Mark-recapture studies sample unevenly over distance and generate biased or distance-weighted movement data, where short distances are sampled more frequently than long distances. I examined how study design affects the degree of distance-weighted sampling and observed movement distributions of stream fish. A modeling study illustrated how distance-weighting increases with the number of mark sites and decreases with the length of stream sampled during recapture. Sub-sampled empirical data sets indicated that longer movements can be detected by increasing the length of the recapture section and that a substantial proportion of fish may move long distances outside of study areas. I also examined factors that were associated with movement in a network of streams. The probability of emigrating from a site was positively related to intermittency and body size and negatively related to distance from the mainstem creek and habitat complexity. Movement rates, measured as the number of fish moving upstream through a trap per day, were positively related to increases in flow, daylength, and water temperature. Distance moved was greater for fish that were initially marked within intermittent reaches. Overall, some species moved in association with several of these factors but others did not respond to any factors. Finally, I identified species-level attributes that were associated with colonization rates after experimental defaunation. Movement rate and abundance explained the most interspecific variation in colonization rates when compared to competing predictors (spatial distribution, body size, and family). Recovery occurred slowly and several species had not restored more than half of their pre-defaunation abundance within a year. Despite slow recovery for some species, defaunation had only a short-term (i.e., < 3 months) effect on relative abundance patterns. This study has important implications for conservation. Improvements in study design will allow detection of longer movements that may be a key component of species invasions, demographic rescue, and colonization. Species that move in association with multiple factors may be better colonists than species that do not. Finally, species that are rare and less-mobile will recover their populations slowly and will be vulnerable to extirpation in systems impacted by frequent pulse disturbances. / Ph. D.

Mutualism is an understudied interaction in ecosystems throughout the world. Within the eastern United States, one fish-fish mutualism is the nest association between Nocomis and other cyprinids. I assessed the role of host parental care while testing for the selfish-herd effect. Additionally, I examined multiple nest associates in order to elucidate potential cheaters. I utilized gonadosomatic index (GSI) to compare reproductive condition among the bluehead chub Nocomis leptocephalus and its putative nest associates in Catawba Creek, Virginia. GSI of potentially obligate associates tracked host GSI more closely than weak associates, while weak associates spawned prior to Nocomis spawning. Given their GSI patterns and behavior, central stonerollers Campostoma anomalum may be cheaters in the interaction. I used multiple experiments to test for the selfish-herd effect, the role of parental care, and how relative risk influences reproductive decisions of associates. Most eggs were located in the bottom upstream quarter of nests, and a molecular analysis revealed that stonerollers and chubs constituted the majority of identified individuals. A comparison of host-associate ratios from four nest sections failed to identify the selfish herd effect. Another experiment found that host egg covering significantly reduced egg predation. Lastly, I assessed relative egg predation risk at four potential spawning locations; predation levels did not differ significantly at any location. While GSI patterns suggest that stonerollers may be cheaters, genetic evidence indicates that stonerollers spawn on Nocomis nests. Because GSI does not completely assess reproduction, secondary stoneroller reproduction on Nocomis nests may have been overlooked. / Master of Science

Many species have evolved to live in groups. Gregarious behavior was believed to be adaptive for whole-population survival and predator evasion until selfish-herd theory was introduced. It proposed that individuals congregate not as a method of protection for the entire population, but instead to better the individual's chance of survival, thereby using the group to benefit itself (i.e., "selfishness"). Selfish behavior is a common part of mutualisms, which are complex, dynamic interactions that often change with biotic or abiotic circumstance. Here, I investigate potential selfish behavior within the mixed-species spawning aggregations hosted by bluehead chub (Nocomis leptocephalus). I hypothesized that the host benefits more directly from the aggregation it supports than previous research suggests – specifically, by using nest associates to decrease its own risk of predation (creating a selfish-herd) and simultaneously forcing associate embryos into marginal nest locations while locating its own embryo in the safer locations within the nest (creating an "embryonic selfish-herd"). In Chapter 1, I investigated the adult spawning aggregation for possible selfishness by monitoring the chub's spatial location within the aggregation and vigilance behavior under varying associate abundances. I found that the host occupied the central location within the aggregation and was less vigilant when associate abundance was high. In Chapter 2, I examined the "embryonic herd" contained within Nocomis nests for possible embryonic selfishness orchestrated by the chub host, leading to increased embryonic survival for chub young and elevated fitness for chub parents. I found that deeper nest sections support higher embryonic survival than shallower sections, and that chub embryo make up a disproportionate percentage of embryos found in those deeper sections. I also conducted a preliminary study investigating embryo-predation by host on associate embryo which produced evidence for embryo-predation by both host and two associates on each other's offspring. Cohesively, my results support the identification of the host as a selfish participant and confirm the presence of both an adult and embryonic selfish-herd in this mutualism. This is the first study to demonstrate selfish behavior on the part of the host in this system and the first to prove the existence of an embryonic selfish-herd. / Master of Science / A fish has three goals: to survive, to grow, and to reproduce. Mutualisms – when all participants experience a net benefit from interacting – arise when two or more species rely on each other to meet these objectives. In many mutualisms, however, not all participants benefit equally. Selfish-herd theory identifies those that maximize their own benefit while minimizing or negating any cost as "selfish" individuals. I examined the mutualistic mixed-species spawning aggregations hosted by a freshwater minnow, bluehead chub (Nocomis leptocephalus), for possible selfish behavior. I found that bluehead chubs disproportionately benefit from the aggregations they host and use the aggregation to improve their own survival, improve their offspring's survival, and obtain food (by eating others' offspring). Thus, I identify bluehead chub as a selfish participant and provide evidence for the existence of two selfish herds in this mutualism – one among the adult fishes and one among their young – both orchestrated by and benefiting the bluehead chub. This study is the first to identify the bluehead chub as such and rewrites our previous understanding of this mutualism, which largely denied bluehead chub as a direct beneficiary. This work contributes to the global discussion of mutualisms by attesting the complexity of these relationships and offers support for re-examination of the classification of many known interspecific interactions, such as those cursorily termed nest parasitisms.

Mutualism is an understudied phenomenon across taxa, but is important to the persistence and structure of communities. The role of positive interactions in supporting threatened species is critically important given that freshwater fish are extremely vulnerable due to the combined effects of climate change and habitat degradation. To disentangle complex positive multi-species interactions, I applied both Eltonian and Hutchinsonian niche approaches to the reproductive mutualism of leuciscids known as nest association, a form of alloparental care characterized by an adult of one species guarding the offspring of another. I conducted this study with the leuciscid community of Toms Creek in which Bluehead Chub Nocomis leptocephalus is the primary nest builder and nest associate species include Rosyside Dace Clinostomus funduloides, Rosefin Shiner Lythrurus ardens, Mountain Redbelly Dace Chrosomus oreas, Crescent Shiner Luxilus cerasinus, White Shiner Luxilus albeolus, Central Stoneroller Campostoma anomalum, Creek Chub Semotilus atromaculatus, and Blacknose Dace Rhinycthys atratulus. I applied Hutchinsonian niche theory with respect to hydrology and water temperature to define the reproductive phenology of each species involved in the reproductive mutualism, then used Eltonian niche theory to define the role of each species in parental and alloparental care. My dual niche theory approach elucidates the reproductive requirements of each species and quantifies the contribution of nest associates to alloparental care, which historically have not been included in definitions of nest association. My results show that Blacknose Dace Rhinichthys atratulus and Creek Chub Semotilus atromaculatus are not true nest associates of Bluehead Chub Nocomis leptocephalus based on their reproductive phenology and observed nesting behaviors. In contrast to previous work on nest association, most associate species did contribute to parental care through nest defense and vigilance behaviors, and their specific behaviors were influenced by morphology. By clearly defining the reproductive niches of these species, this study lays the groundwork for future investigation of how various climate scenarios may impact multi-species reproductive mutualisms. / Master of Science / Positive interactions are understudied throughout ecology, but are important to the persistence and structure of communities. The role of positive interactions in supporting threatened species is critically important given that freshwater fish are at high risk of extinction due to the combined effects of climate change and habitat degradation. To understand the complex positive interactions in freshwater fish, I applied both niche theory approaches to a mutualistic reproductive interaction known as nest association, where an adult of one species builds a nest on which it guards the offspring of other species (formally: a type of alloparental care). I conducted this study with the leuciscid (commonly known as minnow) community of Toms Creek in which Bluehead Chub Nocomis leptocephalus is the primary nest builder and nest associate species include Rosyside Dace Clinostomus funduloides, Rosefin Shiner Lythrurus ardens, Mountain Redbelly Dace Chrosomus oreas, Crescent Shiner Luxilus cerasinus, White Shiner Luxilus albeolus, Central Stoneroller Campostoma anomalum, Creek Chub Semotilus atromaculatus, and Blacknose Dace Rhinycthys atratulus. For each species involved in the reproductive mutualism, I defined the seasonal timing of reproduction with respect to hydrology and water temperature, then defined their role in parental and alloparental care. My approach clarifies the reproductive requirements of each species and establishes the contributions of associate species to alloparental care, which historically have not been included in definitions of nest association. My results show that Blacknose Dace Rhinichthys atratulus and Creek Chub Semotilus atromaculatus are not true nest associates of Bluehead Chub Nocomis leptocephalus based on their reproductive requirements and observed nesting behaviors. In contrast to historic descriptions of nest association, most associate species did contribute to parental care through nest defense and vigilance behaviors, and their specific behaviors were influenced by their size and physical adaptations. By clearly defining the reproductive needs and roles of these species, this study lays the groundwork for future investigation of how various climate scenarios may impact positive relationships among species.

Positive biotic interactions such as mutualism, commensalism and facilitation are ubiquitous in nature, but historically have received considerably less research attention than negative interactions such as competition, predation and parasitism. The paucity of research on positive interactions is particularly evident in stream ecosystems and in vertebrate communities. Stream fishes clearly provide an ideal system for advancing research on positive interactions. Many minnows (Cyprinidae) of eastern North America engage in a potentially mutualistic reproductive interaction known as nest association, in which individuals of one species (nest associates) spawn in nests constructed by host species. In nest association, hosts provide unsilted gravel substrate for spawning nest associates, and increased parental care to associate broods. High associate: host egg ratios can create a dilution effect, reducing the probability that host eggs will be preyed upon by egg predators. Nest associative interactions are common, but are relatively understudied compared to other interactions among stream fishes. The goals of this study were to apply general ecological models to this novel system to (a) gain new insight into the mechanisms structuring nest associative stream fish communities, and (b) to use inference from stream fish communities to potentially expand and improve the general ecological models. These goals required completion of three objectives, including (1) examining the influence of abiotic and biotic contexts on reproductive behavior and fitness outcomes between a cyprinid host and associate, using the biological markets model to generate predictions; (2) examining the utility of the nest web framework (previously only used for cavity nesting vertebrate communities) and the stress gradient hypothesis (previously applied almost exclusively to plant communities) for predicting which associate species spawn on nests built by various nest building species, and the consequences of these choices, respectively; and (3) using two-species occupancy modeling to determine the relative influence of biotic interactions and habitat covariates on the co-occurrence of a host and two nest associates. To accomplish these goals, I conducted a large-scale experiment to manipulate presence of mutualists (Nocomis leptocephalus, host; Chrosomus oreas, associate), egg predators (biotic context) and habitat quality (abiotic context). I conducted behavioral nest observations and conducted repeated stream fish stream fish community surveys to collect demographic data. I constructed a nest web from observational data, and implemented structural equation modeling through an information-theoretic framework to identify nest web plausibility across a large spatial extent. I tested some predictions of the stress gradient hypothesis by regressing juveniles-per-nest and a metric of cyprinid community structure on a composite measure of physical stress (scaled gradients of catchment-scale agricultural land use and catchment area). I used two-species occupancy modeling to model co-occurrence of N. leptocephalus hosts and two associates, C. oreas and Clinostomus funduloides, and used an information-theoretic framework to compare hypotheses representing the importance of biotic interactions, habitat covariates or both at determining species co-occurrence. Results corroborated some (but not all) model predictions, and identified room for improvement in each of the general models. Nest associative spawning by C. oreas was not context dependent; C. oreas did not spawn in the absence of a reproductively active male N. leptocephalus at any treatment level. However, the net fitness outcome of host and associate species was mutualistic, and the interaction outcome switched from commensalistic to mutualistic with abiotic context. N. leptocephalus reproductive success was improved by C. oreas presence in less-silted habitats, but not in heavily-silted habitats. This is most likely because broods were subject to predation in both habitat types, but were also negatively affected by siltation in silted habitats. Accordingly, egg dilution by associates was not sufficient to support a mutualistic relationship in less favorable habitats. Results suggest that the biological markets model may be a useful tool for predicting fitness outcomes of nest associative mutualism, but may not be as useful for predicting the behavioral outcomes of obligate mutualisms. Future applications of the biological markets model should carefully consider species traits, specifically the degree to which trading behavior is obligate for participants. Future work with this model will yield more insight by considering highly facultative associates. Nest webs constructed from nest observational data suggested an interaction topology in which strong (nearly-obligate) associates relied most frequently on N. leptocephalus nests, and less frequently on nests constructed by Campostoma anomalum. Weak (facultative) associates were seldom associated with nests constructed by either species, and probably spawned before hosts began nesting activity. Structural equation models corroborated this topology throughout the New River basin, although some less-supported model evidence specified some nest association by weak associates. Juveniles-per-nest of strong associates responded positively to physical stress, while this metric for other cyprinid reproductive groups showed no relationship. Proportional representation of Nocomis and strong associates also increased predictably with physical stress. This study suggests that the nest web framework can be informative to systems outside the ones for which it was developed; future studies may be able to use this framework to better understand the role of habitat-modifying species in communities other than cavity nesting terrestrial vertebrates and nest associative stream fishes. This work extended the nest web framework by (a) modeling the outcomes of interactions instead of the interactions themselves, and (b) by using structural equation modeling to test nest web predictions with an information-theoretic framework. This study also suggests that the stress gradient hypothesis can be useful for understanding interaction dynamics in vertebrate communities; this represents the first direct evidence that this model can be used in vertebrate communities. Further, I demonstrate that the stress gradient hypothesis may be extended to predict community structure. However, more research in a diversity of systems will be needed to determine the extent to which this can be applied. This study provides some of the first evidence of large-scale positive co-occurrence patterns in vertebrates. However, the precise roles of habitat covariates and biotic interactions were species-specific. Occupancy results suggest that co-occurrence between N. leptocephalus and nest associate C. funduloides is driven only by reproductive behavioral interactions. Alternatively, evidence suggests that co-occurrence between N. leptocephalus and C. oreas is driven by both nest association and habitat covariates. That two-species occupancy modeling can be a useful tool for comparing difficult-to-test hypotheses involving biotic interactions at large spatial scales. This study represents the first quantitative, multi-scale treatment of positive interactions in stream ecosystems. This study demonstrates that applying general ecological models to stream fish communities can yield new insights about both the study system and the models themselves. While models of negative interactions, food webs and dispersal have been applied to stream fishes, we stand to gain much ground by also considering positive biotic interactions. In doing so, stream fish ecologists will also be able to contribute to the advancement of general ecology, and thus raise awareness for these understudied ecosystems and taxa. / Ph. D.