John S. Richardson

Ecological neighborhoods: scaling environmental patterns

In this paper we review, develop, and differentiate among concepts associated with environmental patterning (patch, division, and heterogeneity), spatial and temporal scales of ecological processes (ecological neighborhoods), and responses of organisms to environmental patterning (relative patch size, relative patch duration, relative patch isolation, and grain response). We generalize the concept of ecological neighborhoods to represent regions of activity or influence during periods of time appropriate to particular ecological processes. Therefore, there is no single ecological neighborhood for any given organism, but rather a number of neighborhoods, each appropriate to different processes. Neighborhood sizes can be estimated by examining the cumulative distribution of activity or influence of an organism as a function of increasingly large spatial units. The spatial and temporal dimensions of neighborhoods provide the scales necessary for assessing environmental patterning relative to particular ecological processes for a given species. Consistent application of the neighborhood concept will assist in the choice of appropriate study units, comparisons among different studies, and comparisons between empirical studies and theoretical postulates.

META‐ANALYSIS: TROPHIC LEVEL, HABITAT, AND PRODUCTIVITY SHAPE THE FOOD WEB EFFECTS OF RESOURCE SUBSIDIES

Studies of the effects of cross-habitat resource subsidies have been a feature of food web ecology over the past decade. To date, most studies have focused on demonstrating the magnitude of a subsidy or documenting its effect in the recipient habitat. Ecologists have yet to develop a satisfactory framework for predicting the magnitude of these effects. We used 115 data sets from 32 studies to compare consumer responses to resource subsidies across recipient habitat type, trophic level, and functional group. Changes in consumer density or biomass in response to subsidies were inconsistent across habitats, trophic, and functional groups. Responses in stream cobble bar and coastline habitats were larger than in other habitats. Contrary to expectation, the magnitude of consumer response was not affected by recipient habitat productivity or the ratio of productivity between donor and recipient habitats. However, consumer response was significantly related to the ratio of subsidy resources to equivalent resources in the recipient habitat. Broad contrasts in productivity are modified by subsidy type, vector, and the physical and biotic characteristics of both donor and recipient habitats. For this reason, the ratio of subsidy to equivalent resources is a more useful tool for predicting the possible effect of a subsidy than coarser contrasts of in situ productivity. The commonness of subsidy effects suggests that many ecosystems need to be studied as open systems.

Lake outlets and the distribution of filter feeders : an assessment of hypotheses

Dense assemblages of filter-feeding invertebrates at lake outlets, and their abrupt decline downstream, have been attributed to gradients in food (seston : quantity, quality, particle size), temperature, flow regime (discharge, turbulence, depth), substrate, competition, predation, and to the colonization cycle. In this paper we critically review the evidence for the several hypotheses. Empirical support is strongest for the three food hypotheses and for those addressing depth, competition, and the colonization cycle. The hypotheses are not independent because the capture of seston is dependent on certain environmental factors and the use of filtering sites. Certain species appear to be outlet specialists

Flow refugia for benthic macroinvertebrates during flooding of a large river

Benthic macroinvertebrates shifted from deep water to shallow water of the shore zone during annual flooding of a large, gravel-bed river. The shore zone is seasonally inundated during flooding for up to 4 mo of the year, and is a geomorphic feature of many large rivers in northern latitudes with limited floodplain habitat. We collected samples of invertebrates along with measures of several hydraulic and sedimentary variables 5 times through the flood cycle from 4 fixed water depths; stations shifted laterally over a distance of 30 m between baseflow and peak flow. In deep water (1.5 and 3.0 m), shear velocity and substrate mobility increased as a result of flooding. At shallow depths (0.2 and 0.5 m) within the shore zone, stable substrate and low hydraulic stress remained throughout the flood cycle, providing flow refugia to benthic invertebrates. Invertebrate density and species richness were similar during months on the rising limb of the hydrograph while the wetted area of the channel markedly increased. Persistence of the invertebrate community appears to have been facilitated by a shift in a large proportion of organisms from deep water to shallow depths of the shore zone during flooding. Total density and the density of most collector-gatherers such as Rhithrogena and Baetis was highest at 1.5 m prior to flooding but shifted to depths of 0.5 and 0.2 m at peak flow. The filter-feeding caddisfly Hydropsyche was most abundant at 1.5 m in all months of the study while the location of 1.5 m samples shifted laterally over a distance of 30 m through the flood cycle. The ecological importance of the shore zone as a flow refugium was demonstrated by the broad diversity of species with varying feeding behaviors and morphologies that concentrated in this zone during flooding.

Establishing light as a causal mechanism structuring stream communities in response to experimental manipulation of riparian buffer width

Abstract Previous studies on the effects of logging on streams have suggested that light and water temperature were important variables structuring stream communities but, in many cases, these effects were confounded. We observed pronounced gradients in the flux of solar energy and water temperature in an earlier large-scale experiment in which we manipulated the width of riparian buffers along headwater streams. Associated with these abiotic changes were increases in periphyton biomass and primary consumer abundance. We present results from a study in streamside channels that was designed to isolate the effects of light on stream communities, while holding water temperature constant. Light treatments in the channel experiment simulated inputs of solar radiation created during the prior watershed-scale experiment. Results from the present study suggested that consumers limited periphyton biomass early in the study; however, a rainstorm midway through the experiment reduced periphyton biomass and insect consumer abundance. Following this disturbance, chlorophyll a biomass was 2 to 4 times higher in the full sunlight treatment compared to the 2 lowest light treatments. At the end of the study, primary consumer abundance, biomass, survival, and growth rate were positively related to light and periphyton resources. Therefore, we inferred biotic control of periphyton during the early part of the channel study, whereas light appeared to control periphyton at the end of the study. Results from the large-scale and channel experiments suggested that light was the primary constraint on periphyton biomass accrual. Moreover, both experiments, especially the channel study, showed that light indirectly influenced consumer performance as mediated by increased primary production.

Assessing the Value of the Umbrella-Species Concept for Conservation Planning with Meta-Analysis

The umbrella-species concept, which suggests that conservation strategies designed for one species may benefit co-occurring species, has been promoted as a framework for conservation planning. Nevertheless, there has been considerable variation in the outcome of empirical tests of this concept that has led researchers to question its value, so we used data from 15 published studies in a meta-analysis to evaluate whether conservation of putative umbrella species also conserves co-occurring species. We tested the effectiveness of putative umbrella species categorized by taxonomic group, taxonomic similarity to co-occurring species, body size, generality of resource use, and trophic level to evaluate criteria proposed to guide the selection of umbrella species. We compared species richness and number of individuals (by species and higher taxonomic group) between sites with and without putative umbrella species to test whether more co-occurring species were present in greater abundances when the area or resource needs of umbrella species were met. Species richness and abundance of co-occurring species were consistently higher in sites where umbrella species were present than where they were not and for conservation schemes with avian than with mammalian umbrella species. There were no differences in species richness or species abundance with resource generalist or specialist umbrella species or based on taxonomic similarity of umbrella and co-occurring species. Taxonomic group abundance was higher in across-taxonomic umbrella species schemes than when umbrella species were of the same taxon as co-occurring species. Co-occurring species had similar, or higher, species richness with small-bodied umbrella species relative to larger-bodied umbrella species. The only significant difference among umbrella species categorized by trophic level was that species richness was higher with omnivorous than it was with carnivorous avian umbrella species. Our results suggest there is merit to the umbrella-species concept for conservation, but they do not support the use of the criteria we used to identify umbrella species.

The influence of artificial light on stream and riparian ecosystems: questions, challenges, and perspectives

Artificial light at night is gaining attention for its potential to alter ecosystems. Although terrestrial ecologists have observed that artificial light at night may disrupt migrations, feeding, and other important ecological functions, we know comparatively little about the role artificial light might play in disrupting freshwater and riparian ecosystems. We identify and discuss four future research domains that artificial light may influence in freshwater and associated terrestrial ecosystems, with an emphasis on running waters: (1) dispersal, (2) population genetics and evolution, (3) ecosystem functioning, and (4) potential interactions with other stressors. We suggest that future experimental and modeling studies should focus on the effects of different spectral emissions by different light sources on freshwater organisms, the spatial and temporal scale over which artificial light acts, and the magnitude of change in light at night across the landscape relative to the distribution of running and standing waters. Improved knowledge about the effects of artificial light on freshwater ecosystems will inform policy decisions about changes to artificial light spectral emissions and distributions.

Riparian forest composition affects stream litter decomposition despite similar microbial and invertebrate communities.

Cross-boundary flows of energy and nutrients link biodiversity and functioning in adjacent ecosystems. The composition of forest tree species can affect the structure and functioning of stream ecosystems due to physical and chemical attributes, as well as changes in terrestrial resource subsidies. We examined how variation in riparian canopy composition (coniferous, deciduous, mixed) affects adjacent trophic levels (invertebrate and microbial consumers) and decomposition of organic matter in small, coastal rainforest streams in southwestern British Columbia. Breakdown rates of higher-quality red alder (Alnus rubra) litter were faster in streams with a greater percentage of deciduous than coniferous riparian canopy, whereas breakdown rates of lower-quality western hemlock (Tsuga heterophylla) litter were independent of riparian forest composition. When invertebrates were excluded using fine mesh, breakdown rates of both litter species were an order of magnitude less and were not significantly affected by riparian forest composition. Stream invertebrate and microbial communities were similar among riparian forest composition, with most variation attributed to leaf litter species. Invertebrate taxa richness and shredder biomass were higher in A. rubra litter; however, taxa evenness was greatest for T. heterophylla litter and both litter species in coniferous streams. Microbial community diversity (determined from terminal restriction fragment length polymorphisms) was unaffected by riparian forest or litter species. Fungal allele richness was higher than bacterial allele richness, and microbial communities associated with lower-quality T. heterophylla litter had higher diversity (allele uniqueness and richness) than those associated with higher-quality A. rubra litter. Percent variation in breakdown rates was mostly attributed to riparian forest composition in the presence of invertebrates and microbes; however, stream consumer biodiversity at adjacent trophic levels did not explain these patterns. Riparian and stream ecosystems and their biotic communities are linked through exchange and decomposition of detrital resources, and we provide evidence that riparian forest composition affects stream ecosystem catabolism despite similarities in microbial and invertebrate communities.

Litter breakdown and invertebrate association with three types of leaves in a temperate rainforest stream

Coniferous forests predominate in the boreal and western North American regions, yet most studies of litter breakdown in streams have focussed on litter from deciduous trees. We studied breakdown rates and invertebrate colonization of leaf litter from two common conifer species (western red cedar and western hemlock), along with red alder (a common riparian, deciduous species) in a small, coastal rainforest stream of British Columbia during two seasons (summer, autumn). Alder lost mass 40- 100% more quickly than the two conifer species. During summer, hemlock lost mass significantly more quickly than cedar, but this trend was reversed in autumn. Measures of relative lignin concentration and carbon content did not differ signifi- cantly between litter species. Nitrogen content was nearly twice as high in alder as the two coniferous species. Decomposition rates were positively related to initial nitrogen content of the litter and negatively related to C:N ratio. Invertebrate species associated with particular types of leaf litter were clearly distinct during the autumn, but less so during summer. In the autumn, invertebrate assemblages on alder and cedar were dis- tinguished from those on hemlock by the high numbers of detritivores on the former litter types. Cedar had more mayflies and fewer orthoclad midges than alder. There were no significant differences between litter types in densities of any invertebrate taxon per gram of leaf tissue, although alder always had higher numbers.

Are forested buffers an effective conservation strategy for riparian fauna? An assessment using meta-analysis

Historically, forested riparian buffers have been created to provide protection for aquatic organisms and aquatic ecosystem functions. Increasingly, new and existing riparian buffers are being used also to meet terrestrial conservation requirements. To test the effectiveness of riparian buffers for conserving terrestrial fauna, we conducted a meta-analysis using published data from 397 comparisons of species abundance in riparian buffers and unharvested (reference) riparian sites. The response of terrestrial species to riparian buffers was not consistent between taxonomic groups; bird and arthropod abundances were significantly greater in buffers relative to unharvested areas, whereas amphibian abundance decreased. Edge-preferring species were more abundant in buffer sites than reference sites, whereas species associated with interior habitat were not significantly different in abundance. The degree of buffer effect on animal abundance was unrelated to buffer width; wider buffers did not result in greater similarity between reference and buffer sites. However, responses to buffer treatment were more variable in buffers <50 m wide, a commonly prescribed width in many management plans. Our results indicate that current buffer prescriptions do not maintain most terrestrial organisms in buffer strips at levels comparable to undisturbed sites.