ACROSS

Across Project

Biodiversity is not distributed equally across the globe, and consistent variations of richness have been observed along latitudinal gradients with a myriad of hypotheses explaining such species diversity patterns. However, species-based processes (e.g., extinction and colonization rates) are more difficult to detect than changes in the biological performance of individuals (e.g., survival, reproduction) because the influence of environmental factors occurs at the individual level. Individual body size is a fundamental trait in organisms that plays a key role in bioenergetics and metabolism. Thus, community size structure (i.e., the distribution of individual body sizes regardless of species identity) may provide novel insights to understand global ecological patterns and to represent community facets.

The ACROSS aims to (i) assess latitudinal gradients of community size spectrum of aquatic and terrestrial animals using a meta-analysis approach and (ii) determine species richness variations across these ecosystems. With the ACROSS project we will highlight the importance of using size-based approaches to reflect changes at a global scale, improving the knowledge base for the implementation of a macroecological theory of bioenergetics with individual body size as a key element. The ACROSS project will also involve international collaboration, result dissemination, and publication in top-ranked scientific journals.

The ACROSS project aims at coupling current knowledge on LGB patterns and size-spectrum theory to better explain the global distribution of biodiversity. Specifically, the project will pursue three objectives (O), which include one hypothesis (H) each:

O1 Identify the role of individual-based processes in driving LGB in species richness. H1 The size-based processes occurring at individual level will determine the unexplained variation of a classical species richness-climate correlation (Fig. 1A).

O2 Determine latitudinal biodiversity gradients (LGB) of size spectrum for animal communities H2 There will be a negative relationship between climate temperature and size spectra (i.e., steeper size spectra structure and less biomass supported in the largest body sizes, at warm climates) because increased temperature shrinks individual body size following the body-size–temperature rules (Fig. 1B).

O3 Identify the differences in LGB of size spectrum across different taxa and ecosystems H3 We will observe flatter size spectrum structure in marine than freshwater and terrestrial ecosystems irrespective of the trophic level considered because marine food webs are longer (and hence, sustain more biomass at largest body sizes) than freshwater and terrestrial systems (Fig. 1C).

Figure 1. Hypothetical responses of the size spectrum structure to global climate