Abundance-body mass relationships structuring aquatic food webs across biogeographical gradients

Abstract

Most of the biological rates (growth, metabolic, reproduction) are greatly associated with body mass. Trophic interactions are also highly dependent on body mass due to feeding constraints. Scaling of body mass with abundance, known as size spectrum, provides information on community structure, energy flow, and ecosystem functioning. However, not many studies have incorporated individual body mass-abundance scaling of several trophic levels across biogeographical gradients. In our study, we measured abundance- body mass relationships in multitrophic food webs in the Iberian Pond network. This experimental facility comprises six locations (Murcia, Toledo, Évora, Porto, Jaca, and Madrid) in the Iberian Peninsula, covering a variety of climates ranging from arid to alpine. We collected samples of phytoplankton, zooplankton, and macroinvertebrates from 2016-2018 during the growing season. We quantified the abundances and individual body sizes to construct the multitrophic size spectrum for each location. Results revealed a consistent pattern in size spectrum across different biogeographical regions - a higher abundance of smaller individuals observed across all trophic levels, thus supporting theoretical predictions. Despite substantial differences in environmental conditions across space (e.g. arid, temperate and alpine regions) and time (multiple years), no consistent differences were found in multitrophic size spectra. Overall, these preliminary findings suggest that the role of body mass and abundances in shaping food web and community structure may be generalized across environmental and biogeographical gradients.