Peter Arcese


Research Classification

Research Interests

Conservation Biology
Evolutionary Biology
conservation finance

Relevant Thesis-Based Degree Programs

Affiliations to Research Centres, Institutes & Clusters

Research Options

I am available and interested in collaborations (e.g. clusters, grants).
I am interested in and conduct interdisciplinary research.

Research Methodology

field ecology
mathematical modeling
Evolutionary genetics of free-living species
Spatial optimization


Postdoctoral Fellows
Any time / year round

Applied ecology, conservation, and genetics of free-living species

I support public scholarship, e.g. through the Public Scholars Initiative, and am available to supervise students and Postdocs interested in collaborating with external partners as part of their research.
I support experiential learning experiences, such as internships and work placements, for my graduate students and Postdocs.
I am open to hosting Visiting International Research Students (non-degree, up to 12 months).

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Graduate Student Supervision

Doctoral Student Supervision

Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.

Life history and environmental correlates of survival rates in tropical birds (2020)

Current thinking suggests that survival, and consequently lifespan of organisms, can be understood in terms of trade-offs between self-maintenance and reproduction, and constraints imposed by physiological mechanisms, such as metabolic intensity. While comparative studies show that many life history traits covary predictably with climate, few studies have examined variation in survival across latitudinal or elevational gradients. I paired survival rates with reproductive, morphological, behavioral, and physiological traits, as well as environmental variables to quantify the intrinsic and extrinsic drivers shaping avian life histories. In Chapter 2 I ask whether tropical birds around the world are longer lived than their temperate counterparts. My results suggested an inverse relationship between latitude and survival in the northern hemisphere, but this pattern is dampened or absent for the majority of southern hemisphere species. I also showed that extrinsic factors related to climate were poor predictors of survival compared to latitude alone, and that the relationship between survival and latitude is strongly mediated by intrinsic traits ― larger, non-migratory species with smaller clutch size had the highest survival. In Chapter 3 I focus within the Neotropics to examine how a basic physiological trait (basal metabolic rate; BMR) is linked to survival of montane and lowland birds. I found that lower BMR predicted higher survival, regardless of the elevation at which species occurred. In addition, elevation had a direct negative effect on survival, perhaps due to harsher abiotic conditions, low site fidelity, or both at higher elevations. To help facilitate estimates of age-specific survival in future studies, I determined the molt ageing criteria for South American manakin species in Chapter 4, which can be used to distinguish juveniles from adults. Like many temperate species, the occurrence of a partial preformative molt allowed separation of age classes based on the presence of molt limits. By drawing on both variation within the tropics and across birds globally, this dissertation provides new evidence of the connections between the high survival rate of tropical birds, their life history traits, and the environment.

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Spatial heterogeneity in natural selection and local adaptation to ungulate herbivory in Plectritis congesta (2019)

Understanding how organisms respond to environmental change via genetic and plastic responses can help predict species occurrence and persistence in changing landscapes. I quantified phenotypic and genotypic variation in the annual plant Plectritis congesta to test for the effects of spatial variation in ungulate herbivory on plant traits. I first surveyed 285 island and mainland populations in British Columbia, Canada, to estimate how ungulates, climate, and population isolation affect fruit phenotype and plant height. I then tested for local adaption in common gardens open to and protected from deer, and for adaptive plasticity in common gardens protected from herbivores, using populations exposed and naïve to ungulate herbivory. I then estimated genetic variance, heritability, evolvability and plasticity for plant height, shape and branch number, and assessed how these traits changed in response to intraspecific competition. Ungulate occurrence explained substantial population-level variation in phenotype, but climate and isolation had minor effects. In island populations, plants naïve to ungulate browsers were 2.6 times taller and 3.4 times more likely to produce winged fruits than plants from historically exposed populations. I observed local adaptation in common gardens open to and protected from herbivores, wherein plants from naïve populations were three times more abundant than plants from exposed populations after five years of protection from browsing. In contrast, plants from exposed populations survived three times better and were twice as fecund as plants from naïve populations when browsed, due to later bolting and flowering. Trade-offs in plant height and fecundity occurred in response to intraspecific competition: height increased 1.5 to three times as density increased but led to a ~20-30% decrease in fecundity. Moderate additive genetic variance and evolvability in traits under selection suggest a capacity for rapid evolution in 2-18 generations, similar to that shown in island populations of other taxonomic groups. My results suggest that spatial heterogeneity in browsing by ungulates can drive local adaptation in P. congesta populations, resulting in context-dependent trade-offs that influence fitness and elicit adaptive plasticity. Existing variation between island populations of P. congesta has the potential to provide long-term stability when faced with rapid environmental change.

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The Effects of Habitat Preference, Environmental Heterogeneity, and Inter-Individual Variation on Fitness (2015)

Theory predicts that animals breeding in heterogeneous landscapes should select habitat likely to maximize individual fitness, but identifying the fine-scale environmental characteristics which influence habitat preference and affect fitness is often problematic. While many studies quantify relationships between habitat preference and the reproductive success of their occupants, few are able to separate the independent effects of inter-individual variation among animals in a population from the effects of habitat on indices of fitness. In this thesis, I used up to 39 years of nesting, survival, and pedigree data from a resident, island population of song sparrows (Melospiza melodia) to identify fine-scale environmental characteristics which influenced habitat preference, determine whether preferred habitats positively affected fitness, and distinguish the relative effects of preferred habitats on indices of fitness from those due to inter-individual variation among song sparrows within the population. Song sparrows in this population exhibited marked preference for habitats that conferred positive effects on individual fitness via annual reproductive success and survival. Females nesting in preferred habitats also began breeding earlier, exhibited more energetically efficient incubation behaviour, and produced more offspring that recruited the population than those nesting in less-preferred sites. Preferred habitats in this system had more shrub cover, more edge, and deeper soil. The potential benefits of occupying preferred habitats included greater early season food availability and shelter from predators and inclement weather during both the breeding and non-breeding seasons.Despite the positive effects of preferred habitats on fitness, the relative contributions of habitat to indices of fitness were substantially less than those related to inter-individual variation in phenotype, genotype and developmental stage (measured as relative lifetime reproductive success, additive genetic and permanent individual variance, and age). Together, results from this thesis suggest that inter-individual variation in ‘quality’ can be more influential of fitness than habitat quality in free-living populations, and highlight the importance of estimating the relative contributions of inter-individual variation when attempting to identify the environmental correlates of fitness in natural systems.

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Systematic Conservation Planning in Human-Dominated Landscapes: Maximizing Efficiency in Biodiversity Conservation via Carbon Sequestration and Land Management (2014)

Investments in habitat and biodiversity conservation are critically needed given mounting effects of global climate change and unprecedented rates of ecological degradation and species extinction. However, as more regions of the world are converted to human use, we are also experiencing a shift in the traditional targets of conservation from protecting ‘ecologically intact’ landscapes to restoring degraded habitat by prioritizing conservation investments under triage. The overall goal of this thesis was to evaluate alternative ways of funding conservation initiatives. To reach that goal, I first used 1,770 avian point counts in a 2,520 km2 study area, remote-sensed data and models incorporating imperfect detectability to predict habitat occupancy in 47 widely-distributed native birds, which were also classified by experts according to their habitat association. Forest and Savannah association scores for these species were then used as weights in a composite distribution map of species communities. My results showed that composite maps of widespread indicators improve site prioritization by incorporating the behavioural and demographic responses of a diverse range of indicators to variation in patch size, configuration and adjacent human land use. Using these composite maps, I asked how the sale of forest carbon credits could reduce land acquisition costs, and how the alternate goals of maximizing α or β-diversity in focal communities could affect the prioritization of parcels for acquisition. My results indicate that carbon sales have the potential to enhance conservation outcomes in human-dominated landscapes by reducing the net acquisition costs of land conservation. Maximizing β versus α-diversity may further reduce costs by reducing the total area required to meet conservation targets and enhancing landscape heterogeneity. In cases where land purchase is not an option, private land conservation covenants can provide an alternative; although serious questions exist about long-term monitoring and enforcement costs of covenants given the risk that owners might violate or challenge them in court. My findings suggest that violation or dispute rate can substantially affect long-term costs of covenants and potentially surpass the cost of land purchase. Overall, I tested several ways to successfully fund conservation investments and highlight potential benefits and shortfalls of each.

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The mechanistic pathways of species interactions in an African savanna (2014)

Quantifying the interactions that govern the abundance and distribution of large African mammals is an opportunity to understand the forces structuring ecological communities and a means to inform conservation practice in a changing world. I paired experimental manipulations with correlative observations taken over expansive scales to quantify the mechanisms shaping interactions between trophic levels in an African savanna. Chapter 2 addresses the non-consumptive effects of predation risk on the behavior of a small and territorial antelope, Guenther’s dik-dik (Madoqua guentheri). Studies have suggested that mobile prey avoid areas of heightened risk, but few such studies have been carried out on territorial organisms whose movement is constrained by their neighbors. My findings showed that use of familiar areas increased after exposure to a cue of risk, such that predators may reinforce rather than override territoriality in dik-dik. Chapter 3 unifies risk-avoidance behavior in a medium-sized antelope, the impala (Aepyceros melampus), and plant defense (thorns) to explain the spatial distribution of plant community structure. My findings showed that plants can persist in landscapes characterized by intense herbivory, either by defending themselves or by thriving in risky areas where carnivores hunt. Chapter 4 explores the cascading effects of wild dog recolonization (Lycaon pictus) on dik-dik and trees. Previous work has equated a positive correlation between plant and large carnivore biomass to a trophic cascade, thereby inferring mechanisms by which carnivores suppress herbivores which then releases plants from herbivory. My results showed suppression of herbivores by carnivores and of plants by herbivores, coupled with a positive correlation between carnivore and plant biomass that, together, did not give rise to a trophic cascade. There was no trophic cascade because the effect of herbivory, as measured by replicated herbivore exclosures, was the same in the presence and absence of wild dogs. Chapter 5 summarizes the main findings and limitations of this dissertation, and provides a framework for quantifying trophic cascades in systems dominated by large carnivores. Put together, this dissertation reinforces the vital role of a mechanistic approach to quantifying trophic interactions in large mammals.

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Glaucous-winged gulls Larus glaucescens as sentinels for a century of ecosystem change: long-term trends in population, diet, and egg production in North America's Salish Sea (2013)

Ecological studies characterising population trends over decades or centuries can help to describe the range of variability in a study system, with well-studied species being strong candidates for providing the long-term data required for retrospective studies. Seabirds represent useful real-time monitors of marine systems and may also play this role in studies characterizing historical ecological change. The glaucous-winged gull L. glaucescens is a generalist marine bird occurring in the Salish Sea, an urbanized coastal area of southwestern British Columbia and northwestern Washington, where it has been studied or collected since the mid-1800s. Its twentieth-century populations experienced dramatic growth followed by a steep decline, with recent trajectories unclear. I used multiple methods to characterise long-term trends in gull number, diet, and egg production, and to test hypotheses about causes of population change. My approach combined meta-analysis of historical reproductive traits, statistical modeling of population trend, and stable isotope analysis (δ¹³C, δ¹⁵N) of historical and modern gull feathers and forage fish, with modeled population trend showing a continued decline in gull numbers from the 1970s to the present. Meta-analytical results pointed to decreasing egg and clutch size and a delayed lay date over the twentieth century to the present, while stable isotope analysis showed declining feather δ¹³C and δ¹⁵N since 1860, all of which was consistent with a growing reliance by gulls on non-fish foods. Demographic modeling showed that declining clutch size and productivity were largely sufficient to account for the gull population decline, and pointed to recovery from cessation of nineteenth-century egging as being an important contributor to the increase phase. These modeling results implied that declining consumption of forage fish affected gull productivity. Additional results from stable isotope analysis also supported a hypothesis of dietary change; namely, declining forage fish C:N ratios over time indicated a decrease in fish lipid content, and thus a decline in prey quality. Overall, my results highlight the value of compiling multiple retrospective studies to better understand the complex factors affecting long-term trends in animal populations.

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Multi-Scale Comparison of Native and Exotic Communities in the Garry Oak Ecosystem of British Columbia (2012)

Fundamental debates persist regarding the ecology of species invasions, the risk posed by exotic species, and the most effective management to diminish invasion and promote native-dominated ecosystems. Using vascular plant surveys at three scales (between small-island and ‘mainland’ patches, among patches, within patches) from 86 patches in a threatened meadow ecosystem, I addressed the following questions arising from such debates: 1) Are latent invasions prevalent among exotics, and if so, among which species? 2) What are the relative roles of latent invasions, competition and environmental response in determining native versus exotic biogeographic patterns? 3) How can native and exotic species distribution and richness models at multiple scales be used to improve conservation management? Species-level analyses demonstrated latent invasions among and within patches for short-dispersing exotics, and a positive relationship between exotic species’ abundances and minimum residence time in the study region, suggesting that population expansion of some exotic species is at an early stage. A mix of scale-dependent concordant and discordant relationships with environmental variables, rather than competition, appeared to be the primary determinant of native versus exotic species richness and composition patterns. While incomplete invasion of exotics did not produce substantially different community-level biogeographic patterns between native and exotic communities, exotics were dominated by long-dispersing ruderal species more abundant on disturbed patches, while dominant natives were often short-dispersing stress-tolerant species more abundant on isolated patches. Such complexities, overlooked in most previous comparative analyses of native and exotic communities, can be used to predict future patterns and prescribe efficient management. In addition, spatially explicit distribution models revealed greater predictability for native species, and greater predictability among than within patches. Environmental variables related to native and exotic distributions were often shared within patches. Thus, management prescriptions applied among patches are likely to be most successful and predictable. Finally, native species at risk were more common on isolated small-island patches, contrary to biogeographic theory. Protection of small-island patches would be the most efficient conservation strategy for the study system. Interventions to control large exotic species populations, especially where propagule pressure from nearby disturbed areas is high, represent a far less efficient strategy.

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The role of insularity in promoting intraspecific differentiation in Song Sparrows (2008)

Islands are valuable research systems for evolution and conservation, but most work has focused on oceanic islands. Far less study has occurred on near-shore islands where inter-island and island-mainland dispersal is an important microevolutionary process. Further studies in near-shore systems would aid the expansion of island evolutionary theory and conservation initiatives. In this thesis, I studied populations of Song Sparrows (Melospiza melodia) on near-shore islands along the Pacific coast of North America to examine the causes and consequences of dispersal for microevolutionary and ecological processes. Within an island metapopulation, where inter-island distances ranged from 200m to 2km, male and female immigration rates were influenced by adult density and sex ratio respectively, suggesting that intrasexual territoriality influences immigration. Islands differed in immigration levels, with low immigration and high resident recruitment on more isolated islands. I next examine genetic structuring at a larger spatial scale (0-300km). I found that the scale of genetic structuring within continuously distributed populations was less than 10km, suggesting that Song Sparrows are a sedentary passerine. Regional comparisons revealed that holding geographic distance constant, larger genetic distances occur in areas located at subspecific boundaries or across water barriers. The apparent reduction in dispersal to islands had broad-scale consequences. Across Pacific Coast islands, island populations consistently had lower genetic variation than mainland populations. Small and remote island populations tended to have the lowest genetic variation. From an in situ conservation stance, populations on large, remote islands could be important contributors to intraspecific genetic diversity because of high genetic differentiation. Finally, I link genetic structuring with contemporary dispersal and show that migration rates among the Channel Islands are low, suggesting that these islands are demographically independent. The absence of shared mtDNA haplotypes between extant and extinct populations suggests that inter-island migration was historically low, potentially explaining why the two extirpated islands have not been recolonized. Collectively, my thesis results increase our understanding of the mechanisms of divergence on insular populations by examining factors affecting dispersal, the spatial scale of divergence and estimating the consequences of reduced gene flow on islands for broad-scale patterns of genetic variation, microevolution and demographic stability.

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Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Effect of local habitat and landscape attributes on bird species richness and community completeness in shade coffee plantations in Colombia (2023)

The loss of tropical forest for agriculture is a principal cause of declines in species diversity in the Neotropics. Shade-grown coffee plantations, where coffee plants grow under a canopy of trees, have been found to support a higher diversity of both Neotropical migrant and tropical resident birds compared to agroecosystems without trees. However, how local and landscape factors interact to affect avian biodiversity remains poorly understood. I studied the influence and interaction of local and landscape attributes on bird richness and community completeness in 160 shade coffee plantations in two regions of Colombia differing in extent of regional forest: Antioquia, where forest covered 20% of the study area and Cauca, where only 1% of forest remained. By using generalized linear models, I determined how species richness and community completeness were influenced by the local scale structure and composition of shade-grown coffee plantations (i.e., tree richness, tree abundance, and coffee density) and landscape variables surrounding the plantation (i.e., plantation distance to forest, cover by intact forest, forest-agriculture mosaic, or the combination of the two). My findings suggest that the extent of regional forest cover affects the landscape-level contribution to bird richness and community completeness within plantations. In Antioquia, richness of bird communities increased with the proportion of all forest elements within the surrounding landscape. Community completeness was influenced by the interaction between the local and landscape scales; tree richness enhanced community completeness only when the forest-agriculture mosaic cover at the landscape scale was greater than 73%. In Cauca, higher richness and abundance of trees at the local scale were associated with greater bird richness and community completeness, while there were no landscape-scale effects. Within highly deforested regions, birds are most likely to benefit in the near-term from increasing the diversity of shade trees within farms. However, reforestation efforts at the landscape scale should be considered as a long-term strategy to provide critical resources that support more complete communities of birds in coffee plantations. In more forested regions, bird communities could benefit by protecting and/or increasing the forest cover in the landscape and increasing the diversity of trees within plantations.

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Seasonal variation in marine bird distribution in the northeast Pacific Ocean (2023)

Human impacts can directly (e.g., bycatch, over-fishing, pollution), indirectly (e.g., climate forcing), or in concert affect marine systems and the species that rely on them. These effects can alter ecosystem function, productivity, and the abundance, distribution and demography of many marine predators. Marine birds are particularly sensitive to these impacts and given their ease of observation and diverse foraging tactics and habitat uses are outstanding indicators of ecosystem health. Conserving marine birds and their ecosystems requires robust predictions of species distribution and the identification of ‘hotspots’ of richness and abundance to help mitigate human disturbance in areas and at times when large aggregations of diverse species occur. I modeled seasonal variation in marine bird species diversity (defined by the Shannon Weiner Diversity Index) and in marine bird family occurrence to map the intensity and extent of hotspots in relation to season and climate in Canada’s Pacific Exclusive Economic Zone. To do so, I used 20 years of survey data from the North Pacific Pelagic Seabird Database (1997-2017) and remote sensing data describing marine conditions and local geography (sea surface temperature, chlorophyll a, bathymetry, and distance to shore) to illustrate how seasonality within years and the El Niño Southern Oscillation (ENSO) across years influenced spatial patterns in diversity. Hotspots were most persistent in Hecate Strait, off the west coast of Vancouver Island, and surrounding the Scott Islands in most seasons. Hotspots became less intense and/or shifted northwards as sea surface temperatures rose, reflecting the results of many studies on individual species responses to increasing temperatures and demonstrating such effects at the level of marine bird communities. I describe how my results could be applied to potentially mitigate the deleterious effects of humans on the diversity and distribution of marine birds. I also provide cautions which must accompany such predictions given sparse data for some areas and seasons. Overall, the maps I present provide a template for mapping marine species distribution for the purpose of identifying ‘hotspots’ of diversity, and thereby facilitate planning to minimize harmful impacts in highly diverse and dynamic systems.

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Earthworm invasion: consequences and conservation implications for the endangered Garry Oak (Quercus garryana) and maritime meadow ecosystems (2020)

Biological invasions by non-native ‘ecosystem engineers’ can radically alter the ecological and socio-economic values of ecosystems in ways that may require decades to detect. The invasion of North American glacial refuges by non-native earthworms is a prominent but understudied example of a cryptic invasion by an ecosystem engineer. Non-native earthworms are known to reduce soil carbon, disrupt mycorrhizal networks, and homogenize plant communities in their role as seed predators, root foragers, and in nutrient cycling and redistribution. However, natural resource managers have struggled to discern the scale at which non-native earthworms influence plant species diversity across invaded biomes. With no effective methods to eradicate or control established earthworm populations, there is great need for preemptive strategies to identify high-value conservation areas at risk of invasion. Herein, I address two main questions with implications for forest management: 1) Can the influence of non-native earthworms on plant community assembly be reliably predicted using plant traits? 2) Can abiotic factors be used to identify and predict natural refuges from earthworms in heterogenous habitats? I found that the presence of earthworms contributed to the simplification of plant communities in experimental mesocosms and observational surveys of in-situ forest and meadow habitat. In general, earthworms were associated with plant communities dominated by species with large seeds and fibrous roots, whereas species with small seeds and taproots only persisted in multi-species mesocosms without earthworms. These findings suggest that earthworms shape community composition in the early stages of invasion by acting as ecological filters on morphological plant traits. Last, I constructed an ensemble species distribution model for non-native earthworms using data from 300 survey plots to identify the suite of environmental conditions needed to limit the dispersal and persistence of invading earthworms. This model showed that shallow and dry soils on steep terrain strongly limit the occurrence and abundance of non-native earthworms. My results show that earthworms reduce plant species richness in coastal forest and meadow habitats of southwest British Columbia and highlight the conservation value of shallow-soil habitats that limit earthworm distribution and persistence.

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Conservation planning at multiple scales: a density model and spatial planning tool to facilitate the conservation of Andean bears (Tremarctos ornatus) and the Northern Andes (2019)

Global declines in large-bodied terrestrial vertebrates have been widely linked to human disturbance and habitat loss. Consequently, identifying remaining opportunities to conserve habitats likely to maximize the persistence of such species remains a key challenge to conserving biological diversity globally. Andean bears (Tremarctos ornatus) are among the least-known wide-ranging large mammal species, but occupy montane ecoregions throughout the Northern Andes, a global biodiversity hotspot. Recent evidence suggests the Andean bear range includes forests at the fringe of human development, including the equatorial dry forests of Peru. If Andean bears are to be conserved in this region, a better understanding of their potential densities, use of habitats, and response to human influence is required. This thesis used spatial density models, existing field and remote-sensed data, and spatial planning tools to relate species detection to environmental variables and optimize conservation plans for Andean bears and the Northern Andes. I assessed habitat use by Andean bears in equatorial dry forest at a local scale in Northwestern Peru, using camera-trap data to construct spatially-explicit capture recapture (SCR) models. I compared models for resources thought to affect bear density by their association with threats and food availability; including elevation, slope, forest cover, and proximity to roads. I found that proximity to roads reduced the density of Andean bears, and the influence of factors other than roads varied seasonally. I identified potential areas of equatorial dry forest outside the IUCN range that could support Andean bears, but noted that unmapped roads and smallholder agriculture affected the reliability of results. I also employed systematic prioritization methods to identify configurations of land parcels that maximized biodiversity features at the least cost. I found that the Andean bear range performed better at capturing species richness than a random control feature. I also found that planning for multiple goals in a systematic planning framework greatly increased the area efficiency of the solutions, compared with planning for biodiversity features separately. Overall, this thesis highlights the importance of working at multiple scales for efficient conservation planning, and provides a common framework for conducting such analyses in the future.

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Demographic shifts and the role of climate warming in a switch from migrant to resident life history (2019)

Identifying causes and consequences of variation in species life history should improve predictions about how climate and land use change will affect the demography and distribution of species in future. Sooty fox sparrows (Passerella iliaca unalaschcensis) were documented as obligate migrants, abundant in winter but with only three breeding records in coastal habitats of British Columbia and Washington prior to 1950. Because this subspecies has since established year-round resident populations in this region, I studied resident populations of sooty fox sparrows to test theory on how climate change and life history might affect the demography and distribution of a new partial migrant.I estimated demographic vital rates in one recently established resident population on Mandarte Is., BC, using color-banded birds. Annual fecundity (F) was higher than reported in migrant populations studied previously in Alaska and Newfoundland, supporting the hypothesis that residents invest more in reproduction on average than migrants within species. I also estimated high juvenile and adult overwinter survival (Sj = 0.32 ± 0.06, and Sa = 0.69 ± 0.05) and population growth (λexp = 1.61 ± 0.57), implying rapid population growth. I next tested the hypothesis that climate warming facilitated the establishment of resident populations by reducing the net benefit of migrating out of the wintering area to breed. Because resident sooty fox sparrows breed earlier and longer than migrants, I asked if climate warming during the pre-breeding period coincided with patterns of establishment by: 1) characterizing the pre-breeding climate niche of resident populations using species distribution models, occurrence data, and monthly climate records, and 2) testing if the emergence of the pre-breeding climate niche currently occupied by resident populations corresponds to the first reports of sooty fox sparrows breeding after 1920. Niche models suggest that the mild, near-shore climate niche now occupied by recently established resident populations expanded dramatically from 1920 to 2015 in a pattern matching early records of breeding by sooty fox sparrows within their historic wintering area from 1950.Whereas prior studies focus on climate warming affecting overwinter survival, my results suggest warming may also affect migration through improved fecundity and breeding niches.

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Temporal Variation in the Traits of Individuals and the Extrinsic Environment that Influence Nest Success in an Island Songbird (2016)

Nest success is a key factor affecting the dynamics and life–history evolution of avian populations. While multiple factors affect nest success, their relative influence remains unclear, partly due to the short time periods over which many studies take place relative to the scales of temporal variation in the environment, and the traits of birds that make up populations. I examined the effects of two intrinsic (female age, inbreeding coefficient), two abiotic (rainfall, temperature), and three biotic (breeding densities, cowbird parasitism rates, and brood parasitism) factors potentially affecting nest success (≥ 1 fledged young) in an insular song sparrow (Melospiza melodia) population over 39 years. I also compared the influence of these factors in three 13–year intervals representing the early, mid and late periods of the study to estimate temporal influence. Over 39 years, song sparrow nesting success first increased (1 – 3 years), and then decreased with female age (3+ years), and declined in relation to the degree of inbreeding in females, increased rainfall during the nest period, and by increased breeding densities. Nests that were parasitized by brown–headed cowbirds, or that experienced increased risk of cowbird predation, tended to fail more often. Parallel analyses of nest success in the early, mid and late periods of the study showed that only female age and breeding densities explained success in all periods, whereas the effects of inbreeding, cowbirds, and rainfall were episodic through time. This discrepancy was due to temporal variation in abiotic or biotic conditions that affected which factors were most influential of success. Many studies of nest success in passerine birds are limited in duration and the number of variables that can be considered due to limits on the amount or quality of data, preventing the comparison of many biotic and abiotic factors reported to affect success in the literature. I show that over 39 years, the intrinsic effects of inbreeding, abiotic effects of climate and biotic effects of brood parasites on nest success were each influential but varied through time, indicating that any ranking of their relative influence on demography will also vary temporally.

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Species Colonization and Extinction Processes in an Island Bird Community (2015)

Species invasion and range shifts are widely reported and facilitate novel interactions among potential competitors in plant and animal communities worldwide. However, predicting which novel interactions will result in the extirpation of subordinate competitors is challenging. Coexistence versus extinction as alternative outcomes of competition between resident and colonizing species may arise due to (1) variation in interaction strength, (2) change in other demographic drivers more influential than those linked to competition, or (3) differences in the extent to which resources are equitably partitioned between competitors, which may in turn depend on the spatial scale examined. To date, however, empirical studies suggest these factors rarely align to cause the competitive exclusion of native species. I used a combination of field experiments and demographic analyses to test the hypothesis that colonizing fox sparrows (Passerella iliaca) have caused the 0.6% per year decline of a song sparrow (Melospiza melodia) population resident on Mandarte Island, BC, Canada. Several lines of evidence indicate that interspecific competition for winter food has: a) reduced survival in juvenile song sparrows after colonization by fox sparrows in 1975, b) led to an inverse relationship between juvenile song sparrow survival and fox sparrow population size, c) excluded song sparrows from high-quality foraging sites in winter via consistent behavioural dominance by fox sparrows and complete overlap of fox and song sparrow preference for local seeds, despite d) no evidence of competition for breeding territories or nesting habitat. My results suggest that in the absence of rapid ecological or evolutionary shifts in niche dimension, song sparrows will likely be extirpated from Mandarte Is., thus demonstrating that competitive exclusion of native species can occur when interactions are strong and resources are not easily partitioned.

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Patterns and drivers of selection on laying date in song sparrows (Melospiza melodia) (2014)

Natural selection in the wild has been extensively researched, but few studies have identified the abiotic and biotic drivers of selection or quantified their influence. I characterized and quantified annual selection on laying date in the song sparrow (Melospiza melodia) population of Mandarte Island, British Columbia over 35 years. Selection was approximately linear for annual reproductive success (ARS) and over-winter survival based on cubic splines visualization of fitness surfaces. Fecundity selection (recruited offspring) was roughly 10 times stronger (-0.271 ± 0.031, mean ± SE) than viability selection (-0.028 ± 0.043, mean ± SE). Since opposing selection could constrain evolution, I used multiple measures of fitness, including fecundity measured at sequential offspring life stages, and female over-winter survival, to test if selection was complementary or opposing. Selection favored early breeding through all fitness measures and was therefore complementary. The strength of fecundity selection on recruits was 1.43 times stronger than selection on nestlings, indicating that the effects of early laying were additive and accumulated over time. Despite strong selection and moderate heritability (h² = 0.16), there has been no phenotypic advance of laying date in this population from 1975 to 2010. I also investigated several potential drivers of selection including density, spring temperature, precipitation and the intensity of brood parasitism by brown-headed cowbirds (Molothrus ater), and determined their relative influence on fecundity and viability selection. I found that density was the most influential driver of fecundity selection, and that selection favoring early breeding increased in magnitude at high population density and high intensities of brood parasitism. Because population density and the age and inbreeding structure of this population are correlated, I also included each of these variables as a covariate in calculation of selection differentials, and found weaker selection for some fitness measures. A climate index representing precipitation during the pre-laying period was the most influential driver of over-winter viability selection, with early breeding favored in winters preceded by warm, dry springs, and late breeding favored in winters preceded by cool, wet springs.

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Spatial models of plant species richness for British Columbia's Gerry oak meadow ecosystem (2014)

Garry oak meadow ecosystems in British Columbia are fragmented, increasinglydegraded, and have been prioritized for conservation. While distribution maps of remnantmeadow patches have been developed, the ecological integrity of plant communities inmany of these remnants remains unknown. Modeling and mapping ecological integritycould inform conservation prioritization exercises in the region.The primary goal of this thesis was to develop distribution models of native and exoticplant species richness in Garry oak meadow remnants. Secondly, multiple independentdatasets were used to analyze the effects of sample size and sampling bias on theaccuracy and reliability of resulting predictive maps, which is an active area of researchin species distribution modeling. Finally, I investigated whether Terrestrial EcosystemMapping (TEM) – a publicly available GIS layer of plant community associations –provided a valid geographical extent over which to map predictions.In Chapter 2, different datasets were found to produce different models of speciesrichness. However, different native richness models produced similar distribution maps,while exotic richness maps based on different datasets were less similar. Theincorporation of spatial variables into models did not improve model fit, howeversignificant residual spatial autocorrelation at a broad scale was detected in some cases,suggesting that an important environmental covariate is missing from these models.Examples of potential missing covariates include deer density and disturbance history.Overall, this research demonstrates that multiple independent datasets are very importantiiifor validating species distribution models, especially in heterogeneous landscapes.Additionally, large sample sizes and sampling broadly across of the area of predictionresult in more robust models.The results presented in Chapter 3 suggest that mapping predictions exclusively overGarry oak ecosystem-classified TEM polygons is potentially overly conservative, asspecies richness of native meadow species was found to be high in other TEMclassifications as well. This suggests that Garry oak meadow plant communities do notexist solely in discreet meadow patches, and that they are dispersed throughout otherhabitat types including Douglas-fir – salal forests.

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First year site fidelity and survival in reintroduced captive-bred Vancouver Island marmots (Marmota vancouverensis) (2012)

The Vancouver Island marmot is a critically endangered sciurid endemic to British Columbia, Canada. By 1997, the species had collapsed to fewer than 150 individuals in total. Between 2003 and 2010, 301 captive-bred marmots were implanted with radiotelemetry transmitters and released to new sites and extinct colonies to supplement the wild population. I evaluated reintroduction success based on three short-term measures: first season fidelity to release site, active season survival from release to hibernation, and overwinter survival through early spring. I used generalized linear mixed models to evaluate the influence of sex and age, release practices and procedures, and the local and landscape-level attributes of release habitats on site fidelity and survival. Results suggested that poor overwinter survival has been the limiting factor in first-year reintroduction success. In all years, overwinter survival was lower for newly released captive-bred marmots than for their wild or previously-released counterparts. Release date was the variable most predictive of success, but was positively associated to site fidelity and active season survival and negatively associated to overwinter survival. Release date was the only predictor for overwinter survival, whereas site fidelity was also negatively impacted by the presence of resident females at the release site. Active season survival was highest for females, 2-year olds, and marmots released to sites with talus. I discuss these results in the context of current release practices for Vancouver Island marmots, and make recommendations for future release candidates, site characteristics, and release procedures.

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