Shaped by stress: a trait-based meta-analysis of stream communities across stressor gradients in New Zealand.

Abstract

Environmental filtering shapes communities by filtering out species with certain traits (characteristics, including morphology, behaviour and life history), resulting in communities associated with specific environmental conditions. Understanding how different environmental filters/conditions shape different communities may enable design of more effective restoration strategies which target biological recovery. To investigate if invertebrate community types were associated with different stressor gradients, a meta-analysis of New Zealand streams was conducted using data across drying, flooding, eutrophication, sedimentation and acid mine drainage (AMD) gradients. We hypothesised that whilst some stressors would apply different environmental filters resulting in different trait combinations, others might shape communities in similar ways, resulting in similar trait combinations. A trait-based ordination of communities using non-metric multidimensional scaling was conducted. Significant trait responses to stressor gradients were found for all stressors. Additionally, AMD and sedimentation worked to shape trait composition in the same direction, with higher stressor intensity leading to presence of hardier species. Flooding and eutrophication worked on the same axis but in opposite directions, with flooding selecting for more streamlined, mobile organisms and eutrophication for more sedentary organisms. Knowing that different stressors can work to filter organisms in opposite directions might be applicable as a restoration action to successfully displace less desired taxa. Whilst using stressors to further disturb degraded ecosystems seems counter-intuitive, it could be used to trigger positive community change as a restoration tool. In practice, this might involve identification and artificial application of stressors which act against a degraded community and in favour of a desired community.