Oral Presentation AFSS/NZFSS Joint Conference 2019

Hedging their bets: The relative importance of spatial subsidies and riparian vegetation to insectivorous bat foraging activity along perennial streams in temperate Australia (#9)

Bradley Clarke-Wood 1 , Barbara Downes 1 , Mark Elgar 2
  1. The School of Geography, The University of Melbourne, Carlton, VIC, Australia
  2. School of BioSciences, The University of Melbourne, Carlton, VIC, Australia

Food-web ecology identifies the movement of materials and organisms as a resource pulse across ecotones. To make strides in the field, however, researchers need to consider how these subsidies change the community structure of a diverse group of terrestrial consumers. This is particularly important for those biomes that are underrepresented in the literature. In this study, we tested whether insectivorous bat community dynamics differed along six, 2nd/3rd order perennial streams that each span an agricultural land-use gradient in temperate Australia. At each site, nocturnal aerial insects and insectivorous bat activity were sampled in two locations (1) within 5 m from the stream and, 2) 300 m from the stream), twice over the austral summer using light traps and ultrasonic call detectors, respectively. In-stream temperature and vegetation structure were also surveyed. Emergent aquatic invertebrates and insectivorous bats were more abundant within 5 m of the stream regardless of land-use intensity. Further, bat foraging activity tracked longitudinal land-use changes at perennial streams. We also assessed the relative importance of environmental variables to bat and prey communities. Our results suggest that canopy structure was highly influential on flying invertebrate abundance and biomass. While bat responses were complex, total bat activity was sensitive to the availability of emergent aquatic invertebrates and mature tree stem density. Aquatically-derived subsidies were identified as important variables of five insectivorous bat taxa including C. gouldii, Mi. schreibersii oceanensis, Mo. planiceps, Nyctophilus-Myotis complex and V. regulus. Our results suggest that longitudinal changes in riparian vegetation structure along perennial streams influence insectivorous bat community composition and foraging activity, and these responses are often species-specific. Both habitat structure and prey (aquatic and otherwise) availability needs to be considered when assessing the direct impact of land clearance on a diverse group of terrestrial consumers.