Browsing by Subject "Ecology, Evolution and Behavior"

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Acoustic communication in noisy environments:Signal recognition in fluctuating backgrounds.
(2012-04) Meléndez, Alejandro Vélez
Following one conversation in multi-talker environments is a difficult perceptual task that we encounter frequently. How the human auditory system solves this problem has been the focus of research for decades. While many nonhuman animals also communicate in noisy social aggregations, we know very little about how they solve analogous problems. Dip listening, an ability to catch `acoustic glimpses' of target signals when the level of fluctuating backgrounds momentarily drops, represents one way by which receivers may recognize signals in noise. It has even been suggested that animals may be adapted to exploit level fluctuations of the natural soundscape (i.e., the mixture of sounds in the environment) to recognize communication signals. This hypothesis, however, is not yet supported by empirical evidence because (i) we know little about the characteristics of level fluctuations in natural soundscapes, (ii) very few studies have investigated the ability of nonhuman animals to recognize communication signals in fluctuating backgrounds, and (iii) no study has investigated signal recognition in the presence of noises with level fluctuations of natural soundscapes. I addressed these gaps in knowledge using gray treefrogs (Hyla chrysoscelis) and green treefrogs (Hyla cinerea) as model systems. I found that level fluctuations of the noise generated in social aggregations vary across species. I also show that gray treefrogs, but not green treefrogs, have an ability to listen in the dips of fluctuating backgrounds when recognizing communication signals. This ability, however, is not specifically `tuned' to exploit level fluctuations of natural soundscapes. Together, my findings offer little support for the hypothesis that receivers are adapted to exploit level fluctuations of the natural soundscape to recognize communication signals.
Carbon dioxide sequestration and heterotrophy in shallow lakes.
(2009-10) Kenning, Jon M.
Research has recently begun to show the importance of lakes in controlling global CO2 budgets, but this work has only been done on a few large lakes. Small, shallow lakes and wetlands are the most plentiful lake ecosystems in world, but the most ignored. Here, I explore their ability to sequester CO2 and in some cases release the greenhouse gas to atmosphere. I found that pristine shallow lakes where macrophytes (aquatic vegetation) dominated, the lakes sequestered much more CO2 than disturbed lakes where phytoplankton dominated. Furthermore, I found that heterotrophs in shallow lakes respired tremendous amounts of carbon of terrestrial origin, thus calling into question the net ability of terrestrial ecosystems to sequester carbon. Finally, I found that some of the underlying mechanisms, including the productivity of different autotrophs and growth efficiencies of bacteria, favor greater carbon sequestration by macrophyte-rich shallow lakes. All of my observations form a basis for future work into the ability of shallow lakes to sequester CO2 and stresses the importance of not only saving shallow lakes and wetlands, but preserving them in a macrophyte-rich state.
Carbon soil dynamics in secondary tropical dry forests in Northwestern Costa Rica regenerating from grazing
(2012-04-18) Nowicki, Jesse
The goal of my research project is to understand how ecosystem processes like carbon sequestration in soils changes as young forests regenerate on lands that were previously used for grazing. The objective is of my project is to re-visit the same area that Dr. Powers studied 5 years ago and determine if the chronosequence and longitudinal studies reveal the same soil carbon dynamics as previously predicted, as well as to see if soil carbon sequestration increases with forest age, as many conceptual models predict. From the data analysis, the carbon concentration and carbon isotope followed our predicted assumptions for the concentration to increase slightly and the carbon isotope would become more negative. We predicted the bulk density would decrease over time as the soil became less dense but our data showed mixed results on whether it increase or decreased.
Change and reliability in the evolution of learning and memory.
(2009-05) Dunlap-Lehtilä, Aimee Sue
Why do animals learn to perform some behaviors while others are innate? Why do animals learn some things more easily than others? And, why do animals remember some things better than others? Theoreticians argue that patterns of environmental change explain these patterns, but we have little data to support these claims. I used statistical decision theory to model behaviors and fitness consequences, and experimental evolution studies with fruit flies where I manipulated patterns of environmental change across evolutionary time, to address the first two of these fundamental questions about the evolution of learning. The first experiment tested the effects of the reliability of experience and the fixity of the best action upon the evolution of learning and non-learning across 30 generations. I found that indeed, the interaction of these two variables determined when learning, and when non-learning evolved. The second study was a full factorial experiment manipulating the reliabilities of two modes of stimuli: olfactory and visual. After 40 generations, I found that as predicted, flies in environments where olfactory stimuli are reliable learned better about olfactory than color stimuli, with the same being true for color stimuli. Finally, I addressed the question of why animals remember some things better than others using a dynamic programming technique and experiment with blue jays, finding interactions between rates of change and time. These novel studies show the importance of reliability and change in evolution of learning and memory.
Colony-level immunity benefits and behavioral mechanisms of resin collection by honey bees.
(2010-10) Simone, Michael Dominick
The general goal of this thesis is to understand the proximate and ultimate mechanisms of resin collection and use in honey bees, Apis mellifera. While there has been significant research on bee-collected resins with respect to human health and various chemical component analyses, this thesis provides the first review and studies on the direct implications of the role of resin in regard to honey bee health, and thus, pioneers a new area of research. I also provide novel information concerning the stimuli that may be involved in the recruitment of foragers and initiation of resin foraging. Overall my thesis provides the first evidence that resin collection is a form of social immunity in honey bees and may both have direct and indirect effects on individual immunity and colony health. I have also shed new light on the behavioral mechanisms that may be mediating this behavior at both the colony level (self-medication) and individual level (assessment of tactile information). I tested original hypotheses that led to new questions and opportunities for further research that will be conducted by me and others for a long period of time.
Consumer nutrient stoichiometry : patterns, homeostasis, and links with fitness.
(2010-10) Hood II, James Michael
The linkages between food webs and nutrient cycles are heterogeneous and often influenced by human activities. Ecological stoichiometry provides one framework for understanding and predicting these linkages. Yet, as it has been extended underlying assumptions are often not evaluated. This dissertation shows that examination of implicit and explicit assumptions reveals unknown mechanisms, interactions, and linkages. For instance, theory assumes that invertebrate stoichiometry does not vary with diet stoichiometry (i.e., strict homeostasis), even though many invertebrates are not strictly homeostatic. Chapters one and two examine the role of stoichiometric homeostasis in shaping the fitness of Daphnia species. Chapter one shows that the long-‐term phosphorus (P) use efficiency of stoichiometrically flexible Daphnia species is higher in habitats with temporally variable diets, resulting in higher fitness relative to strictly homeostatic species. Chapter two shows that the P cost of a unit of growth increased with growth rate and structures tradeoffs among growth rate, sensitivity to P limitation, and stoichiometric flexibility. Stoichiometric theory can be extended to novel ecosystems, such as streams, to predict the role of consumers in food web and nutrient cycles. To do To do this, the balance between consumer and diet stoichiometries is a logical starting point. Chapter three examines intra-‐specific variation in consumer-‐resource stoichiometries at a suite of sites within a river network. In contrast to previous work, this chapter describes wide intra-‐ specific variation in consumer stoichiometry, similar in magnitude to the variation among invertebrate taxa. Intra-‐specific variation in nitrogen and phosphorus content was related to both ontogeny and diet. These results suggest that the role of a species in stream nutrient cycles could vary spatially with diet and temporally through ontogeny.Chapter four examines the influence of diet stoichiometry on nutrient release ratios of four stream detritivores. Predictions of nutrient release ratios from bulk diet stoichiometries were misleading for these detritivores, which selectively consumed a nutrient rich portion of the bulk diet. Selective feeding greatly reduced stoichiometric mismatches between these consumers and their diets. Taken together, this dissertation demonstrates that examination of stoichiometric assumptions improves our understanding of consumer-‐resource dynamics, competition, and the role of consumers in nutrient cycles.
Deterministic and stochastic forces in community ecology: integrating competing paradigms in theory and observation.
(2012-02) Hawthorne, Peter Loken
An important goal in community ecology is to understand the interactions between multiple mechanisms - species differences and niche differentiation, stochasticity, environmental heterogeneity, and spatial processes - and their consequences to community structure. In this dissertation, I address three distinct issues within this general program. First, using a spatially explicit model, I compare assembly, structure, and invasibility of communities with varying levels of neutrality versus niche-differentiation. Communities' responses to invasions are determined by the extent of functional variation in the local species pool, predicting varying responses to inter-biome exchange and evolutionary diversification along the niche-neutral gradient. Second, I demonstrate statistical bias in the standard test for monoculture overyielding and develop a bootstrap correction algorithm. Correcting this bias is important to evaluating the relative importance of selection and complementarity effects to community processes. Finally, I analyze the extent to which species differences, dispersal, and stochasticity influence metacommunity dynamics in a long-term nitrogen addition experiment. I find that all three mechanisms are active in the study system, necessitating further development of metacommunity models.
Dynamics of intergroup competition in two neighboring chimpanzee communities.
(2010-07) Mjungu, Deus Cyprian
Among group-living animals, larger groups tend to win intergroup fights. In chimpanzees, larger groups are likewise believed to win most intergroup interactions. Because intergroup fights in chimpanzees sometimes lead to the death of individuals, larger groups are expected to eliminate smaller groups - as observers witnessed in Gombe, in the 1970s, when the Kasekela group exterminated the smaller Kahama group. However, in some cases, smaller groups continue to persist alongside larger groups. How smaller groups are able to do this is poorly known. Gombe National Park provides a unique natural settings for examining how smaller groups of chimpanzee manage to survive against difficult odds. Currently the park contains two neighboring habituated groups: the large Kasekela group and the much smaller Mitumba group. Despite the Mitumba group being sandwiched by the Kasekela group and cultivated lands, the Mitumba group has not only survived but also increased in size over the past 10 years. I explored how the smaller Mitumba group managed to survive alongside the larger group. First, I investigated the factors that caused changes in range size and population of the Mitumba group over the past 25 years. I found that, both anthropogenic habitat destruction and intergroup competition influenced the range size of the Mitumba chimpanzee group. Then, I examined whether large group size conferred competitive advantage by examining the range size and range use of two neighboring groups and outcome of territorial contests. I found that, group size influenced the range use of neighbors. Each group used more contested area when numerical strength was in its favor. Furthermore, I found that, the number of males in a party and not the location of the range determined whether the Mitumba chimpanzees would counter-call. Mitumba chimpanzees were less likely to call when in a party contained zero or one male. However, the probability of counter-calling increased when number of males in a party increased. My study suggests that, anthropogenic habitat destruction and intergroup competition could interact in a complex way to influence the survival and reproduction of individuals in this population. Furthermore, my study also suggests on the importance of numerical strength in intergroup competition in chimpanzees.
Effect of topography and glaciation history on the movement of carbon and nitrogen within arctic hillsides.
(2010-04) Whittinghill, Kyle A.
The transport of dissolved organic matter (DOM) down hillslopes to aquatic ecosystems has important implications for both terrestrial and aquatic primary productivity. DOM is an important energy and nutrient source for both terrestrial and aquatic microbes. Within watersheds, physical, chemical, and biological processes transform DOM, but it not well known how landscape heterogeneity may affect these processes in arctic watersheds. In the northern foothills of the Brooks Range, expansion and contraction of mountain glaciers over the last several ice ages have created a mosaic of landscape ages with similar climate and vegetation. My research indicates that younger landscapes (<50,000yrs) have significantly lower pH, 10x higher exchangeable base cation concentrations, and significantly lower rates of DOM production and microbial respiration than older landscapes, which could significantly affect fluxes of carbon and nutrients across the landscape. At the watershed scale, I examined patterns in soil and stream water concentrations of DOM within hillslopes across the chronosequence. I found that while concentrations of dissolved organic carbon decreased significantly moving downslope from the hilltop to the stream; dissolved organic nitrogen concentrations remain similar within the hillslope, but are significantly different among landscape ages. I also used a variety of indices to examine spatial patterns in the biodegradability of DOM within hillslopes and among landscape ages in northern Alaska. My results suggest the low biodegradability of DOM found in streams and rivers in the region is not due to microbial processing of labile DOM in terrestrial ecosystems, but rather to production of recalcitrant DOM throughout the landscape.
The effects of temperature and phosphorus availability on the biomass composition, phosphorus allocation, size and morphology of freshwater bacteria.
(2012-07) Phillips, Katherine N.
Freshwater bacteria play a key role in the regulation of nutrients in aquatic ecosystems. Bacteria mediate the availability of nutrients tied up in organic molecules and are therefore capable of constraining both primary production and higher trophic levels in aquatic ecosystems. To assess how changes in temperature and phosphorus availability impact three diverse strains of heterotrophic bacteria (Agrobacterium sp., Flavobacterium sp.,and Arthrobacter sp.isolated from Lake Itasca State Park, MN, I investigated 1) the effects of phosphorus availability on bacterial biomass composition, 2) the effects of temperature on bacterial biomass composition and 3) the combined effects of phosphorus availability and temperature on bacterial biomass composition. To assess how phosphorus availability impacts biomass composition in photoautotrophic bacteria Synechocystis sp PCC 6803, the effect of phosphorus availability was investigated. Under phosphorus limitation I observed two distinct strategies adopted by the three heterotrophic strains. Either the cells became large, long and thin or they stayed relatively small and coccoid in shape. Both strategies observed under phosphorus limitation resulted in different patterns of cellular phosphorus allocation. Controlling for growth rate across changing temperatures, I observed that as temperature increased, all three strains decreased their cellular size, and their carbon, phosphorus, and nucleic acid content. However, a pronounced decrease in DNA content was observed in only one strain. The combined impact of increasing temperature and phosphorus limitation resulted in a more dramatic decrease in cellular size and cellular carbon than when phosphorus was not limiting. These findings suggest no one strategy is adopted by heterotrophic bacteria under phosphorus limitation or across changing temperature. Secondly, I observed that changes in phosphorus availability resulted in a much more flexible C:P biomass composition in Synechocystis than changes in nitrogen availability. These findings suggest that less carbon may be in bacterial biomass when cells are nitrogen limited than when cells are phosphorus limited. These results provide insights into the impact that both increasing temperature and phosphorus has on microbial composition and the potential effects of that composition on the microbial loop in aquatic ecosystems.
Effects of vertebrates, insects, and pathogens on patterns of early plant recruitment in tropical forests.
(2010-07) Beckman, Noelle Gabriele
Vertebrate seed dispersers and seed predators, insect seed predators, and pathogens are known to influence plant survival, population dynamics, and species distributions. The selective pressure of these mutualists and antagonists have resulted in a myriad of plant adaptations, including morphological and nutritional fruit traits to attract seed dispersers, and plant defenses to deter seed predators and pathogens. The importance of vertebrates, insects, and pathogens for plant communities has long been recognized, but their absolute and relative importance in early recruitment of multiple coexisting tropical plant species has not been quantified. Further, little is known about the relationship of fruit traits to seed dispersal and natural enemy induced seed and seedling mortality in tropical plants. My dissertation investigates the importance of these groups of organisms in the sequential stages of early plant recruitment (i.e. from fruit developing in the crown to seedlings on the ground) in tropical forests. I used a combination of empirical and theoretical studies: an experimental study of pre-dispersal seed mortality in plant canopies of seven species, a bioassay experiment examining patterns of fruit toxicity for eleven species, a simulation study of the interacting effects of seed dispersal and enemy attack on spatial patterns of surviving seedlings in theory, and a field study of the effects of partial defaunation of vertebrates (by hunting) on pre-dispersal seed predation and seed removal in two tree species. To determine the influences of vertebrates, insects, and pathogens on reproduction of plants varying in fruit traits, I investigated reductions in fruit development and seed germination due to vertebrates, insects, and fungal pathogens through experimental removal of these enemies using canopy exclosures, insecticide, and fungicide, respectively at the Canopy Crane Access System in Parque Natural Metropolitano in Central Panama. Results suggest that predispersal seed mortality is attributable to different natural enemies in different canopy species. Fruit morphology explained some of the interspecific variation in fruit development and seed survival in response to natural enemy removal treatments. This is the first experimental test of the relative effects of vertebrates, insects, and pathogens on seed survival in the canopy. To investigate patterns of fruit toxicity, I used bioassays involving brine shrimp (Artemia franciscana) and two foliar fungal pathogens (Fusarium sp, Phoma sp.) to understand how chemical defenses of coexisting canopy plants differ from the immature to the mature stage of fruit development and between the seed and pericarp. Every plant species tested in this study exhibited toxicity to at least one bioassay organism but patterns of toxicity depended on plant species and bioassay organism. To explore how patterns of natural enemy attack and seed dispersal affect seedling recruitment patterns, I developed a spatially-explicit, individual-based model to study plant life stages following seed dispersal. With this model, I explored how different seed deposition patterns and natural enemies affect the spatial patterns of surviving seedlings in a simulated model community. The seedling recruitment patterns observed in the model reproduced the range of patterns observed empirically. Recruitment patterns were sensitive to the type of natural enemy attack and the movement distances and fecundity of natural enemies, as well as to seed dispersal distances and the degree of clumping. To investigate how hunting alters seed dispersal and seed predation, I compared these processes for two canopy tree species that differ 16-fold in seed size in both hunted and protected forests in Central Panama. The results of this study suggest that in hunted areas there are greater reductions in seed removal and seed predation of the larger-seeded compared to the smaller-seeded tree. Overall, the results of my dissertation contribute to an emerging, but still very incomplete, trait-based approach to understanding interspecific variation in biotic interactions. Determining the relative roles of vertebrates, insects, and pathogens throughout the stages of plant recruitment will aid in our understanding of the mechanisms that limit plant populations, contribute to our knowledge of diversity maintenance, and is critical to predicting the consequences of anthropogenic pressures on plant communities.
From pattern to process: ecology and evolution of host specificity in the fig-pollinator mutualism.
(2011-09) Moe, Annika M.
One of the greatest challenges in the study of coevolution, indeed, for biology in general, is to understand how evolutionary and ecological processes shape patterns in nature. Ecologists routinely observe patterns of association among organisms, such as parasites infecting hosts or insects pollinating flowers and systematists routinely infer patterns of phylogenetic relationship. Such patterns invite explanation and suggest hypotheses about the evolutionary process, but it is difficult to investigate contemporary processes, including natural selection and, of course, impossible to directly observe historical processes. Observation of patterns in various ecological contexts, inference of phylogenetic patterns, model and simulation of processes, and direct experimentation aim to test specific predictions about the role of ecology in shaping evolutionary trajectories, and evolutionary processes in shaping ecological associations. The fig-wasp pollinator mutualism provides a unique opportunity to examine fundamental processes of coevolution, namely, reciprocal adaptation where interacting partners are the agents of selection. Because pollinating wasp reproduction is directly linked to host plant reproduction, it is possible to estimate the fitness consequences of interaction for both partners simultaneously. By manipulation of interacting individuals and species, or by examination of natural variation within and among populations, it may be possible to estimate the strength and direction of selection on each mutualistic partner. This work employs molecular genetic patterns, ecological observations, and direct experimentation to investigate host specificity in Ceratosolen (Agaonidae, Hymenoptera) pollinators of Ficus subgenus Sycomorus (Moraceae) and potential processes affecting the origin and evolution of species diversity in this system. The first chapter examines genetic variation in Ceratosolen pollinators of widespread Ficus across the geographic range of several host species. Deep mitochondrial DNA sequence divergence between host-specific populations distributed across Wallacea suggests host conservatism during ancient range expansion and subsequent isolation by distance. Geographic patterns of sequence divergence and host association are more consistent with a model of allopatric speciation than speciation by host switching. The second chapter investigates pollinator host choice by morphotyping and DNA barcoding of floral visitors in a community of closely related and sympatric fig species. Host specificity was very high, but rare pollinator sharing among sympatric fig species was observed at a rate of 1-2%. Even such rare events could be evolutionarily significant and pose challenges for species delimitation. The third chapter examines fitness consequences of pollinator sharing by experiment. A new method of manipulating fig pollinators investigated the reproductive consequences of intra- and interspecific pollinator visitation for both mutualistic partners. When pollinators were introduced to a novel host species, hybrid seed set was comparable to results of conspecific crosses. Hybrids germinated, established, and grew at rates comparable to non-hybrids. Pollinator fitness, however, was compromised after oviposition in the novel host. Although heterospecific pollinators induced gall formation, offspring did not develop to maturity in the new host. Microsatellite genotypes of a New Guinea fig community indicated a substantial but not absolute barrier to gene flow among sympatric species. That hybrids constituted fewer than 2% of individuals in populations may be explained by selection against pollinator host switching in this system. Collectively, these studies suggest that the extreme species-specificity of associations between Ceratosolen pollinators and Sycomorus figs is maintained by the fitness cost of colonizing new hosts. At the same time, hybridization resulting from rare instances of pollinator sharing in even the most extremely specialized of pollination mutualisms has the potential to influence diversification and coevolution.
The impact of trees on temporal variability in urban carbon and water budgets.
(2010-07) Peters, Emily Beth
Urbanization is responsible for some of the fastest rates of land-use change around the world, with important consequences for local, regional, and global climate. Vegetation can represent a significant proportion of many urban and suburban landscapes and modifies climate by altering local exchanges of heat, water vapor, and CO2. To assess the contribution of plant functional types to urban ecosystem processes of water loss and carbon gain in a suburban neighborhood of Minneapolis-Saint Paul, Minnesota, USA, I investigated 1) the microclimate effects of different forest types over time, 2) the relative importance of environmental and biological controls on urban tree transpiration and canopy photosynthesis, and 3) the relative importance of trees and turfgrass on the spatial and seasonal variation in suburban evapotranspiration. Regardless of plant functional type, I found that seasonal patterns of soil and surface temperature were controlled by differences in stand-level leaf area index, and that sites with high leaf area index had soil and surface temperatures 7°C and 6°C lower, respectively, than sites with low leaf area index. Plant functional type differences in canopy structure and growing season length largely explained why evergreen needleleaf trees had significantly higher annual transpiration (307 kg H2O m-2 yr-1) and canopy photosynthesis (1.02 kg C m-2 yr-1) rates per unit canopy area than deciduous broadleaf trees (153 kg H2O m-2 yr-1 and 0.38 kg C m-2 yr-1, respectively), offering an approach to scale up the tree component of urban water and carbon budgets. Turfgrass represented the largest contribution to annual evapotranspiration in recreational and residential land-use types (87% and 64%, respectively), due to a higher fractional cover and greater daily water use than trees. Component-based estimates of suburban evapotranspiration underestimated measured water vapor fluxes by 3%, providing a useful approach to predict the seasonal patterns of evapotranspiration in cities. These finding have implications for the management of urban ecosystem services related to climate, carbon sequestration, and hydrology, and for predicting the impacts of climate change on urban ecosystems.
Limits to range expansion in the native annual legume Chamaecrista fasciculata.
(2011-08) Stanton-Geddes, John Louis
Species range limits are determined by historical (e.g., range expansion), ecological (e.g., biotic interactions) and genetic (e.g, gene flow) processes, but comprehensively understanding the relative role of these processes in limiting any single species‟ range has been elusive. This research is timely for understanding species‟ responses to climate change. The goal of this research was to examine the processes that limit the range of the native annual legume Chamaecrista fasciculata, by integrating ecological-genetic field studies and population genetic laboratory studies. In Chapter 1, I investigate the extent to which C. fasciculata is in demographic range edge equilibrium at its western and northern range edges, and the effect of biotic interactions at these range edges. I find that C. fasciculata fitness is reduced to zero when planted beyond the western and northern range limits, indicating it is in equilibrium with its range. Neighbors increase early-season survival, but decrease seedpod production. The goal of Chapter 2 was to examine if the mutualism between C. fasciculata and its associated rhizobia was disrupted beyond the range edge, potentially limiting range expansion. The results demonstrate that compatible rhizobia are nearly absent beyond both range edges, which may limit range expansion. In Chapter 3, I ask how the habitat where C. fasciculata establishes may change with range shifts. I conclude that habitat type influences C. fasciculata fitness, but the outcome depends on both the substrate and competitive environments. Finally, in Chapter 4, I use population genetic methods to gain insight into the history of range expansion, population structure and gene flow. Population genetics indicate that the edge populations have reduced genetic diversity compared to the southernmost interior population, and are highly differentiated from each other. However, there is little evidence for contemporary gene flow between populations at the scale investigated. Overall, this work suggests that ecological-genetic or metapopulation dynamics are likely to be involved in setting the northern and western range limits. Further, it highlights the value of integrated approaches to studying species‟ range limits.
Nature's genes in space and time: using DNA to uncover the history and formation of biodiversity.
(2011-08) McKay, Bailey Dale
Modern science is tasked with explaining biological diversity: where it is, where it comes from, and how it evolves. Molecular tools have revolutionized this endeavor and given us the ability to peer into the evolutionary past like never before. Drawing on examples from the birds and mammals of East Asia, I present a progression of methods for uncovering the history and formation of species using molecular approaches. Because the characterization of diversity must necessarily precede the study of diversity, I begin in Chapter 1 with a species delimitation study aimed at resolving evolutionary lineages. I conclude that fixed character differences are better indicators of lineage limits than statistical approaches and that both morphological and molecular characters may be necessary to reveal lineages when divergence is recent. In Chapter 2 I describe the evolutionary history of a single-species in which I found evidence for a recent range-wide demographic expansion. This particular example demonstrates how phylogeography and ecological niche modeling can reciprocally illuminate aspects of evolutionary history. Finally, in Chapter 3 I discuss a comparative study of the evolutionary histories of multiple co-distributed species. Comparative studies reveal the generalities involved in evolution and allow us to discern the major drivers of biological diversity.
Paternity and father-offspring relationships in wild chimpanzees, Pan troglodytes schweinfurthii.
(2010-03) Wroblewski, Emily Elizabeth
Hamilton's seminal theory of kin selection asserts that because relatives share a certain proportion of genes, individuals can increase their inclusive fitness by helping and/or not harming kin, as long as the benefits to kin outweigh the costs to the individual. We would expect animals to attain maximal inclusive fitness by discriminating both the available maternal and paternal kin from non-kin in their social groups. The primate order is a useful taxon in which to study kin selection and kin discrimination because most primates live in permanent social groups with both kin and non-kin between which to discriminate, and their complex social interactions provide many opportunities to both hurt and aid others. However, the prevailing view has been that the discrimination of paternal kin does not occur in most species. Despite emerging studies that suggest otherwise, study of paternal kin discrimination thus far has been limited in primates. Furthermore, study has been restricted to matrilineal species with male-biased dispersal. Paternal kinship could also be important in a patrilineal species such as chimpanzees as males will remain with fathers and other paternal kin for life, as will females until they disperse. Thus, this study aimed to further our understanding of importance of paternal kinship in social behavior by examining the most direct paternal relationship, that of fathers and offspring, in the chimpanzees of Gombe National Park, Tanzania. Identifying fathers and offspring and characterizing their relationship is a necessary first step on the way to testing for kin discrimination amongst non-descendent paternal kin. Thus, in Chapter 1, I first determined paternal relationships and explored patterns of male reproductive success relative to dominance rank and the priority of access model, as well as fathers' mating strategy and age. Then in Chapter 2, I examined whether fathers showed parental investment in their juvenile and adolescent sons. Finally, in Chapter 3, I investigated whether there was inbreeding avoidance between fathers and daughters.
Phylogeography of Douglas-fir: testing hypotheses from the fossil record.
(2010-06) Gugger, Paul Francis
Paleobotanical records and molecular data from modern forests can provide a synergistic understanding of the ecological and evolutionary history of an organism. I used the fossil record to generate hypotheses that I tested with statistical phylogeographic methods for Douglas-fir (Pseudotsuga menziesii). In Chapter 1, I describe alternative scenarios of glacial refugia and postglacial migration based on compiled fossil pollen and macrofossil evidence from the late Quaternary. In Chapter 2, I test those hypotheses using coalescent analyses of mitochondrial and chloroplast DNA sequence data. I also test the paleobotanical hypothesis that Douglas-fir’s two varieties diverged coincident with the Cascade orogeny in the late Pliocene. Finally in Chapter 3, I test whether Mexican Douglas-fir diverged from U.S. populations in the Miocene or Pleistocene, consistent with alternative interpretations of limited fossil evidence in the region. The present patterns of molecular variation in Douglas-fir are well-described by Pliocene (or early Pleistocene) divergence of its varieties, mid-Pleistocene colonization of Mexico, and restriction to multiple glacial refugia in the late Quaternary. Holocene expansion into Canada resulted in recontact among varieties and hybridization driven entirely by pollen dispersal but not seed dispersal. Douglas-fir populations have responded individualistically to past climatic and geologic change, such that some underwent expansions while others contracted to higher elevation and some diverged while others coalesced. These findings highlight the complementary insights that fossil and molecular data provide and can be used to inform the conservation and taxonomy of Douglas-fir.
Predicting disease dynamics in African lion populations
(2008-12) Craft, Meggan E.
In 1994, one-third of Serengeti lions died from canine distemper virus (CDV). I estimated the epidemiological network structure of the Serengeti lion population using long-term data. I found that the lion population is a mix of local pride-to-pride contacts (driven by territory adjacencies) and transient nomad-to-pride contacts (driven by gamma variance process). When canine distemper virus (CDV) was introduced into the network, I found that although nomads are numerous, travel long distances, and are likely candidates to be considered "superconnectors" (connecting distant parts of a network), their impacts on CDV disease dynamics were surprisingly low. Analysis of the data-driven, Levins-type network model demonstrates that the epidemic probably was not propagated solely by within-species transmission but rather involved multiple introductions from other carnivore species, such as jackals and hyenas. The social network model further suggests that the epidemiological observations from the 2000 km2 Serengeti study area may not have reflected the larger-scale dynamics because the sample was (1) located at the periphery of the pride-pride contact network and (2) confined to a small region relative to the scale of the ecosystem. If lions could not produce the observed CDV outbreak, and other wild carnivores were repeatedly involved in transmission to the lion population, could a multi-host spatial model account for the patchy pattern of CDV spread seen in lions in 1994? A stochastic susceptible-infected-recovered model was constructed which allowed transmission between a highly territorial species, like lions, and 1-2 more gregarious hosts, such as hyenas and jackals. When other gregarious species were coupled with lions with low interspecific contact rates, the erratic patterns of CDV spatial spread were similar to those seen in lions in 1994. The results of both the network and the multi-host models suggest that lions are a non-maintenance population for canine distemper virus, and more broadly address issues of spatial disease ecology and multi-host pathogens in complex ecosystems.
Resource hoarding facilitates cheating in the legume-rhizobia symbiosis and bet-hedging in the soil.
(2010-06) Ratcliff, William C.
The carbon that rhizobia in root nodules receive from their host powers both reproduction and the synthesis of the storage polyester poly3-hydroxybutyrate (PHB), as well as N2 fixation, which mainly benefits the host. Rhizobia escaping nodules can use stored PHB to survive starvation and reproduce up to 3-fold, but PHB synthesis is energetically expensive and trades-off with N2 fixation. As a result, PHB synthesis is a central mechanism in the evolution of conflict between rhizobia and legumes, and should be included in estimates of rhizobial fitness. Some rhizobia have evolved sophisticated mechanisms to increase PHB accumulation, such as the production of rhizobitoxine, a chemical inhibitor of legume ethylene synthesis. Rhizobitoxine reduces host growth, decreasing rhizobia per nodule for all strains on a plant, but substantially increases PHB accumulation for rhizobitoxine-producing rhizobia. In addition to enhancing reproduction, PHB has a role in bet-hedging: when starved, free-living high-PHB rhizobia divide asymmetrically, forming dormant, high-PHB „persisters‟ that survive long-term starvation and antibiotic treatment, and low-PHB „growers‟ that are sensitive to these stresses. Sinorhizobium meliloti integrates bet hedging and phenotypic plasticity, forming fewer high-PHB persister cells when low competitor density predicts shorter-term starvation. Declining populations may select for delayed reproduction when there is a trade-off between reproduction and longevity, as there is with starving S. meliloti.
The role of photodegradation in plant litter decomposition in grassland ecosystems
(2009-08) Brandt, Leslie Alyson
Decomposition of plant litter is the primary process by which carbon and nutrients are returned from plants to the soil and atmosphere. Although plant litter decomposition is primarily driven by plant litter chemistry, temperature, and precipitation these factors have failed to fully explain decomposition patterns in arid and semiarid grassland ecosystems. In my dissertation, I tested the hypothesis that solar radiation, particularly in the UV range (280-400 nm) contributes to the decomposition process in these systems via the process of photodegradation. In a three-year field study in the semiarid shortgrass steppe in Colorado, I examined whether photodegradation by UV radiation played a role in plant litter decomposition and whether the role of photodegradation in the decomposition process was affected by plant litter chemistry and precipitation. In a series of laboratory experiments, I examined the pathways by which mass is lost via photodegradation. In a two-year cross-site field experiment, I examined whether photodegradation may explain the difference in litter decomposition patterns among mesic, semiarid, and arid grassland ecosystems. The combined results of this research show that photodegradation is an important process in plant litter decomposition in mesic grassland ecosystems as well as arid and semiarid grassland ecosystems, accounting for up to 50% of litter mass loss. Results also show that litter mass loss via photodegradation is the result of photochemical production of carbon dioxide, which can be up to 4 g C m-2 y-1 in arid ecosystems. This research has important implications for future basic research in biogeochemical modeling, photochemistry of natural compounds, and plant litter decomposition in arid ecosystems.

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