Climate drives the geography of marine consumption by changing predator communities

Abstract

The global distribution of primary production and consumption by humans (fisheries) is well-documented, but we have no map linking the central ecological process of consumption within food webs to temperature and other ecological drivers. Using standardized assays that span 105° of latitude on four continents, we show that rates of bait consumption by generalist predators in shallow marine ecosystems are tightly linked to both temperature and the composition of consumer assemblages. Unexpectedly, rates of consumption peaked at midlatitudes (25 to 35°) in both Northern and Southern Hemispheres across both seagrass and unvegetated sediment habitats. This pattern contrasts with terrestrial systems, where biotic interactions reportedly weaken away from the equator, but it parallels an emerging pattern of a subtropical peak in marine biodiversity. The higher consumption at midlatitudes was closely related to the type of consumers present, which explained rates of consumption better than consumer density, biomass, species diversity, or habitat. Indeed, the apparent effect of temperature on consumption was mostly driven by temperature-associated turnover in consumer community composition. Our findings reinforce the key influence of climate warming on altered species composition and highlight its implications for the functioning of Earth's ecosystems.

Keywords: biogeography; latitudinal gradients; macroecology; seagrass; trophic processes.

Fig. 1.

Distributions of bait consumption by generalist marine predators and temperature across the 42 sites in this study. (A) Consumption rate of tethered dried squid bait peaks at midlatitudes in both hemispheres. Point color represents habitat, and lines show independent quadratic generalized linear models fitted for each habitat type in each hemisphere. (B) Map of study sites. (C) Latitudinal pattern of mean annual SST.

Fig. 2.

Composition of consumer assemblages reflects global gradients in environmental temperatures and consumption rate. (A) Principal-coordinate analysis, where locations of symbols reflect compositional differences among sites and habitats based on family-level presence–absence data. Symbol color represents mean annual sea surface temperature (°C), and symbol size corresponds to bait consumption rate. (B) The same ordination showing scores for consumer families driving differences in composition and consumption rate among sites. Symbol color represents average in situ temperature at sites where the predator family was observed; label color represents positive (red), negative (purple), or nonsignificant (black) correlations with consumption rate; and body length (width for crabs) is proportional to the magnitude of the correlation. Asterisks denote families that were seen feeding on bait in video footage.

Fig. 3.

Predator composition mediates the effect of thermal environment on consumption rates. (A–C) Bivariate relationships between consumer composition (PCoA1, Fig. 2A), thermal environment (SST), and consumption rate. Lines show predictions from models used in mediation analysis (A, linear regression; B, logistic regression; C, generalized additive modeling). (D) Paths represent causal hypotheses about relationships. Numbers next to paths leading to and from consumer composition are standardized regression coefficients and SEs. Numbers above and below the path from thermal environment to consumption rate are estimated degrees of freedom and χ² values for the smooth term in the presence and absence of mediation, respectively. Numbers above the path diagram are estimates of the direct and indirect (mediation) effects with 95% bootstrapped CIs.