Local adaptation of fish consumers alters primary production through changes in algal community composition and diversity

Abstract

Ecological research has focused on understanding how changes in consumer abundance affects community structure and ecosystem processes. However, there is increasing evidence that evolutionary changes in consumers can also alter community structure and ecosystem processes. Typically, the effects of consumer phenotype on communities and ecosystem processes are measured as net effects that integrate numerous ecological pathways. Here, we analyze new data from experimental manipulations of Trinidadian guppy Poecilia reticulata presence, density and phenotype to examine how effects on the algal community cause changes in gross‐primary production (GPP). We combine analytical tools borrowed from path analysis with experimental exclosures in mesocosms to separate the ecological and evolutionary effects of guppies into direct and indirect components. We show that the evolutionary effects of guppy phenotype act through different ecological pathways than the effects of guppy presence and density on GPP. As reported in previous studies that used a different measure of algal biomass, adding guppies and doubling their densities decreased algal biovolume through direct effects. In contrast to these previously reported results, exchanging guppy phenotypes that live without predators for phenotypes that live with predators did not affect algal biovolume. Instead, guppies from populations that live with predators increased the diversity of algal species and increased GPP compared to guppies that live without predators. These changes in the algal community were driven primarily by guppy phenotypes that live with predators—algal communities in mesocosms without fish were similar to those with guppies from predator‐free locations, but both were different from mesocosms with guppies from populations that live with predators. Changes in the algal community were driven directly by differences in foraging behavior between the two consumer phenotypes. We reconcile these results with our previous findings, thereby enhancing our understanding of the relationship between ecological and evolutionary processes.

Predictable adaptive trajectories of sexual coloration in the wild: Evidence from replicate experimental guppy populations*

“…We know for example that experimental populations experienced rapid intrinsic rates of increase, which in‐turn substantially altered the composition of resident algal communities (Bassar et al. ). This has direct relevance for orange spots because algae provide the carotenoid pigments needed to express such markings.…”

“…In addition, reciprocal feedbacks between guppies and their newly colonized environments (e.g., El-Sabaawi et al 2015) will modify the nature of selection over time. We know for example that experimental populations experienced rapid intrinsic rates of increase, which in-turn substantially altered the composition of resident algal communities (Bassar et al 2017). This has direct relevance for orange spots because algae provide the carotenoid pigments needed to express such markings.…”

Predicting Coexistence in Species with Continuous Ontogenetic Niche Shifts and Competitive Asymmetry

“…Guppies from these two localities are also know to consume different resources (i.e. they occupy different, but broadly overlapping, resource niches; Bassar et al 2010, Zandonà et al 2011, Bassar et al 2015, El-Sabaawi et al 2015, Bassar et al in press-a ) and may differ in the competitive abilities.…”

Variability of functional traits and their syndromes in a freshwater fish species (Phoxinus phoxinus): The role of adaptive and nonadaptive processes

“…Quantifying excretion rate on starved individuals was done to avoid an effect of differential consumption, which is a strong factor affecting the rate of nitrogen excretion (Glaholt & Vanni, ). Changes in concentration in water can affect ecosystem functioning through an increase in nutrient availability (Capps & Flecker, ) and primary production (Bassar et al, ; Schmitz, Hawlena, & Trussell, ). Following Villéger et al (), individuals were placed in plastic bags containing 500 ml of spring bottled water for 1 hr at 17°C.…”