martin and Pfennig 2010;Agashe and Bolnick 2010;Tinker et al 2012, Evangelista et al 2014). An increase in intraspecific competition can increase IS by driving individuals to use novel or less 78!…”

“…First, many individual specializations are often influenced by ecological conditions, and these conditions can change over time. For example, IS is greater when intraspecific competition is high (Svanäck and Bolnick 2007;Agashe and Bolnick 2010;Frédérich et al 2010;Tinker et al 2012;Evangelista et al 2014), when interspecific competition is low ; however see Bolnick et al 2010: AbbeyLee 2013, and when some form of ecological opportunity is available (Nosil and 3! Reimchen 2005;Parent and Crespi 2009;Darimont et al 2009).…”