Doctor of Philosophy / Department of Biology / Jesse B. Nippert / Ecological thresholds are breakpoints where small increases in external pressure can generate rapid and difficult to reverse ecological transitions. Often, ecological thresholds are not recognized until they are crossed at a large-scale, leading to unintended and lasting externalities. In tallgrass prairie, we identified ecological thresholds of 3-year fire returns and ~60% grass cover, based on mechanistic field studies and long-term fire and grazing experiments. When tallgrass prairie is pushed passed these thresholds, it makes an abrupt transition to a self-reinforcing shrubland state. Demographic bottlenecks, niche partitioning, and altered fire feedback mechanisms account for both the non-linear nature of grassland-shrubland transitions and the resistance of established shrublands to fire and drought. In the last decade, only ~27% of Central Great Plains tallgrass prairie was burned every 1-2 years, and therefore ~73% of this region is susceptible to shrubland and woodland transitions in the next two to three decades. If transitions to shrublands and woodlands do occur, we expect a multi-trophic loss of grassland biodiversity, decreased cattle production, and the potential for damaging woodland fires in close proximity to human development. However, knowledge of fire thresholds, adaptive management tools, and bottom-up citizen action campaigns are creating a rare window of opportunity to avoid transformation of the remaining tallgrass prairies.

Doctor of Philosophy / Department of Biology / Walter K. Dodds / Much of the North American tallgrass prairie ecosystem has been converted to cropland or urbanized. One threat to the remaining prairie ecosystems, and the streams within, is woody vegetation encroachment. Stream productivity, measured as metabolism, is a fundamental process comprised of gross primary production (GPP) and (CR) community respiration. Understanding GPP and CR is important because these processes are vital to ecosystem function and can be impacted by a change in canopy cover. First, I investigated improvements in existing methods for estimating whole-stream metabolism as estimated from diel patterns of oxygen (O2). I compared measured and modeled O2 and aeration (a physical parameter required for measurement of metabolism) rates to determine if direct measurement of aeration is necessary and the importance of temperature correction of metabolism. Modeling was moderately successful in determining aeration rates, and temperature correction of GPP and CR substantially improved model fits. Second, effects of woody vegetation encroachment on prairie stream function were investigated. Stream metabolism was measured for four years in duplicate reaches with varying canopy cover (closed canopy, naturally open canopy, and vegetation removal reaches). The removal reaches had closed canopy for the first two years and open canopy for the last two years. Canopy cover increased CR rates and had minimal effects on GPP. Third, the same experiment was used to determine the effects of woody vegetation encroachment on prairie stream ecosystem structure and food web interactions. Chlorophyll a and filamentous algal biomass were greater in naturally open and vegetation removal reaches, although the effects were stronger on filamentous algal biomass. As canopy cover decreased, the filamentous algal biomass to chlorophyll ratio increased, indicating a shift in algal community structure. Stable isotope analysis indicated some shift in pathways of nitrogen and carbon flux into the food web related to degree of canopy cover, but overlap in the signature of food sources made distinct food sources difficult to identify. The data indicate that riparian encroachment can influence ecosystem structure and function in prairie streams and restoration to remove woody riparian cover may restore some ecosystem features of naturally open canopy streams.

Master of Science / Department of Biology / Kimberly A. With / Organisms exist within complex landscapes, and landscape features may influence multiple aspects of a species’ distribution within the landscape, including patch occupancy, abundance within patches, and population genetic diversity at a local or regional scale. We took two approaches to identify the relative importance of landscape context for populations of the Eastern Collared Lizard (Crotaphytus collaris collaris) in the northern Flint Hills of Kansas. First, we conducted surveys at limestone outcrops in experimental watersheds managed under different burning and grazing practices. Habitat occupancy and lizard abundance were estimated by constructing models that incorporated aspects of the environment at multiple scales. Both abundance and occupancy were higher on rock ledges that had more crevices, greater complexity in vegetation, covered a larger area, and were more prominent than available habitat. Abundance and occupancy were also higher in watersheds that were burned frequently (1–2 year intervals), but grazing only had a significant effect in less frequently burned (four–year burn interval) watersheds. Our second approach was to measure genetic diversity and population genetic differentiation and relate these measures to differences in landscape context. We sampled collared lizard DNA at four locations (sample sites < 45 km apart) and analyzed trends in 10 polymorphic microsatellite loci. We found evidence for low genetic variability and moderate population differentiation among our sample sites relative to estimates reported in the literature at the core of the species’ range. Differences in migration rates and ancestry among sampling locations also appear to correspond to differences in landscape resistance based on land cover and rock availability. Thus, it appears that habitat management may influence the suitability of habitat patches at the local scale, and that differences in land cover and rock availability may influence the connectivity of populations at the landscape scale.

Doctor of Philosophy / Division of Biology / Keith B. Gido / This dissertation consists of three research-based chapters which focus on habitat association of prairie stream fishes and how these fish communities influence stream ecosystem properties. Chapter one introduces important concepts used throughout the chapters, and describes my study streams. In chapter two, I identify local habitat factors associated with the diversity and density of fishes in two protected prairie watersheds. Specifically, the relative importance of habitat factors associated with fish communities were evaluated along a stream-size gradient and across multiple seasons and years. I found that species richness was positively associated with pool area and discharge. Redundancy analyses showed common prairie fish species exhibit ontogenetic habitat associations, with adults in deep and juveniles in shallow pools. Chapter 3 addresses how fish species richness in small prairie streams affects whole-stream metabolism and biomass distribution of benthic organic matter, algal and macroinvertebrates. This study was conducted by stocking experimental stream mesocosms that included pool-riffle habitats with three different communities that represent a gradient of species richness of headwater prairie streams from one to three common prairie stream fish species. I illustrated how species influence ecosystems across multiple spatial scales and found that different communities altered the distribution of algal biomass from benthic surfaces to floating mats and from pools to riffles. The objective of the fourth chapter was to quantify how two size classes of herbivorous prairie stream fish species, central stoneroller Campostoma anamolum and southern redbelly dace Chrosomus erythrogaster differentially affect stream ecosystem properties. This study was also conducted in experimental stream mesocosms, where each unit consisted of one riffle and one pool. Using ANOVAs, I found large dace were associated with longer filaments (F = 7.5, P = 0.002, df = 4) and small fishes with less benthic organic matter (F = 4.2, P = 0.02, df = 4). There was no evidence for ontogenetic shifts in diet and likely differences in energetic requirements and behavior drove the differences among treatments. My research finds that small-bodied prairie stream fishes have predictable habitat preferences and effects on stream properties are dependent on species identity, richness and size structure.

Doctor of Philosophy / Department of Biology / Walter K. Dodds / Streams exist in a state of dynamic equilibrium with frequent floods and drought. The frequency and intensity of stream disturbances are projected to increase with greater water withdrawal for agriculture and biofuel production, watershed development, and altered climate. Changes in the hydrologic regime may alter stream ecosystems. I studied how stream communities return after disturbances and how nutrients, consumers, and substrata heterogeneity influence recovery trajectories. Large consumers were excluded from pools following a severe drought to assess how community structure and function returned in their absence. Large consumers reduced algal biomass, primary productivity, and nutrient uptake rates, and delayed macroinvertebrate recolonization. However, grazer effects were temporary and their influence weakened after five weeks. In a second experiment, I assessed the relative influence of grazer density and nutrient loadings on algal recovery from flood. Nutrients had a stronger effect on recovery than grazers, but the strength of each varied temporally. Grazer control decreased and nutrient control increased over time. A third experiment addressed the physical properties of stream substrata on algal development. The relationship among algal accumulation and substrata surface topography was assessed by growing algae on substrata with varying orientation and roughness. Total algal biomass decreased on surfaces with angles > 45 degrees, and peaked at an intermediate roughness (pit depth of [similar to]17 [Mu]m). Rougher surfaces collected more tightly attached (grazer resistant) forms and less loosely attached (grazer susceptible) forms. Individual algal forms responded differently to grazing pressure, nutrient availability, and surface features. I developed a method using Fourier-transform infrared microspectroscopy to measure single-cell physiological responses in benthic algae. Nutrients and consumers were strong regulators of ecosystem succession following disturbance, but nutrient influence was stronger. The influence of nutrients and consumers were context dependent, and changed over the course of recovery. Rougher surfaces increase algal growth and shifted algal assemblages to more grazer resistant forms, which may decrease the influence of large consumers on stream function. Altering the severity and frequency of disturbances can change the trajectory of stream recovery and ultimately change community composition and stream metabolic activity, which may alter ecosystem services such as water purification and recreation.

Doctor of Philosophy / Department of Biology / Keith B. Gido / A fundamental goal of ecology is to understand environmental associations of species. These associations can provide a basis for predicting spatial distributions in contemporary habitats as well as how those distributions might change in response to anthropogenic environmental change. Developing species distribution models is limited by an incomplete understanding of functional traits, spatial scaling, and the mechanisms and generalities of correlations among abundance and environmental gradients. I address these four issues using observational and experimental approaches. First, I tested opposing mechanisms of community assembly by measuring the dispersion (i.e., diversity) of three types of functional strategies at three spatial scales and along environmental gradients. I found that communities are assembled via abiotic environmental filtering, but the strength of this filtering depends on the spatial scale of investigation, longitudinal network position, and type of functional strategy. Second, I quantified community-environment relationships across thirteen sub-basins, nested within the three major basins within Kansas to evaluate the consistency (i.e., generality) in predictive capability of environmental variables among sub-basins and across spatial extents. I found that longitudinal network position is consistently the strongest predictor of community composition among sub-basins, but in-stream and catchment predictors become stronger correlates of community composition with increasing spatial extent. Third, I used environmental niche models to quantify distributions of four pairs of congeneric cyprinids and found that species within each pair exhibited contrasting stream-size preferences. I then used field experiments to test for differences in individual-level performance between one pair of species (Pimephales notatus and P. vigilax) along a gradient of stream size. I found that adult spawn success and juvenile growth and condition increased with stream size for both species, indicating that these congeners respond similarly to abiotic gradients associated with the river continuum. I concluded that complementary distributions are a consequence of biotic interactions, differential environmental filtering evident in an unmeasured performance metric, or differential environmental filtering by an environmental factor operating at longer timescales. These studies demonstrate the context dependencies of characterizing habitat associations of stream fishes, but also reveal the general importance of stream size and associated environmental gradients in structuring stream fish communities.

Master of Science / Division of Biology / Walter K. Dodds / Understanding the variability of ecological processes across spatial scales is a central issue in ecology, because increasing scale is often associated with increasing complexity. In streams, measurements of biogeochemical fluxes are important for determining ecosystem health and the downstream delivery of nutrients, but are often collected at scales with benthic areas measured in spatial areas from ~10 cm[superscript]2 to ~100 m[superscript]2 (referred to here as patch and reach, respectively), which are smaller than the scale that management decisions are made. Both biotic and abiotic factors will be important when attempting to predict (i.e. scale) biogeochemical rates, but few studies have simultaneously measured rates and their primary drivers at different spatial scales. In the first chapter, I used a conceptual scaling framework to evaluate the ability to additively scale biogeochemical rates by comparing measurements of ecosystem respiration (ER) and gross primary production (GPP) from patch to reach-scales across multiple sites over a two-year period in a prairie stream. Patch-scale measurements with and without fish (biotic factors) and abiotic factors measured simultaneously with metabolic rates suggest that abiotic conditions are stronger drivers of these rates. Patch-scale rates significantly overestimated reach rates for ER and GPP after corrections for habitat heterogeneity, temperature and light, and a variety of stream substrata compartments. I show the importance of determining abiotic and biotic drivers, which can be determined through observational or experimental measurements, when building models for scaling biogeochemical rates. In the second chapter, I further examined patch-scale abiotic and biotic drivers of multiple biogeochemical rates (ER, GPP, and ammonium uptake) using path analyses and data from chapter 2. Total model-explained variance was highest for ER (65% as R[superscript]2) and lowest for GPP and ammonium uptake (38%). Fish removal directly increased ammonium uptake, while all rates were indirectly affected by fish removal through changes in either FBOM and /or algal biomass. Significant paths of abiotic factors varied with each model. Large-scale processes (i.e. climate change and direct anthropogenic disturbances), and local biotic and abiotic drivers should all be considered when attempting to predict stream biogeochemical fluxes at varying spatial scales.

Doctor of Philosophy / Department of Biology / Jack F. Cully, Jr. / Black-tailed prairie dogs (Cynomys ludovicianus) are epizootic hosts for plague (Yersinia pestis); however, alternate enzootic hosts are important for the maintenance of the pathogen. We determined small rodents and prairie dog associations and quantified rodent and flea relationships in the presence and absence of prairie dog colonies and plague. We identified potential alternate hosts and flea vectors for the maintenance and transmission of plague in the prairie ecosystem. This is the first multi-year study to investigate associations between prairie dogs, rodents and fleas across the range of the black-tailed prairie dog. Few rodent species associated with black-tailed prairie dogs and were found to be highly abundant on colonies. Rodent species implicated in plague were present at study areas with and without plague. Peromyscus maniculatus and Onychomus leucogaster, two widely occurring species, were more abundant in areas with a recent history of plague. Flea community characteristics varied within each study area in the presence and absence of prairie dogs. Based on flea diversity on rodents, and the role of rodents and fleas in plague, we identified P. maniculatus and O. leucogaster and their associated fleas, Aetheca wagneri, Malareus telchinus, Orchopeas leucopus, Peromyscopsylla hesperomys, and Pleochaetis exilis to be important for the dynamics of sylvatic plague in our study areas. Peromyscus maniculatus and O. leucogaster were consistently infected with Bartonella spp., another blood parasite. Presence of prairie dog fleas on other rodents at both off and on prairie dog colonies suggests the potential for intra and interspecific transmission of fleas between rodent hosts, and between other small rodents and prairie dogs.

Doctor of Philosophy / Department of Biology / David C. Hartnett / In perennial grasslands, the belowground population of meristems (the bud bank) plays a fundamental role in local plant population structure and dynamics. I tested the “meristem limitation hypothesis” prediction that bud banks increase along an increasing precipitation/productivity gradient in North American grasslands. I sampled bud populations quarterly at six sites across a 1,100 km gradient in central North America. Bud banks increased with average annual precipitation, which explained 80% of variability in bud banks among sites. Seasonal changes in grass bud banks were surprisingly similar across a 2.5-fold range in precipitation and a 4-fold range of aboveground net primary productivity (ANPP). Secondly, I tested the hypothesis that tallgrass prairie plants respond to increases in a limiting resource (nitrogen) through demographic effects on the bud bank. I parameterized matrix models for individual genets, considering each genet as a population of plant parts (buds and stems). Nitrogen addition significantly impacted bud bank demography of both Sporobolus heterolepis and Koeleria macrantha. In 2005, emergence from the bud bank and growth rates (λ) of the tiller population were significantly higher in S. heterolepis genets that received nitrogen. In contrast, nitrogen addition decreased λ in K. macrantha. Both prospective and retrospective analyses indicated that bud bank dynamics are the key demographic processes driving genet responses to nutrient availability. Lastly, I tested the hypothesis that the effects of fire and grazing on plant species composition and ANPP are mediated principally through demographic effects on bud banks. I found that plants respond to fire and grazing with altered rates of belowground bud natality, bud emergence, and both short-term (fire cycle) and long-term changes in bud density. The size of the bud bank is an excellent predictor of long-term ANPP, supporting my hypothesis that ANPP is strongly regulated by belowground demographic processes. Meristem limitation due to water or nutrient availability or management practices such as fire and grazing may constrain grassland responses to inter-annual changes in resource availability. An important consequence is that grasslands with a large bud bank may be the most responsive to future climatic change or other phenomena such as nutrient enrichment, and may be most resistant to exotic species invasions.

Master of Science / Department of Biology / Brett K. Sandercock / Translocations are a useful management tool for restoring wildlife species to their native ranges, but require post-release monitoring to determine project success. We report results of a 4-year effort to reestablish a breeding population of Evermann's Rock Ptarmigan (Lagopus mutus evermanni) on Agattu Island in the Aleutian Archipelago, Alaska. This endemic subspecies of ptarmigan was extirpated from most of the Near Islands by introductions of arctic fox by fur traders, and natural recolonizations did not occur after fox eradication. All females surviving the 2-week post-release period attempted to nest but initiated clutches later in the season and laid fewer eggs than resident females. Nest success was similar for resident and translocated females. Brood survival was greater for translocated than resident females and differed significantly; however, brood survival varied among years and was reduced by adverse weather conditions in 2006. Seasonal survival of radio-marked birds during the breeding season was 100% for translocated and resident ptarmigan. Over-winter mortality resulted in a low return rate in 2006. Returning birds in 2006 showed strong site fidelity and nest locations in two consecutive years were closely spaced. We examined nest site selection and determined brood movements and home range size of recently translocated and resident females. Nest sites of translocated females averaged 4.2 km from their respective release location and were not different from nest locations of resident females with regard to topographical features. Female nest site selection was influenced by percent composition of rock and forb coverage but was unaffected by slope, aspect, or general habitat. Broods of both resident and translocated females made movements to higher elevations after hatching. While size of brood home range was similar for resident and translocated females, distances traveled between the nest site and the arithmetic center of the brood home range were greater for translocated females. Overall, we conclude that translocations are an effective technique for reestablishing island populations of Rock Ptarmigan. Our study provides successful methods which may benefit future projects to reestablish endemic populations of ptarmigan and landbirds elsewhere in the Aleutian Islands.