Browsing by Subject "population dynamics"
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Item Arctic Peregrine Falcon Abundance on Cliffs Along the Colville River, Alaska, 1981-2002 and Covariate Input Files(2015-04-15) Bruggeman, Jason E.; Swem, Ted; Andersen, David E; Kennedy, Patricia L.; Nigro, Debora; brug0006@umn.edu; Bruggeman, Jason E.Arctic peregrine falcons (Falco peregrinus tundrius; hereafter Arctic peregrine) have a limited and northern breeding distribution, including the Colville River Special Area (CRSA) in the National Petroleum Reserve-Alaska, USA. We quantified influences of climate, topography, nest productivity, prey habitat, density dependence, and interspecific competition affecting Arctic peregrines in the CRSA by applying the Dail-Madsen model to estimate abundance and vital rates of adults on nesting cliffs from 1981 through 2002. Arctic peregrine abundance increased throughout the 1980s, which spanned the population's recovery from DDT-induced reproductive failure, until exhibiting a stationary trend in the 1990s. Apparent survival rate (i.e., emigration; death) was negatively correlated with number of adult Arctic peregrines on the cliff the previous year, suggesting effects of density-dependent population regulation. Apparent survival rate and arrival rate (i.e., immigration; recruitment) were higher during years with earlier snowmelt and milder winters, and apparent survival was positively correlated with nesting season maximum daily temperature. Arrival rate was positively correlated with average Arctic peregrine productivity along a cliff segment from the previous year and initial abundance was positively correlated with cliff height. Higher cliffs with documented higher productivity, and presumably indicative of higher quality habitat, are a priority for continued protection from potential nearby development and disturbance to minimize population-level impacts. Our work provides insight into factors affecting a population during and after recovery, and demonstrates how the Dail-Madsen model can be used for any unmarked population with multiple years of abundance data collected through repeated surveys.Item Biology and population dynamics of the eastern larch beetle, Dendroctonus simplex LeConte, and its interactions with eastern larch (tamarack), Larix laricina.(2015-09) McKee, FraserThe range of the eastern larch beetle, Dendroctonus simplex LeConte (Coleoptera: Scolytinae), is concomitant with its primary host, eastern larch (tamarack), Larix laricina (Du Roi) K. Koch, throughout the North American boreal forest. Since 2000, an ongoing outbreak of eastern larch beetles in the south-central part of tamarackās range throughout the Great Lakes region has caused extensive mortality to mature tamaracks, affecting over 86,500 hectares of tamarack forest in Minnesota. Extended outbreaks in live trees are atypical of this insect, so the eastern larch beetleās biology and ecology were studied under laboratory and field conditions in Minnesota from 2011 ā 2014 to decipher the factors contributing to this ongoing outbreak. In the laboratory, the minimum and optimal developmental temperatures for eastern larch beetles were determined to be 7.5 and 27.9Ā°C, respectively. Some progeny were able to reproduce in the absence of an overwintering period, suggesting that a reproductive diapause may not be obligate in all individuals. This was confirmed by field studies, which found that a second generation of eastern larch beetles successfully completed development during the summer and fall of 2012. Confirmation of two generations instead of three sibling broods established by re-emerging parents in one year was established by detailed phenological and physiological methods. As beetle infestations progressed through tamarack stands, beetles initially preferred to attack the largest tamaracks before killing smaller hosts at random in successive years. Reproductive success of females increased in larger and older tamaracks, and those āchallengedā by unsuccessful attacks in the recent past. Higher concentrations of resin pockets within the phloem consistently reduced beetle reproduction. The size of male and female beetle offspring, as well as the total lipid content of female offspring, increased with tamarack size and phloem thickness. Development within āchallengedā tamaracks reduced both the total and proportional lipid contents of all beetle offspring. New understandings of the population dynamics of eastern larch beetles are discussed. Expanding growing seasons, for example, may facilitate fractional voltinism, or, two generations in one year, among a portion of the population. Synchronous beetle emergence the following spring ā shown in phenological studies ā would enhance host procurement, especially of the largest and most preferred hosts that produce the most vigorous offspring, thus exacerbating the outbreak.Item Data Supporting 'When things donāt add up: quantifying impacts of multiple stressors from individual metabolism to ecosystem processing'(2018-01-11) Galic, Nika; Sullivan, Lauren L; Grimm, Volker; Forbes, Valery E; ngalic@umn.edu; Galic, NikaThese data were produced with an individual-based model of amphipod populations exposed to combinations of hypothetical stressors. Stressors targeted feeding, reproduction, maintenance and growth processes in individual amphipods. We measured body sizes and cumulative reproduction in each individual in the simulation, population abundance and biomass and, finally, amount of unprocessed leaf litter which was consumed by the amphipods. Files contain 20 year time series of those endpoints in different stressor combinations; each combinations was replicated 50 times.Item Data, R Code, and Output Supporting "An Historical Overview and Update of Wolf-Moose Interactions in Northeastern Minnesota"(2017-10-06) Fieberg, John R; Mech, L. David; Barber-Meyer, Shannon; jfieberg@umn.edu; Fieberg, John RThese files contain data and R code (along with associated output from running the code) supporting all results reported in, "Mech, L. D., J. Fieberg, and S. Barber-Meyer. In press. An historical overview and update of wolf-moose interactions in Northeastern Minnesota. Wildlife Society Bulletin." In this paper, we explored relationships between wolf numbers, monitored in part of the Minnesota moose range, and moose calf:population and estimated log annual growth rates of moose in Northeast Minnesota.Item Environmental contributions to value computations and population dynamics in ventromedial prefrontal cortex(2021-06) Mehta, PriyankaOn a hot summer day, thereās nothing nicer than giving a kid on the roadside a dollar in exchange for an ice cold cup of lemonade. That is, unless you just turned down a fifty-cent cup of lemonade. From a traditional perspective, the disappointment you feel when you pay the full dollar for that cup of lemonade is quantifiable: youāve missed out on an offer that was twice as good as the one you ended up with. However, our brains did not evolve in a world of mathematical equations.The early primate brain had access to no lemonade stands; no dollar values were attributed to its food sources. Instead, early humans then (and other primates now), obtained food a slightly different way: they foraged. Foraging theory is an approach to studying decision making where we assume that because the brain evolved in a naturalistic environment, it is built to make decisions in naturalistic situations. Many foraging studies claim the ventromedial prefrontal cortex (vmPFC)- a brain region strongly associated with value (local) encoding - does not participate in foraging-related (environmental) computations. However, we posit here that the vmPFC contributes to the foraging process by encoding not just local value but also environmental variables. To this end, we designed a novel diet-search task, for monkeys to complete while we record neural activity in their vmPFC First, we sought out the contribution of local and environmental factors to vmPFC neuronsā processing of value. Specifically, we found relationships between several environmental variables and the animalās threshold for accepting an offer, as well as encoding in vmPFC in response to the variable. Next, we were interested in examining vmPFC neurons as a population in the same context of foraging-based decision making..Here, we examined how the population of vmpfc neurons moves through stages of the foraging process. Specifically, we determined that distinct computations involving the reward rate occur during travel time versus foraging. Taken together, our results suggest that when we limit ourselves to only looking at how local value is encoded in the brain, we miss out on a valuable slice of cognition. Ultimately, the power of the foraging framework is that it takes everything that is generally a pesky impediment to clear science - uncontrollable, outside variables - and turns it into an advantage.Item Factors Influencing Beaver (Castor Canadensis) Population Fluctuations, And Their Ecological Relationship With Salmonids(2019-08) Johnson-Bice, SeanWithin the western Great Lakes (WGL) U.S. region (Michigan, Minnesota, Wisconsin), the ecological impacts that North American beavers (Castor canadensis) have on cold- water streams are generally considered to negatively affect salmonid populations where the two taxa interact. Here, we review the history of beaver-salmonid interactions within the WGL region, describe how this relationship and management actions have evolved over the past century, and review all published studies from the region that have evaluated beaver-salmonid interactions. Our review suggests the impact beavers have varies spatially and temporally, depending on a variety of local ecological characteristics. We found beaver activity is often deleterious to salmonids in low-gradient stream basins, but generally beneficial in high- gradient basins; and ample groundwater inputs can offset the potential negative effects of beavers by stabilizing the hydrologic and thermal regimes within streams. However, there was an obvious lack of empirical data and/or experimental controls within the reviewed studies, which we suggest emphasizes the need for more data-driven beaver-salmonid research in the WGL region. Resource managers are routinely faced with an ecological dilemma between maintaining natural environmental processes within cold-water ecosystems and conducting beaver control for the benefit of salmonids, and this dilemma is further complicated when the salmonids in question are a non-native species. We anticipate future beaver-salmonid research will lead to a greater understanding of this ecologically-complex relationship that may better inform managers when and where beaver control is necessary to achieve the desired management objectives. Understanding how wildlife populations respond to density-dependent (DD) and density- independent (DI) factors is critically important for wildlife management and research, as this knowledge can allow us to predict population responses to forcing mechanisms such as climate, predation, and exploitation. Recent advancements in statistical methods have allowed researchers to disentangle the relative influence each factor has on wildlife population dynamics, but this work is ongoing. Using a long-term dataset collected from 1975 to 2002, we sought to evaluate the relative influence DD and a suite of covariates (weather, harvest, habitat quality, and wolf [Canis lupus] predation) had on annual rates of change in the number of beaver (Castor canadensis) colonies among 15 populations in northern Minnesota, USA. We modeled changes in beaver colony densities using a discrete-time Gompertz model within a Bayesian inference framework, and compared model performance among three global models using Deviance Information Criterion (DIC) widely available information criterion (WAIC): a DI model without covariates; a DD model without covariates; and a DD model with covariates. Our results provide strong evidence for compensatory (negative) DD within beaver colony dynamics. We found no evidence that covariates related to harvest, wolf predation, or habitat quality significantly influenced beaver colony growth rates, but cold winters (lag-0), spring drought (lag-0), and fall drought conditions (lag-2) were correlated with greater colony growth rates. Despite strong evidence of the effect of environmental covariates on beaver colony dynamics, prediction of colony dynamics using these covariates showed only minimal improvements. We suggest the lack of improvement in prediction was the result of model over-fitting, indicating our significant covariate effects may not be biologically relevant. Our analysis demonstrates how reliance on information criterion values may lead to erroneous conclusions in time-series analyses, and using a hindcasting approach like the one we present here may help determine whether model results are biologically relevant or merely statistically significant. Our results highlight the importance of long-term monitoring programs for evaluating the efficacy of predictive ecological models. That beaver populations are primarily intrinsically regulated has important management implications depending on whether the objectives concern eradicating beavers from unwanted regions, mitigating conflicts, or facilitating rewilding or colonization efforts.Item Population Ecology Of Aphelinus Certus, An Adventive Parasitoid Of Soybean Aphid In North America, With Implications For Biological Control(2020-05) Miksanek, JamesParasitoids are excellent model systems in addressing fundamental aspects of biology and ecology while offering a high degree of economic and ecological value in regulating the population densities of their host species in both natural and agroecological settings. The single most important arthropod pest of soybean is the soybean aphid (Aphis glycines). Although not recommended for release due to its broad host range, the parasitoid Aphelinus certus has since been accidentally introduced into North America and has been hypothesized to be a key natural enemy of soybean aphid. However, the overall impact of A. certus in the biological control of soybean aphid is uncertain. The chapters in this thesis are united by broader theories and concepts addressing the role of A. certus in biological control. Chapter 1 presents a coupled-equations matrix population model parameterized by a series of laboratory bioassays outlining the life history of soybean aphid and A. certus; analysis of the model suggested that a parasitism rate of 0.21 dā1, which would be equivalent to at least 3.4% mummies, is capable of maintaining soybean aphid below economically damaging levels in 31.0% of simulations. Chapter 2 further explores the effects of host density on parasitoid lifespan and reproduction as well as establishes a quantitative wing wear index for estimating the age of field-collected parasitoids. Moving from theoretical to in-field efficacy, Chapter 3 evaluates the impact of A. certus on soybean aphid in soybean fields across central and western Minnesota (United States) from 2017ā2019; contrary to the predictions of the model in Chapter 1, the results of this field experiment did not find a strong effect of A. certus in reducing the population growth rates of soybean aphid. Finally, Chapter 4 evaluates the prevalence of parasitism by A. certus on the native aphid species Aphis asclepiadis and Aphis monardae in prairie ecosystems; these results suggest that A. certus readily colonizes or is already established in natural habitats and poses a potential threat to endemic aphid populations. Lastly, I offer conclusions by more broadly discussing this work within the context of population dynamics, ecology, and biological control.Item R Code and Data Supporting: Ecological forecasts reveal limitations of common model selection methods: predicting changes in beaver colony densities(2020-04-20) Johnson-Bice, Sean M; Ferguson, Jake M; Erb, John D; Gable, Thomas D; Windels, Steve K; s.johnsonbice@gmail.com; Johnson-Bice, Sean MThis repository contains the R and JAGS code supporting results reported in: Johnson-Bice, S.M., J.M. Ferguson, J.D. Erb, T.D. Gable, S.K. Windels (2020). Ecological forecasts reveal limitations of common model selection methods: predicting changes in beaver colony densities. Ecological Applications [In Press].