Nicholas C. Collins

Synergistic interactions between fish and stoneflies: facilitation and interference among stream predators

A series of experiments examined rates of prey consumption by mottled sculpins (Cottus bairdi) and perlid stoneflies (Agnetina capitata) separately, and when they were together in artificial streams. Two types of Ephemeroptera prey (Ephemerella subvaria and Baetis tricaudatus) were used in separate experiments. When both types of predators were present consumption of Baetis larvae was significantly less than model predictions of combined prey consumption, indicating a negative interaction between predators. Consumption of Ephemerella was significantly higher than predicted by the model indicating a positive interaction between predators. Analysis of gut contents indicated that Agnetina captured fewer Baetis larvae in the presence of sculpins, and sculpins captured significantly more Ephemerella larvae in the presence of stoneflies. Negative effects of sculpins on the number of Baetis larvae captured by Agnetina were found even when the sculpins were unable to feed. Positive effects of Agnetina on the number of Ephemerella captured by sculpins were still found even when Agnetina density was reduced by more than half. Understanding the complexity of interaction between fish and stoneflies may provide explanations for the contradiction between observed and expected results of fish removal experiments in streams.

Importance of Diurnal and Nocturnal Nest Defense in the Energy Budget of Male Smallmouth Bass: Insights from Direct Video Observations

Abstract Reproductive behavior has never been considered an important contributor to overall activity costs for fish and is usually ignored in fish bioenergetics models. We provide evidence that parental care by male smallmouth bass Micropterus dolomieu substantially affects both activity costs and food intake. We used timelapse underwater video with infrared illumination to monitor nests of male smallmouth bass continuously for nearly 2 weeks from oviposition to swim-up of larvae, and we discovered that unlike nonnesting bass, nestguarding males were active during both night and day. Guarding males constantly sculled their caudal and pectoral fins (swimming in place) while on nests. We used caudal fin beat frequencies to relate the costs of swimming in place to those of nonguarding swimming. Combining these estimates with predictions of a respiration model for largemouth bass M. salmoides, we estimated that the metabolic rate of guarding smallmouth bass was up to 60% greater than that of nonguarding indi...

TREE REGRESSION ANALYSIS ON THE NESTING HABITAT OF SMALLMOUTH BASS

Habitat conditions may determine locations of patchily distributed small- mouth bass nests in lakes, since young smallmouth bass are fragile and are therefore vulnerable to suboptimal physical characteristics in their typically variable nesting area, the littoral zone. Knowing which habitat conditions are important to nest locations would ultimately be useful in protecting optimal nesting areas from anthropogenic disturbances in lakes. To evaluate factors related to the nest distributions of a smallmouth bass (Mi- cropterus dolomieui) population, physical habitat conditions were measured at 36 1-km- long and 31 100-m-long sites in Lake Opeongo (Ontario, Canada). Both tree regression analysis (a recently devised and unique statistical tool) and standard multiple regression were used to determine the relationships between nest density and four habitat variables. Tree regression analysis does not require assumptions of linearity or homoscedasticity of variances, and it automatically identifies interactions among variables. Furthermore tree regression results were more accurate and more precise than standard multiple-regression results. Mechanisms underlying the significant relationships between nest densities and both littoral zone temperatures and shoreline reticulation in 1-km-long sites and the non- significant results at the 100-m-long scale, are discussed. Cross-validation results quantify the difficulty in extrapolating sample findings to whole populations in ecological research.

Balancing risks? Responses and non-responses of mayfly larvae to fish and stonefly predators

SummaryIn a series of laboratory experiments we examined the hypothesis that larvae of stream mayflies would respond to the presence of two different types of predators in such a way as to minimize their risk of being consumed by each. Positioning of larvae (whether they frequent the top, sides, or bottom of stones) of Baetis tricaudatus and Ephemerella subvaria was altered by the presence of predaceous stoneflies (Agnetina capitata) with a larger proportion of the population occurring on the upper surfaces, where the probability of encountering the predator was lowest. The presence of a benthivorous fish (Cottus bairdi) had no significant effects on positioning of the mayfly larvae. Lack of fish effects may reflect an inability of the mayflies to detect or respond to sculpins, or alternately may indicate that sculpins do not normally present a important predation risk for these mayflies. Failure of mayfly prey to account for fish predators when responding to the presence of stoneflies appcars to explain facilitation previously observed between stoneflies and sculpins.

Developmental Responses to Food Limitation as Indicators of Environmental Conditions for Ephydra Cinerea Jones (Diptera)

Adaptive developmental responses to suboptimal conditions should preserve the life history traits most important to fitness at the expense of less critical traits. This paper compares responses to food limitation of Ephydra cinerea Jones (new data) to those of other Diptera (literature data) and concludes that the differences are indeed related to differences in demographic situations and other environmental characteristics. All the flies surveyed respond to larval food limitation by sacrificing adult body size, fecundity, and development time; these responses will moderate increases in prereproductive mortality, which demographic analyses identify as the most influential component of fitness for all the species. Differ- ences between E. cinerea and the other flies in the degree to which: (a) body size is reduced, (b) development time is extended, and (c) mass-relative reproductive investment is increased under larval food limitation are associated with differences in: (a) the importance of size-related adult social interactions and range of larval food availability, (b) the safety of larval environments, and (c) de- mographic conditions. Similar comparisons generated predictions that, in comparison to other higher Diptera, adult size should be unusually important to fitness in house flies (Musca domestica, and the risks of mortality late in the larval period should be unusually high in the natural environments of blowflies (Chrvsomvia spp., Lucilia spp.). Adult life-span and fecundity of fly species with poor access to adult food are relatively insensitive to reductions in adult food availability. Similarly, starvation resistance of newly eclosed larvae is correlated with the difficulty larvae have in locating food in nature, while absolute and relative egg size are not. In contrast to some other insects and mites, all the flies surveyed maintain nearly constant egg size (and where measured, egg quality) over a wide range of larval food limitation, suggesting that reduced egg size would have drastic effects on larval success. Where environmental data are available for the flies, conditions would favor evolution of near minimal investment per offspring.

RELATIVE ABUNDANCE OF LITTORAL ZONE FISHES: BIOTIC INTERACTIONS, ABIOTIC FACTORS, AND POSTGLACIAL COLONIZATION'

We used multivariate ordination techniques to establish relationships among the abundances of the most frequently occurring littoral zone fishes (fishes that occurred in >60% of the lakes) in 25 central Ontario lakes. Previously, most large-scale comparative studies of freshwater fish communities only measured species presence/absence. Abundance estimates provide an alternative, and perhaps more sensitive, means of assessing the relative importance of biotic processes, geological/chemical factors, and historical determinants of present-day community structure. Seventy percent of the variation in abundances was described by the first two axes from a correspondence analysis. Abundances of white sucker (Catostomus commersoni) and rock bass (Ambloplites rupestris), and abundances of brown bullhead (Ictalurus nebulosus) and smallmouth bass (Micropterus dolomieui) were negatively related. However, abundances of these species pairs were not related where the species occurred in sympatry, suggesting that species presence/absence strongly influenced these patterns of abundance. Most of the variation in species abundance and distribution was attributed to physical factors associated with species colonization processes (i.e., differences in postglacial colo- nization rates may have caused negative associations between white sucker and rock bass). An independent 45-lake data set was used to confirm these zoogeographic patterns. Pre- dation by northern pike (Esox lucius) may be partly responsible for variation in abundance and distribution of white sucker. Where pike and sucker co-exist, sucker abundance is lower than where sucker exist without pike. Habitat differences between lakes provided the best explanation for the variation in abundance of smallmouth bass and brown bullhead. Biogeographic processes, physical environmental factors, and predatory processes have been very influential in shaping abundances and distributions of ubiquitous littoral zone fishes in Ontario.

Lazy males? Bioenergetic differences in energy acquisition and metabolism help to explain sexual size dimorphism in percids

1. Differences in energy use between genders is a probable mechanism underlying sexual size dimorphism (SSD), but testing this hypothesis in the field has proven difficult. We evaluated this mechanism as an explanation for SSD in two North American percid species--walleye Sander vitreus and yellow perch Perca flavescens. 2. Data from 47 walleye and 67 yellow perch populations indicated that SSD is associated with the onset of maturation: typically, males of both species matured smaller and earlier and attained a smaller asymptotic size than females. Males also demonstrated equal (perch) or longer (walleye) reproductive life spans compared with females. 3. To examine whether reduced post-maturation growth in males was due to lower energy acquisition or higher reproductive costs we applied a contaminant mass-balance model combined with a bioenergetics model to estimate metabolic costs and food consumption of each sex. Mature males exhibited lower food consumption, metabolic costs and food conversion efficiencies compared with females. 4. We propose that slower growth in males at the onset of maturity is a result of decreased feeding activity to reduce predation risk. Our finding that SSD in percids is associated with the onset of maturity is supported by laboratory-based observations reported elsewhere, showing that changes in growth rate, consumption and food conversion efficiency were elicited by oestrogen (positive effects) or androgen (negative effects) exposure in P. flavescens and P. fluviatilis. 5. Researchers applying bioenergetic models for comparative studies across populations should use caution in applying bioenergetic models in the absence of information on population sex ratio and potential differences between the sexes in energetic parameters.

A mechanism for interference between stream predators: responses of the stonefly Agnetina capitata to the presence of sculpins

SummaryMottled sculpins (Cottus bairdi) have a strong negative effect on the ability of the stonefly Agnetina capitata to capture some types of mayfly prey. To determine the mechanism for this interference effect, behavior of Agnetina in the presence and absence of sculpins was observed over 24 h periods (12 h light, 12 h dark), using an infra-red sensitive camera and a time-lapse video recorder. Agnetina larvae reacted to the presence of sculpins by significantly reducing the time they spent off the bottom of the substrate, and by significantly decreasing the amount of time spent moving on the substrate. These experiments suggest that in the presence of fish, stonefly diets may contain a smaller proportion of prey that tend to frequent tops and sides of stones. This behavioral flexibility may be important in streams in that it allows stoneflies to advantageously shift their diets when fish population densities are low.

Linking fish population dynamics to habitat conditions: insights from the application of a process-oriented approach to several Great Lakes species

One of the major challenges facing fishery scientists and managers today is determining how fish populations are influenced by habitat conditions. Many approaches have been explored to address this challenge, all of which involve modeling at one level or another. In this paper, we explore a process-oriented model approach whereby the critical population processes of birth and death rates are explicitly linked to habitat conditions. Application of this approach to five species of Great Lakes fishes including: walleye (Sander vitreus), lake trout (Salvelinus namaycush), smallmouth bass (Micropterus dolomieu), yellow perch (Perca flavescens), and rainbow trout (Onchorynchus mykiss), yielded a number of insights into the modeling process. One of the foremost insights is that processes determining movement and transport of fish are critical components of such models since these processes largely determine the habitats fish occupy. Because of the importance of fish location, an individual-based model appears to be a nearly inescapable modeling requirement. There is, however, a paucity of field-based data directly relating birth, death, and movement rates to habitat conditions experienced by individual fish. There is also a paucity of habitat information at a fine temporal and spatial scale for many important habitat variables. Finally, the general occurrence of strong ontogenetic changes in the response of different life stages to habitat conditions emphasizes the need for a modeling approach that considers all life stages in an integrated fashion.

Diel and seasonal variation in foraging activities of pumpkinseeds in an Ontario pond

Abstract We used time-lapse video with infrared illumination to record feeding activity of pumpkinseeds Lepomis gibbosus in two patches of littoral habitat in a shallow, mesotrophic Ontario pond. Observations were made for 72 consecutive hours in each of eight ice-free months and include extensive, relatively nonintrusive field observations of pumpkinseed behavior at night. We tallied numbers of passes above the substrate and numbers of substrate strikes (at substrate or at vegetation). Variation among months accounted for 40–50% of the total variation in rates of daytime passing and substrate striking, which peaked in May and September. Among-day variation in daytime foraging activity within months was high, accounting for 50–57% of the total variance, and the variances we measured can be used to plan replication levels necessary to achieve adequate statistical power in future studies involving measurements of daily ration or comparisons of exploitation rates in different habitats. Simultaneous video mon...