Biological interactions mediate context and species-specific sensitivities to salinity.

Toxicants have both sub-lethal and lethal effects on aquatic biota, influencing organism fitness and community composition. However, toxicant effects within ecosystems may be altered by interactions with abiotic and biotic ecosystem components, including biological interactions. Collectively, this generates the potential for toxicant sensitivity to be highly context dependent, with significantly different outcomes in ecosystems than laboratory toxicity tests predict. We experimentally manipulated stream macroinvertebrate communities in 32 mesocosms to examine how communities from a low-salinity site were influenced by interactions with those from a high-salinity site along a gradient of salinity. Relative to those from the low-salinity site, organisms from the high-salinity site were expected to have greater tolerance and fitness at higher salinities. This created the potential for both salinity and tolerant-sensitive organism interactions to influence communities. We found that community composition was influenced by both direct toxicity and tolerant-sensitive organism interactions. Taxon and context-dependent responses included: (i) direct toxicity effects, irrespective of biotic interactions; (ii) effects that were owing to the addition of tolerant taxa, irrespective of salinity; (iii) toxicity dependent on sensitive-tolerant taxa interactions; and (iv) toxic effects that were increased by interactions. Our results reinforce that ecological processes require consideration when examining toxicant effects within ecosystems.This article is part of the theme issue 'Salt in freshwaters: causes, ecological consequences and future prospects'.

Vive la résistance: reviving resistance for 21st century conservation.

Confronted with increasing anthropogenic change, conservation in the 21st century requires a sound understanding of how ecological systems change during disturbance. We highlight the benefits of recognizing two distinct components of change in an ecological unit (i.e., ecosystem, community, population): 'resistance', the ability to withstand disturbance; and 'resilience', the capacity to recover following disturbance. By adopting a 'resistance-resilience' framework, important insights for conservation can be gained into: (i) the key role of resistance in response to persistent disturbance, (ii) the intrinsic attributes of an ecological unit associated with resistance and resilience, (iii) the extrinsic environmental factors that influence resistance and resilience, (iv) mechanisms that confer resistance and resilience, (v) the post-disturbance status of an ecological unit, (vi) the nature of long-term ecological changes, and (vii) policy-relevant ways of communicating the ecological impacts of disturbance processes.

Transdisciplinary synthesis for ecosystem science, policy and management: The Australian experience.

Mitigating the environmental effects of global population growth, climatic change and increasing socio-ecological complexity is a daunting challenge. To tackle this requires synthesis: the integration of disparate information to generate novel insights from heterogeneous, complex situations where there are diverse perspectives. Since 1995, a structured approach to inter-, multi- and trans-disciplinary(1) collaboration around big science questions has been supported through synthesis centres around the world. These centres are finding an expanding role due to ever-accumulating data and the need for more and better opportunities to develop transdisciplinary and holistic approaches to solve real-world problems. The Australian Centre for Ecological Analysis and Synthesis (ACEAS ) has been the pioneering ecosystem science synthesis centre in the Southern Hemisphere. Such centres provide analysis and synthesis opportunities for time-pressed scientists, policy-makers and managers. They provide the scientific and organisational environs for virtual and face-to-face engagement, impetus for integration, data and methodological support, and innovative ways to deliver synthesis products. We detail the contribution, role and value of synthesis using ACEAS to exemplify the capacity for synthesis centres to facilitate trans-organisational, transdisciplinary synthesis. We compare ACEAS to other international synthesis centres, and describe how it facilitated project teams and its objective of linking natural resource science to policy to management. Scientists and managers were brought together to actively collaborate in multi-institutional, cross-sectoral and transdisciplinary research on contemporary ecological problems. The teams analysed, integrated and synthesised existing data to co-develop solution-oriented publications and management recommendations that might otherwise not have been produced. We identify key outcomes of some ACEAS working groups which used synthesis to tackle important ecosystem challenges. We also examine the barriers and enablers to synthesis, so that risks can be minimised and successful outcomes maximised. We argue that synthesis centres have a crucial role in developing, communicating and using synthetic transdisciplinary research.

An experimental examination of colonization as a generator of biotic nestedness.

Species assemblages of systems of islands and other fragmented habitats frequently show a "nested-subset" structure in which the biotas of sites with low species richness are non-random subsets of the biotas of richer sites. Much literature suggests that extinction is more likely to produce strongly nested patterns than colonization, although very few experiments have been conducted on the generation of nested-subset patterns. Here, we describe an experiment on nestedness of benthic invertebrates occupying rocks in the littoral zone of a lake in western Victoria, Australia. Data collected from previous work indicated that the invertebrate biotas of rocks were nested. We used initially defaunated, different-sized habitat patches (half house-bricks, full house-bricks, double house-bricks) and followed the time-course of occupation to assess whether nested-subset patterns would emerge, and whether extinction or colonization best accounted for the patterns. We predicted that nestedness would increase through time up to the end of the experiment. This was found to be the case with colonization dominating the establishment of a strongly nested system; extinction appeared to be of relatively little importance over the duration of the experiment. These results suggest that at least in some circumstances, differential colonization may be influential in producing nested-subset patterns but experiments conducted over longer times may be needed to more completely understand the respective roles of extinction and colonization in generating nested-subset patterns in this system.