The diversity of life in headwater streams (intermittent, first and second order) contributes to the biodiversity of a river system and its riparian network. Small streams differ widely in physical, chemical, and biotic attributes, thus providing habitats for a range of unique species. Headwater species include permanent residents as well as migrants that travel to headwaters at particular seasons or life stages. Movement by migrants links headwaters with downstream and terrestrial ecosystems, as do exports such as emerging and drifting insects.

/pdf/the-contribution-of-headwater-streams-to-biodiversity-in-55aehboa1f.pdf

The contribution of headwater streams to biodiversity in river networks

Dynamics of headwater stream ecosystems are generally regarded as occurring at the interface of aquatic and terrestrial ecosystems Terrestrial arthropod inputs can provide an energy subsidy and increase the abundance of predatory fish, and the ensuing effects potentially can cascade through the food web and ultimately affect primary producers Nevertheless, the community-based effects of such inputs on stream food web dynamics are still poorly understood We present experimental evidence that terrestrial arthropod inputs have an indirect but prominent effect on a stream benthic community by altering the intensity of fish predation in the food web Two key elements of the stream food web, terrestrial arthropod inputs and the presence of predatory fish, were experimentally manipulated by using greenhouse-type covers and enclosures (or exclosures) in a forest stream located in northern Japan When terrestrial arthropod inputs to the stream were experimentally reduced, fish predation pressure shifted dramatically from terrestrial to aquatic arthropods The ensuing depletion of aquatic arthropods resulted in a subsequent increase in periphyton biomass This field experiment revealed that terrestrial arthropod inputs were a primary factor controlling cascading trophic interactions among predatory fish, herbivorous aquatic arthropods, and benthic periphyton These results provide empirical support for the perspective that transfers of energy and biomass from donor systems are frequently significant for the maintenance of biotic communities in recipient systems

https://www.jstor.org/stable/pdfplus/176923.pdf

Terrestrial–aquatic linkages: riparian arthropod inputs alter trophic cascades in a stream food web

▪ Abstract Predator-induced phenotypic plasticity is widespread in nature and includes variation in life history, morphology, and behavior. In organisms with complex life histories, predator-induced phenotypic plasticity in the larval period has been widely documented. Several models predict how organisms should alter their size at and time to metamorphosis in response to an increased risk of predation. A survey of empirical studies finds that these theoretical predictions are frequently met. However, no one model performs the best. Additionally, there are several results not predicted by any model. Predator-induced plasticity in metamorphic traits may be related to predator-induced changes in larval morphology and behavior. Predictions of predator effects on larval traits are generally met, except for direct costs of predator-induced morphological phenotypes. Future work should incorporate more detailed studies of growth rate, morphology, and behavior during the larval period, as well as studies of size-...

https://www.jstor.org/stable/pdfplus/30034130.pdf

Predator-induced phenotypic plasticity in organisms with complex life histories

Progress in biomass torrefaction: Principles, applications and challenges

Meta-analysis is the statistical synthesis of the results of separate studies. It was adapted from other disciplines for use in ecology and evolutionary biology beginning in the early 1990s, and, at the turn of the century, has begun to have a substantial impact on the way data are summarized in these fields. We identify 119 studies concerned with meta-analysis in ecology and evolution, the earliest published in 1991 and the most recent in 2000. We introduce the statistical methods used in modern meta-analysis with references to the well-developed literature in the field. These formal, statistically defensible methods have been established to determine average treatment effects across studies when a common research question is being investigated, to establish confidence limits around the average effect size, and to test for consistency or lack of agreement in effect size as well as explanations for differences in the magnitude of the effect among studies. Problems with popular but statistically flawed methods for the quantitative summary of research results have been pointed out, and their use is diminishing. We discuss a number of challenges and threats to the validity of meta-analysis in ecology and evolution. In particular, we examine how difficulties resulting from missing data, publication bias, data quality and data exclusion, non-independence among observations, and the combination of dissimilar data sets may affect the perceived utility of meta-analysis in these fields and the soundness of conclusions drawn from its application. We highlight particular applications of meta-analysis in ecology and evolution, discuss several controversies surrounding individual meta-analyses, and outline some of the practical issues involved in carrying out a meta-analysis. Finally, we suggest changes that would improve the quality of data synthesis in ecology and evolutionary biology, and predict future directions for this emerging enterprise.

Meta-analysis in ecology

In high-elevation streams of western Colorado, mayflies ( Baetis bicaudatus) develop faster, but mature at a smaller size where trout are present compared to streams where fish are absent. These life history traits reduce the time of larval exposure to trout predation, but cost reduced fecundity. We designed a field experiment involving manipu- lation of whole streams to determine whether these changes were caused by the presence of brook trout, and specifically, whether they could be triggered by trout chemical cues. In 1999 and 2000, we introduced water from containers with brook trout (Salvelinus fon- tinalis) into five naturally fishless streams, and fishless stream water into five adjacent control streams, to determine whether these cues alone could induce the mayfly life history traits we have observed in natural trout streams. As in previous small-scale experiments, the size at which mayflies matured declined significantly in streams with added trout chem- icals but did not change in streams with fishless water only. Thus, life history traits similar to those observed in the field were induced within the natural variability inherent in streams. These results demonstrate the strength of this predator-prey interaction and indicate that brook trout are an important agent of natural selection on mayfly life history traits.

Predator chemicals induce changes in mayfly life history traits: a whole-stream manipulation

The impact that predators have on invertebrate prey density in running waters is the subject of debate. Some studies show strong effects of fish predation on benthic prey density whereas others show little or no effects. Recent reviews discuss different factors that affect interactions between predators and invertebrate prey. These include differences in enclosure size, mesh size, predator densities, small sample sizes and the role of invertebrate predators. We suggest the complementary hypothesis that vertebrate predators used in experiments differ in foraging methods. Some predators feed primarily on benthic prey (e.g. sculpins, blacknose dace, creek chub, darters) whereas other predators feed on both drift and benthic prey (predominantly salmonids). Potentially, if the amount of drifting terrestrial animals is large, the impact of drift-feeding fish on the benthic community should be low. We conducted a meta-analysis on the results of field studies that manipulated these two types of predators and found that benthic feeding predators have significantly larger impacts on benthic prey than drift feeding predators. Four methodological variables, mesh size, size of enclosures, duration of experiments, and predator density were analysed to determine whether these could explain the differences between studies involving benthic and drift feeding predators. No correlations existed between any of these four methodological variables and predator impact, indicating that the difference was not due to methodological differences between experiments.

Impact on stream benthic prey by benthic vs drift feeding predators: a meta-analysis

Phenotypic plasticity may enable organisms to optimize their phenotypes in environments that are heterogeneous over time or space. For example, inducible defenses are favored for prey populations faced with variable predation risk. We studied the impact of brook trout (Salvelinus fontinalis) on the development of defensive morphological characters in larvae of the mayfly, Drunella coloradensis, both in natural streams and in a series of experiments carried out in streamside, circular, flow-through chambers. Drunella larvae in natural streams with trout had Ion-er caudal filaments per unit body size and relatively heavier exoskeletons than Drunella in fishless streams. Female larvae that developed in fish streams were also significantly smaller and less fecund at metamorphosis than those living in fishless streams, suggesting a possible fitness cost associated with development of morphological defenses. However, timing of metamorphosis of Drunella larvae to the adult stage did not differ between fish and fishless streams. Larvae originating from fish and fishless streams were reared and exposed to water with fish cues or fishless control water for three weeks (1998) or until they developed black wing pads, i.e., just before emergence (1999). In both experiments waterborne fish cues induced the development of relatively longer caudal filaments, but only in Drunella originating from sites without fish. Waterborne fish cues had no effect oil Drunella growth rates, behavior, or size at emergence. Drunella originating from fish streams had significantly lower mortality when exposed to predation by trout than Drunella originating from fishless streams. Caudal filament length appears to enhance survival, as Drunella with intact caudal filaments had lower predation rates than Drunella with their tails artificially shortened. This study provides evidence of chemically induced morphological plasticity that could reduce predation rates of these mayflies in natural stream environments. (Less)

Induced morphological defenses in the wild: Predator effects on a mayfly, Drunella coloradensis

In two laboratory experiments, we examined short- and long-term responses of the detritivorous amphipod Gammarus pulex to chemical cues from potential predators fed various diets. In the first experiment we studied the short-term effect on G. pulex (locomotory activity) when exposed to chemical cues from three co-existing predators; sculpin (Cottus gobio), trout (Salmo trutta), and signal crayfish (Pacifastacus leniusculus). Chemicals from sculpins and trout induced a short-term decrease in locomotory activity in G. pulex, whereas crayfish did not. There was no difference in activity between G. pulex exposed to water scented by trout or sculpin, and these responses were independent of predator diet (G. pulex, Asellus aquaticus and starved). In the second experiment we examined whether longer-term exposure (4 week) to chemical cues from sculpins affects rates of leaf processing by G. pulex. During the first week, G. pulex consumed significantly more leaves in the control (i.e., no fish cue) than in the fish cue treatment. After 4 weeks, however, there was no difference in total leaf processing rate between treatments indicating an adaptation to the cue.

Influence of predator and dietary chemical cues on the behaviour and shredding efficiency of Gammarus pulex

Combined torrefaction and pelletization are used to increase the fuel value of biomass by increasing its energy density and improving its handling and combustion properties. However, pelletization of torrefied biomass can be challenging and in this study the torrefaction and pelletizing properties of wheat straw have been analyzed. Laboratory equipment has been used to investigate the pelletizing properties of wheat straw torrefied at temperatures between 150 and 300 °C. IR spectroscopy and chemical analyses have shown that high torrefaction temperatures change the chemical properties of the wheat straw significantly, and the pelletizing analyses have shown that these changes correlate to changes in the pelletizing properties. Torrefaction increase the friction in the press channel and pellet strength and density decrease with an increase in torrefaction temperature.

Jonas Dahl

Papers

Predator chemicals induce changes in mayfly life history traits: a whole-stream manipulation

Impact on stream benthic prey by benthic vs drift feeding predators: a meta-analysis

Induced morphological defenses in the wild: Predator effects on a mayfly, Drunella coloradensis

Influence of predator and dietary chemical cues on the behaviour and shredding efficiency of Gammarus pulex

Pelletizing properties of torrefied wheat straw