Population and Community Body Size Structure Across a Complex Environmental Gradient

We monitored the invertebrate community of leaf litter in and around a drying intermittent pool bed to explore patterns of ecological organisation across a complex environmental gradient, with particular focus on population and community size structure. We measured the body size of 24,609 individuals from 313 taxa ranging over 6 orders of magnitude in size to explore how the functional properties of individuals, populations and communities are affected by moisture (aquatic vs. terrestrial) and light (diurnal vs. nocturnal), and how these properties change across the aquatic-terrestrial habitat transition that occurs as the pool bed dried. We found strong effects of moisture on some population (size structure) and many community (species richness, abundance, evenness, biomass and size structure) properties, with additional temporal effects across the aquatic-terrestrial ecotone. There was no difference between diurnal and nocturnal populations or communities. Our results facilitate understanding of how the physical environment influences functional attributes, and particularly the size structure, of natural populations and communities.