Body size variation in aquatic consumers causes pervasive community effects, independent of mean body size

• Published in: Ecology and evolution 2017-12, Vol.7 (23), p.9978-9990
• Main Authors: Carlson, Bradley E., Langkilde, Tracy
• Format: Article
• Language: English
• Subjects: Animal behavior; Biodiversity; Body size; Communities; Community composition; Consumers; Ecological effects; Forage; Genetic variability; Interspecific; intraspecific trait variation; Mesocosms; Original Research; Phenotypic variations; Populations; Predation; Predators; Prey; size structure; tadpoles; Trophic levels; Variability; Zooplankton
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.3511

Intraspecific phenotypic variation is a significant component of biodiversity. Body size, for example, is variable and critical for structuring communities. We need to understand how homogenous and variably sized populations differ in their ecological responses or effects if we are to have a robust understanding of communities. We manipulated body size variation in consumer (tadpole) populations in mesocosms (both with and without predators), keeping mean size and density of these consumers constant. Size‐variable consumer populations exhibited stronger antipredator responses (reduced activity), which had a cascading effect of increasing the biomass of the consumer's resources. Predators foraged less when consumers were variable in size, and this may have mediated the differential effects of predators on the community composition of alternative prey (zooplankton). All trophic levels responded to differences in consumer size variation, demonstrating that intrapopulation phenotypic variability can significantly alter interspecific ecological interactions. Furthermore, we identify a key mechanism (size thresholds for predation risk) that may mediate impacts of size variation in natural communities. Together, our results suggest that phenotypic variability plays a significant role in structuring ecological communities. The degree of variation in body size may be an important factor for understanding how a population affects a community. We found that populations of tadpoles that were more variable in size, but of the same average size, had contrasting effects on tadpole behavior, resource biomass, predator behavior, and the abundance of an alternative prey. We propose size‐based thresholds for predation risk as a mechanism producing these effects.