The greater Everglades ecosystem, including Florida Bay, has undergone significant anthropogenic manipulation over the past century. These actions resulted in a series of ecologically undesirable events in the Everglades ecosystem, prompting passage of the Comprehensive Everglades Restoration Plan (CERP). It is necessary to understand the variability in, and relationship between, salinity and ecology to fully evaluate the potential effects of CERP on Florida Bay. A seven-year dataset on surface salinity along with eleven-year and eight-year datasets on mesozooplankton and planktivorous fish were analyzed. Overall, mean Bay-wide salinity varied from a low of 24.2 just after the passing of Hurricane Irene in October 1999 to a high of 41.8 near the end of a drought period in July 2001. Bay-wide mean salinity exhibited dramatic decreases, up to 0.5 per day, whereas increases in bay-wide salinity were slower, with a maximum rate of 0.1 per day. Meteorological phenomena, such as tropical cyclones and ENSO, dramatically altered the salinity patterns of Florida Bay on interannual time scales. There was a large degree of spatial heterogeneity in salinity between sub-regions of Florida Bay due to differing freshwater sources and geomorphology. Mesozooplankton abundance displayed interannual variability and a positive correlation with salinity. Both of these features were also closely correlated with abundance of the dominant planktivorous fish, Anchoa mitchilli, indicating the importance of top-down control. The hypersaline periods appear to provide a refuge from predators, allowing mesozooplankton to increase in abundance during periods of increased physiological stress. The interaction between mesozooplankton and A. mitchilli, along with its correlation to salinity, was further investigated through the development of a mechanistic model of the populations in Florida Bay. The model indicated predation alone was insufficient to control mesozooplankton populations; rather, it was necessary to incorporate density-dependence utilizing a logistic prey population. With both mechanisms the model was able to replicate the observed interannual variability pattern and positive correlation between mesozooplankton and salinity. A preliminary management scenario evaluation suggests a two to six-fold difference in A. mitchilli and mesozooplankton populations between targeted and general salinity reductions. This suggests alternative freshwater management scenarios could produce drastically different ecological consequences.

Contest outcomes are usually determined by differences in resource holding potential, the social histories of the combatants, and perceptions of resource value. One understudied aspect of gaining an advantage is the residency effect. Prior occupancy of a particular place can affect the knowledge and motivation of the resident. There could be a tactical advantage in knowing the terrain or an increased willingness to fight to maintain control of a familiar area. In this study we evaluated the importance of shelter residency effects relative to size differences between rusty crayfish (Orconectes rusticus) as potential competitors for access to shelter. The intensity of any residency effects was manipulated by altering the number of shelters in the arena. Our results suggest that any residency effect is very weak in this system, and if present may often be masked by the strong and pervasive influence on contest outcome of the relative body sizes of the contestants. We also found that both shelter number and crayfish size asymmetries had strong, independent effects on levels of aggression. Dominance, but not residency status, was a factor in shelter use.

Social insect colonies are complex systems with emergent properties that arise from the cooperation and interaction amongst individuals within colonies. By dividing reproduction and physical labor amongst them, individuals contribute to the growth and ecological success of their colonies, a success that is greater than individuals could achieve on their own. A key characteristic of social insects is a division of labor amongst workers that is determined primarily either by age, morphology, or dominance. Social insects are considered one of the most ecologically successful groups of organisms on earth. Colony life cycles include: 1) growth, in which workers are produced, 2) reproduction, in which queens and males with reproductive capabilities are produced, and 3) senescence. In life history theory, phenotypic plasticity (i.e. a change in phenotype in response to an environmental change), allows organisms to adjust and optimize fitness in response the change in environments. Central to life history theory is the idea that traits have costs and benefits. Using an energetics framework that considers the costs and benefits of traits contributes to our understanding as to why organisms exhibit the sets of traits that they have within their ecological environments. Using the annual bumble bee Bombus impatiens, my dissertation investigates the effects of resource availability on worker production and on the relative allocation of energy towards growth and reproduction within colonies. Bumble bees have a morphological division of labor and concomitantly, they show large intra-colony size variation amongst workers. Because body size is an important life history trait, I also examined the costs and benefits of producing various sized workers. Lastly, I examined the association among worker body size, metabolic rate (a measure of maintenance costs), and lifespan.

Long-term ecological research in deep lakes offers valuable insights into understanding changes in trophic states and organization of phytoplankton assemblages. Utilizing five decades of phytoplankton taxonomic trait data from pre-alpine Lake Constance, a confirmed negative relationship was found between phosphate and light affinity at the annual community trait level. Drawing inspiration from the stronger community-level tradeoff observed between the affinity for phosphate and light among phytoplankton species in Lake Constance, I hypothesized that resource acquisition traits, characterized by the half-saturation constants for nutrient-limited growth (Mi) and light-limited growth (Hi), should exhibit a negative trade-off mechanism at the community mean trait level, derived from the traits of the species in Lake Constance. The developed model was parametrized using empirical data from the lake. Intra- and inter-annual variation in environmental conditions were incorporated in the model by considering seasonal changes in temperature, light intensity, temperature-influenced exchange rates of the vertical water column, and decadal changes in nutrients in Lake Constance. Simulations reflected observed seasonal dominance patterns of phytoplankton species and predicted differences in relative abundance under varying nutrient supplies, aligning with resource limitation trends. Consistent with empirical observations, a negative relationship between light and phosphorous affinity is observed in the 60-year simulation of Lake Constance. The elucidation of such a trade-off mechanism is expected to facilitate the understanding of the coexistence of phytoplankton species in Lake Constance amidst the decadal changes in phosphorus loading by selecting for higher light affinity during eutrophic phases and higher phosphorus affinity during oligotrophic phases.

Aciphylla species (wild spaniard/speargrass) are an iconic component of the Australasian high country flora, but their reproductive system is enigmatic. They are insect-pollinated dioecious mast seeders (synchronous highly variable seed production), which seems maladaptive. The resource supply to pollinators is highly variable, yet dioecious plants are dependent on pollinators, and dioecious masting requires male and female plants to flower synchronously. Floral display in Aciphylla is relatively large, with tall inflorescences bearing thousands of flowers, suggesting that plants would not have the resources to produce such large stalks every year. But why do they have such huge inflorescences in the first place? I tested whether pollinator attraction is providing an economy of scale which favours intermittent production of very large inflorescences, by manipulating floral display size during a high-flowering year and measuring insect visitation rates and seed set (female reproductive success). Using space-for-time substitution and selective removal of male inflorescences, I also tested whether female seed set was affected by distance to flowering male plants (i.e. changes in local pollen availability) to see if flowering asynchrony would reduce pollination success. Bags were used to exclude pollination by insects and test for wind pollination, and hand pollination was done to test for pollen limitation. Insect surveys suggest that Aciphylla has a generalist pollination system (to avoid satiating a specialist pollinator during 'mast' years'). Male inflorescences received significantly more visits than females, and some seeds were set inside bags (although only 20-30%), suggesting wind pollination may occur at low levels. Seed set rate was higher for taller inflorescences with greater flowering length in A. aurea but tall inflorescences with excess flowers led to a decrease in seed set rates in A. scott-thomsonii. Hand pollination significantly increased seed set rates although these effects were not as large as expected (e.g. 10% increases from natural to hand-pollinated inflorescences were typical). There was no evidence for resource limitation in any species. Female plants in dense flowering populations had higher seed set rates, and individual floral display size in females was particularly important when females were 'isolated' from males. Insect visitation rates were generally higher on inflorescences with a larger floral display, suggesting that display size is important for pollinator attraction. Overall, these results suggest that the pollinator-attraction benefits of such a large floral display (at both the plant and population level) are possibly providing an economy of scale, although the relative effects are small.

Arctic ecosystems are sensitive to climate change and this biome is experiencing accelerated warming. Climate change in the arctic is projected to further alter precipitation and temperature patterns, which may influence land-water interactions in the future. Such changes have the potential to affect aquatic biofilm communities (i.e., algae, bacteria, and fungi) that form the base of riverine food webs, yet are sensitive to changes in thermal and light regimes, and are potentially limited by macronutrients like carbon (C), nitrogen (N) and phosphorus (P). This study investigated the patterns of resource limitation for autotrophic and heterotrophic biofilms in the Arctic using nutrient diffusing substrata (NDS) in a river network in northern Sweden (Miellajokka). Continuous NDS deployments (March until September) in a birch forest stream were combined with a spatial survey of nutrient limitation in late summer across 20 sites that encompassed a variety of nutrient, light, and temperature combinations. Results show that nutrient limitation of autotrophic processes was common during summer, but also that light inhibited algal growth in early season, and that temperature accelerated rates of activity throughout the growing season. By comparison, heterotrophic processes were less influenced by temperature, unless experimentally supplied with N and P. Alongside persistent N limitation, co-limitation by macronutrients (NP: autotrophic and heterotrophic biofilm, or CNP: heterotrophic biofilm) dominated the overall pattern of limitation over time and space. However, results from the spatial survey suggested that the identity of the primary limiting nutrient can change from N to P, based on differences in chemistry that arise from varying catchment features. As arctic studies are often conducted at individual sites during summer, they may miss shifts in the drivers of stream productivity that arise from variable nutrient, temperature, and light regimes. This study attempted to capture those changes and identify conditions where one might expect to see transitions in the relative importance of physical and chemical factors that limit biofilm development. These results also highlight the challenge of identifying the single most important limiting nutrient (e.g., N versus P) in streams and rivers across the Arctic, as I found that both nutrients could play this role within a single, relatively small drainage system.

Aciphylla species (wild spaniard/speargrass) are an iconic component of the Australasian high country flora, but their reproductive system is enigmatic. They are insect-pollinated dioecious mast seeders (synchronous highly variable seed production), which seems maladaptive. The resource supply to pollinators is highly variable, yet dioecious plants are dependent on pollinators, and dioecious masting requires male and female plants to flower synchronously. Floral display in Aciphylla is relatively large, with tall inflorescences bearing thousands of flowers, suggesting that plants would not have the resources to produce such large stalks every year. But why do they have such huge inflorescences in the first place? I tested whether pollinator attraction is providing an economy of scale which favours intermittent production of very large inflorescences, by manipulating floral display size during a high-flowering year and measuring insect visitation rates and seed set (female reproductive success). Using space-for-time substitution and selective removal of male inflorescences, I also tested whether female seed set was affected by distance to flowering male plants (i.e. changes in local pollen availability) to see if flowering asynchrony would reduce pollination success. Bags were used to exclude pollination by insects and test for wind pollination, and hand pollination was done to test for pollen limitation. Insect surveys suggest that Aciphylla has a generalist pollination system (to avoid satiating a specialist pollinator during 'mast' years'). Male inflorescences received significantly more visits than females, and some seeds were set inside bags (although only 20-30%), suggesting wind pollination may occur at low levels. Seed set rate was higher for taller inflorescences with greater flowering length in A. aurea but tall inflorescences with excess flowers led to a decrease in seed set rates in A. scott-thomsonii. Hand pollination significantly increased seed set rates although these effects were not as large as expected (e.g. 10% increases from natural to hand-pollinated inflorescences were typical). There was no evidence for resource limitation in any species. Female plants in dense flowering populations had higher seed set rates, and individual floral display size in females was particularly important when females were 'isolated' from males. Insect visitation rates were generally higher on inflorescences with a larger floral display, suggesting that display size is important for pollinator attraction. Overall, these results suggest that the pollinator-attraction benefits of such a large floral display (at both the plant and population level) are possibly providing an economy of scale, although the relative effects are small.

Identifying the resources that limit bee populations is essential both for bee conservation and pollination management in agroecosystems. Land-use change typically leads to decreased habitat availability for wild pollinators including loss of nesting habitat, which is an essential but often-overlooked resource for wild bees. Cavity-nesting bees, such as many Osmia spp. (Hymenoptera: Megachilidae), occupy holes in wood or reeds to build their nests; due to their nesting habits, they are frequently scarce in agricultural settings, although, under the right circumstances, these bees can be ideal pollinators of apple and other orchard crops. Artificial nesting structures (“bee hotels”, “trap nests”, or “nest boxes”) are used to study cavity-nesting bees and have been posited as solutions for promoting bee conservation. To evaluate the effects of additional nesting habitat on the local abundance of Osmia spp., and on bees more generally, artificial nesting structures for cavity-nesting bees were installed at 24 sites in apple orchards around Ottawa in 2021 and 2022. Each site had two treatments: one with nest boxes, and one without (control). Transect walks were conducted to measure overall bee contact (including contact by Osmia spp.) with apple blossoms and, after the end of apple bloom, with flowers in the undergrowth and/or in shrubs. Numbers of apple buds and developing fruit were also recorded. Osmia spp. and overall bee numbers were both significantly higher in the treatment with nest boxes (44% and 15% higher, respectively, in 2021, and 113% and 47% higher, respectively, in 2022); however, there was no difference in fruit set (apple count/bud count) between the two treatments. Thus, nest boxes seem to locally increase Osmia spp. numbers as well as total bee numbers, but they have no apparent effect on apple yield, likely because apple production was not pollinator limited in the years of this study. These findings suggest that bee populations in apple orchards are limited by nesting resources, which has important implications for orchard management practices and bee conservation policy.

<p>Temporal and spatial variations of pelagic microorganisms in the northern Baltic Sea were studied, as well as factors influencing their abundance and growth rates. Three main questions were asked 1) How does increased productivity influence the structure of the microbial food web? 2) Does predation limitation vary between trophic levels? 3) What is the relative importance of resource and predation limitation at different trophic levels?</p><p>A field study in the northern Baltic Sea showed that dominating protozoa, flagellates and ciliates, increased with increasing primary productivity from north to south. Furthermore, relatively small protozoan cells dominated in the low productive north, while larger cells became more dominant in the south. The relationship between plankton size structure and productivity was further studied in an experimental system. In agreement with present theories regarding nutrient status of pelagic food webs, increased productivity caused a lengthening of the food chain as well as a change in plankton size structure. While microplankton dominated in nutrient rich treatments pico- and nanoplankton dominated during nutrient poor treament. The flagellate community was dominated by a potentially mixotroph, <i>Chrysochromulina</i> sp., at low nutrient concentrations. To our knowledge this is the first experimental study showing that <i>Chrysochromulina</i> sp. in resemblance with other mixotrophs is favoured by nutrient poor conditions compared to strict autotrophs and heterotrophs.</p><p>During a stratified summer period autotrophic microorganisms in the northern Baltic Sea did not respond to removal of potential predators, indicating that they were primarily limited by inorganic nutrients. An exception was small eucaryotic picoplankton that showed a large response to predator removal. Among the heterotrophic microorganisms direct effect of predation seemed to increase from ciliates, heterotrophic bacteria, small heterotrophic flagellates, medium flagellates to large flagellates. No quick indirect effect was observed, but after four days trophic cascades were detected.</p><p>The relative importance of resource and predation limitation was studied among heterotrophic bacteria, flagellates and ciliates in the northern Baltic Sea. For all these groups, resource limitation seemed to prevail during the summer period. The results also indicated that the relative importance of predation increased with the productivity of the system. To our knowledge there are no earlier measurements on the relative importance of resource and predation limitation for micoorganisms in the pelagic environment.</p>

<p>Heterotrophic microorganisms are important for the flow of carbon and nutrients in the sea. Bacteria, nanoflagellates and ciliates are relevant components of the pelagic food web. In order to be able to predict the outcome of e.g. eutrophication or climate change we need to know how the different components of the pelagic food web are regulated. With the focus on the northern Baltic Sea food web, this thesis deals with limitation and control of heterotrophic protists, the effect of resource heterogeneity on food web efficiency and diversity of nanoflagellates.</p><p>In-situ microcosm experiments showed that the net growth of heterotrophic flagellates were resource limited throughout the year. Field data confirmed that the abundance of flagellates was bottom-up controlled. Furthermore, field data also showed that the annual average biomass of protists, flagellates and ciliates increased with primary productivity. On a smaller seasonal scale temperature and bacterial biomass were able to explain most of the variation in flagellate biovolume. The temporal variation in ciliate biovolume could not be explained by any bottom-up factors like bacterial biomass, flagellate biomass or chlorophyll a. This and an in-situ microcosm experiment implied that the seasonal dynamics of ciliates were more regulated by predators like mesozooplankton.</p><p>The food web efficiency i.e. how much of production at the resource level is converted to production at the top trophic level, may be affected by specific size or type of resource. Indoor mesocosms revealed that the food web efficiency was 11 times lower when heterotrophic bacteria dominated basal production instead of nano- and micro-sized phytoplankton. This was due to a lengthening of the food web when pico-sized bacteria constituted the main resource.</p><p>The PCR-DGGE molecular biological method was used to study the diversity of heterotrophic or mixotrophic chrysomonads. The focus was set on chrysomonads due to their relatively large contribution to the nanoflagellate community. Group-specific PCR primers were optimized for the target group. A field survey in the northern Baltic Sea showed that a handful of chrysomonad sequences were present throughout the year. Significantly more chrysomonads were recorded in the basin with higher primary productive and salinity. In total 15-16 different chrysomonad sequences were recorded. Most of them matched uncultured chrysomonad clones.</p>