Life history theory assumes that correlations among fitness-related life history traits should be negative among individuals, reflecting resource allocation constraints among traits such as growth and reproduction. These traits trade off because they cannot be simultaneously maximized in individuals facing finite resource acquisition. Positive correlations among traits that are expected to be negative (e.g. between energetically costly traits) have been regularly observed, however, and have usually been ascribed to genetic or resource acquisition differences. In the freshwater zooplankton Cladoceran Daphnia, positive correlations have been particularly well documented even when genetic and environmental variation have been controlled. The sign of these correlations represent a problem for life history theory, which is underpinned by the notion of universal and unavoidable costs associated with investing in a given trait. It has been suggested, however, that costs vary with environment and thus can change the sign of a correlation. A change in correlation sign over an environmental gradient may indicate that the assumed universality of costs and constraints are not as universal as expected by life history theory. Few life history experiments have examined traits in multiple environments, and fewer have done so while controlling resource acquisition and genetic variation. Here I ask whether the positive genetic correlations among somatic growth rate, egg production rate, and longevity are present in the face of equal ingestion, clonal individuals, and a finely resolved gradient of food quality, an environmental factor that frequently affects Daphnia. I partition trait covariation into genetic and residual, or environmental, sources. All resulting genetic correlations were non-significant. Residual correlations trended from significantly positive to negative between longevity and growth rate and remained near zero between longevity and egg rate. The residual correlation between growth and reproduction, two expensive traits, displayed significantly positive residual correlations across the food quality gradient remained significantly positive. Given the experimental controls in place, I suggest that differences in individual ontogeny may give rise to differential resource utilization or assimilation efficiency. This may be a mechanism for differential resource acquisition in the absence of ingestion variation. Additionally, the different ways genetic and residual correlations change over an environmental gradient may provide insight on one manner by which genotypes might coexist and provide a candidate explanation for the second paradox of the plankton. / Thesis (Master, Biology) -- Queen's University, 2014-03-31 07:01:21.774

In light of increasing harmful algal blooms and the need to protect human health and aquatic resources, proactive management approaches merit further study. For this purpose I conducted field samplings to characterize plankton community composition and laboratory experiments to test some approaches to new management schemes in the lower Rincon Delta. On site measurements and microscopic analysis showed that environmental parameters and plankton community composition varied considerably among sampling stations and sampling dates. A recent modeling study suggested that manipulation of freshwater inflow to estuaries might prevent phytoplankton blooms and enhance secondary productivity. To test this theory I conducted three semi-continuous design and flow-through incubation design experiments using natural plankton assemblages. I investigated the effect of two different pulsing regimes of inflow and nutrient loading on zooplankton densities, and phytoplankton biomass and diversity. Despite differences in zooplankton structure and phytoplankton community composition between the two experiment designs, the results confirmed that pulsed inflows might alter plankton dynamics. My findings showed that 3-day pulse treatments consistently supported greater zooplankton densities and higher phytoplankton species diversity when compared to 1-day pulse treatments. In addition, accumulation of phytoplankton biovolume remained low during 3-day pulse treatments. Differences in zooplankton performance between 3-day pulse and 1-day pulse inflow treatments were likely due to the ability of phytoplankton to uptake and store greater amounts of nutrients under conditions of 3-day pulse inflow. This resulted in food of higher quality for zooplankton, and might have supported greater zooplankton population growth rates. Additionally, in an attempt to understand the mechanisms leading to high biodiversity in aquatic ecosystems, I built a resource-storage model and studied the effects of resource-storage on competition of multiple phytoplankton species on multiple abiotic resources. I compared this model with a well-established multi-species competition model. My results showed that for certain species combinations a resource-storage-based model can generate dissimilar outcomes when compared to a model without resource-storage.

In light of increasing harmful algal blooms and the need to protect human health and aquatic resources, proactive management approaches merit further study. For this purpose I conducted field samplings to characterize plankton community composition and laboratory experiments to test some approaches to new management schemes in the lower Rincon Delta. On site measurements and microscopic analysis showed that environmental parameters and plankton community composition varied considerably among sampling stations and sampling dates. A recent modeling study suggested that manipulation of freshwater inflow to estuaries might prevent phytoplankton blooms and enhance secondary productivity. To test this theory I conducted three semi-continuous design and flow-through incubation design experiments using natural plankton assemblages. I investigated the effect of two different pulsing regimes of inflow and nutrient loading on zooplankton densities, and phytoplankton biomass and diversity. Despite differences in zooplankton structure and phytoplankton community composition between the two experiment designs, the results confirmed that pulsed inflows might alter plankton dynamics. My findings showed that 3-day pulse treatments consistently supported greater zooplankton densities and higher phytoplankton species diversity when compared to 1-day pulse treatments. In addition, accumulation of phytoplankton biovolume remained low during 3-day pulse treatments. Differences in zooplankton performance between 3-day pulse and 1-day pulse inflow treatments were likely due to the ability of phytoplankton to uptake and store greater amounts of nutrients under conditions of 3-day pulse inflow. This resulted in food of higher quality for zooplankton, and might have supported greater zooplankton population growth rates. Additionally, in an attempt to understand the mechanisms leading to high biodiversity in aquatic ecosystems, I built a resource-storage model and studied the effects of resource-storage on competition of multiple phytoplankton species on multiple abiotic resources. I compared this model with a well-established multi-species competition model. My results showed that for certain species combinations a resource-storage-based model can generate dissimilar outcomes when compared to a model without resource-storage.