Abstract
Population variation in trophic niche is widespread among organisms and is of increasing interest given its role in both speciation and adaptation to changing environments. Trinidadian guppies (Poecilia reticulata) inhabiting stream reaches with different predation regimes have rapidly evolved divergent life history traits. Here, we investigated the effects of both predation and resource availability on guppy trophic niches by evaluating their gut contents, resource standing stocks, and δ15N and δ13C stable isotopes across five streams during the wet season. We found that guppies from low predation (LP) sites had a consistently higher trophic position and proportion of invertebrates in their guts and assimilate less epilithon than guppies from high predation (HP) sites. Higher trophic position was also associated with lower benthic invertebrate availability. Our results suggest that LP guppies could be more efficient invertebrate consumers, possibly as an evolutionary response to greater intraspecific competition for higher quality food. This may be intensified by seasonality, as wet season conditions can alter resource availability, feeding rates, and the intensity of intraspecific competition. Understanding how guppy diets vary among communities is critical to elucidating the role of niche shifts in mediating the link between environmental change and the evolution of life histories.
Highlights
Trophic niche differentiation and resource polymorphisms are important and ubiquitous ecological phenomena[1, 2], and are often the result of the exploitation of new resources or habitats in response to extrinsic environmental change[3]
The “efficiency” hypothesis is supported by our findings that guppies in low predation (LP) sites consumed and assimilated less detritus and had higher estimated trophic position than high predation (HP) guppies
Differences in trophic position between HP and LP guppies were small in magnitude, and were negatively correlated with invertebrate biomass, which is different from what previous studies conducted in the dry season had shown
Summary
Trophic niche differentiation and resource polymorphisms are important and ubiquitous ecological phenomena[1, 2], and are often the result of the exploitation of new resources or habitats in response to extrinsic environmental change[3]. The lower predation intensity is associated with increased guppy population density and reduced food availability[14,15,16] In addition to these differences, HP and LP locations often present broad environmental differences, which might significantly alter the resources available to guppies. Understanding how guppy diets vary among predation environments and across gradients in resources is critical to elucidating the role of niche shifts in mediating the link between environmental change and the evolution of life histories. Longer guts often represent an adaptation to low quality food[24, 25], supporting the hypothesis that LP guppies are more herbivorous/detritivorous, feeding on lower quality resources. We refer to this as the “specialization” hypothesis, which suggests that HP guppies are more selective and specialized on higher quality resources (i.e. invertebrates)
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