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Population Biology and Restoration of Intertidal Cockle BedsAdkins, Suzanne Craig January 2012 (has links)
There is evidence that infaunal bivalves in New Zealand are not as abundant as they once were with overfishing and habitat modification contributing to the decline in density and health of cockles. The population biology and abundance of the bivalve Austrovenus stutchburyi (tuangi) in eight beds in four estuaries was assessed both seasonally (13 seasons) and annually (7 years) as little is known about the cockle beds in the Canterbury region of New Zealand. As with populations of similar species worldwide, there were site specific differences in population structure (density and size ranges) with the highest densities at Takamatua (>1500/m²), and the lowest at Port Levy (<350/m²). Gonad indices varied between male and female cockles. Male reproductive cycles were similar at all sites with male cockles being reproductively active year round, while females were more active in spring and summer. Temporal and spatial site specific differences occurred in cockle condition with high salinity sites having higher condition indices (CI) than low salinity sites. There were spatial and temporal variations in salinity (3-35ppt), sediment structure (fine sand through to predominantly silt), water temperature (6-20°C), nutrient supply (total volatile solids (TVS) 0.002- 0.15mg/L) and contaminant levels. Metal pollution indices (MPI) ranged between 3 and 11.
Three cockle transplant trials were undertaken both within and between estuarine systems. Caged cockles survived well, and cage design needed to allow vertical movement of the bivalves within the substrate to reduce mortality. At the end of the 12 month trial, approximately 45% of the cockles remained in the plots. The condition of transplanted cockles was similar to naturally occurring cockles. Recommendations are made to optimise the success of cockle transplants. Large scale, un-caged placement of 25-30mm length cockles in the mid-low tide region of areas with stable, but not necessarily uncontaminated substrate, moderate salinity and temperature and with a reliable nutrient supply is recommended. The results from the thesis research can be applied to other infaunal bivalves in New Zealand allowing more successful restoration processes leading to increased species diversity and ecosystem functioning.
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Larval competition and cannibalism in the Indian meal mouth, Plodia interpunctellaReed, Douglas James January 1998 (has links)
No description available.
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Field management and the structure of arable weed communitiesMcCloskey, Moya January 1995 (has links)
No description available.
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Genetic variation in Pyrenopeziza brassicae and its interaction with its host Brassica napus ssp. oleiferaMajer, Dorothea January 1997 (has links)
No description available.
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Ecological and genetic perspectives on dispersal in European shags (Phalacrocorax aristotelis)Barlow, Emily J. January 2011 (has links)
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.
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Demography and breeding phenology of a marine top predatorCordes, Line Søltoft January 2011 (has links)
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.
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Intrinsic fluctuations in discrete and continuous time modelsParra Rojas, César January 2017 (has links)
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.
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Demographic Profile of the Arab Region: Realizing the Demographic DividendGoujon, Anne, Weber, Daniela, Loichinger, Elke 26 September 2016 (has links) (PDF)
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.
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Ecology And Evolution Of Heavily Exploited Fish PopulationsRicard, Daniel 25 May 2012 (has links)
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.
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The Texas Quail Index: Evaluating Predictors of Quail Abundance Using Citizen ScienceReyna, Kelly Shane 15 May 2009 (has links)
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.
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