Warming strengthens food web effects of predator phenotypic variation

Intraspecific variation modifies ecological processes and ecosystem
functioning. Still, we know relatively little of how the nature and
strength of ecosystem effects caused by intraspecific variation may
interact with climate change. We conducted a mesocosm experiment to test
if, and to what extent, ocean warming modifies the ecological impacts of
intraspecific variation in a predatory fish. The mesocosms consisted of a
simplified coastal food web with threespine stickleback (Gasterosteus
aculeatus) as the top predator, from a population where two stickleback
phenotypes with either complete or incomplete lateral armour plating
coexist and display differentiated predation behavior: The completely
plated phenotype often feeds more on invertebrate herbivores compared to
the incompletely plated phenotype. Presence of stickleback reduced biomass
of arthropod shredders (crustaceans, insect larvae). Warming (+4 °C)
strengthened this predation, releasing benthic primary producers (diatoms)
from top-down control, causing a trophic cascade. This trophic cascade was
attributed to one of the plate phenotypes: the completely plated
stickleback increased their predation on shredders under warming, while
the incompletely plated stickleback instead decreased their predation.
Diatom biomass responded accordingly: warming increased diatom biomass in
the presence of completely plated stickleback but not when incompletely
plated stickleback were present. Our results suggest that different plate
phenotypes of threespine stickleback differentially affect lower trophic
levels, and that warming may exacerbate these cascading effects. These
trait-dependent effects on trophic cascades highlight the consequences of
intraspecific variation on ecosystem functioning.

# Warming strengthens food web effects of predator phenotypic variation
Dataset DOI: https://doi.org/10.5061/dryad.kprr4xhhn
Salo_et_al_predation.csv Salo_et_al_plate_phenotypes.csv
Salo_et_al_stomach_contents.csv Contact information:
[[email protected]](mailto:[email protected]) Data for
Salo_et_al_predation.csv include: temperature: temperature treatment in
the study (ambient, high) predation: presence or absence of top predators
in the mesocosm (fish, no fish) plate_phenotypes: three-spine stickleback
plate phenotype (completely plated, incompletely plated, both, no_fish)
waterbath: waterbath id for nested analyses shredder_biomass: the biomass
(g dw) of shredders in the mesocosm shredder_survival: the survival of
shredders in the mesocosm shredder_recruitment: the recruitment of
shredders to the mesocosm gastropod_biomass: the biomass (g dw) of
gastropods in the mesocosm theodoxus_eggs: the biomass (g dw) of Theodoxus
fluviatilis eggs in the mesocosm diatom_biomass: the biomass (g dw) of
diatoms in the mesocosm epiphyte_biomass: the biomass (g dw) epiphytic
macroalgae in the mesocosm turbidity: turbidity in the mesocosm Data for
Salo_et_al_plate_phenotypes.csv include: temperature: temperature
treatment in the study (ambient, high) plate_phenotypes: three-spine
stickleback plate phenotype (completely plated, incompletely plated, both,
none) waterbath: waterbath id for nested analyses shredder_biomass: the
biomass (g dw) of shredders in the mesocosm shredder_survival: the
survival of shredders in the mesocosm shredder_recruitment: the
recruitment of shredders to the mesocosm gastropod_biomass: the biomass (g
dw) of gastropods in the mesocosm theodoxus_eggs: the biomass (g dw) of
Theodoxus fluviatilis eggs in the mesocosm diatom_biomass: the biomass (g
dw) of diatoms in the mesocosm epiphyte_biomass: the biomass (g dw)
epiphytic macroalgae in the mesocosm turbidity: turbidity in the mesocosm
Data for Salo_et_al_stomach contents.csv include: temperature: temperature
treatment in the study (ambient, high) phenotype_teatment: three-spine
stickleback plate phenotypes in the mesocosm (completely plated,
incompletely plated, both) plate_phenotype: plate phenotype of the fish
(completely plated, incompletely plated) mesocosm_code: mesocosm id for
any nasted analyses waterbath: waterbath id for any nested analyses
shredders: biomass (g dw) of shredders in the stomach