<p>Elastic energy plays important roles in biology across scales, from the molecular to organismal level, and across the tree of life. The ubiquity of elastic systems in biology is partly due to the variety of useful functions they permit such as the simplification of motor control in running cockroaches and the efficient recycling of kinetic energy in hopping kangaroos. Elastic energy is also responsible for ultrafast movements; the fastest movements in animals are not powered directly by muscle, but instead by elastic energy stored in a spring. By demonstrating that the power required to generate ultrafast movements exceeds the limits of muscle, many studies conclude that energy storage is necessary; but, what these studies do not explain is how the properties of a biological structure affect its capacity for energy storage. In this dissertation, I test the general principles of energy storage by investigating elastic systems at three hierarchical levels of organization: a single structure, multiple connected structures, and a spring system connected to muscle. By using a multi-level approach, my aim is to demonstrate, at each of the mentioned levels, how properties of the spring system affect where or how much energy is stored in the system as well as how these conclusions can be combined to inform our understanding of the biomechanics of hierarchical elastic systems.</p><p>When considering spring systems at the level of a single structure, morphology is one major structural aspect that affects mechanics. Continuous changes in morphology are capable of dividing a structure into regions that are responsible for the two contradicting functions that are essential for spring function: energy storage (via deformation) and structural support (via resistance to deformation). Using high quality micro computed tomography scans, I quantify the morphology of the mantis shrimp (Stomatopoda) merus, a single structure of the raptorial appendage hypothesized to store the elastic energy that drives ultrafast strikes. Comparing the morphology among the species, I find that the merus in smashers, species that depend heavily on elastic energy storage, have relatively thicker ventral regions and more eccentric cross-sections than spearers, species that strike relatively slower. I also conclude that differential thickening of a region can provide structural support for resisting spring compression as well as facilitate structural deformation by inducing bending. This multi-level morphological analysis offers a foundation for understanding the evolution and mechanics of monolithic systems in biology.</p><p>When two or more structures are connected, their relative physical properties determine whether the structures store energy, provide structural support, or some combination of both. Although the majority of elastic energy is stored via large deformations of the merus in smashers, some spearer species show relatively little meral deformation, and it is unclear whether elastic energy is stored in these systems. To determine whether the apodeme (arthropod tendon) provides energy storage in species that exhibit low meral deformation, I measure the physical properties of the lateral extensor apodeme and the merus to which it is connected. Comparisons of these properties show that in the spearer species I tested, the merus has a relatively higher spring constant than the apodeme, which results in the merus providing structural support and the apodeme storing the majority of elastic energy. Comparing the material properties of the apodemes with those of other structures reveals that apodemes and other biological spring systems share similar material characteristics. This study demonstrates that in order to understand the biomechanics of spring systems comprised of connected structures, it is necessary to compare their relative mechanical properties.</p><p>Finally, because muscles are responsible for loading spring systems with potential energy, muscle dynamics can affect elastic energy storage in a spring system. Although spring systems can circumvent the limits imposed by muscle via power amplification, they are not entirely independent from muscle dynamics. For example, if an organism has relatively low time to prepare and stretch the spring prior to the onset of movement, the limits of muscle power can dominate energy storage. To test the effects of muscle dynamics on spring loading, I implement a mathematical model that connects a Hookean spring model to a Hill-type muscle model, representing the muscle-tendon complex of the hindlimbs of American bullfrogs, in which the muscle dynamics are well understood and the duration of spring loading is low. I find that the measured spring constants of the tendons nearly maximize energy storage within the duration of in vivo spring loading. Additionally, the measured spring constants are lower than those predicted to produce maximal energy storage when infinite time is available for spring loading. Together, these results suggest that the spring constants of the tendons of American bullfrogs are tuned to maximize elastic energy for small durations of spring loading. This study highlights the importance of assessing muscle dynamics and their effect on energy storage when assessing the functional significance of spring constants.</p> / Dissertation

Apesar de vários estudos terem demonstrado que a presença de abelhas resulta em aumento da produtividade de culturas agrícolas, os mecanismos que determinam a eficácia da polinização em escalas espaciais mais amplas ainda são desconhecidos. Avaliamos a influência da composição e configuração da paisagem sobre a composição da comunidade de abelhas e a polinização do café (Coffea arábica). Nosso estudo foi realizado em uma das regiões cafeeiras mais importantes do Brasil, em nove paisagens compostas de cafezais e diferentes quantidades de remanescentes de Mata Atlântica. Utilizando experimentos de exclusão floral, avaliamos a polinização em 15 pés de café por paisagem. A eficiência da polinização foi medida através da contagem e pesagem dos frutos formados. Também coletamos e identificamos os visitantes florais. Nossas análises foram feitas no nível de paisagem, com 1 e 2 km de raio, e no nível do pé de café, com 300 m de raio em torno de cada árvore. Foram coletados 241 indivíduos de abelhas e identificadas um total de 22 espécies. A abelha Apis mellifera (Apini) foi a espécie mais abundante, seguida de Trigona spinipes (Meliponini). A abundância A. mellifera foi afetada pela composição da matriz na paisagem e a composição da comunidade de abelhas nativas mudou com a distância ao fragmento florestal mais próximo. A presença das abelhas, por sua vez, resultou em um aumento 28% na produção de frutos. A abundância de A. mellifera afetou positivamente a frutificação, enquanto a composição da comunidade de abelhas nativas afetou a frutificação de modo diferente no nível da paisagem e do pé de café. Nossos resultados indicam que a estrutura da paisagem afeta a composição da comunidade de visitantes florais e que as flores expostas às abelhas apresentam um aumento na frutificação. Embora nossos resultados não permitam separar claramente os mecanismos responsáveis pelo aumento observado na frutificação, nosso trabalho mostra que o serviço de polinização das abelhas pode ser afetado pela estrutura da paisagem. Estes resultados podem ser utilizados na conservação e planejamento agrícola a fim de maximizar a produção de culturas e, ao mesmo tempo, conservar a biodiversidade e o serviço de polinização. / Although several studies have shown that the presence of bees results in increased crop yields, the mechanisms that determine pollination effectiveness on broader spatial scales are still largely unknown. We evaluated the influence of landscape composition and configuration over bee community composition and coffee (Coffea Arabica) pollination. Our study was undertaken in one of the most important coffee-producing regions of Brazil, and comprised nine landscapes of sun coffee plantations surrounded by different amounts of Atlantic Forest remnants. Using floral exclusion experiments we evaluated pollination effectiveness in 15 coffee trees per landscape. Pollination effectiveness was measured by counting and weighing the fruit set. We also sampled the bees visiting coffee flowers. Our analyses were made at the landscape level, with 1 and 2 km radii, and at the coffee tree level, with 300 m radius around each tree. We collected 241 bee individuals and identified a total of 22 species. The honeybee Apis mellifera (Apini) was the most abundant species followed by Trigona spinipes (Meliponini). Honeybee abundance was affected by landscape matrix composition while native bee community composition changed with distance to the nearest forest fragment. The presence of bees resulted in an increase in coffee fruit set of 28%. A. mellifera abundance positively affected fruit set at both levels, while the composition of the native bee community affected fruit set differently at the landscape level than at the tree level. Landscape structure was found to affect the community composition of floral visitors, and coffee flowers exposed to bees showed an increase in fruit set compared to flowers excluded from pollinators. Although our results do not allow disentangling the mechanisms responsible for the observed increase in fruit set, our work shows that bee pollination services can be affected by landscape structure. These findings can be used in conservation and agricultural planning to maximize crop production while safeguarding biodiversity and the provision of pollination services.

Apesar de vários estudos terem demonstrado que a presença de abelhas resulta em aumento da produtividade de culturas agrícolas, os mecanismos que determinam a eficácia da polinização em escalas espaciais mais amplas ainda são desconhecidos. Avaliamos a influência da composição e configuração da paisagem sobre a composição da comunidade de abelhas e a polinização do café (Coffea arábica). Nosso estudo foi realizado em uma das regiões cafeeiras mais importantes do Brasil, em nove paisagens compostas de cafezais e diferentes quantidades de remanescentes de Mata Atlântica. Utilizando experimentos de exclusão floral, avaliamos a polinização em 15 pés de café por paisagem. A eficiência da polinização foi medida através da contagem e pesagem dos frutos formados. Também coletamos e identificamos os visitantes florais. Nossas análises foram feitas no nível de paisagem, com 1 e 2 km de raio, e no nível do pé de café, com 300 m de raio em torno de cada árvore. Foram coletados 241 indivíduos de abelhas e identificadas um total de 22 espécies. A abelha Apis mellifera (Apini) foi a espécie mais abundante, seguida de Trigona spinipes (Meliponini). A abundância A. mellifera foi afetada pela composição da matriz na paisagem e a composição da comunidade de abelhas nativas mudou com a distância ao fragmento florestal mais próximo. A presença das abelhas, por sua vez, resultou em um aumento 28% na produção de frutos. A abundância de A. mellifera afetou positivamente a frutificação, enquanto a composição da comunidade de abelhas nativas afetou a frutificação de modo diferente no nível da paisagem e do pé de café. Nossos resultados indicam que a estrutura da paisagem afeta a composição da comunidade de visitantes florais e que as flores expostas às abelhas apresentam um aumento na frutificação. Embora nossos resultados não permitam separar claramente os mecanismos responsáveis pelo aumento observado na frutificação, nosso trabalho mostra que o serviço de polinização das abelhas pode ser afetado pela estrutura da paisagem. Estes resultados podem ser utilizados na conservação e planejamento agrícola a fim de maximizar a produção de culturas e, ao mesmo tempo, conservar a biodiversidade e o serviço de polinização. / Although several studies have shown that the presence of bees results in increased crop yields, the mechanisms that determine pollination effectiveness on broader spatial scales are still largely unknown. We evaluated the influence of landscape composition and configuration over bee community composition and coffee (Coffea Arabica) pollination. Our study was undertaken in one of the most important coffee-producing regions of Brazil, and comprised nine landscapes of sun coffee plantations surrounded by different amounts of Atlantic Forest remnants. Using floral exclusion experiments we evaluated pollination effectiveness in 15 coffee trees per landscape. Pollination effectiveness was measured by counting and weighing the fruit set. We also sampled the bees visiting coffee flowers. Our analyses were made at the landscape level, with 1 and 2 km radii, and at the coffee tree level, with 300 m radius around each tree. We collected 241 bee individuals and identified a total of 22 species. The honeybee Apis mellifera (Apini) was the most abundant species followed by Trigona spinipes (Meliponini). Honeybee abundance was affected by landscape matrix composition while native bee community composition changed with distance to the nearest forest fragment. The presence of bees resulted in an increase in coffee fruit set of 28%. A. mellifera abundance positively affected fruit set at both levels, while the composition of the native bee community affected fruit set differently at the landscape level than at the tree level. Landscape structure was found to affect the community composition of floral visitors, and coffee flowers exposed to bees showed an increase in fruit set compared to flowers excluded from pollinators. Although our results do not allow disentangling the mechanisms responsible for the observed increase in fruit set, our work shows that bee pollination services can be affected by landscape structure. These findings can be used in conservation and agricultural planning to maximize crop production while safeguarding biodiversity and the provision of pollination services.

Ecological communities are most commonly structured by a mixture of bottom-up processes such as habitat or prey, competition within the same trophic level, and top-down forces from higher trophic levels. Carnivore guilds play a vital role in the broader ecological community by stabilizing or destabilizing food webs. Consequently, factors influencing the structure of carnivore guilds can be critical to patterns in ecosystems. Coyotes (Canis latrans), bobcats (Lynx rufus), gray foxes (Urocyon cinereoargenteus), raccoons (Procyon lotor), red foxes (Vulpes vulpes), and striped skunks (Mephitis mephitis) occur sympatrically throughout much of their geographic ranges in North America and overlap in resource use, indicating potential for interspecific interactions. Although much is known about space use, habitat relationships, and activity patterns of the individual species separately, little is known about factors that facilitate coexistence and how interactions within this guild influence distribution, activity, and survival of the smaller carnivores. For example, gray fox populations appear to have declined in Illinois since the early 1990s and it is unknown if the increase in bobcat and coyote populations during the same time period is the cause. I conducted a large-scale non-invasive carnivore survey using an occupancy modeling framework to quantify factors affecting the structure of this widely-occurring carnivore guild. I used baited remote cameras during 3-week surveys to detect carnivores at 1,118 camera-points in 357 2.6-km2 sections (clusters of 3-4 cameras/section) in the 16 southernmost counties of Illinois (16,058 km2) during January-April, 2008-2010. I collected microhabitat data at each camera-point and landscape-level habitat data for each camera-cluster. In a multi-stage approach, I used information-theoretic methods to develop and evaluate models for detection, species-specific habitat occupancy, multi-species co-occupancy, and multi-season (colonization and extinction) occupancy dynamics. I developed hypotheses for each species regarding the occupancy of areas based on anthropogenic features, prey availability, landscape complexity, and vegetative landcover. I used photographic data, Poisson regression, and mixed-model logistic regression to quantify temporal activity of carnivores in the study area and how interspecific factors influence temporal patterns of activity. Of the 102,711 photographs of endothermic animals I recorded photographs of bobcats (n = 412 photographs), coyotes (n = 1,397), gray foxes (n = 546), raccoons (n = 40,029), red foxes (n = 149) and striped skunks (n = 2,467). Bobcats were active primarily during crepuscular periods, and their activity was reduced with precipitation and higher temperatures. The probability of detecting bobcats at a camera point decreased after a bobcat photograph was recorded, suggesting avoidance of remote cameras. Across southern Illinois, bobcat occupancy at the camera-point and camera-cluster scale (point = 0.24 ± 0.04, cluster = 0.75 ± 0.06) was negatively influenced by anthropogenic features and infrastructure. Bobcats had high rates of colonization (0.86) and low rates of extinction (0.07) during the study, suggesting an expanding population, but agricultural land was less likely to be colonized. The number of coyote photographs decreased with increased temperature, but increased with previous coyote photographs, suggesting an attraction to bait in cold weather. Nearly all camera clusters were occupied by coyotes (cluster = 0.95 ± 0.03) during the entire study. At the camera-point scale, coyote occupancy (overall point = 0.58 ± 0.03) was higher in hardwood forest stands with open understories than in other habitats. Similar to coyotes, gray foxes were more likely to be photographed in cold weather and after a previous detection had occurred. However, gray fox occupancy was much lower (point = 0.13 ± 0.01, cluster = 0.29 ± 0.03) at all scales. At the camera-cluster scale, with a buffer-area size that represented 20% of the estimated home-range size of gray foxes, the species selected spatially-complex areas with high proportions of forest, and low proportions of grassland and agriculture land cover. Gray fox occupancy of camera clusters was positively related to anthropogenic features within 100% estimated home-range buffers. Collectively, the results suggest gray fox occupancy was greatest near, but not in, anthropogenic developments. Red foxes occupied a similar proportion of the study area as gray foxes (point = 0.12 ± 0.02, cluster = 0.26 ± 0.04), but were more closely associated with anthropogenic features. Indeed, at all three scales of red fox occupancy analysis, anthropogenic feature models received more support than other hypotheses. Camera-cluster extinction probabilities were higher for both gray foxes (0.57) and red foxes (0.35) than their colonization rates (gray fox = 0.16, red fox = 0.06), suggesting both species may be declining in southern Illinois. I recorded more striped skunk photographs in January and February (i.e., during the breeding period) than in March and April. Striped skunks occupied a large portion of the study area (point = 0.47 ± 0.01, cluster = 0.79 ± 0.03) and were associated primarily with anthropogenic features, especially if the features were surrounded by agricultural land and not forest. Raccoons were essentially ubiquitous within the study area, being photographed in 99% of camera clusters. In some instances, the presence of other carnivores appeared to be an important factor in the occupancy of the 4 smaller species, but in general, habitat models were more supported than co-occurrence models. Habitat had a stronger influence on the occupancy of gray foxes and red foxes than did the presence of bobcats. However, the level of red fox activity, represented by the number of photographs recorded in a camera cluster, was negatively correlated with bobcat activity. Gray fox occupancy and level of activity were reduced in camera-clusters occupied by coyotes, but were not related to bobcat occupancy. When not considering the presence of coyotes, gray foxes appeared to use camera points with fewer hardwood and more conifer trees, which was counter to previous findings. However, when adding the effect of coyote presence, gray fox point models indicated a positive relationship with hardwood stands. Therefore, gray foxes were more likely to occupy camera points in hardwood stands than conifer stands if coyotes were also present; suggesting that hardwood stands may enhance gray fox-coyote coexistence. The 2 fox species appeared to co-occur with each other at the camera-point scale more frequently than expected on the basis of their individual selection of habitat. Similarly, camera-point occupancy of red foxes was higher when coyotes were present. These apparent canid associations may be a response to locally-high prey abundance or an unmeasured habitat variable. Activity levels of raccoons, bobcats, and coyotes were all positively correlated. Collectively, my results suggest that although gray foxes and red foxes currently coexist with bobcats and coyotes, the foxes have reduced activity in the areas occupied by larger carnivores, especially when bobcats and coyotes are highly active. Further, hardwood stands may contain trees with structure that enhances tree-climbing by gray foxes, a behavior that probably facilitates coexistence with coyotes. Therefore, efforts to manage gray foxes should focus on maintaining and increasing the amount of mature oak-hickory forest, which presumably provides a suitable prey base and refugia from intraguild predation. Additionally, the varying results from different scales of analyses underscore the importance of considering multiple spatial scales in carnivore community studies.