Browsing by Subject "Recruitment"

Now showing 1 - 6 of 6
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    Assessment of techniques to evaluate American woodcock population response to best management practices applied at the demonstration-area scale
    (2014-09) Daly, Kyle O'keefe
    American woodcock (Scolopax minot; hereafter, woodcock) have experienced long-term population declines across their breeding range based on the American woodcock Singing-ground Survey. Wing-collection surveys have also indicated a decline in woodcock recruitment across their range, especially in the Central Management Region. These declines have been widely attributed to loss or alteration of young forest cover types that support woodcock reproduction across their breeding range. In response to these apparent declines in woodcock abundance and recruitment, a system of woodcock habitat demonstration areas is being developed throughout the woodcock breeding range where specific Best Management Practices (BMPs) are applied with the goal to stabilize and ultimately increase populations. Application of BMPs at a demonstration-area scale (~200-800 ha) is designed to positively influence woodcock population growth by improving habitat quality and abundance at a landscape scale. However, how woodcock vital rates are influenced by BMPs applied at a landscape scale is not fully understood, and techniques used to evaluate woodcock populations at the demonstration-area scale have not been assessed. The objectives of our research were to (1) estimate survival of adult females, nests, and juveniles using radio telemetry and assess relationships between survival and vegetation structure resulting from BMPs, life history traits, and weather, (2) directly estimate a measure of woodcock recruitment (juveniles/adult female during late summer) at a landscape scale by using survival estimates in a population model, and use direct estimates of recruitment to evaluate the accuracy and usefulness of indirect estimates of recruitment based on less costly and effort-intensive methods (specifically mist netting and night lighting on summer roosting fields), and (3) test for effects of radio transmitters on juvenile woodcock survival. In 2011 and 2012, we radio-marked and tracked 41 adult female and 73 juvenile woodcock, and monitored 51 broods and 48 nests. Breeding season cumulative survival for adult females was consistent between years, whereas nest and juvenile survival were related to year. Juvenile survival was also positively related to age, minimum temperature, and stem density, and negatively related to precipitation. We found no effects of radio-marking juvenile woodcock. In July of 2011 and 2012, we captured 204 woodcock using mist nets during crepuscular movements from diurnal feeding cover to roosting fields and 69 woodcock via night-lighting on roosting fields. Our recruitment estimates (juveniles/adult female) derived from our demographic model were higher in 2012 than 2011 due to higher nest and juvenile survival rates during that year, suggesting that nest and juvenile survival, and factors related to nest and juvenile survival, may be key to understanding woodcock population ecology. Our assessment of indirect methods to estimate woodcock recruitment at a landscape scale indicated that the indirect methods we considered of estimating woodcock recruitment at a landscape scale are likely not reliable proxies for estimating recruitment directly.
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    Effects of bluegill predation, lake productivity, and juvenile dispersal on common carp recruitment dynamics in lake-marsh systems in Minnesota
    (2016-02) Lechelt, Joseph
    Processes that regulate common carp (Cyprinus carpio) recruitment (i.e. survival of eggs, larvae and juveniles) are largely unknown. In interconnected lake-marsh systems of Minnesota, young of year (YOY) carp are generally found in marshes that winterkill and lack bluegill sunfish (Lepomis macrochirus), an abundant native predator. This suggests that bluegills might function as a biocontrol agent for carp. Further, whereas YOY carp are commonly found in winterkill marshes of south-central Minnesota, they are not found in similar systems in northern Minnesota where lake productivity is much lower, suggesting an aquatic productivity bottleneck on carp recruitment. Finally, in marshes where carp recruit (productive and bluegill-free), YOY must disperse into adjacent lakes to drive high population abundance. In this study, I conducted three experiments to test 1) the effect of bluegills on carp recruitment; 2) the effect of aquatic productivity on larval carp survival, growth and diet; 3) natural dispersal tendencies of YOY carp from a marsh into an adjacent lake. The first experiment employed four (20 m diameter) impermeable enclosures from 2011-2014. Each year, enclosures were stocked with carp eggs and every other one was stocked with bluegills. Backpack electrofishing surveys conducted five weeks later showed that carp catch per unit of effort (CPUE) was over 10-fold lower in the enclosures stocked with bluegills than in the controls. The second experiment, conducted in 2014 and 2015 used aquaria stocked with carp larvae and supplied with zooplankton densities and community structures from lakes of three different trophic states (oligo-, meso-, and eutrophic). It showed that carp larvae selectively consumed macrozooplankton (> 200 μm) and their growth rates were highest in the eutrophic lake and lowest in the oligotrophic lake. Survival, however, was high in all treatments. The third study was conducted in a natural lake-marsh system and utilized passive integrated transponder (PIT) tags to quantify the outmigration of YOY carp from the marsh to the lake. It showed that < 6% YOY carp outmigrated to the lake, supporting previous indirect estimates. The results of these three studies are important to understanding recruitment dynamics of carp in lake-marsh systems in Minnesota.
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    Poor Recruitment is Changing the Structure and Species Composition of an old-growth Hemlock-hardwood forest
    (2013-07) Salk, Theodore Thomas
    Anthropogenic factors such as elevated deer populations, invasive earthworms, or climate change may alter old-growth forests of the Upper Midwest region of the United States. We examined demographic trends of woody species across all size classes for a period of 35 years in a late-successional forest dominated by hemlock (Tsuga canadensis), sugar maple (Acer saccharum), and yellow birch (Betula alleghaniensis) in Michigan's Upper Peninsula using two sets of permanent plots. For the duration of the study period, species that were less-preferred white-tailed deer (Odocoileus virginianus) forage, especially sugar maple, comprised a much higher fraction of all seedlings and saplings compared to their fraction of overstory trees. The density of small sugar maple declined across the study period, but no other species became more abundant, creating a more open forest understory. By the most recent census, preferred species for deer browse had been nearly eliminated from the understory, and declines in unpreferred species such as sugar maple were also apparent. We found small changes in temperature (<0.5-1°C rise in minimum and maximum temperatures depending on season) and precipitation (±28 mm depending on season) and little evidence of invasive earthworms impacts. Our results suggest that a sustained elevated deer density is shifting the structure and composition of this old-growth forest. A demographic model showed that if current recruitment, growth, and mortality rates were to continue for 500 years the forest would reach a new equilibrium with virtually no hemlock or yellow birch remaining.Tree coring, or increment boring, has been a common research tool for foresters, ecologists, and climatologists for over a century. Despite its widespread use, there has been very little research into the effect of this practice on the growth and mortality of trees. Using data from two of the permanent plots, we compared the growth and mortality rates of cored trees to a similar set of uncored trees for 16-18 years. While there might have been some slight bias in selecting trees for coring, it is unlikely to have affected our overall results. Cored trees did not differ in their mortality rate from uncored trees and had only minute differences in growth, either when considered collectively or when looking at species individually.
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    Recruitment and Retention in Minneapolis Public Schools
    (HHH, 2015-05-11) Bitton, Naor R.; Kessenich, Katherine; Kurth, Leif; Long, Mari Jo; Schilz, Aaron
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    The role of predator removal and density-dependence on mallard production in northeastern North Dakota
    (2010-05) Amundson, Courtney Linda
    Density-dependence is a central tenet of wildlife population dynamics and harvest management, yet the pathways and mechanisms by which density-dependence operates remain unclear. In 1994, Delta Waterfowl Foundation began trapping meso-predators in northeastern North Dakota to determine if it was a viable technique for increasing waterfowl production. Subsequent research on replicated experimental sites found that trapping predators increased nest success by about 2-fold, and nest success was the most important factor regulating population growth in previous studies of midcontinent mallards. Given the philopatric nature of most waterfowl species, higher nest success on trapped sites was predicted to lead to 36% greater annual population growth on trapped sites versus controls, which should have led to doubling of pair densities approximately every two years. This backdrop provided me with the unique opportunity to examine the role of density-dependence on waterfowl production at a local scale in North Dakota. My dissertation focuses on the role of density-dependence and predator removal on mallard duckling survival, duckling body condition, and overall mallard productivity in northeastern North Dakota from 2006-2007. Contrary to predictions, predator removal had no beneficial effect on mallard duckling survival. Duckling density was weakly negatively associated with mallard duckling survival, but had no effect on duckling condition. Duckling survival, not nest success, was the most important factor influencing population growth and production and appeared to be functioning as the key limiting factor in our populations. Overall, predator removal did not lead to local population increases on trapped sites and added far fewer incremental ducks to the fall flight than originally predicted. The perils of duck hunting are great - especially for the duck. - Walter Cronkite.
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    Structure, dynamics, and climate sensitivity of range-margin jack pine forests in central Minnesota
    (2014-12) Gill, Kyle Gregory
    Species' ranges are expected to shift in response to changes in climate and disturbance regimes. Individuals and populations along the edge of their range are expected to be most affected because of their proximity to climatically limiting factors and the unique dynamics relative to non-marginal portions of their range. However, limited empirical knowledge exists concerning the historic range of ecological variability in range-margin populations and systems.Jack pine (Pinus banksiana) reaches its southwestern range limit in central Minnesota where it displays traits, including low-levels of cone serotiny, that differ from other portions of its range. However, the stand dynamics (establishment, age structures, and disturbance regimes) and linkages with climate have never been documented for these populations. Our aim was to quantify the natural range of variability of stand dynamics and climate relationships to establish reference conditions for monitoring future climate impacts, informing refinement of forest ecosystem models, and assisting in the development of management decisions for conservation.Our results indicate that jack pine stands in this region are structurally complex even and un-even aged systems that follow a variety of developmental pathways. These patterns are attributed to the non-serotinous cones of jack pine in this region, which allow for both episodic and extended recruitment patterns over time. Annual growth and recruitment were both significantly sensitive to moisture and temperature variables, especially during the winter-to-spring transition, yet the directionality of associations displayed much seasonal variation. Our results suggest that management and modeling practices should be broadened to account for the variety of structural conditions and developmental pathways that historically characterized these range-margin jack pine forests. Such changes will help to conserve jack pine forests for the short-term while promoting the propensity for long-term resilience and adaptability.