Oral Presentation Australian Society for Limnology Conference 2017

Longitudinal trends in land-use, spatial subsidies and food-webs of north-eastern Victorian perennial streams. (#57)

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

Spatial subsidies are resources that flow from one ecosystem to another, either actively in terms of dispersing organisms or passively as a result of abiotic factors. The seasonal emergence of aquatic invertebrates, for example represents an active spatial subsidy. Adult aquatic invertebrates disperse from stream systems and become available as a food source for terrestrial predators, such as spiders and insectivorous bats. Conversely, the shedding of leaves and bark from riparian trees represents a passive spatial subsidy. Wind conditions and flooding regimes transport resources otherwise suspended in terrestrial systems, into adjacent streams. This process then couples these ecosystems by providing allochthonous (external) resources that are energetically significant to local consumers. While the flow of resources is an ecologically significant process, disturbance and habitat fragmentation disrupt these linkages. According to the 2016 State of the Environment Report, as much as 60% of native vegetation has been cleared with significant flow-on effects in local food-webs. This study seeks to investigate trends in land-use and aquatic spatial subsidies along a land-use gradient, and how they influence community dynamics of terrestrial consumers (i.e spiders) in north-eastern Victorian perennial streams. We used digital canopy photography to characterise vegetation structure as well as light and sticky traps to quantify aquatic invertebrates emergence. Spider communities were also surveyed as vector for aquatic resources to entered terrestrial systems. We found a close association between vegetation structure and invertebrate communities. These surveys forms the first phase of an on-going project relating to food-web responses and habitat fragmentation.