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Migratory birds face the distinct challenge of travelling between widely separated and environmentally distinct areas for their breeding and non-breeding periods. They may be faced with different pressures at different points in their life cycle, and a solid understanding of the drivers of individual fitness and population demography is crucial to understanding the ecological and evolutionary trajectories of their populations. In this thesis, I combine long-term data and experimental manipulations to study migratory patterns and arrival dynamics, density dependence, and reproductive behaviour in a long-distance migratory bird, the American redstart. First, I show that non-breeding season weather is associated with redstart phenology on the breeding grounds. Greater winter rainfall corresponds to earlier arrival and egg-laying dates at both the population and individual level, indicating that individual birds may be able to adjust their phenology in response to conditions in winter. Furthermore, I demonstrate these associations independently at two breeding populations at opposite sides of the redstart breeding range and their corresponding putative non-breeding areas: greater rainfall in Jamaica and Mexico was associated with advanced redstart phenology in Ontario and Alberta, respectively. Second, I performed a manipulation experiment to delay the arrival of male redstarts to the breeding grounds. I show that delayed males suffer reduced fledging success in comparison to early-arriving males that bred early or late, but equivalent success in comparison to males that arrived and bred late. These results provide evidence against the importance of either timing or individual quality, but instead suggest that other aspects of quality, namely mate and territory quality, may be important factors driving the success of early-arriving males. Third, I examine the consequences of density dependence for reproductive success and mating behaviour in a population of redstarts for which I showed density-dependent population growth over a period of 11 years. Greater breeding density, both at an annual scale and at a local scale, was associated with reduced success and greater paternity loss. Overall, my findings contribute to a broader understanding of the selective pressures and regulatory mechanisms acting on migratory birds, from the individual up to the population level. / Thesis (Ph.D, Biology) -- Queen's University, 2012-09-25 13:17:33.172

Using 12 years of monthly sweep-net data from 9-12 permanent sampling stations, we evaluated the variability and stability of the dragonfly assemblage in Bays Mountain Lake (northeastern Tennessee, USA). To do this, we adopted the view that a stable assemblage (i.e. one capable of recovering quickly from disturbances) should have low variability (i.e. high persistence of taxa, relatively constant densities, and high rank concordance), except with disturbances more intense and frequent than those in this system. Moreover, a stable assemblage should contain populations that exhibit density dependence and should tend to remain within a restricted range of densities (boundedness), shifting toward a narrow density interval between generations (attraction). To test some specific predictions derived from these views, we analyzed 12-year sequences of larval population sizes just before the onset of emergence for the 13 dominant dragonfly taxa in the lake. Most but not all of the 13 dominant taxa persisted during the 12-year period. Variabilities of taxon densities, measured as standard deviations across generations of log-transformed population sizes, were representative of the broad range for other invertebrates but somewhat higher than those of terrestrial vertebrates. There were fewer than three significant abundance trends over the 12-year period, and rank concordance between generations was high (W=0.716). Density dependence was detected among some of the dragonfly density sequences by five different methods. Using techniques presented in the companion paper, we found strong indications of both boundedness and attraction in the whole assemblage. We conclude tentatively that an assemblage consisting of at least 11 of the 13 dominant dragonfly taxa at Bays Mountain Lake has low-to-moderate variability and is stable, but that the complete 29-species assemblage is probably not stable at the scale of this single lake. We emphasize the need for coupling such long-term descriptive analyses with studies of responses to experimental disturbances.

Predation, egg production and survivorship of Laricobius nigrinus Fender, L. rubidus, LeConte, and L. osakensis Montgomery and Shiyaki (proposed), predators of hemlock woolly adelgid, Adelges tsugae, Annand, were investigated in the laboratory and in the field. In individual assays, L. rubidus oviposited fewer eggs than either L. nigrinus or L. osakensis. In assays containing congeneric or conspecific groups of adult Laricobius, L. osakensis preyed upon the greatest number of ovisacs. When all three species were together, the numbers of ovisacs preyed upon were similar to the mean of all three individual species. Adult predators fed on few eggs and did not exhibit any species preference. The numbers of A. tsugae ovisacs fed upon did not differ significantly by groups of congeneric or conspecific Laricobius larvae. Laricobius adults and larvae had high survival rates throughout all experiments. In the field, predators were enclosed in sleeve cages with both high (> 120 ovisacs) and low (< 90 ovisacs) A. tsugae densities for 1 wk. All branches with caged beetles had significantly greater numbers of ovisacs preyed upon than branches caged without beetles. No differences in predation or egg production were found among the conspecific and congeneric groupings. Predation was uniformly higher at the high prey-density than at the low prey-density. Survivorship among predators did not differ significantly at either prey density. Results from both laboratory and field experiments suggest that these species are able to co-exist and can be in the same location for biological control of A. tsugae. / Master of Science in Life Sciences

Various models of density dependence predicted different evolutionary outcomes for Helicoverpa zea, Diabrotica virgifera, and Ostrinia nubilalis using simple and complex resistance evolution models, different dose assumptions and refuge proportions. Increasing available refuge increased durabilities of pyramided Plant-Incorporated-Protectants (PIPs), especially between 1-5%. For some models of density dependence and pests, additional refuge resulted in faster adaptation rates. Significant considerations should be given to a pest’s intra-specific competition in simple and complex theoretical models when designing insect resistance management plans. Life-history, refuge, and dose characteristics of a PIP had different effects on the adaptation rate of a generic pest of Bt, and unexpected outcomes occurred. Intrinsic growth rate ‘R0’ was the strongest evolutionary force, and large R0’s reduced time to resistance for a high dose PIP to similar levels as projected for a low dose PIP. This was caused by differential density dependent effects in refuge and Bt fields that elevated generational resistance increases beyond those from selection alone. Interactions between density dependence and R0 were always present and further affected the life-time of the PIPs. Varying ‘average dispersal distance’ did not affect evolutionary outcomes; however, increasing the proportion of the population engaging in dispersal often increased the durability of high dose PIPs. When resistance genes spread from a hypothetical hotspot, local resistance phenomena developed in the immediate surroundings. Higher growth rates lead resistance to spread faster through the landscape than lower rates. Increasing available refuges slowed adaptation rates to single PIPs and low dose pyramids, although non-linear trends were possible. Integrated Pest Management (IPM) practices at the onset of PIP commercialization slowed pest adaptation rates. For corn rootworm, interspersing non-selective periods with IPM+IRM delayed resistance evolution, yet crop rotation was the best strategy to delay resistance. For bollworm inclusion of isoline corn as an IPM tool did not increase the life-time of the PIP. A local resistance phenomenon for rootworm was maintained immediately surrounding the hotspot; random selection of mitigatory strategies in the landscape slowed adaptation rates while mitigation in the hotspot alone did not. Mitigation extended the life-time of the pyramid minimally for both corn rootworm and bollworm.

Understanding regulation of wild animal populations is important in ecological investigations and applied wildlife management. Progress in understanding regulatory processes has been hindered by a long-running debate over the role of density-dependent and density-independent variables in population regulation. Population regulation of exploited species is of particular interest because harvest theory is predicated on assumptions of density-dependent feedback. However, for many exploited species, the functional relationships and mechanisms of population regulation via density dependence are not quantified (e.g., Northern bobwhite (Colinus virginianus). Compounding this task is the lack of a mechanistic understanding of the influence of density-independent factors in population regulation. The overall goal of this dissertation is to investigate the roles of density-dependent and density-independent processes in bobwhite populations. Bobwhites are an excellent species to investigate the role and influence of density-dependent and density-independent factors due to their unique life history, wherein they can exhibit density dependence in survival, reproduction, or both. I provide support for the concomitant influence of density-dependent and density-independent processes operating to regulate bobwhite populations. My results support the importance of food and cover and the additive influence of density-dependent and density-independent factors on bobwhite annual survival. I also report evidence for the differential effects of covariates on survival phases. My results represent the first evidence of support for the Tub and Tap hypotheses on bobwhite survival. I also quantify a density-dependent effect on bobwhite recruitment. Collectively, these results provide new evidence for understanding the role of internal and external factors in bobwhite populations.

Egg masses of Epitheca cynosura were collected from Bays Mountain Park, Tennessee, USA, in June, 1999. Newly hatched individuals were placed into enclosures and sampled at scheduled time intervals throughout the summer. Enclosures were exposed to combinations of high and low densities and presence/absence of a second-year class E. cynosura predator. Survivorship, mean head widths, and mean dry masses were compared across treatments. Due to poor recovery of early-instar larvae, survivorship showed no significant differences in mortality among treatments. The predator present treatment caused significantly smaller head widths and dry masses only on days 42 and 55. The density treatment had a significant effect on larval growth from day 28 through day 86 (end of the experiment). Larvae from low density treatments had larger head widths and dry masses. The effects observed within the density treatments were likely to have resulted in a cohort split. Those individuals in the low density treatment followed a univoltine life history, and high density individuals followed a semivoltine life history. Density is probably a very important factor influencing the voltinism of E. cynosura at Bays Mounain Lake.

Short-lived rodents are sensitive to changes in environmental conditions and exhibit annual fluctuations under seasonal environments in northern temperate regions. I analyzed 34 years of monthly live-trapping data on whiteooted mice (Peromyscus leucopus) collected in Carter Woods, Ohio. I used a theoretic-information approach to select the best approximating models and analysis of deviance to infer effects of climate and density on survival of mice. I tested for a cost of reproduction to females and found no difference in survival between reproductive states. Directions and magnitudes of effects of climate and density varied over time. Increased variability in temperature reduced effects of density on survival. I detected an Allee effect and density dependent effects on survival. Long-term trapping data are needed to study temporal effects of climate and density on the demography of rodents. Recruitment had a greater impact on population growth rate than survival

Individual-level life-history strategies are the rails that guide population dynamics. Due to the difficulty of conducting long-term, individual-based studies, current management practices often focus on estimating and controlling demographic rates with little consideration for the individual-level responses that guide them. This approach cannot account for important factors such as age-specific responses to changes in population density or long-term impacts of conspecific density and resource limitation. As such, population-level approaches may fail to predict age structure or the rate of population growth. Recent studies of mammals and birds have shown that short-term changes in factors such as population density can have lasting impacts on vital rates of individuals. These results highlight the importance of long-term individual-based analyses in understanding population dynamics. However, very few researchers have thus far been able to isolate and study interacting effects of density and resources on life histories apart from processes such as predation, interspecific competition, and management of anthropogenic disturbance. The feral horses (Equus ferus caballus) of Sable Island, Nova Scotia, Canada, exist in a natural though simplified system without predation, human interference, or interspecific competition (they are the island’s only terrestrial mammal, numbering approximately 500 individuals). Here I determined the roles of local conspecific density and an interacting resource gradient in guiding the reproduction and survival of adult female Sable Island horses (2008–2012). I used body condition (estimates of subcutaneous fat) as an indication of resource allocation towards the often conflicting purposes of reproduction and maintenance. Reproduction was best predicted by body condition (reproducing females were in relatively poorer condition) but there was also evidence of density-dependence in reproductive success. Survival was predicted by and positively related to body condition. Survival was also predicted by an interaction between conspecific density and location on the island consistent with expectations of a known east-west resource gradient that occurs on Sable Island (in available water and forage). Greater variability in fitness estimates in resource-poor, eastern Sable Island suggests that regions of low density and resources may be high risk/high reward habitats. Such habitats may be disproportionately avoided by young animals and exploited by senescent animals. All feral horses are descended from domesticated animals and recent work has found evidence of artificially selected life-history traits in unmanaged populations of domestic mammals like cattle, sheep, and horses (e.g., reproducing even at high densities and earlier in life than expected). I therefore attempted to determine if effects of artificial selection existed in the Sable Island population by examining age-based contributions to population growth and the relationship between reproduction (foaling) and female mortality. Perhaps due to the population’s long history of low management (>250 years), I failed to find any strong evidence of artificially selected life-history traits in Sable Island horses. That is, life history trade-offs in survival and reproduction in Sable Island horses were more similar to wild species of large herbivores inhabiting natural environments, than other populations of feral ungulates. My research suggests a rarely documented but fascinating instance of reversal of artificial selection by natural selection for a domesticated species like the horse.

Ontogenetic niche shifts generally coincide with changes in size, morphology, behavior, and/or feeding preferences during development, resulting in a shift in preferred habitat. In aquatic species, these ontogenetic niche shifts are often associated with habitat-dependent changes in competition and/or predation dynamics, expressed as a size-depth relationship where the larger-bodied adults occupy deeper habitats while the smaller-bodied juveniles primarily reside in shallower regions. While the influence of interspecific interactions on size-structured habitat occupancy has been well studied, few have examined the potential role of intraspecific agonistic interactions between size classes in ontogenetic niche shifts. A simulation model was developed to test whether the size-specific habitat occupancy observed in signal crayfish can be explained by the size-structured individual responses to agonistic interaction, where the smaller-bodied juvenile responds to the interaction with an escape movement, to avoid engagement and the risk of mortality or injury from the adult. The simulated movements of signal crayfish resulted in higher juvenile occupancy of riffles relative to pools reflecting a greater rate of escape from adults into riffles, away from the higher densities of adults in their preferred habitat (i.e. pools). This provides evidence that the juvenile escape response to size-structured, intraspecific, agonistic interactions may contribute to ontogenetic niche shifts.