PRISM :: Browsing by Author "Post, John R."

Browsing by Author "Post, John R."

Now showing 1 - 20 of 23

Open Access
Climate warming and northern lake trout (salvelinus namaycush): energetics, production and conservation under climate warming
(2004) Mackenzie-Grieve, Jody L.; Post, John R.
Open Access
Competition of a nectar-robbing bumble bee with a legitimate forager and its consequences for female reproductive success of Fuchsia magellanica
(2018-09-14) Rosenberger, Nick Martin; Harder, Lawrence D.; Aizen, Marcelo A.; Post, John R.; Cartar, Ralph Victor
In pollination systems, competition can cause floral visitors to adopt behaviors at high densities that may antagonize floral reproduction. I evaluated the density-dependence of nectar robbing by a short-tongued bumble bee, Bombus terrestris, and its consequences for both competition with an effective pollinator, Bombus dahlbomii, and female reproduction by the shrub Fuchsia magellanica. Daily sampling documented an abrupt, density-dependent transition from no robbing to almost exclusive robbing by B. terrestris. Robbing facilitated flower visitation by B. terrestris while aggravating its competition with B. dahlbomii. Nectar depletion and flower damage caused by robbing reduced pollen receipt by F. magellanica flowers, depressed pollen-tube success and reduced fruit quantity and quality. This research demonstrates that by modifying floral conditions to suit their foraging needs nectar robbers can gain a competitive advantage over effective pollinators, possibly promoting their long-term decline, while also compromising reproduction by the affected plant species.
Open Access
Consequences and trade-offs of variation in growth rate in juvenile animals
(2023-10-26) Mogensen, Stephanie; Post, John R.; Harder, Lawrence; Syme, Douglas
Growth is a crucial life history trait in juvenile organisms that can influence survival and adult reproductive capacity. In this thesis, I investigate how variation in growth and its trade-offs with other traits affect important life-history outcomes, both across and within species. I first used a meta-analytic approach to assess the magnitude and direction of key trade-offs (immune function, structural function, starvation resistance, and predation mortality) across animal taxa. Trade-offs are not ubiquitous and vary in both magnitude and direction. Although taxon-specific differences are apparent, for most trade-offs the lack of coverage across species constrained my assessment of taxon-specific patterns. I then assessed the extent to which intra-population variability in growth rate was coupled to behavioural and physiological differences and whether these differences were grouped into behavioural syndromes. I assessed this question using an experiment with a single strain of young-of-the-year rainbow trout (Oncorhynchus mykiss). I did not find evidence of behavioural syndromes in the assessed behavioural traits. In addition, growth rate did not vary with the measured traits during the experiment. Finally, I used an individual-based model to assess the importance of inherent growth rate for shaping end-of-growing-season distributions of growth in teleost fish, using basic assumptions about predation risk and density dependence. In and of themselves, realistic distributions of growth did not convey much benefit to faster growing fish. However, in the presence of even modest initial variation in size (particularly if that variation is correlated with growth rates) the benefits of fast growth increase. These findings have important implications for the life-history of juvenile animals.
Open Access
Consequences of Spatial Exploitation in Complex Adaptive Social-Ecological Systems: Managing for Sustainable Freshwater Fisheries
(2018-01-23) Wilson, Kyle Logan; Post, John R.; Cartar, Ralph Victor; Galpern, Paul; Pope, Kevin L.; McDermid, Gregory J.
Freshwater fisheries are complex adaptive social-ecological systems structured by coupled feedbacks between fish and people (e.g., anglers). For example, fishing quality influences angler site choices, and anglers reciprocally impact fish populations at chosen sites through size-selective harvest, thus demonstrating how feedbacks between fish and anglers permeate through whole ecosystems. Overexploitation increasingly threatens these fisheries challenging management with finding robust solutions to sustain these important resources. Yet, we often lack generalization on the social and ecological processes that limit system resilience. This thesis attempts to gain some of that generalization by exploring how whole-system outcomes emerge from cross-scale interactions between fish and anglers. To do this, I used a combination of theory-driven models and empirical case studies on the rainbow trout Oncorhynchus mykiss and lake trout Salvelinus namaycush fisheries of British Columbia and Yukon to find the landscape, social, and ecological consequences of spatial exploitation on these complex systems. In general, I found that system outcomes, like sustainable or overexploited fisheries, strongly depended on both landscape contexts and the strength of social-ecological feedbacks. In doing so, I was able to generalize the kinds of freshwater landscapes at risk of overexploitation. Next, I found that spatial exploitation patterns had cascading effects across freshwater landscapes by influencing ecological processes like the demographic tradeoff between fish body size and abundance or variation in fish life histories. Additionally, I found that angler site choices were influenced by multiple characteristics, like trip contexts, travel costs and fishing quality, allowing me to better identify potential angler impacts on fish populations. I then integrated these spatial, social, and ecological processes to evaluate the kinds of policies that may improve management of the lake trout fishery and found that conservative regulations better balanced both social and ecological objectives. The results of these studies can help inform management on the feedbacks and processes that drive fishery dynamics, how a landscape of fish populations may respond to spatial exploitation, the kinds of landscapes (and populations within those landscapes) at risk of overexploitation, and the efficacy of regulations that target key spatial, social, and ecological processes to sustain freshwater fisheries.
Open Access
Considering multiple anthropogenic threats in the context of natural variability: Ecological processes in a regulated riverine ecosystem
(Wiley, 2020-06-09) Sinnatamby, R. Niloshini; Mayer, Bernhard; Kruk, Mary K.; Rood, Stewart B.; Farineau, Anne; Post, John R.
Rivers are among the most altered environments globally, but identifying which threats are responsible for observed biotic and abiotic changes is complicated by natural drivers of variation. The Bow River, Canada provides an ideal model to resolve these influences and explore spatial relationships. It originates from pristine Rocky Mountain headwaters and is subsequently impacted by typical human alterations: damming, municipal channelization and effluent release, and agricultural impacts (nutrient enrichment and water withdrawal for irrigation). By coordinating studies of the Bow River's biota, we demonstrate how threat–driver interactions depend on season and the abiotic factor and biotic community or species of interest. We conclude that impact severity and riverine recovery depend on the threat magnitude, its longitudinal position and proximity to other threats and natural drivers. We found that river regulation, water extraction and bank armouring interact to limit geomorphic processes resulting in depleted riparian woodlands and numbers of fish species, though a large, undammed tributary nearby allows quick recovery downstream. We highlight the implications of the longitudinal position of the threats because cold-water fish species are disproportionately impacted through the area where the human impacts on the Bow River overlap. We illustrate how the interactions between flow, nutrients and temperature lead to macrophyte- or algae-dominated communities and associated shifts in fish composition and biomass. Finally, we applied our increased understanding of ecological riverine processes to conclude that management techniques such as flushing flows or functional environmental flows are likely to have only minimal or conditional success in the Bow River.
Open Access
Demographic and life-history responses of an over-exploited bull trout (Salvelinus confluentus) population to zero harvest regulations.
(2005) Johnston, Fiona D.; Post, John R.
The study of an over-exploited bull trout (Salvelinus confluentus) population after the introduction of zero harvest regulations, demonstrated the ability of this population to recover from overharvest. Adult abundance increased 25 fold over a decade and approached a carrying capacity, providing an opportunity to characterize the demographics and life history traits of a threatened species. Density-dependent changes in survival, growth, maturation and spawning frequency were observed. Density-dependent survival of juvenile bull trout prior to age-1 was found to be the primary factor limiting further population growth. However, density-dependent adult survival and changes in maturation and fecundity may also have influenced population dynamics. Density-dependent changes in life history characteristics also provided insight into how energetic tradeoffs between growth and reproduction differ between the genders. The importance of all life stages in the management of species with complex life histories was demonstrated in this study.
Open Access
Direct and indirect effects of interference competition in size-structured rainbow trout (Oncorhynchus mykiss) populations
(1997) Landry, Francois; Post, John R.
Open Access
Evironmental and genotypic influences on body size and survival of juvenile rainbow trout in seasonal ecosystems
(2011) Lea, Ellen Victoria; Post, John R.
Open Access
Frost Heave as the Main Process Defining Natural Unforested Areas below a Temperature Treeline
(2018-05-22) Toloui-Semnani, Moujan; Johnson, Edward A.; Martine, Yvonne Elizabeth; Post, John R.
Jumping Pound is a treeless ridge, with a SE-NW strike of faults and thrust sheets in the Foothills of the Canadian Rockies, stretched more or less perpendicular to the direction of the winter wind that transports the snow off the ridge. This thesis examines the occurrence of frost-heave as well as the yearly frost-heave temporal window in Jumping Pound ridge. Seeds from the trees in the forested adjacent SW slope are dispersed at the end of fall and travel primarily toward the direction of the dominant wind into the ridge crest where they overwinter. This thesis demonstrates that in the growing season, there is sufficient regolith moisture for germination. However, in the following fall and winter the seedlings are uprooted due to constant regolith movement. The snowless, cold soil surface temperatures create a steep gradient of temperature at lower depths, driving the process of frost-heave. The driving mechanisms for the frost heave in this region are identified and analyzed.
Open Access
Habitat Structures Rainbow Trout Population Dynamics Across Spatial Scales
(2018-12-19) Cantin, Ariane; Post, John R.; Bender, Darren J.; Askey, Paul J.
Density-dependent processes play an important role in structuring population dynamics – as the number of organisms within a set area increases, population vital rates and life history traits will also change arising from increased competition for limited food and space. In this thesis I explore how variation in the quantity of habitat available impacts size-structured animal populations using lake-dwelling rainbow trout (Oncorhynchus mykiss). First, I developed hypotheses on the biological processes by which habitat impacts population dynamics using a multi-habitat age-structured population model. This theoretical model showed that habitat limitations at any life stage can bottleneck the population and impact its dynamics, but that the timing of regulation influences population outcomes. Limited habitat in early life led to high early mortality, resulting in low overall population density of larger fish, while limited habitat in adult life led to high early survival and a high density of stunted fish populations. I then compared the model predictions to empirical data from 39 wild rainbow trout populations and to results of a harvest experiment. The field results corroborated the model predictions and showed that lakes with a higher early (stream) to late (lake) life stage habitat ratio presented higher number of recruits, later age at maturity and a smaller maximum size than lakes in which stream habitat was limiting. The density manipulation also supported the model predictions as the lake with the lowest habitat ratio presented the lowest compensatory reserve and showed a density-dependent growth response to harvest. Finally, I used the knowledge acquired at the lake-scale to predict rainbow trout production at the landscape-scale. I developed a methodology that describes rainbow trout distribution based on stream network characteristics and connectivity. Then I used a landscape-scale proxy of stream habitat availability, stream order, and lake area to predict stream to lake habitat ratio and infer population dynamics. I combined this landscape-scale production information with recreational fishing demand to identify regions more prone to being impacted by overfishing or habitat perturbations. My research details how local habitat availability influences fish populations and can be used to predict population dynamics across a landscape of lakes providing a valuable tool to managers.
Open Access
In Search of Physical Explanation of Co-development of Plants and Landscape
(2018-06-11) Ding, Junyan; Johnson, Edward Arnold; Martin, Yvonne E.; Post, John R.; Yeung, Edward C.
The physical structure of the landscape is the subject of geology and geomorphology based on physical and chemical principles of material and energy movement under climatic and tectonic forces. The biological inhabitants of this physical landscape, area subject rooted in biological, ecological and evolutionary theories, but the primary focus has been on how the physical environment shaped life on land. It is only recently that we begin to recognize the evolution of the abiotic and biotic worlds are intimately intertwined via complex feedback loops of physical hydrological, and biological pathways, and at a range of spatial and temporal scales. In my thesis, I addressed a subset of these complex interactions: the coevolution of the landform organized as hills-valleys and the plants that occupy the different landscape positions. I used an integrated modeling approach that captures the first-order, well recognized, and mechanistic links to explore feedbacks and to shed new lights on the coupled evolution of the landform and the plants. The landscape is a battleground of tectonics (mountain building) vs. denudation (weathering/erosion that destroy the mountains). The landscape structure, e.g. hillslope shape/size and stream density, depends on the relative dominance of diffusive type erosion (e.g., soil creep and shallow landslides) vs. the advective type (e.g., runoff erosion and channel incision). Climate exerts strong regulation on the dominance erosion processes with increasing rainfall intensity resulting in more advective type erosion landform. The result is a landscape evolution model, with three levels of diffusive vs. advective dominances. Diffusion dominated landscapes tend to have wider/longer hillslopes, more rounded hilltops, and fewer streams (i.e., less dissected). This will have consequences to water movement on land and the resulting soil hydrology. These distinct landforms lead to distinct patterns of soil hydrology. A simple and powerful way to characterize soil hydrology is the Topographic Index (TI) a proxy of equilibrium of water table depth, defined for each point in a watershed as the ratio of drainage area above the point (proxy of rain caught upstream) and local slope at the point (proxy for outflow). Using TI, I translated the three landscape structures above into three hydrologic structures. Higher TI occurs in flat valley bottoms with a large slope above it, low TI on ridge tops, and intermediate TI on hillslopes. These patterns will influence the distribution of plants genetically adapted to different soil moisture conditions. Plants have evolved genetic traits to survive and optimize their performance in given environmental niches. Soil hydrology is a powerful discriminator of plants according to their drought and waterlogging tolerance. To a first order watershed, I represented plants in three tolerance curves: hydric (waterlogging tolerant), xeric (drought tolerant), and mesic (moderate moisture tolerance), each with a preferred distribution along the TI index. This allows me to connect hydrology to plant distribution for each tolerance type. Each plant type occupies a distinct hydrologic position in all three landscapes, but more mesic plants are found in diffusive landscapes. Water and nutrients move from soils to roots, stems, shoots, leaves, and to the atmosphere through a series of resistant flow paths. Plant hydraulic traits reflect evolutionary trade-offs between efficiency and safety. For leaves, denser veins, lower stomatal resistance, wider and larger leaves all decrease leaf hydraulic resistance and increase net primary productivity (NPP), but the same traits also increase risks of embolism and leaf death. I developed a leaf NPP optimization model to explore the joint adjustment of several leaf traits to different levels of soil water stress. It offered a theoretical framework to explain leaf traits seen across hydrologic gradients; e.g., narrow-leaved species tend to occupy xeric habitats on hilltops, and species of large and wide leaves occupy hydric habitats in valleys. In this thesis, by using aboveground traits, I provided a mechanistic connection between abundance and distribution of plant functional groups (PFG) on landscape and the geomorphic processes that created it. It sets the foundation for further investigating how landscape composition of PFGs can regulate topography and hillslope hydrology under the regulation of changing climate thus close the feedback cycle. A missing component here is a mechanistic expressing of soil water-root interaction that creates the dynamic rooting structure across landscape. This should be the focus of future study.
Open Access
Linking ecology and angler dynamics for optimal management of a spatially-structured recreational fishery
(2007) Askey, Paul J.; Post, John R.
Open Access
Locomotor biomechanics and behaviour in the ocellate river stingray
(2020-04-22) Seamone, Scott G.; Syme, Douglas A.; Bertram, John Edward Arthur; Post, John R.; Standen, Emily M.; MacInnis, Martin J.
Stingrays are fishes that are dorsoventrally flattened in the same plane as the substrate, similar to a hydrofoil, with long thin tails that have an absent or reduced caudal fin, and anterior to the pelvic girdle the longitudinal body axis is relatively rigid. These characteristics would appear to constrain or preclude many of the locomotor behaviours that are employed by fishes that typically swim via undulations of the longitudinal body axis and caudal fin, and which tend to dominate descriptions of fish swimming in the literature. In contrast, stingrays exhibit a variety of locomotor behaviours powered via enlarged and flexible pectoral fins that wrap around the body and head (i.e. the pectoral disc), yet an in-depth understanding of the biomechanical mechanisms that permit these behaviours has not been formed. Potamotrygon motoro, the ocellate river stingray, lives along the substrate in a benthic environment, and possesses an extremely rounded pectoral disc, from the dorsal view. It is used in these studies to represent the flattened shaped, low profile, and relatively rounded disc common to benthic stingrays, to better understand how these animals achieve different locomotor behaviours. The studies described in this thesis offer insight into how the shape of P. motoro is employed to accomplish behaviours exhibited by many benthic stingrays such as fast-start maneuverability, station holding and burying. Chapter 1 reviews our current and somewhat limited understanding of how shape impacts swimming behaviour in fishes that are flattened in the same plane as the substrate, described here as foil fishes, and explores relationships of shape and ecology observed in stingrays. Chapter 2 describes studies where video analysis was used to reveal that flexibility in the movements of the pectoral fins around the flattened and nearly symmetrical disc shape permits fast-start escape in all directions across the benthic plane with similar performance, regardless of initial orientation of the fish, which appears to challenge the conventional description of maneuverability typically used to evaluate fishes. Chapter 3 describes studies where recordings of changes of pressure beneath the pectoral disc, and video observations of movements of dye, are used to argue that stingrays can exercise movements of the body and fins to flush water from beneath the ventral surface to create and maintain a seal between the pectoral disc and benthos, to achieve suction pressures via a vacuum and possibly Stefan adhesion, that can resist an upwards displacing force to hold station along the benthos. Chapter 4 describes studies that used video analysis and particle image velocimetry to explain how rapid and vigorous movements of the body and fins in stingrays fluidize and suspend vortices of sediment below the ventral surface of the fins, which are then directed up and over onto the dorsal surface to cover the fish with sediment and effect burying, and that the fish appear to direct and control these vortices to modulate the extent and pattern of burying. Chapter 5 describes studies that used time-lapse photography and video analysis to reveal that in the presence of sediments that differ in grain size, stingrays mostly choose to inhabit and bury in finer grained sediments when threatened, and this appears to reflect these fishes being more effective at burying in finer sediments, such that the rate of coverage of the dorsal surface is faster for a given finbeat speed. Chapter 6 provides a summary of what has been revealed by these studies, conclusions and future directions. These studies advance our understanding of how a flattened and rounded disc shape in P. motoro might find success in a benthic environment, and might inspire engineers interested in fish for the design of underwater robotics.
Open Access
Mapping shrub biomass in a boreal continental fen
(2019-01-24) He, Annie; McDermid, Gregory J.; Post, John R.; Strack, Maria
Biomass estimation is a heavily explored topic in the literature, as biomass information can provide valuable insight into understanding an ecosystem’s health. However, few studies exist on quantifying aboveground biomass (AGB) in peatlands. This thesis summarizes how allometric equations and unmanned aerial vehicles (UAV) can be used to map AGB across a 2-hectare peatland site. Prior to using UAVs to measure AGB, accurate field measurements are required to calibrate and validate the UAV-AGB model. We developed allometric equations for three dominant shrub genera found in boreal peatlands and found that equations based on shrub genus were not significantly different from a pooled equation of all shrub genera. The UAV study revealed that UAV-derived volume was the best predictor of AGB (R2=0.885) and was subsequently used as the dependent variable for our AGB model. This thesis reports the findings revealed through the process of estimating AGB using allometric equations and UAVs.
Open Access
Migration, diel movement and habitat use of juvenile bull trout (salvenlinus confluentus)
(2003) Mushens, Craig, J.; Post, John R.
Open Access
Physical and bioenergetic approaches for modeling instream habitat quality of drift-feeding fish
(2012) Laliberte, Jacson Jonathon; Post, John R.
Physical fish habitat models have been criticized for poor biological realism and a failure to relate with population metrics. I modeled channel hydraulics using a twodimensional hydrodynamic model and varied fish size, invertebrate drift density, and temperature to compare longitudinal and seasonal trends in physical and bioenergetic fish habitat quality in two idealized stream systems differing in hydraulic geometry (gradient, depth, and velocity) and a natural fourth-order stream, respectively. In the idealized streams, physical and bioenergetic habitat quality increased asymptotically with stream size for all fish sizes, while peaking in adult trout due to the positive and negative effects of increased drift densities and temperatures, respectively. Although similarities between fish sizes were observed, significant correlations between seasonal physical and bioenergetic habitat quality for all fish sizes in the natural stream were not detected. Revisions to the bioenergetic model framework and the inclusion of temperature-dependent consumption may improve model predictions.
Open Access
Population consequences of behaviourally-mediated tradeoffs between growth and mortality in age-0 rainbow trout (oncorhynchus mykiss) cohorts
(2003) Biro, Peter A.; Post, John R.
Open Access
Recruitment dynamics in bull trout (salvelinus confluentus): linking theory and data to species management
(2000) Paul, Andrew J.; Post, John R.
Open Access
Spatial distributions of 33 fish species in the mainstem rivers of the south Saskatchewan river basin under changing thermal regimes
(2009) Robins, Geneva Lin; Post, John R.
The impact of climate change on longitudinal distributions of 33 fish species in the mainstem rivers of the South Saskatchewan River Basin was assessed. Mean July water temperature was the most common variable in multivariate logistic regression models of present-day species' presence followed by slope, nitrate-nitrite, phosphate, turbidity, and channel width. Most water control barriers in the rivers cause an abrupt change in the presence of at least one fish species. Most species' associations were positive, but may not be due to causal relationships. Water temperatures were estimated using a downscaled model of air and water temperatures using climate scenarios from CRCM 3.5 for 2040 and 2080. Local extinctions were predicted for five species and major habitat losses were predicted for three more species under future climates. Substantial expansions in ranges were predicted for eight warm-adapted species and one cooladapted species. Water control barriers altered future distributions of six species.
Open Access
Testing for Unimodal Relationships between Diversity, Disturbance, and Productivity
(2020-01-30) Tessier, Rachel Suzanne; Fox, Jeremy W.; Post, John R.; Yeaman, Sam; Galpern, Paul
Many unimodal ecological theories, though implemented into resource management, remain contentious in the literature and are often analyzed with inappropriate techniques, namely quadratic regressions. Two of these theories, the intermediate disturbance and productivity hypotheses, are assessed as case studies to explore the hypotheses themselves, characterize the conditions in which various relationship shapes take place, and underscore the disparities between the analytical techniques that can be used to detect them. The power of various traditional and novel techniques used to distinguish between unimodal versus monotonic relationships is simulated to conclusively determine which are the most appropriate. The two-lines test has been found to display the most powerful detection of unimodal shapes and breakpoints regressions to have the most power to detect monotonic, concave shapes. According to these tests, diversity-disturbance and diversity-productivity relationships display primarily peaked shapes, dependent on various characteristics. The quadratic regression, even when paired with the Mitchell-Olds & Shaw test, is an inefficient and inappropriate test for unimodality. While the intermediate disturbance and productivity hypotheses are too simplistic, misused, and misunderstood, the findings within this thesis warrant further exploration into the scenarios in which they occur and can be implemented. Future analyses of unimodal hypotheses should consider the recommendations of technique usage within this thesis.