Kevin J. Cash

Anti-Predator Responses of Mayfly Larvae to Conspecific and Predator Stimuli

Hydrodynamic and water-borne chemical stimuli are considered important cues that initiate anti-predator behaviours of mayfly larvae. We tested the hypotheses that chemical stimuli from conspecifics and the predacious fish Rhinichthys cataractae and hydrodynamic stimuli from a Rhinichthys model would initiate anti-predator responses by mayfly larvae of Ephemerella aurivillii, Paraleptophlebia heteronea, and Baetis tricaudatus. A second set of experiments tested the hypotheses that chemical stimuli from conspecifics and the predacious stonefly Claassenia sabulosa and hydrodynamic stimuli from a Claassenia model would initiate responses by Baetis. These hypotheses were tested in laboratory streams where mayfly larvae received either chemical stimuli, hydrodynamic stimuli, or the combination of hydrodynamic and chemical stimuli. Responses by larvae to these stimulus types, in terms of use of substratum surfaces and drift rates, were compared with those by larvae in control streams without conspecific and predator stimulus types. Responses to chemical stimuli were variable depending upon mayfly species and the chemical stimulus type. For instance, while Ephemerella and Paraleptophlebia responded to Rhinichthys odours, Baetis did not respond to either Rhinichthys or Claassenia odours. Paraleptophlebia responded to conspecific odours whereas Ephemerella and Baetis did not. In contrast, all three mayfly species responded to hydrodynamic stimuli either alone or when combined with chemical stimuli. Responses by Baetis were more complex when chemical stimuli were combined with hydrodynamic stimuli. For instance, although Baetis did not respond to conspecific odours alone, drift was significantly higher in streams receiving the three stimuli of conspecific odours, predator odours from Rhinichthys, and hydrodynamic stimuli from a Rhinichthys model when compared with streams that received only the conspecific odours combined with the fish model. Similarly, an enhanced response was observed when Baetis odours were combined with Claassenia odours and the Claassenia model. Thus, the lack of a response to a chemical stimulus did not preclude an enhanced response when combined with other stimulus types. These observations suggest that although some mayflies are capable of detecting the presence of some chemical stimuli, a response is not elicited unless the stimulus is accompanied by additional stimuli.

Utility of field-based artificial streams for assessing effluent effects on riverine ecosystems

Experimentation using field-based artificial streams provides a promising, complimentary approach to biomonitoring assessments because artificial streams provide control over relevant environmental variables and true replication of treatments. We have used large and small artificial stream systems, based in the field, to examine the effect of treated bleached kraft pulp mill effluent (BKME) on the benthos of three large rivers in western Canada. Under natural regimes of temperature, water chemistry, and insolation, these artificial streams provide current velocities and substrata to food chains or food webs that are representative of those in the study river. With these tools we have shown that BKME stimulated mayfly growth in the Thompson River above that which could be accounted for by fertilization of their algal food supply. In contrast, moulting frequency was inhibited at high BKME concentrations. Results from artificial streams also indicate that increased algal biomass and abundances of benthic communities downstream of BKME outfalls were induced by nutrient enrichment from the effluent. BKME treatments did not change diatom species richness in the Fraser River, or diatom species diversity in either the Athabasca or Fraser Rivers. Artificial streams provide a means of understanding the mechanisms of stressor effects over a continuum ranging from single stressor effects on specific taxa to the effects of multiple stressors on communities and ecosystems. Because riverside deployment provides environmental realism within a replicated experimental design, this approach can (i) address questions that cannot be examined using laboratory tests or field observations, (ii) improve our mechanistic understanding of stressor effects on riverine ecosystems, and (iii) can contribute directly to the development, parameterization, and testing of models for predicting ecosystem-level responses.

The ecosystem approach to environmental assessment: moving from theory to practice

The “ecosystem approach” to environmental management is viewed by many as being fundamental to the development of appropriate management strategies. While this approach represents a major advance in the way researchers view environmental assessment, the approach in itself does not provide practical information as to what questions to ask and what tools to use in assessing and managing ecosystems. Similarly, the concept of ecosystem health, as it is usually defined, has little practical value for ecosystem managers. We suggest the next stage in environmental assessment will be the development of specific frameworks designed to assess individual ecosystems. Of primary importance is the need to consider the basic structure and function of the ecosystem itself. Such consideration, together with explicit identification of anthropogenic stresses particular to the system, serves to identify those components most at risk and those issues most deserving of attention. Researchers should explore critical linkages between environmental stressors and their observable, measurable and predictable effects on ecological parameters and use this understanding to develop a management strategy that incorporates appropriate ecological indicators. The importance of these considerations will be illustrated using examples from the Northern River Basins Study.

Short- And Long-Term Consequences of Grouping and Group Foraging in the Free-Living Flatworm Dugesia tigrina

We evaluated the short-term effect of group size on the per capita ingestion rates, and the long-term reproductive and fitness consequences of group living in the free-living triclad, Dugesia tigrina. As D. tigrina group size increased, daily per capita ingestion rates first increased and peaked at a group size of approximately four, then decreased until, at larger group sizes, ingestion rates did not differ from those experienced by solitary foragers. The general qualitative pattern of changing per capita ingestion rates with changes in group size was not affected by changes in prey density, prey species or predator size

7.1 – INSIGHT INTO POLLUTION EFFECTS IN COMPLEX RIVERINE HABITATS: A ROLE FOR FOOD WEB EXPERIMENTS

This chapter summarizes examples of how food web experiments can improve the understanding of pollution effects from pulp mill and metal mining effluents in complex river environments and how an understanding of the food web aids interpretation of ecological responses to stressor gradients. Assessing pollution impacts in rivers is particularly challenging, because flowing water environments receive multiple, interacting effluent discharges from cities and industries, as well as nonpoint source inputs. Field biomonitoring in rivers is further hindered by uncertainties in estimating exposure to pollutants. River ecologists are faced with the dilemma that large-scale experiments, which incorporate contaminant or nutrient stressors, are not feasible on ethical and practical grounds because they may cause severe acute and chronic effects on riverine communities. In complex environments in situ food experiments can elucidate dose–response relationships between components of the model food web and single or multiple stressors better than standard field observations. The results of ecotoxicological experiments in model food webs can provide a wealth of information on possible species interactions within a community, including knowledge of functional redundancy of species and various indirect effects.