Dispersal is a fundamental ecological and evolutionary process that can create demographic and genetic linkage between neighbouring and distant locations, influencing the dynamics, structure and ultimately the persistence of populations. To understand observed population dynamics and structure and to predict future change, accurate and comprehensive data are required describing the pattern and magnitude of dispersal and gene flow across all relevant spatial scales. However, this is a major empirical challenge. In this thesis, I aimed to obtain comprehensive empirical data quantifying natal dispersal patterns and population genetic structure across multiple spatial scales using the European shag (Phalacrocorax aristotelis) as a model species. I used a combination of field observations of shags individually ringed on the Isle of May, Scotland and molecular genetic techniques to accomplish these aims. By locating adult shags that had been ringed as chicks on the Isle of May at their breeding locations across eastern Scotland, I demonstrated divergent dispersal distributions at small versus large spatial scales. Using both mitochondrial DNA markers and a newly developed set of microsatellite markers, I quantified population genetic structure across a pan-European scale. This was weak across both molecular markers suggesting a role for occasional effective long-distance dispersal. However, a suite of evolutionary forces besides gene flow can create observed population genetic structure. Therefore, I quantified population genetic structure across populations in eastern Scotland, and quantitatively linked this indirect estimate of gene flow with my direct field observations of dispersal. Dispersal parameters derived explicitly from field observations and the spatial organisation of populations were shown to strongly influence observed population genetic structure. Overall, these data demonstrate the need to utilise both field observations and genetic methods to comprehensively estimate the extent and effectiveness of dispersal and highlight the importance of accurately quantifying long-distance dispersal in particular for predicting future change.

Worldwide harbour seal populations are showing differing and fluctuating trends in abundance, but the drivers of change remain uncertain. Within the Moray Firth, NE Scotland, count surveys carried out over the last 20 years highlighted the development of a new breeding site, providing a unique opportunity to carry out an individual-based study of harbour seal demography and pupping phenology using photo-identification techniques within a mark-recapture framework. Sightings of individual seals suggested that a large proportion of harbour seals are year-round residents at haul-out sites. Both sexes displayed high levels of between-year breeding site fidelity as well as seasonal variation in their haul-out behaviour. Apparent sex-specific survival rates (0.89♂, 0.97♀) and birth rates (0.88) were high. There was a strong correlation between lactation durations and the timing of pupping, suggesting that shifts in pupping phenology are a result of energetic constraints. This highlights the potential for using the timing of pupping as an indicator of ecosystem conditions. This study provided the first concurrent real-time estimates of survival and fecundity in a naturally regulated population of harbour seals. Demographic parameters and physiological responses indicate that prevailing conditions within the Moray Firth are favourable, and that this population should be recovering. However, observed patterns may also be an artefact of the long-term decline having caused an increase in per capita food availability through the reduction in intra-specific competition. This study highlights the current and long-term importance of individual-based data in understanding population dynamics. Through the identification of sentinel sites around the world, harbour seals could provide a single-species indicator of coastal ecosystem conditions in the Northern Hemisphere.

This thesis explores the stochastic features of models of ecological systems in discrete and in continuous time. Our interest lies in models formulated at the microscale, from which a mesoscopic description can be derived. The stochasticity present in the models, constructed in this way, is intrinsic to the systems under consideration and stems from their finite size. We start by exploring a susceptible-infectious-recovered model for epidemic spread on a network. We are interested in the case where the connectivity, or degree, of the individuals is characterised by a very broad, or heterogeneous, distribution, and in the effects of stochasticity on the dynamics, which may depart wildly from that of a homogeneous population. The model at the mesoscale corresponds to a system of stochastic differential equations with a very large number of degrees of freedom which can be reduced to a two-dimensional model in its deterministic limit. We show how this reduction can be carried over to the stochastic case by exploiting a time-scale separation in the deterministic system and carrying out a fast-variable elimination. We use simulations to show that the temporal behaviour of the epidemic obtained from the reduced stochastic model yields reasonably good agreement with the microscopic model under the condition that the maximum allowed degree that individuals can have is not too close to the population size. This is illustrated using time series, phase diagrams and the distribution of epidemic sizes. The general mesoscopic theory used in continuous-time models has only very recently been developed for discrete-time systems in one variable. Here, we explore this one-dimensional theory and find that, in contrast to the continuous-time case, large jumps can occur between successive iterates of the process, and this translates at the mesoscale into the need for specifying `boundary' conditions everywhere outside of the system. We discuss these and how to implement them in the stochastic difference equation in order to obtain results which are consistent with the microscopic model. We then extend the theoretical framework to make it applicable to systems containing an arbitrary number of degrees of freedom. In addition, we extend a number of analytical results from the one-dimensional stochastic difference equation to arbitrary dimension, for the distribution of fluctuations around fixed points, cycles and quasi-periodic attractors of the corresponding deterministic map. We also derive new expressions, describing the autocorrelation functions of the fluctuations, as well as their power spectrum. From the latter, we characterise the appearance of noise-induced oscillations in systems of dimension greater than one, which have been previously observed in continuous-time systems and are known as quasi-cycles. Finally, we explore the ability of intrinsic noise to induce chaotic behaviour in the system for parameter values for which the deterministic map presents a non-chaotic attractor; we find that this is possible for periodic, but not for quasi-periodic, states.

The paper provides a detailed overview of population dynamics and trends in the Arab region. Furthermore, it explains the concept of demographic dividend and timing of the window of opportunity. With a view to enable countries in the region to reap the benefits of the changing population structure, the window is calculated for each country. The last part of the paper presents four case studies of countries that benefitted from their demographic dividend.

Commercial harvest of sh stocks and their appropriate management requires an understanding of their population dynamics and of their ability to sustain exploitation. Here, some ecological and evolutionary consequences of excessive exploitation are examined. In Chapter 2 I evaluate the knowledge base and status of commercially exploited marine populations that undergo formal stock assessment. Despite a bias towards industrialised countries and stocks of commercial importance, I show the pervasiveness of overexploitation and, by using reference points of stock status, identify important regional di erences in the e ectiveness of sheries management. In Chapter 3 I develop a data format suitable for ecological analyses to best disseminate the valuable information contained in scienti c trawl surveys. This data format is suitable for inclusion into the public Ocean Biogeographic Information System (OBIS) and provides detailed observations that are suitable to the reconstruction of important sheries-independent stock indices. In Chapter 4 I examine the spatiotemporal dynamics of ground sh populations. A positive abundance-occupancy relationship was estimated for the majority of ground- sh populations examined suggesting that this well-described terrestrial pattern is also pervasive in the marine environment. Spatial hysteresis was exhibited by numerous populations, indicating that the spatial distribution of individuals failed to recover despite recoveries in abundance. In Chapter 5 I estimate the demographic consequences of changes in growth and maturation characteristics. The ability of a population to sustain harvest, and its ability to recover from previous depletions can be overestimated because of trends towards earlier maturation and slower growth. In Chapter 6 I conclude the thesis by discussing the implications of my research to sheries science and management. I argue that trends in the spatial distribution and the overall productivity of populations must be accounted for when determining sustainable shing levels and when predicting recovery trajectories under various catch abatement scenarios. While successful management measures have been implemented in a number of marine ecosystems, this thesis highlights the importance of improving our capacity to understand the dynamics of exploited populations and to fully use the wealth of available monitoring and assessment data.

Annual abundance of northern bobwhite (Colinus virginianus) and scaled quail (Callipepla squamata) fluctuates drastically in Texas, which complicates a quail manager’s ability to forecast quail abundance for the ensuing hunting season. The Texas Quail Index (TQI) was a 5-year citizen-science project that evaluated several indices of quail abundance and habitat parameters as predictors of quail abundance during the ensuing fall. I found that spring cock-call counts explained 41% of the variation in fall covey-call counts for all study sites in year 1–4, and 89% of the variation in year 5. Further investigation revealed that year 5 was a drought year and had a significantly lower percentage of juveniles in the hunter’s bag. These results suggest that during drought years, fall quail abundance is more predictable than during non-drought years and that low breeding success may be the reason. If these data are correct, quail managers should have a better ability to predict the declines of their fall quail abundance in the dry years. The TQI relied on citizen scientists (cooperators) to collect data. Since most (66.1%) cooperators dropped out of the program, and <8% of all data sets were complete, I surveyed the cooperators by mail to determine the rate and cause of cooperator decline and to identify characteristics of a reliable cooperator (i.e., one that did not drop out of the study). I found that cooperator participation declined earlier each year for year 1–4, and that year 5 demonstrated a steady trend with the least amount of cooperators. Most respondents who dropped out (61.5%) reported their motive for leaving was that it was too time consuming. I found no difference in mean cooperator demographics, satisfaction, or landownership goals between those respondents who dropped out and those that did not. However, 38% of those who dropped out were not completely satisfied with communication from TQI coordinators compared to only 15% of those who did not drop out, indicating that communication, or perhaps overall volunteer management, might have been improved. Future studies should maintain better communication with participants, require less time, and provide an incentive for retention.

Commercial harvest of fish stocks and their appropriate management requires an understanding of their population dynamics and of their ability to sustain exploitation. Here, some ecological and evolutionary consequences of excessive exploitation are examined. In Chapter 2 I evaluate the knowledge base and status of commercially exploited marine populations that undergo formal stock assessment. Despite a bias towards industrialised countries and stocks of commercial importance, I show the pervasiveness of overexploitation and, by using reference points of stock status, identify important regional differences in the effectiveness of fisheries management. In Chapter 3 I develop a data format suitable for ecological analyses to best disseminate the valuable information contained in scientific trawl surveys. This data format is suitable for inclusion into the public Ocean Biogeographic Information System (OBIS) and provides detailed observations that are suitable to the reconstruction of important fisheries-independent stock indices. In Chapter 4 I examine the spatiotemporal dynamics of groundfish populations. A positive abundance-occupancy relationship was estimated for the majority of groundfish populations examined suggesting that this well-described terrestrial pattern is also pervasive in the marine environment. Spatial hysteresis was exhibited by numerous populations, indicating that the spatial distribution of individuals failed to recover despite recoveries in abundance. In Chapter 5 I estimate the demographic consequences of changes in growth and maturation characteristics. The ability of a population to sustain harvest, and its ability to recover from previous depletions can be overestimated because of trends towards earlier maturation and slower growth. In Chapter 6 I conclude the thesis by discussing the implications of my research to fisheries science and management. I argue that trends in the spatial distribution and the overall productivity of populations must be accounted for when determining sustainable fishing levels and when predicting recovery trajectories under various catch abatement scenarios. While successful management measures have been implemented in a number of marine ecosystems, this thesis highlights the importance of improving our capacity to understand the dynamics of exploited populations and to fully use the wealth of available monitoring and assessment data.

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Understanding whether groups of individuals represent a single panmictic gene pool, or multiple genetically structured populations across a species range should aid in predicting whether specific conservation strategies would be more or less effective for species preservation. Further, contrasting the population structures of multiple coexisting taxa could foster an even deeper understanding of evolutionary divergence among demes and potentially even suggest local adaptation in the form of tight coevolutionary relationships. Finally, the analysis of population dynamics within small and isolated populations could improve our understanding of the relative importance that different evolutionary mechanisms have in predicting population persistence in the wild. Using microsatellite markers I characterized the population genetic structure in the critically endangered Cyclura cychlura cychlura iguanas on Andros Island. I found significant differences between inferred and realized rates of gene flow. This finding demonstrates that evolutionarily independent populations can occur even with high rates of dispersal. In the second and third study I contrasted patterns of genetic variability in Cyclura cychlura cychlura iguanas, ticks in the genus Amblyomma parasitizing these iguanas, and Rickettsia spp., potential pathogens transmitted by these ticks. I determined that genetic differences among Rickettsia samples and Amblyomma samples are highly concordant with genetic divergence among iguana populations. This finding suggests largely vertical dispersal of ticks and their super-parasite, a high specificity of this reptile-tick interaction, and historically low rates of dispersal in iguanas. This finding also indicates that island populations of iguanas may be locally adapted due to tight coevolutionary relationships. Finally, I investigated the mechanisms that eliminate harmful mutations in small isolated and natural populations of the critically endangered Cyclura cychlura cychlura iguanas. Using molecular tools I found indirect evidence suggesting that small natural populations can maintain significant levels of genetic variation in spite of strong selection acting against harmful mutations. Under regimes of random mating, the buildup of harmful mutations in small populations may result in a large number of inviable young. However, harmful mutations may also be eliminated when exposed to natural selection through increased competition, as population density increases. However, quantification of the relative role of competition was not feasible in this study.

Multisystem length limits are a popular output control implemented to regulate harvest of many gamefishes. Evaluating the direct effects of length limits is crucial in selecting a regulation, but to my knowledge, no formal methodology exists to model length limits for multiple systems. Without a formalized process, complexities associated with multisystem scales of management can preclude effective communication and interpretation of information. I created a quantitative decision model as an approach for comparing length limits applied to multiple systems. This approach combined an extension of the Beverton-Holt yield-per-recruit function and an additive utility function to compare multisystem length limits. I also conducted a sensitivity analyses to clarify the effect of input parameters and uncertainty on the expected utility, and on performance metrics. This approach provides a consistent methodology for evaluating multisystem length limits, and as a decision support tool, can improve transparency of the length-limit-selection process.