Summary
1. Stream ecosystems are increasingly impacted by multiple stressors that lead to a loss of sensitive species and an overall reduction in diversity. A dominant paradigm in ecological restoration is that increasing habitat heterogeneity (HH) promotes restoration of biodiversity. This paradigm is reflected in stream restoration projects through the common practice of re-configuring channels to add meanders and adding physical structures such as boulders and artificial riffles to restore biodiversity by enhancing structural heterogeneity.

2. To evaluate the validity of this paradigm, we completed an extensive evaluation of published studies that have quantitatively examined the reach-scale response of invertebrate species richness to restoration actions that increased channel complexity/HH. We also evaluated studies that used manipulative or correlative approaches to test for a relationship between physical heterogeneity and invertebrate diversity in streams that were not in need of restoration.

3. We found habitat and macroinvertebrate data for 78 independent stream or river restoration projects described by 18 different author groups in which invertebrate taxa richness data in response to the restoration treatment were available. Most projects were successful in enhancing physical HH; however, only two showed statistically significant increases in biodiversity rendering them more similar to reference reaches or sites.

4. Studies manipulating structural complexity in otherwise healthy streams were generally small in scale and less than half showed a significant positive relationship with invertebrate diversity. Only one-third of the studies that attempted to correlate biodiversity to existing levels of in-stream heterogeneity found a positive relationship.

5. Across all the studies we evaluated, there is no evidence that HH was the primary factor controlling stream invertebrate diversity, particularly in a restoration context. The findings indicate that physical heterogeneity should not be the driving force in selecting restoration approaches for most degraded waterways. Evidence suggests that much more must be done to restore streams impacted by multiple stressors than simply re-configuring channels and enhancing structural complexity with meanders, boulders, wood, or other structures.

6. Thematic implications: as integrators of all activities on the land, streams are sensitive to a host of stressors including impacts from urbanisation, agriculture, deforestation, invasive species, flow regulation, water extractions and mining. The impacts of these individually or in combination typically lead to a decrease in biodiversity because of reduced water quality, biologically unsuitable flow regimes, dispersal barriers, altered inputs of organic matter or sunlight, degraded habitat, etc. Despite the complexity of these stressors, a large number of stream restoration projects focus primarily on physical channel characteristics. We show that this is not a wise investment if ecological recovery is the goal. Managers should critically diagnose the stressors impacting an impaired stream and invest resources first in repairing those problems most likely to limit restoration.

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River restoration, habitat heterogeneity and biodiversity: a failure of theory or practice?

Scientists' warning to humanity on insect extinctions

River restoration is an increasingly common approach utilized to reverse past degradation of freshwater ecosystems and to mitigate the anticipated damage to freshwaters from future development and resource-extraction activities. While the practice of river restoration has grown exponentially over the last several decades, there has been little empirical evaluation of whether restoration projects individually or cumulatively achieve the legally mandated goals of improving the structure and function of streams and rivers. New efforts to evaluate river restoration projects that use channel reconfiguration as a methodology for improving stream ecosystem structure and function are finding little evidence for measurable ecological improvement. While designed channels may have less-incised banks and greater sinuousity than the degraded streams they replace, these reach-scale efforts do not appear to be effectively mitigating the physical, hydrological, or chemical alterations that are responsible for the loss of sensitive taxa and the declines in water quality that typically motivate restoration efforts. Here we briefly summarize this new literature, including the collection of papers within this Invited Feature, and provide our perspective on the limitations of current restoration.

River restoration: the fuzzy logic of repairing reaches to reverse catchment scale degradation

▪ Abstract Studies of the production of stream insects are now numerous, and general factors controlling the secondary production of stream communities are becoming evident. In this review we focus on how life-history attributes influence the production dynamics of stream insects and other macroinvertebrates. Annual production of macroinvertebrate communities in streams world-wide ranges from approximately 100 to 103 g dry mass m−2. High levels are reported for communities dominated by filter feeders in temperate streams. Filter feeding enables the accrual and support of high biomass, which drives the very highest production. Frequently disturbed communities in warm-temperate streams are also highly productive. Biomass accrual by macroinvertebrates is limited in these streams, and production is driven by rapid growth rates rather than high biomass. The lowest production, reported for macroinvertebrate communities of cool-temperate and arctic streams, is due to the constraints of low seasonal temperatures ...

Life History and Production of Stream Insects

The use of molecular genetic techniques is becoming increasingly widespread in analyses of hybrid zones. Yet, exactly how many molecular markers are required to provide a given degree of resolution remains an open question. We present statistical models that relate the number of markers examined to their power to discriminate between pure species, F1’s, and backcross individuals. Our models indicate that only about four or five markers are required to provide a coarse classification of individuals in hybrid zones, whereas upwards of 70 markers are required to discriminate between pure species and advanced backcrosses. The models provide hybrid zone researchers a basis upon which to balance the time and expense of examining large numbers of markers against the magnitude of classification errors when smaller numbers of markers are examined.

Genetic analysis of hybrid zones: numbers of markers and power of resolution

The chewing lice: world checklist and biological overview.

World checklist of chewing lice with host associations and keys to families and genera

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The biology, ecology, and evolution of chewing lice

The chewing lice

Stream restoration attempts to reverse the global degradation of rivers and streams, but rigorous evaluations are needed to advance the science. We evaluated a 3rd-order channelized Indiana (USA) stream that was restored in 1997 by constructing two meanders, each ∼400 m long. Pool and riffle sequences were constructed, coarse substrate and wood were added to the channel, banks were stabilized and revegetated, and sedimentation was reduced by creating a sediment retention basin upstream. Habitat, periphyton, macroinvertebrates, and fishes were measured before restoration and for 5 y after restoration in the restored reaches and in an upstream, unrestored reach. Restoration improved habitat conditions (e.g., more pools, fewer fine sediments) in both restored reaches compared to the unrestored reach. Within 1 y after restoration, major trophic groups (i.e., periphyton, macroinvertebrates, and fishes) recovered to or exceeded levels in the degraded, unrestored reach. However, biotic responses varied w...

Ronald A. Hellenthal

Papers

The chewing lice: world checklist and biological overview.

World checklist of chewing lice with host associations and keys to families and genera

The biology, ecology, and evolution of chewing lice

The chewing lice

Restoration of an Indiana, USA, stream: bridging the gap between basic and applied lotic ecology