Malcolm G. Butler

Mallard duckling growth and survival in relation to aquatic invertebrates

Identification and assessment of the relative importance of factors affecting duckling growth and survival are essential for effective management of mallards on breeding areas. For each of 3 years (1993-95), we placed F 1 -generation wild mallard (Anas platyrhynchos) females on experimental wetlands and allowed them to mate, nest, and rear broods for 17 days. We manipulated invertebrate densities by introducing fathead minnows (Pimephales promelas) at high densities in half of the wetlands on which broods were confined. Day-17 body mass of surviving ducklings (n = 183) was greater for ducklings that were heavier at hatch; the difference averaged 1.7 g at day 17 for each 1.0 g at hatch (P = 0.047). Growth ratio (the proportion of body mass attained by ducklings when they were last measured relative to that predicted for wild female mallard ducklings) also was positively related to body mass at hatch (P = 0.004). Mean day-17 body mass and mean growth ratio of ducklings per brood (each adjusted for body mass at hatch) were positively related to numbers of aquatic invertebrates (Ps < 0.001) and negatively related to variance in the daily minimum air temperature during the exposure period (Ps < 0.020). Early growth of mallards was more sensitive to variation in numbers of invertebrates than to air temperature or biomass of invertebrates. Duckling survival was positively related to growth ratio (P < 0.001). Our study provides parameter estimates that are essential for modeling growth and survival of mallard ducklings. We emphasize the need for conserving brood-rearing wetlands in the Prairie Pothole Region that are capable of supporting high densities of aquatic invertebrates.

Responses to food web manipulation in a shallow waterfowl lake

We evaluated effects of fish removal from a large, shallow lake that historically was an important feeding area for migrating diving ducks. In the decade before fish removal, turbidity was high, submerged macrophytes and benthic macroinvertebrates were not abundant, and waterfowl use was negligible. Zooplankton and benthic macroinvertebrates increased during the first three post-treatment years. Water clarity improved initially in response to cladoceran grazing, allowing expansion of submerged macrophytes.Subsequent increases in water transparency may have been related to decreased sediment resuspension and lower algal biomass owing to allelopathic inhibition or nutrient competition from submerged macrophytes. Use by migrating diving ducks increased dramatically, apparently owing to changes in macroinvertebrate and plant foods.

WEAK CORRESPONDENCE BETWEEN MACROINVERTEBRATE ASSEMBLAGES AND LAND USE IN PRAIRIE POTHOLE REGION WETLANDS, USA

To evaluate the potential development of a macroinvertebrate Index of Biotic Integrity (IBI) for Prairie Pothole Region wetlands, we sampled the aquatic macroinvertebrate and fish communities in 24 semipermanent wetlands located throughout central North Dakota. Wetland basins were selected to encompass a range of surrounding land-use, ranging from 100% grassland to 100% cropland. We used redundancy analysis (RDA) to identify the influences of fish, and temporal and spatial variation on the macroinvertebrate community. We also used RDA to look for relationships between wetland macroinvertebrate communities and land-use. Seventeen potential invertebrate metrics were tested by graphical analyses. We identified a strong influence on the macroinvertebrate community due to the presence of fish. A number of invertebrate taxa decreased in abundance as the summer progressed, and there was noticeable variation in the invertebrate community among individual wetlands of the region. However, we detected no strong relationships between the varying degrees of agricultural land-use in the wetland catchments and the invertebrate community. Consequently, we were unable to identify and effective IBI metrics indicative of land-use disturbance. Lack of correspondence between land-use and macroinvertebrates in this habitat is most likely due to a high degree of natural disturbance (e.g., presence of fish, temporal changes) and a low diversity community of resilient taxa in Prairie Pothole Region wetlands.

Effects of Fathead Minnow Colonization and Removal on a Prairie Wetland Ecosystem

Fish communities in prairie wetlands are extremely dynamic. Due to complete winterkills and periodic colonization, individual basins alternate between supporting a fish population and being fishless. Here we assess the ecological consequences of colonization and subsequent extinction of a fathead minnow population in a prairie wetland. We used a BACI-type approach (before-after control impact) in which data from the colonized wetland were paired with data from a similar fishless site first when both wetlands were fishless (1996), then when the minnow population reached moderate densities in the colonized site (1998), and then again when the colonized site became fishless after treatment with rotenone (1999). Fish colonization resulted in significant increases in turbidity, total phosphorus, and chlorophyll a in the water column; it also caused significant decreases in the abundance of aquatic insects and large cladocerans. Elimination of the minnow population largely reversed the effects of minnow colonization. Our results indicate that characteristics of prairie wetlands can vary as they alternate between supporting fathead minnow populations and being fishless and that ecological characteristics may change rapidly in response to minnow colonization or elimination.

Early responses of plankton and turbidity to biomanipulation in a shallow prairie lake

We evaluated the effect of a fish removal from a shallow, turbid, eutrophic lake. By late May (following an October fish removal), the cladoceran community shifted from small-bodiedBosmina andChydorus (less than 100 l−1) to largerDaphnia (over 100 l−1). During the periods of peak daphnid abundance (late May–June) chlorophyll-a concentrations and edible diatoms were reduced and water transparency improved dramatically. Total phosphorus was not significantly lowered during this period. Although this clear-water phase was short-lived (May, June and early July), it corresponded to the critical period of plant growth and allowed dramatic increases in submergent macrophytes.

A 200‐year perspective on alternative stable state theory and lake management from a biomanipulated shallow lake

Multiple stressors to a shallow lake ecosystem have the ability to control the relative stability of alternative states (clear, macrophyte-dominated or turbid, algal-dominated). As a consequence, the use of remedial biomanipulations to induce trophic cascades and shift a turbid lake to a clear state is often only a temporary solution. Here we show the instability of short-term manipulations in the shallow Lake Christina (Minnesota, USA) is governed by the long-term state following a regime shift in the lake. During the modern, managed period of the lake, three top-down manipulations (fish kills) were undertaken inducing temporary (5-10 years) unstable clear-water states. Paleoecological remains of diatoms, along with proxies of primary production (total chlorophyll a and total organic carbon accumulation rate) and trophic state (total P) from sediment records clearly show a single regime shift in the lake during the early 1950s; following this shift, the functioning of the lake ecosystem is dominated by a persistent turbid state. We find that multiple stressors contributed to the regime shift. First, the lake began to eutrophy (from agricultural land use and/or increased waterfowl populations), leading to a dramatic increase in primary production. Soon after, the construction of a dam in 1936 effectively doubled the depth of the lake, compounded by increases in regional humidity; this resulted in an increase in planktivorous and benthivorous fish reducing phytoplankton grazers. These factors further conspired to increase the stability of a turbid regime during the modern managed period, such that switches to a clear-water state were inherently unstable and the lake consistently returned to a turbid state. We conclude that while top-down manipulations have had measurable impacts on the lake state, they have not been effective in providing a return to an ecosystem similar to the stable historical period. Our work offers an example of a well-studied ecosystem forced by multiple stressors into a new long-term managed period, where manipulated clear-water states are temporary, managed features.

BIOTIC INTERACTIONS AS DETERMINANTS OF ECOSYSTEM STRUCTURE IN PRAIRIE WETLANDS: AN EXAMPLE USING FISH

Wetlands are abundant throughout the prairie pothole region (PPR), an area comprising over 700,000 km2 in central North America. Prairie wetland communities are strongly influenced by regional physiography and climate, resulting in extreme spatial and temporal variability relative to other aquatic ecosystems. Given the strong influence of abiotic factors, PPR wetland communities have been viewed traditionally in the context of their responses to chemical and physical features of landscape and climate. Although useful, this physical-chemical paradigm may fail to account for ecosystem variability due to biotic influences, particularly those associated with presence of fish. Spatial and temporal variability in fish populations, in turn, may reflect anthropogenic activities, landscape characteristics, and climate-mediated effects on water levels, surface connectivity, and hydroperiods. We reviewed studies assessing influences of fish on prairie wetlands and examined precipitation patterns and biological data from PPR wetlands in east-central North Dakota and western Minnesota, USA. Our review and analysis indicated that native fish influence many characteristics of permanently flooded prairie wetlands, including water clarity and abaundance of phytoplankton, submerged macrophytes, and aquatic invertebrates. We suggest that ecologists and managers will benefit from conceptual paradigms that better meld biotic interactions associated with fish, and perhaps other organisms, with chemical and physical influences on prairie wetland communities.

Changes in macrophyte community structure in Lake Christina (Minnesota), a large shallow lake, following biomanipulation

Macrophyte community structure in Lake Christina, a large shallow lake in west-central Minnesota, changed in response to a biomanipulation treatment in 1987. Three years of pre-treatment and 11 years of post-treatment data were analyzed. Using a combination of cluster analysis and indicator species analysis, three distinct macrophyte communities were identified: a pre-treatment community of low plant abundance, an early post-treatment community dominated by Najas flexilis, N. marina, Myriophyllum sibiricum and Ruppia maritima, and a late post-treatment community characterized by Chara vulgaris, C. canescens, Potamogeton pectinatus, and P. pusillus. Canonical correspondence analysis (CCA) showed that these changes in plant community structure are associated with improvements in water clarity and annual variation in abundance of filamentous algae.

PALEARCTIC AND NEARCTIC CHIRONOMUS (CAMPTOCHIRONOMUS) TENTANS (FABRICIUS) ARE DIFFERENT SPECIES (DIPTERA: CHIRONOMIDAE)

Morphological comparison of populations of Chironomus (Camptochironomus) tentans (Fabricius) from Europe, Asia and North America has confirmed earlier cytogenetic evidence that two distinct species inhabit the Palearctic and the Nearctic under this name. The Palearctic species is the true C. tentans, whereas Nearctic populations constitute a new species described here under the name Chironomus (Camptochironomus) dilutus. Descriptions of the larva, pupa and adult male of both species are presented, and the taxonomic structure of the subgenus Camptochironomus is examined.

Effects of rotenone on aquatic invertebrate communities in prairie wetlands

We assessed the effects of rotenone on aquatic invertebrate communities by comparing four prairie wetlands treated with rotenone to four control sites. Data collected one week before and three weeks after treatment in the fall of 1998 were paired to assess short-term effects, while data collected in spring 1998 and spring 1999 were paired to assess longer-term effects and recovery rates. Data were collected on 14 taxa of benthic invertebrates collected in Ekman grab samples, and 23 taxa of planktonic-nektonic invertebrates collected in water-column samples. Each data set was analyzed separately with redundancy analysis to assess effects in the two habitats sampled. Significant short-term effects were detected on invertebrates in the water column and abundance of several taxonomic groups declined sharply after treatment. The greatest declines were observed in zooplankton abundance; effects on macroinvertebrates were much less pronounced. Suppression of water-column taxa was short-lived, as significant effects were no longer evident during May 1999. In contrast, no significant short-term effect was evident in the benthic taxa. Our results indicate that fall applications of rotenone may briefly suppress plankton communities, but effects are short-lived. From a fisheries management perspective, fall applications may minimize effects on invertebrate communities and facilitate rapid recovery.