Population-level dynamics are affected by temporal variation in individual vital rates of survival and reproduction, which are in turn influenced by habitat-specific processes. Variation in habitat quality within a population’s range can drive movement of individuals between different areas, and so there may be a relationship between variation in vital rates and spatial heterogeneity in population growth (λ). I investigated this relationship for the feral horses (Equus ferus caballus) of Sable Island, Nova Scotia, Canada, from 2008−2010. The horses (n = 484 in September 2010) form a closed population that is free from human interference and predation. I analyzed annual population growth using age-structured projection matrix models parameterized with survival and fertility data collected from almost every female (98.7% of females). I found some evidence of temporal variation in growth during the two years I studied the population (λ2008−2009 = 1.065, λ2009−2010 = 1.117). Age structure appears to have converged to a stable age distribution, suggesting this growth rate has been sustained in the years leading up to the end of my study. Variation in vital rates of adult fertility and foal survival made the largest contribution to annual variation in population growth. Future growth is predicted to be most influenced by proportional changes in adult survival, which remained relatively unchanged between 2008 and 2010. The population can be stratified into three spatially distinct subunits found across a west−east longitudinal gradient of water resources (access to permanent ponds vs. ephemeral water sources and holes dug in sand). I assessed the existence of source-sink dynamics to determine if individual movements between subunits could explain spatial heterogeneity in population growth. I found that spatial heterogeneity in growth appears to be most influenced by immigration and emigration events between subunits. Evidence suggests that current growth of the overall Sable Island horse population is made possible by individual emigration from more productive into less productive subunits; in particular, a source presented in the west of the island where permanent water ponds are located.

The natural instability of hydrothermal vents creates variable environmental conditions among habitat patches. Habitat differences correspond to phenotypic variation in Ridgeia piscesae, the only ‘vent tubeworm’ on the spreading ridges of the Northeast Pacific. Ridgeia piscesae that occupy high fluid flux habitats have rapid growth rates and high reproductive output compared to tubeworms in habitats with low rates of venting fluid delivery. As recruitment occurs in all settings, worms in the “optimal habitat” may act as source populations for all habitat types. Ridgeia piscesae is a foundation species in the Endeavour Hydrothermal Vents Marine Protected Area of the Juan de Fuca Ridge. The objective of this thesis was to assess fine scale population structure in Ridgeia piscesae within the Endeavour vent system using genetic data. Population structure was assessed by analysis of the mitochondrial COI gene in 498 individuals collected from three vent sites of the Juan de Fuca Ridge; Middle Valley (n=26), Endeavour Segment (n=444) and Axial Volcano (n=28). Genotyping using microsatellite markers was attempted but all loci developed for closely related tubeworm species failed to amplify microsatellites in Ridgeia piscesae. Sequence analysis identified 32 mitochondrial COI haplotypes; one dominant haplotype (68%), three common haplotypes (4%-7%) and the remainder were rare (<2%). Axial Volcano was differentiated from Middle Valley and Endeavour. Within Endeavour, genetic sub-structuring of Ridgeia piscesae occurred among vent fields (Clam Bed, Main Endeavour and Mothra) and habitat types < 10 km apart. Patterns of genetic variation and coalescent based models suggested that gene flow among vent fields moved in a north to south direction in individuals from high flux habitat but from south to north in individuals from low flux habitat. Tubeworms from low flux habitat had more nucleotide polymorphisms and haplotypes than those from high flux habitats. Estimates of the number of immigrants per generation moving from high flux to low flux subpopulations was four times higher than in the reverse direction. The effective population size was estimated to be three times greater in high flux habitat when the generation times for individuals from each habitat type were considered. Demographic tests for population equilibrium identified a recent and rapidly expanding metapopulation at Endeavour. Models of gene flow in Ridgeia piscesae reflected the general oceanographic circulation described at Endeavour. Genetic data illustrate that dispersing larvae exploit the bi-directional currents created through plume driven circulation within the Endeavour axial valley and suggest that adult position on or near chimneys may influence larval dispersal trajectories upon release. Building on known ecological and biological features, this study also showed that Ridgeia piscesae from limited and ephemeral high flux habitat act as sources to the overall metapopulation and that asymmetrical migration and habitat stability sustain high genetic diversity in low flux sinks. The overall metapopulation at Endeavour experiences frequent extinction and recolonization events, differences in individual reproductive success, and source-sink dynamics that decrease the overall effective size and genetic diversity within the population. These factors have important implications for the conservation of a foundation species. / Graduate / 0307 / 0329 / 0369 / lcpuetz@uvic.ca

The dynamics of natural populations may be influenced by a variety of factors, ranging from feeding interference and territoriality to the risk of predation and climatic effects. The relative influence of these factors may be contingent upon the quality of the habitat in which individuals reside. A factor that can largely affect population dynamics and that often covaries with habitat structure is predation risk. However, the combined effect of habitat and predation risk can vary according to the social context and intrinsic characteristics that affect individual behavioural responses. This thesis investigates the effects of habitat quality at the level of the population and the individual, and examines how it relates to the above factors in Siberian jays (Perisoreus infaustus), a territorial, group-living species in which the main cause of mortality is predation. The results demonstrate a strong effect of habitat on survival, reproduction and behaviour. Mortality was generally higher in open areas and managed forests and reproductive success decreased after forest management. Breeding females were more sensitive to environmental factors than males, possibly because of higher reproductive costs. Estimates of spatial demography suggested that there were more sinks than sources, and that they were located in open, managed forests. Behavioural decisions confirmed that open forests were associated with higher predation risks. However, decisions depended on social context; immigrants took highest risks and were the recipients of most aggression, largely an effect of social subordination. Also, parents provide their offspring with benefits that are withheld from immigrants. As a result, first-year survival was higher in retained offspring. Investigating the effects of multi-scale habitat quality on individual behaviour and population dynamics has generated an increased understanding of the effects of forest management on the dynamics of this population. This approach should facilitate development of an effective conservation management policy for this species.

Understanding energy fluxes within and between floodplain water bodies, and between rivers and their floodplains is essential for comprehending the dynamics of modern, altered river systems. Floodplain aquatic invertebrates may move between habitats deliberately (through emergence and dispersal) or through passive transport during flooding. This movement may represent a significant flux of energy and an essential food web subsidy. I assessed the usefulness of the stable isotopes of hydrogen and oxygen (D and 18O respectively) for identifying the origins and movements of macroinvertebrates in Mississippi River floodplain water bodies. I sampled water and invertebrates from the Mississippi River, intermittent and permanent floodplain wetlands, and tributaries during 2007 and 2008. Results showed consistent relationships between δD and δ18O signatures in invertebrate tissues and their home water bodies. I also investigated whether δD and δ18O could be used as a multivariate "fingerprint" to trace a captured invertebrate back to its environment of origin. Results showed that δD can be a useful tracer of the movement of floodplain invertebrates in some cases, although δ18O is likely not suitable for that purpose.

No description available.

Long-term population dynamics across heterogeneous environments can be a major factor in determining species’ ability to expand their ranges and persist in novel environments. Whether and how the relative performance of populations in different microsites over time impacts invasion into new microsites is poorly understood. Though largely restricted to disturbed semi-shaded microhabitats in its home range, the invasive herb Alliaria petiolata (garlic mustard) successfully invades intact forest understories – a novel microhabitat – in its introduced range, where it is known to impact above and below ground community composition. To test the hypothesis that source-sink metapopulation dynamics may be promoting A. petiolata’s incursion into the forest understory, I utilized two multi-season field surveys – approximately a decade apart – to evaluate trait variation, biomass allocation, and long-term population demographics of A. petiolata growing at the forest edge, within the intact forest understory, and in the intermediate transition zone between the two. My results show that adult plants in the edge were taller and branchier, produced more fruits, and had higher total and reproductive biomass than plants in the intermediate and forest microhabitats. Over time, seedling density remained highest in the edge microhabitat compared to the forest and intermediate microhabitats, which had similar densities. Reproductive adult densities were similar among all microhabitats at the beginning of the study, but a decade later, all microhabitats exhibited a decline in the number of adult plants they supported. Populations in the intermediate microhabitat displayed the steepest decline in reproductive adults between sampling periods but still supported more adult plants than the forest microhabitat. Populations in all microhabitats were predicted to grow (λ>1) at the onset of the study. A decade later, declines in population size were only predicted in the forest understory (λ1). Since edge and intermediate patches had higher densities of adult plants which produced the most fruit and had larger reproductive biomass, it appears that the edge populations, and possibly the intermediate populations, have sustained the low-density forest populations through source-sink dynamics at my study sites.

Thesis (Ph. D.)--Miami University, Dept. of Botany, 2006. / Title from second page of PDF document. Includes bibliographical references.

During the summers of 2007-2009, I studied the population growth and reproductive and foraging ecology of the Razorbill (Alca torda) at Matinicus Rock (MR), Maine. This medium-sized marine bird in the family Alcidae (auks) was extirpated from the Gulf of Maine in the late 19th century by hunting, collecting, and colony disturbance. Following legislation protecting seabirds and their nesting habitats, the Razorbill has recolonized probable former nesting habitat in the Gulf of Maine during the past several decades. Six small colonies comprise the Maine population, which is listed as threatened and forms the southern extension of the species breeding distribution. In Chapter 1, I present a population model of the MR breeding colony, based on studies of population growth and reproductive success, and supplemented with previously collected data from the National Audubon Society Seabird Restoration Program (Project Puffin), with whom I collaborated. I also describe chick diet (supplemented with Project Puffin data) and draw connections between diet and reproductive success. I found that reproductive success was too low to account for the observed population growth rate, and conclude that the colony is a sink population supported by substantial immigration. Because annual fledging success was positively associated with prey quality, I suggest that substandard chick diet may contribute to the sink population dynamic via diet-driven depressed fledging success. In Chapter 2, I report on the foraging behavior of chick-rearing Razorbills fitted with bird-borne data-loggers at MR in 2008-2009. I describe diving behavior including depth, duration, and profile shape of dives, as well as diel patterns. Diving activity was restricted to daylight hours, and dives were shallowest and most frequent in the evening. Though generally similar to diving behavior reported at four European and Canadian colonies, Razorbills at MR performed three times as many dives per day as at the Gannet Islands, Labrador, and the mean dive depth was greater than three of four previous studies. Deeper and more frequent dives may indicate higher foraging effort and lower prey availability. Reproductive success would suffer if parents cannot buffer chicks against the effects of low prey availability through increased foraging effort or other behavioral modifications. Together, the pieces of our research indicate that prey availability may be negatively affecting reproduction and population growth at MR. Rapid colony growth cannot be explained by local reproductive success, and is likely the result of substantial immigration from other colonies. Chick diet is varied and includes multiple high-quality forage fish species, yet chicks also consume poor-quality prey (larval fish and euphausiids) that may signal periods of very poor prey availability. Frequency and depth of dives made by chick-provisioning adults are also suggestive of parents allocating extra effort to foraging, relative to other colonies.