Michael J. Wiley

PATHOGEN OUTBREAKS REVEAL LARGE-SCALE EFFECTS OF COMPETITION IN STREAM COMMUNITIES

The ability of small-scale experiments to predict dynamics and patterns observed at larger scales is an important issue in ecology. In this paper, we describe responses of benthic, trout stream communities to replicated, whole-ecosystem perturbations resulting from pathogen-induced reductions in populations of a dominant grazer, the cad- disfly Glossosoma nigrior. Previous small-scale experiments suggested that Glossosoma had strong competitive effects on other grazers (through exploitation) and small-bodied filter-feeders (through interference). Glossosoma populations collapsed in a number of Michigan trout streams since the late 1980s and have been maintained at low levels by recurrent pathogen outbreaks. Here we address the effects on periphyton, grazers, and filter- feeders of parasite-induced Glossosoma reductions in six streams for which considerable pre- and post-collapse data are available, and we compare the results of this large-scale perturbation to responses predicted from a small-scale experiment that had been previously conducted in one of these streams. Periphyton and most grazers and filter-feeders showed marked increases in abundance following reduction in Glossosoma populations. Several grazers that were rare or absent prior to- Glossosoma collapse have established sizable populations, suggesting that they had been excluded by competition with Glossosoma. The small-scale experiment successfully predicted the direction of response of most taxa to whole-stream reductions in Glossosoma abundance, but it tended to underestimate the extent and magnitude of Glossosomas effects in the community. In these systems, observations at larger spatial and temporal scales have been essential to developing a clearer under- standing of the mechanisms structuring communities.

Classifying Regional Variation in Thermal Regime Based on Stream Fish Community Patterns

Abstract Although the importance of water temperature to the ecology of stream fishes is well documented, relatively little information is available on the extent of regional variation in thermal regime and its influence on stream fish distribution and abundance patterns. In streams draining the heterogeneous glacial landscape of Michigans Lower Peninsula, regional variation in summer mean temperature and temperature fluctuation is among the highest reported in the literature. We developed a habitat classification to simplify the description of thermal regimes and to describe the relationships between available thermal regimes and distribution patterns of stream fishes. Changes in community composition, species richness, and standing stocks of key fish species occurred across gradients in mean temperature and temperature fluctuation. These changes were used to identify three mean temperature categories (cold, <19°C; cool, 19–<22°C; and warm, ≥22°C) and three temperature fluctuation categories (stable, <5...

Distributions of stream fishes and their relationship to stream size and hydrology in Michigan's lower peninsula

Abstract We examined the distribution and abundance patterns of 69 fish species that commonly occur in the rivers of Michigans lower peninsula to develop a simple, empirically based model for describing fish assemblages. We used cluster analysis to group fishes that shared similar abundance patterns at 226 stream sites. The 17 clusters we identified explained about 39% of the variation in species abundances among the stream sites, providing a reasonable, albeit simplified, picture of general associations of fishes in lower Michigan streams. Known ecological differences among species and further analyses suggested that a measure of cluster abundance should not be used to predict the abundances of its constituent species. We selected catchment area (CA) and low-flow yield (LFY; 90% exceedence flow divided by catchment area) as axes for plotting fish distributions and rivers because these variables link catchment-scale features of the landscape to multiple, site-scale characteristics of stream habitat (e.g....

An assessment of biological interactions in an epilithic stream community using time-lapse cinematography

In situ time-lapse cinematography was used to record and enumerate behavioral interactions between members of an epilithic insect community in a small Michigan (U.S.A.)trout stream. 145 interactions were observed during 78 hours of filming. Most of these (98%) involved simuliid larvae. Interactions between simuliid larvae occurred at about the same frequency as interactions between simuliids and other taxa. However, interactions between simuliid larvae were less likely to lead to emigration than were interactions between blackflies and other groups. Significant short-term fluctuations of faunal density on filmed surfaces were also observed. The causes of these fluctuations appeared varied. The results of a preliminary assessment of interactions and the usefulness of this technique are discussed.

Interacting Influences of Density and Preference on the Emigration Rates of Some Lotic Chironomid Larvae (Diptera:Chironomidae)

The effects of manipulations of density and sediment type on the emigration rates of chironomid larvae (Diptera:Chironomidae) from Hunt Creek, Montmorency County, Michigan, USA, were examined in artificial stream chambers. Both basic sediment suitability and population density were found to affect larval emigration rates. Furthermore, their interaction lead to rates of emigration not predictable from an examination of either factor alone. A simple model of habitat suitability was developed and fit to the experimental data. The fitted model provided estimates of habitat carrying capacities for two important chironomid species and for a generalized chironomid assemblage. A comparison of these estimates with observed field densities indicated that competitive displacement of individuals probably occurs regularly in sand sediments. An examination of field data from 1975—1976 revealed a suppression of species diversity and of competitor standing crops by the dominant sand species. Together these results suggest that competitive interactions have an important influence on the spatial distribution of chironomid larvae in Hunt Creek.

A Multimetric Assessment of Stream Condition in the Northern Lakes and Forests Ecoregion Using Spatially Explicit Statistical Modeling and Regional Normalization

Abstract We sampled fish communities, water temperature, water chemistry, physical habitat, and catchment characteristics for 94 stream sites selected randomly throughout the Northern Lakes and Forests ecoregion and used those data to explicitly model reference conditions and assess ecological stream condition at each site via a regional normalization framework. The streams we sampled were first order through fourth order, and the catchments ranged from 0.9 to 458 km2. We developed multiple linear regression (MLR) models that predicted fish community metrics, water chemistry characteristics, and local physical habitat from catchment characteristics; we used these models to compare existing conditions with the conditions that would be expected based on the regression models. Our results indicated that the fish communities were relatively unimpaired because the catchment variables associated with human-induced land use change were important in only 1 of the 10 fish metric models. Agricultural land use was a...

Influence of stream location in a drainage network on the index of biotic integrity

Abstract The index of biotic integrity (IBI) has become a widely used tool for assessing the condition of stream fish communities and the overall biological status of streams. Because the location of a stream in a drainage network can influence the species richness offish communities and because species richness is an important component of the IBI, we examined the influence of stream spatial location on the IBI. We found that IBI scores for headwater streams in three Illinois drainage basins were significantly lower than those calculated for tributary streams of similar size connecting directly to larger streams. This difference in IBI was related to the increased species richness and to a greater number of sucker and darter species in tributaries that drain into larger, main-channel streams. Because of the influence of tributary location on the IBI, expected values for headwater tributary streams should be developed independently from those developed for main-channel tributary streams. Failure to do so ...

A spatially constrained clustering program for river valley segment delineation from GIS digital river networks

River valley segments are adjacent sections of streams and rivers that are relatively homogeneous in hydrology, limnology, channel morphology, riparian dynamics, and biological communities. River valley segments have been advocated as appropriate spatial units for assessing, monitoring, and managing rivers and streams for several reasons; however, methods for delineating these spatial units have been tedious to implement or have lacked objectivity, which arguably has limited their use as river and stream management units by natural resource agencies. We describe a spatially constrained clustering program that we developed for delineating river valley segments from geographic information system digital river network databases that is flexible, easy-to-use, and improves objectivity in the river valley segment delineation process. This program, which we refer to as the valley segment affinity search technique (VAST), includes a variety of options for determining spatial adjacency in stream reaches, as well as several data transformation methods, types of resemblance coefficients, and cluster linkage methods. The usefulness of VAST is demonstrated by using it to delineate river valley segments for river network databases for Michigan and Wisconsin, USA, and by comparing river valley segments delineated by VAST to an expert-opinion delineation previously completed for a Michigan river network database.

Predicting future changes in Muskegon River watershed game fish distributions under future land cover alteration and climate change scenarios.

Abstract Future alterations in land cover and climate are likely to cause substantial changes in the ranges of fish species. Predictive distribution models are an important tool for assessing the probability that these changes will cause increases or decreases in or the extirpation of species. Classification tree models that predict the probability of game fish presence were applied to the streams of the Muskegon River watershed, Michigan. The models were used to study three potential future scenarios: (1) land cover change only, (2) land cover change and a 3°C increase in air temperature by 2100, and (3) land cover change and a 5°C increase in air temperature by 2100. The analysis indicated that the expected change in air temperature and subsequent change in water temperatures would result in the decline of coldwater fish in the Muskegon watershed by the end of the 21st century while cool- and warmwater species would significantly increase their ranges. The greatest decline detected was a 90% reduction i...

An Ecological Assessment of Great Lakes Tributaries in the Michigan Peninsulas

ABSTRACT Michigan stream fish and macroinvertebrate community data from multiple sources were combined to conduct a statewide assessment of riverine ecological condition. Using regionally normalized metrics to correct for methodological inconsistencies and natural variation and statistically based scoring criteria, about 50% of all sampled sites were in expected or better ecological condition, 30% were ecologically impaired, and 20% were marginal. Structural Equation Modeling with this regional assessment dataset indicated that land use effects were more important than effects of point-source discharges. Biological metrics appeared to be more sensitive to urban than agricultural land use, and riparian than basin-wide agricultural land use. Invertebrate communities were marginally more sensitive than fish communities to the suite of anthropogenic stressors examined. Using the observed assessment status from sampled sites, Classification and Regression Tree models were used to estimate ecological condition in the states remaining unsampled river segments. Combining observed and estimated site scores, 25% of the states river kms were estimated to be impaired, with the Erie and St Clair basins having the highest degree of impairment (52% and 44% of total channel lengths, respectively) and lakes Superior, Michigan, and Huron basins had the lowest degree of impairment at 4%, 21% and 31%, respectively. We argue that correlations between the state of the Great Lakes and the ecological conditions of their tributary systems reflect both direct impact transmission from watershed to receiving waters, and also non-causal correlation due to shared anthropogenic stressors.