Peter Arcese


Research Interests

Conservation Biology
Evolutionary Biology

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Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - Mar 2019)
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 (2010-2017)
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 Garry 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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Recent Tri-Agency Grants

The following is a selection of grants for which the faculty member was principal investigator or co-investigator. Currently, the list only covers Canadian Tri-Agency grants from years 2013/14-2016/17 and excludes grants from any other agencies.

  • Variation in natural selection, population demography and individual life history in insular plant and bird populations - Natural Sciences and Engineering Research Council of Canada (NSERC) - Discovery Grants Program - Individual (2015/2016)
  • Phenotypic, genetic and demographic responses to environmental variation and inbreeding in the song sparrow - Natural Sciences and Engineering Research Council of Canada (NSERC) - Discovery Grants Program - Individual (2013/2014)

Current Students & Alumni

This is a small sample of students and/or alumni that have been supervised by this researcher. It is not meant as a comprehensive list.

Adam Ford

Doctor of Philosophy in Zoology (PhD) [2014]

Research Topic
The Mechansitic Pathways of Species Interactions in an African Savanna

Job Title
Assistant Professor; Canada Research Chair in Wildlife Restoration Ecology

University of British Columbia


Membership Status

Member of G+PS

Program Affiliations


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