Animal population densities are thought to be "regulated" by density-dependent processes (Haldane, 1953; Royama, 1977: Berryman, 1991). The perceived importance of these processes to biologists is evident from the vast amount of research dedicated to this idea (Inchausti, 1994). Most of this research addresses the problem(s) of detecting the effect of density-dependent regulatory processes using time series data. However, the question of the relative importance of density-dependent factors upon rates of change of population abundances is rarely addressed. In this thesis, I quantify the importance of density-dependent factors in 303 natural animal populations. I found that, on average, only $\approx$19% of the temporal variability in per capita growth rate could be statistically related to population density. Yet research effort concentrates overwhelmingly on density-dependent processes. I conclude that the effects of density-dependent processes within natural animal populations are generally weak and disproportionately studied. Because many, if not all, ecological processes act on some characteristic temporal or spatial scale (O'Neill et al., 1986; Wiens, 1989; Pimm, 1991; Maurer, 1994; Fleishman, 1995) I also address the question of how the characteristic time of density-dependent regulatory processes might affect the estimates of the influence of regulatory processes on a population's per capita growth rate. I hypothesized that if density-dependent regulatory processes operate on a characteristic temporal scale that sampling with a sampling period commensurate with the characteristic time of these processes would yield the maximal amounts of variability in the per capita growth rate statistically related to the variability in N. Simulated population time series were generated using a logistic growth model with a stochastic term added. Based on the analysis of the simulated time series, the characteristic time of density-dependent regulatory processes is predicted to be independent of life-history traits correlated with body size. The characteristic times are predicted to be integral multiples of 1 year (1, 2, 3 and 4 years) for all modelled body sizes. These predictions, regarding characteristic times, were found to be suspect after further testing supported the contention that these results may be methodological artifacts. I suggest that these results are due to the pragmatic criteria imposed to constrain the number of possible subsamples to be analyzed. I further suggest that to better address the characteristic time hypothesis, time-slices with different time periods between successive population densities are required.

New legislation which entrenches regulation of the turr hunt in Newfoundland into the Migratory Birds Convention Act, will require good knowledge of thick-billed murre (Uria lomvia) population biology for proper implementation. The impact of hunting on the population is determined by factors such as total bag, season length and timing, and the age of birds killed. These in turn depend on the temporal and spatial distribution of murres of different ages and from different colonies. Birds in their first winter were recovered in greater numbers than birds from older age categories and were usually recovered earlier in the season. Recovery rates of first winter and second winter birds from Digges Island were significantly lower than those for birds of the same age from the adjacent colony on Coats Island suggesting different spatial distributions of the young birds from the two colonies. Differences in the overwintering areas for adults from Coburg Island and Cape Hay, again located closely together, differed significantly with Coburg adults recovered in greater numbers in Newfoundland while Cape Hay adults were recovered most often in Western Greenland. Using recoveries of birds banded on Coats Island, annual survival from fledging to first year was estimated at 0.53 using the program SURVIV. Survival from second to third year was estimated at 0.83, from third to fourth year was 0.74, from fourth to fifth year was 0.86. The estimate from third to fourth year was considered to be an underestimate as a result of the high mobility of third year birds at the colony. Based on these survival probabilities, survival to breeding age, using the best estimates from band recoveries and resightings was estimated at 0.27. (Abstract shortened by UMI.)

The factors regulating the development and trophic interactions of planktonic communities were determined in 31 medium to large size temperate rivers. In addition, the Rideau River, Ontario, was studied in detail over three field seasons. Variables measured included: phytoplankton biomass as measured by chlorophyll $\alpha$ concentration; zooplankton biomass (rotifers and crustaceans); heterotrophic bacterial abundance; heterotrophic flagellate abundance; nutrient concentrations (phosphorus and nitrogen); dissolved organic carbon concentration; river discharge; water residence time; depth; temperature; and light attenuation. Phytoplankton was abundant in eutrophic rivers ($>$15 $\mu$g L$\sp{-1}$ of chlorophyll a) and was most strongly related to nutrient concentrations, primarily total phosphorus, which explained up to 76% of the variation in chlorophyll a. Phytoplankton biomass in the rivers was not related to the hydrological parameters of water residence time or discharge, possibly due to the short generation time of phytoplankton (hours to days). Light did not appear to limit phytoplankton biomass due to shallow depths and extensive vertical mixing. In the Rideau River phytoplankton biomass exhibited longitudinal heterogeneity, but in general increased in a downstream direction, concomitant with increases in nutrient concentrations. Phytoplankton biomass did not appear to be affected by zooplankton grazing in the rivers. However, phytoplankton biomass may have been negatively impacted by benthic filter feeders, in particular the invasive zebra mussel (Dreissena polymorpha), in the downstream reaches of the Rideau River. Zooplankton biomass in the rivers was low (usually 20 $\mu$g L$\sp{-1}$ dry mass) and small taxa dominated the zooplankton communities (e.g. rotifers, bosminids). Large zooplankton taxa, such as Daphnia sp., were much less abundant. Due to longer generation times (days to weeks), zooplankton biomass was primarily related to water residence time which explained 33% of the variation. Zooplankton appeared susceptible to advective loss in the rivers. A positive resource effect of either nutrients or phytoplankton on zooplankton biomass, typically observed in lakes, was weaker in the rivers. In comparison to lakes, zooplankton appeared less tightly coupled to phytoplankton. As with phytoplankton, zooplankton biomass in the Rideau River increased with downstream travel and appeared to be negatively affected by benthic filter feeders. Heterotrophic bacteria were abundant in the rivers (4.5 $\times$ 10$\sp6$ cells ml$\sp{-1})$ and, as in lakes, bacteria were most strongly related to nutrient concentrations (total phosphorus) and phytoplankton biomass (chlorophyll a). In contrast to lakes, no relationship between bacterial abundance and dissolved organic carbon was observed, possibly due to the more allochthonous, refractory nature of river dissolved organic carbon. Heterotrophic flagellates were also abundant in the rivers $(4.0\times10\sp{3}$ cells ml$\sp{-1})$ and were most strongly related to bacterial abundance and nutrient concentrations (total phosphorus). Neither bacterial nor flagellate abundance was related to water residence time. A negative relationship between zooplankton biomass and bacterial or flagellate abundance was not observed, possibly because of the low biomass (hence low grazing pressure) of zooplankton in the rivers. Due to the scarcity of zooplankton in rivers, there may be little transfer of energy from the planktonic microbial food web to planktonic metazoans.

Several hypotheses have been proposed to explain the occurrence of polygyny in birds. The purpose of this study is to test those hypotheses using data from a marsh-nesting population of the red-winged blackbird (Agelaius phoeniceus). This study consists of two sections. The first section deals with theoretical aspects of the hypotheses and contains four chapters. I review all hypotheses and describe in detail their assumptions and predictions. I argue that the asynchronous settlement model cannot explain polygyny as stated and propose a new version of the model. I examine one assumption and four predictions of the sexy son hypothesis. Using examples, I demonstrate that the assumption and three predictions do not follow from the hypothesis. I argue that the the fourth prediction (mathematical model for the calculation of reproductive success of polygynous females) is flawed and propose a corrected version of the model. I review hypotheses that explain polygyny through "random" female settlement and propose a new ("status indifference") hypothesis. I conclude the first section by hierarchically classifying the plausible hypotheses by their key assumptions. The second section of this study presents the results of field experiments that tested the key assumptions. I tested female preferences for unmated or monogamously mated males by offering newly settling females a choice of two adjacent territories, one defended by an unmated male and the other by a monogamously mated male. Male mating status was randomized with respect to the variation in territory quality and male quality. Early in the breeding season, significantly more females settled with the unmated males than with the mated males. Although a similar trend was evident late in the breeding season, the difference was no longer significant. The consequences of polygamy on female reproductive success was then investigated. After randomizing harem size with respect to territory and male quality, I found that (1) monogamous females fledged as many young as bigamous females; (2) nestlings on monogamous and bigamous territories were provisioned equally often by both parents; (3) on bigamous territories, asynchronous broods were provisioned by males significantly more frequently than synchronous broods; (4) Ten-day-old female nestlings on monogamous territories were better developed than their bigamous peers. Finally, I establish whether females exhibit preferences for selected habitat characteristics. On a broad spatial scale (choice of a nesting area within a marsh), univariate analyses established that female selection of nesting areas was non-random with respect to six characteristics. However, a multivariate analysis revealed that females settle non-randomly only with respect to water depth. Females preferred nesting areas located in deep water to those in shallow water. On the narrow spatial scale (choice of a nest site within a nesting area), females preferred dense clumps of vegetation surrounded by sparse vegetation. (Abstract shortened by UMI.)

The conservation of biological diversity requires simple, predicative models that yield quantitative guidelines for management. This is illustrated by contemporary problems in managing wetlands. Riparian wetlands, in particular, are under heavy pressure from the hydrological changes produced by dam construction and water diversion projects. There has been ample documentation of the significance of substrate and hydrologic variables on the composition of shoreline plant communities, yet we have few models that yield quantitative predictions for conservation management. My goal has been to provide quantitative decision rules that predict the composition of wetland plant communities. A principal obstacle to generating predictions for wetland vegetation is the large species pool. One solution is the assignment of species to functional groups that are recognizable by a few, simple traits. The distribution of these functional groups could then be described by trait-environment relationships. I have investigated the relationship between the distribution of functional groups and a set of hydrological and substrate variables, using the wetlands of the Ottawa River as my study system. I first identified two fundamental functional groups of wetland species, woody and herbaceous. The model with the highest accuracy was composed to two hydrologic variables, the last day of the first flood and the time of the second flood. The combination of these two variables correctly identified which group was the cover type for over 80% of the original data points. I then investigated the relationships between functional groups defined by the presence or absence of floating leaves and/or flexuous stems and the environmental variables. The duration of flooding best described the distribution of this group, again with an accuracy of over 80%, using the original data points. Finally I compared the merits of five classifications of emergent species in identifying functional groups that can be predicted from hydrological and substrate variables. The traits used in these classifications included leaf shape, area or arrangement; stem characteristics; ramet biomass; ramet height; and the number and length of rhizomes. The most accurate models (based on the original data) related the distribution of the functional groups that were defined by leaf shape, leaf area and stem diameter to hydrology and the sand fraction in the soil. I generated and tested quantitative predictions from the 11 models with the highest accuracy (using the original data) from the above work. Four models performed well when tested with data from other regions or from Ottawa River sites not previously included in the analysis. The corresponding functional groups were woody plants, floating leaved/flexuous stemmed plants, plants with leaf area equal to zero and plants with lanceolate, elliptical or compound emergent leaves. Using the model parameters I formulated inclusion and exclusion rules to predict the presence or absence of these functional groups at various ranges of the significant environmental variables. These decision rules provide valuable tools for the conservation management of the vegetation of riverine wetlands.

Tropical American Piper spp. have insecticidal activities comparable to those of previously studied African and Asian species. Effects of dietary administration of the crude ethanolic extracts of Piper spp. to the European corn borer, Ostrinia nubilalis Hubner, include a reduction of larval growth, a high death rate of larvae, pupae and adults, and a limited effect on the consumption and digestion of food. Among 16 Piper extracts the most active American species were, in decreasing order of growth reducing activity: P. tuberculatum, P. aduncum, P. pseudo-lindenii, P. lanceiaifolium, P. guanacastensis, P. decurrens, P. carilloanum, and P. auritum. Bioassay-guided isolation, using mosquito larvae, led to the isolation of a monolignan, dillapiol, as an active principle of P. aduncum, two neolignans as active principles of P. decurrens, and an amide, piperlonguminine as an active principle of P. tuberculatum. The new isolation of the neolignans and the amide gives further evidence of the biological significance of these two classes of compounds as chemical defenses of the piperaceae. The activities of a series of 15 pure monolignans, lignans, and neolignans were investigated with the polyphagous lepidopteran herbivore, the European corn borer, which has a high adaptive capacity to tolerate plant allelochemicals. The lignans (at a dose of 100 $\mu$g/g in the diet) were generally not highly toxic to the larvae, except for the monolignan dillapiol. However, delayed toxicity was revealed as mortality increased later in the life cycle, reaching at the adult stage a cumulative mortality of 95%, 68%, 60%, 43% and 40% with dillapiol, epiashantin, podophyllotoxin, epiyangambin and cubebin, respectively. The growth profile of larvae further showed that lignans are slow acting toxins, except for dillapiol and cyclolignans of the podophyllotoxin series. Antifeedant activity of the lignans was generally poor. Cubebin was the most active antifeedant with respect to the ECB with a protective concentration, PC$\sb{50}$, of 74 $\mu$g/g. There was a trend of increasing toxicity of lignans which generally parallelled the evolutionary advancement in biosynthesis. Because of their role in reversing insecticide resistance, lignans were tested for their activity on multidrug resistant (MDR) cells with overexpression of the membrane P-glycoprotein. MDR cells responded to the group of cyclolignans in a way similar to the response of other drugs which belong to the multiresistant group, while they showed important collateral sensitivity to the furans and even more to the monolignan dillapiol. An increased uptake of the anticancer drug vinblastine was observed upon co-administration of dillapiol. This activity constitutes a novel mode of action of this lignan, and possibly other insecticide synergists such as piperonyl butoxide, with regards to resistance to drugs and insecticides.

The "microbial loop" of aquatic systems consists of picoplankton (heterotrophic and photosynthetic), nanoflagellates (heterotrophic and mixotrophic forms), and ciliates. Heterotrophic flagellates (HNAN) are considered to be the principal grazers of both photosynthetic picoplankton (PICO) and heterotrophic bacteria (HBAC). The factors controlling PICO and HBAC abundances have been studied extensively. However, the factors which regulate HNAN remain less clear. An experimental study was conducted to examine the effects of nutrients and planktivorous fish additions on HNAN in freshwater systems using large enclosures (8m in diameter) installed at both 4 m and 11 m depths in a small oligotrophic lake. In addition to obligate heterotrophs, mixotrophic flagellates (MIXO) were also examined as were their prey, HBAC and PICO. Experimental results did not demonstrate that increases in nutrient levels would lead to increases in HNAN as current empirical models imply. The relationship between HBAC and HNAN was therefore examined within the range of trophy manipulated in the enclosures. A lake survey was conducted in dimictic lakes in Ontario and Western Quebec. (Abstract shortened by UMI.)

Populations of redwinged blackbirds (Agelaius phoeniceus phoeniceus) vary in density in different habitats in the Ottawa area. Population densities in three sample areas are defined in terms of numbers of breeding birds and numbers of nests. An attempt is made to define environmental factors which influence population densities in the different sample areas and affect census methods. Feeding of wild and captive birds were studied.

Age-specific reproductive parameters, including reproductive success, of young (four and five-year old) and older (>7 years old) breeding Thick-billed Murres (Uria lomvia) were compared on a colony at Coats Island, N.W.T. in 1990 and 1991. Young birds laid smaller eggs later in the season than older birds. Older birds had higher hatching and reproductive success than young birds, but fledging success did not differ. The chicks of young birds at 14 days were lighter and smaller than those of older birds. There was a seasonal decline in hatching and reproductive success in both years for the total sample, but no seasonal decline in fledging success. Most losses occurred during the incubation period, with a decreasing likelihood of laying a replacement egg as the season progressed. Age-related improvement in breeding success may have been due in part to breeding experience. Second time breeders laid earlier than in their first year, and improved their reproductive success. Five-year olds breeding for the second time bred earlier and more successfully than five-year olds breeding for the first time. Differential survival in relation to reproductive success was not observed. Birds which performed poorly in their first year were not less likely to return to breed in the next year than birds which performed well in their first year. Different proportions of young and older birds breeding throughout the season affected the seasonal decline in reproductive success of the overall colony. Young and older birds separately showed no seasonal changes (except a slight decline in reproductive success in older birds in one year), but when combined they had a similar seasonal decline in hatching and reproductive success as the total sample. In order to control for differences in timing of laying between young and older birds, a sample of early laying, presumably older breeders were experimentally delayed c. 14 days. Age, rather than timing of laying influenced the decline in reproductive success. Young birds had significantly lower hatching and reproductive success than experimental breeders. Although the chicks of younger birds were significantly smaller than experimental chicks, there was no decline in food availability detected at the end of the season, suggesting that young birds were not able to provision their chicks as well as more experienced breeders. Breeding site characteristics had some effect on the reproductive success of young and older breeders. Older birds were more successful on sites which had neighbours. Site characteristics did not affect the success of young birds in 1990, but birds nesting on sites with neighbours and walls showed improved success in 1991. Young birds were less successful than older birds on all types of sites, and more likely to be found on suboptimal sites. The lack of decline in reproductive success with date when age was controlled, and the high reproductive success of experimentally delayed birds suggest that it is the competence of young breeders, rather than the date at which they lay, that determines their reproductive success. The high proportion of young Thick-billed Murres that lay later in the season may be the main cause of the seasonal decline in reproductive success for the colony as a whole.

Fenitrothion was applied as an emulsion in water to a small lake at the rate of 420 g active ingredient per hectare. Peak residues of 21.6 ug/ℓ were present in surface waters one hour after treatment, but rapidly dispersed throughout the lake, with complete mixing within the epilinnion after 12 hours and maximum penetration into the hypolimnion (2.14 ug/ℓ) after 24 hours. All fish species in the lake rapidly accumulated fenitrothion residues with each species accumulating distinctly different residue levels. The highest residue found in each species was 1.01 mug/g in white suckers, Catastomus commersoni (Lacepede), 0.76 mug/g in fallfish, Semotilus corporalis (Mitchill), 0.44 mug/g in brown bullheads, Ictalurus nebulosus (Lesueur), and 0.34 mug/g in smallmouth bass, Micropterus dolomieu Lacepede. Rapid loss of accumulated residues was seen in all species except white suckers. The fenitrothion application had little effect on populations of fish food organisms or on the diet of native fish species, with the possible exception of cladoceran populations and their contribution to the diets of planktivorous fish species. Static bioassays in the laboratory gave 24 to 96 hour LC50 values between 1.2 and 5.4 mg/ℓ fenitrothion for seven species representing five families. Sensitivity to fenitrothion followed family lines with Salmonidae (trout) the most susceptible family and Ictaluridae (catfish) and Cyprinidae (minnows) the least sensitive. The results of the field and laboratory studies carried out indicate that fenitrothion applied at dosages registered for forest insect control does not appear to present a serious hazard to native fish populations in lakes exposed to aerial applications.