Suppression of canopy tree recruitment beneath rapidly spreading thickets of Rhododendron maximum L. (Ericaceae) in southern Appalachian forests is an issue of major concern because of the potential impacts on forest productivity, hydrology and wildlife habitat. Many studies have investigated the causes of seedling inhibition beneath dense shrub understories, but few have uncovered specific mechanisms leading to seedling decline. In this study, I have examined the influence of the evergreen understory (R. maximum and Kalmia latifolia L.) on tree recruitment processes at multiple stages - seed rain, seed bank, and post-establishment seedling growth and survivorship. Effects of dense shrub cover on seed rain and seed bank density and composition were examined using a paired treatment design in which samples were collected beneath shrub-influenced and open understories. A second experiment investigated the influence of R. maximum and K. latifolia density on the growth and survivorship of Quercus seedlings, resource availability, and the rates / causes of seedling damage. I found that neither seed rain, nor seed bank density or species richness was inhibited by the presence of R. maximum or K. latifolia. Forest seed banks were dominated by sweet birch (Betula lenta L.), and were compositionally disparate from the overstory. Analysis of resource competition between shrubs and seedlings indicated that seedling performance and survivorship was a negative function of R. maximum density. Open-canopy light availability, nitrogen content in the organic horizon (litter and humus), and soil nutrient availability were potential resource-related mechanisms. Further, I found that the rates of insect herbivory on Quercus seedlings were positively correlated with R. maximum density. Kalmia latifolia had little influence on resource availability, seedling performance or herbivory rates, and does not appear to have a suppressive effect on tree seedlings. Overall, this research indicates that resource competition is the primary mechanism by which seedling suppression occurs beneath R. maximum, and that increased herbivory on seedlings may be an additional mechanism that demands further study. / Master of Science

Non-native species are a major cause of endangerment for native species, but the mechanisms are often unclear. As species invasions continue to rise, it is important to understand how to mitigate this threat. Our field experiment quantified the impact of introduced Abert's squirrels (Sciurus aberti) on rates of food removal within the range of the critically endangered Mount Graham red squirrel (Tamiasciurus hudsonicus grahamensis). In the presence of Abert's squirrels, the time until 50% of cones were removed was 5.55 days faster than when Abert's squirrels were excluded (95% confidence interval 2.25 to 11.63 days). The impact on food availability as a result of cone removal by Abert's squirrels suggests the potential of food competition as a mechanism of endangerment for the Mount Graham red squirrel. Eradication of established non-native populations is rare. Management targeted at specific mechanisms by which non-natives cause endangerment is an essential tool for conservation.

No description available.

Ecological processes have the potential to influence evolution through their effects on selection. This thesis explores the effects of two ecological factors - competition and ecological opportunity. Intraspecific (within-species) competition is often expected to drive adaptation and diversification by increasing selection for the use of novel resources, thereby alleviating the detrimental effects of competition. However, this is not always the expected outcome; theory suggests that intraspecific competition can also drive convergent evolution. On the other hand, interspecific (between-species) competition is usually expected to impede adaptation and diversification because competitor species occupy potential available niches, preventing the focal species from diversifying to do so. In this thesis, I review previous experimental studies exploring the effects of competition on adaptive diversification, and then directly test these effects using experimental evolution of the bacterium Pseudomonas fluorescens. I confirm that intraspecific competition drives adaptive diversification, while the effects of interspecific competition are varied. Strong interspecific competition impedes adaptation and diversification, while the presence of weak, non-diversifying interspecific competitors drives diversification through increased resource competition. The presence of ecological opportunity is essential for adaptation and diversification, and so variation in attributes of those opportunities is expected to have important effects on the dynamics of adaptive evolution. In another evolution experiment with P. fluorescens, I tested the effects of variation in ecological opportunity on adaptive evolution and found that the type and arrangement of ecological opportunities drives adaptation but, in this system, not diversification. I also show that ecological opportunity drives differences in the degree of parallel evolution at the phenotypic and genotypic level. Finally, I explore some unexpected genetic changes identified in one of these evolved populations - two synonymous mutations that conferred fitness benefits, and show that the observed fitness improvements are the result of increased gene expression. I have shown that ecological processes can play an important role in shaping the evolutionary trajectories taken by populations. Understanding the interactions between ecological and evolutionary processes is vital for our understanding of evolutionary dynamics as a whole, and the studies laid out in this thesis represent valuable contributions to this field of study.

Most animals grow substantially during their lifetime and change in competitive ability, predatory capacity and their susceptibility to predation as they grow. This thesis addresses the implications of this on regulation and dynamics within populations as well as between population interactions. In size-structured populations either reproduction or maturation may be more limiting. If juveniles are competitively superior, the competitive bottleneck will be in the adults and reproduction will be limiting. Mortality will in this case result in overcompensation in juvenile biomass through increased reproduction. Compensation in biomass was demonstrated in Daphnia pulex populations subjected to size-independent mortality, where juvenile biomass did not decrease when a substantial harvest was imposed due to increase per capita fecundity. This supported that juveniles were superior competitors and that population cycles seen in Daphnia are juvenile-driven. Compensatory responses in biomass may lead to that predators facilitate eachothers existence by feeding on a common prey, a phenomenon coined emergent facilitation. In an experimental test of the mechanism behind emergent facilitation it was demonstrated that the invertebrate predator Bythotrephes longimanus was favoured by thinning of its prey Holopedium gibberum. The thinning mimicked fish predation and targeted large individuals while Bythotrephes preferrs small prey. Size dependent predation also occurs within populations, i.e. cannibalism, were large individuals feed on smaller conspecifics. Two populations of the common guppy (Poecilia reticulata) originating from different environments were demonstrated to differ in cannibalistic degree. Cannibalism was also affected by the presence of refuges and females and juveniles from one population were better adapted to structural complexity than the other. The effects of these differences in cannibalism on population regulation and dynamics were studied in long term population experiments. Both populations were regulated by cannibalism in the absence of refuges, and displayed cannibal-driven cycles with suppression of recruitment and high population variability. The presence of refuges decreased density dependence and population variability and harvesting of large females in the absence of refuges led to population extinctions in the more cannibalistic population. The less cannibalistic population had higher population biomass and stronger density-dependence in the presence of refuges. When refuges were present, cohort competition increased and cycles with short periodicity were seen. Large individuals were not only cannibals, but could successfully prey on other species. Small and large guppies were allowed to invade resident populations of Heterandria formosa. Small invaders failed while large invaders succeeded as predation from large invaders broke up the competitive bottleneck that the resident population imposed on juveniles of the invader.

Honeybees (Apis mellifera) are important pollinators of many plant species and are employed globally for crop and honey production. However, little is known about the effects of this species on native pollinator and plant species in areas to which they have been introduced; and previous research has not been able to reach a general consensus as to the type of impact honeybees have on pollination systems. In addition to the effects of exotic pollinators, the loss and fragmentation of natural habitats is also of major concern to the continuing diversity of pollinators and plant populations. Here, the impact of honeybee density on other pollinator guilds, and levels of remaining pollen and nectar standing crop among 18 patches of the New Zealand native shrub – manuka (Leptospermum scoparium) is examined at three different regions within the North Island. The same sites were also used to test the reproductive capabilities of manuka and subsequent pollen limitation among patches. A further 11 sites were utilised to examine biodiversity via intercept and pitfall traps within manuka patches, and the patch variables driving taxa composition. Large fly (Diptera = 5 mm) abundance was negatively correlated with honeybee abundance and instances of physical disturbance of large flies by honeybees were observed. There was no significant correlation between honeybee abundance and other pollinator guilds. Nectar was a limiting resource for both honeybees and large flies, whereas, pollen was not a limiting resource among any of the major pollinating insect guilds. Pollination treatments revealed that manuka is partially self-compatible, but relies more heavily on cross pollination for higher yields of capsule and seed set. Pollen limitation did not occur significantly at any of the sites. A total of 159 Coleoptera, 125 Diptera, 131 Hymenoptera morphospecies, and 50 other groups of taxa from various orders were collected among sites. Invertebrate richness was higher at lower altitudes and litter invertebrate richness was significantly higher with an increase in the proportion of manuka cover. There were distinct differences in taxa composition between the three regions, with plant community composition and altitude the most significant factors. Patch size also played a part, but a lack of overall variation in patch sizes may understate the effect this has on insect composition. Overall, honeybees are competing for nectar resources and displacing large flies as a consequence; however, capsule and seed set among manuka patches did not significantly suffer as a consequence. Regional variation in patch characteristics such as altitude, plant community composition, patch size, proportion manuka cover, and plant evenness appear to be influencing insect composition found within manuka patches to varying degrees. Further investigation into the impact of patch size and patch connectivity is also warranted.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / This study involved two experiments that addressed mate choice, male competition for mature females and the communication pathways used by both sexes in Aegla longirostri. In the first experiment, males were paired according to body and cheliped size, and they were acclimated in the laboratory for a week. Next, they were accommodated in opposite sides of an aquarium that was divided in three parts. A container with a female inside was inserted in the center of the aquarium, according to four treatments: Fimat, perforated and translucent container holding an immature female (N = 10); FmatCV, the same container holding a mature female (N = 10); FmatV, translucent and non-perforated container holding a mature female, (N = 10); FmatC, perforated opaque container with a mature female (N = 10); NF = no female in the container. Afterwards, the males were released and left interacting for 20 min. The following variables were quantified: time of the first three bouts, time spent in aggressive acts, latency period, time that animals remained near the container and the number of antennal whips per bout second. Thus, we observed that males fight more quickly and less intensely in the presence of mature females, independently of the communication pathway used. However, both stimuli were needed to elicit a guarding behavior by the winner. Therefore, the female might be controlling the cues that advertise her receptivity, only releasing them when the preferred male is near. This causes information asymmetry between the males, which makes shorter fights. We also demonstrated the importance of bimodal stimuli (chemical + visual) for reproductive behaviors, since the behavioral repertory presented was more complex when both could be used. To assess mate choice in A. longirostri, we used a different experimental design. Animals were grouped in triads, two of them were used as choices ( targets ) and one as the choosing individual ( focal ). They were accommodated in a Y-maze in four different treatments: MD, adult male as focal animal and two females, one immature and one mature as targets (N = 8); FD, mature female as focal animal and two adult males, a large male and a smaller one as targets (N = 7); Q, like FD but the female could choose based only in chemical cues provided by the targets (N = 7); F, like FD but the female could choose based only in visual cues (N = 7). The eglids were acclimated for 10 min and then the focal animal was released for 20 min. We quantified the time spent in the corridor as an index of preference. Males did not choose between females, however the time spent in the mature female corridor was highly variable. On the other hand, the females only chose the large males when they could assess them through visual and chemical stimuli. Thus, females may control the release of cues that advertise her receptivity, and so, only preferred males could actually make the choice. The females may also need more information to choose between potential mates, since they only showed preference when two stimuli were present. / Este estudo envolveu dois experimentos que abordaram a escolha de parceiros, a competição por fêmeas maduras e os meios de comunicação utilizados pelos indivíduos de Aegla longirostri. No primeiro, machos desta espécie foram pareados conforme o tamanho corporal e dos quelípodos e, após uma semana de aclimatação em laboratório, foram acomodados em lados opostos de um aquário dividido em três partes. No centro deste aquário foi inserido um recipiente que continha uma fêmea, conforme quatro tratamentos: Fimat, recipiente translúcido e perfurado que continha uma fêmea imatura (N = 10); FmatCV, igual ao anterior, porém com uma fêmea madura (N = 10); FmatV, recipiente sem perfurações, translúcido e com fêmea madura (N = 10); FmatC, recipiente perfurado, opaco e com fêmea madura (N = 10); NF = sem fêmea, recipiente vazio (N = 5). Então, os machos eram liberados e deixados para interagir por 20 min. Foram quantificados: o tempo dos três primeiros confrontos, tempo que os animais passaram em atos agressivos, tempo de latência, tempo que permaneceram próximos ao recipiente e o número de antenadas dividido pelo tempo de confronto. Com isso, foi observado que os machos possuem embates mais rápidos e menos intensos na presença de fêmeas maduras, independente do meio de comunicação. Porém, foram necessários ambos os estímulos para que o macho vencedor ficasse mais tempo próximo do recipiente, em um comportamento possivelmente de guarda. Logo, a fêmea pode estar controlando o estímulo que anuncia sua receptividade, liberando-o apenas quando o macho preferido está próximo, o que causa assimetria de informações entre os combatentes, fazendo com que o confronto termine mais cedo. Também foi demonstrada a importância de estímulos bimodais (químico + visual) para comportamentos reprodutivos, uma vez que na presença destes, o repertório apresentado foi mais complexo. Para verificar a escolha de parceiro pelos sexos de A. longirostri, foi utilizado outro design experimental que foi composto de três animais, sendo dois para serem escolhidos ( alvos ) e um para escolher ( discriminante ), dispostos em um aquário em Y, em quatro tratamentos: MD, macho adulto como animal discriminante e duas fêmeas, uma imatura e outra madura, como alvos (N = 8); FD, fêmea madura como discriminante e dois machos adultos, um grande e outro pequeno, como alvos (N = 7); Q, igual ao anterior, porém a fêmea poderia escolher baseada apenas em estímulos químicos dos alvos (N = 7); V, igual ao FD, porém a fêmea poderia escolher utilizando apenas os estímulos visuais dos alvos (N = 7). Os eglídeos eram aclimatados por 10 min e, após, o animal discriminante era liberado por 20 min; o tempo que este permanecia em cada corredor era quantificado e utilizado como índice de escolha. Os machos não realizaram escolha, porém houve muita variação de tempo permanecido no corredor que havia fêmea madura. Já as fêmeas só escolheram machos grandes quando este poderia liberar estímulos visuais e químicos concomitantemente. Portanto, a fêmea provavelmente controla a liberação dos químicos que indicam sua receptividade, por isso só alguns machos realizaram a escolha. Elas também necessitam de mais informações para escolher um parceiro, uma vez que só realizaram escolha quando havia dois estímulos presentes.

Ecological processes have the potential to influence evolution through their effects on selection. This thesis explores the effects of two ecological factors - competition and ecological opportunity. Intraspecific (within-species) competition is often expected to drive adaptation and diversification by increasing selection for the use of novel resources, thereby alleviating the detrimental effects of competition. However, this is not always the expected outcome; theory suggests that intraspecific competition can also drive convergent evolution. On the other hand, interspecific (between-species) competition is usually expected to impede adaptation and diversification because competitor species occupy potential available niches, preventing the focal species from diversifying to do so. In this thesis, I review previous experimental studies exploring the effects of competition on adaptive diversification, and then directly test these effects using experimental evolution of the bacterium Pseudomonas fluorescens. I confirm that intraspecific competition drives adaptive diversification, while the effects of interspecific competition are varied. Strong interspecific competition impedes adaptation and diversification, while the presence of weak, non-diversifying interspecific competitors drives diversification through increased resource competition. The presence of ecological opportunity is essential for adaptation and diversification, and so variation in attributes of those opportunities is expected to have important effects on the dynamics of adaptive evolution. In another evolution experiment with P. fluorescens, I tested the effects of variation in ecological opportunity on adaptive evolution and found that the type and arrangement of ecological opportunities drives adaptation but, in this system, not diversification. I also show that ecological opportunity drives differences in the degree of parallel evolution at the phenotypic and genotypic level. Finally, I explore some unexpected genetic changes identified in one of these evolved populations - two synonymous mutations that conferred fitness benefits, and show that the observed fitness improvements are the result of increased gene expression. I have shown that ecological processes can play an important role in shaping the evolutionary trajectories taken by populations. Understanding the interactions between ecological and evolutionary processes is vital for our understanding of evolutionary dynamics as a whole, and the studies laid out in this thesis represent valuable contributions to this field of study.

No description available.

Understanding why some species coexist and others do not remains one of the fundamental challenges of ecology. While several lines of evidence suggest that closely related species are unlikely to occupy the same habitat because of competitive exclusion, there are many cases where closely related species do co-occur. Research comparing sympatric and allopatric populations of co-occurring species provides a framework to understand the role of phenotypic diversification in species coexistence. In this study I focus on the livebearing fish Poeciliopsis baenschi and ask if differences in phenotypic traits among populations can be explained by the presence or absence of the congeneric species P. turneri. I focus on phenotypic divergence in life history traits and in body shape, two sets of integrated traits likely to respond to variation in competition. Additionally, I compare explore the effects of sympatry and allopatry on sexual dimorphism. I take advantage of a natural experiment in western Mexico where P. baenschi co-occur with P. turneri in some locations (sympatric populations) but also exist in isolation in other locations (allopatric populations). My results show that sympatric populations of P. baenschi differed significantly in life history traits and body shape when compared to their allopatric counterparts. Additionally, the amount of sexual dimorphism differed between sympatric and allopatric populations of P. baenschi, suggesting different constraints might exist in sympatry and allopatry for sexual dimorphism. Lastly, I explore my results in the context of trait evolution as it relates to species coexistence.