Thesis (Dr. P.H.)--University of Texas Health Science Center at Houston, School of Public Health, 1977. / Source: Dissertation Abstracts International, Volume: 38-11, Section: B, page: 5304. Dissertation Abstracts International order no. 79-6549. Includes bibliographical references (leaves 167-173).

Movement patterns and space use by mature fishes are critical in determining the effectiveness of marine reserves in conserving spawning stock biomass and/or providing biomass to adjacent fisheries through 'spillover'. Home range sizes, activity patterns, site fidelity and habitat preferences were determined for acoustically-tagged snappers and groupers using a rigorously-calibrated array of omnidirectional hydroacoustic receivers deployed in the diverse coral reef environments of a no-take marine reserve (NTMR) network in the Dry Tortugas, Florida. An individual-based localizing tendency model of reef fish movement was parameterized from fine-scale acoustic telemetry data and integrated into a Spatial Management Performance Assessment (SMPA) simulation model for reef fish populations developed to quantitatively evaluate performance of no-take marine reserves in the Dry Tortugas, Florida. Spatially-explicit SMPA models were parameterized for three overfished stocks in the lucrative snapper-grouper fishery: red grouper (Epinephelus morio), black grouper (Mycteroperca bonaci), and mutton snapper (Lutjanus analis). SMPA models were used to evaluate the impacts of a variety of life histories, movement strategies and speeds, and management regulations upon long-term stock sustainability, as measured by annual changes in spawning potential ratio (SPR), and long-term stock productivity, as measured by annual changes in fisheries yield-in-weight per recruit (Yw/R). Under assumptions of constant regional fishing pressure, constant recruitment, and 'realistic' fish movement, SMPA simulation runs from initial conditions in 2000 suggested that by 2014, the Tortugas NTMR network should function to restore red grouper populations to 30% SPR, a Federal management benchmark for sustainability. Mutton snapper were the most mobile of the species investigated; if mutton snapper movements are ignored, their population is predicted to attain 30% SPR by 2014, but given 'realistic' mobility, they may not attain this target by 2021 without additional protections. Black grouper are currently fished at over 9 times sustainable levels. SMPA simulations suggest coupling an increase in minimum size at capture of 20 - 25 cm with NTMR implementation would result in substantial short term losses in yield, but would restore both black grouper and mutton snapper populations to 30% SPR by 2021 and lead to increased long-term yields. Although marine reserve sites are often chosen opportunistically, these findings strongly suggest that reserve designs (e.g. proper sizes and configurations) must take into account the scales and patterns of movement exhibited by the exploited stocks they are intended to protect. These modeling efforts also suggested reserves are not a panacea; in order to promote sustainability for severely depleted stocks, they must be accompanied by an overall reduction in fishing capacity. Although important questions remain concerning the movements of reef fish in response to habitat and density dependent processes, our analyses of realistic reef fish behaviors suggest that the NTMRs of the Dry Tortugas promote substantial gains in SPR, promoting long-term stock sustainability and enhanced egg production. Increased rates of movement diminish these benefits, but may also mitigate short-term losses in yield associated with NTMR establishment.

Myrmecochory, i.e. dispersal of seeds by ants towards and around their nests, plays an important role in temperate forests. Yet hardly any study has examined plant population spread over several years and the underlying joint contribution of a hierarchy of dispersal modes and plant demography. We used a seed-sowing approach with three replicates to examine colonization patterns of Melampyrum pratense, an annual myrmecochorous herb, in a mixed Scots pine forest in northeastern Germany. Using a spatially explicit individualbased (SEIB) model population patterns over 4 years were explained by short-distance transport of seeds by small ant species with high nest densities, resulting in random spread. However, plant distributions in the field after another 4 years were clearly deviating from model predictions. Mean annual spread rate increased from 0.9 m to 5.1 m per year, with a clear inhomogeneous component. Obviously, after a lag-phase of several years, non-random seed dispersal by large red wood ants (Formica rufa) was determining the species’ spread, thus resulting in stratified dispersal due to interactions with different-sized ant species. Hypotheses on stratified dispersal, on dispersal lag, and on non-random dispersal were verified using an extended SEIB model, by comparison of model outputs with field patterns (individual numbers, population areas, and maximum distances). Dispersal towards red wood ant nests together with seed loss during transport and redistribution around nests were essential features of the model extension. The observed lag-phase in the initiation of non-random, medium-distance transport was probably due to a change of ant behaviour towards a new food source of increasing importance, being a meaningful example for a lag-phase in local plant species invasion. The results demonstrate that field studies should check model predictions wherever possible. Future research will show whether or not the M. pratense–ant system is representative for migration patterns of similar animal dispersal systems after having crossed range edges by long-distance dispersal events.

This thesis deals with the evolution of individuals within a species adapted to utilize specific resources, i.e. resource polymorphism. Although a well-known phenomenon, the understanding of the mechanisms behind is not complete. Considering the ruling theories, resource polymorphism is suggested to depend on severe competition for resources, the presence of open niches to be occupied leading to a reduction in competition, and disruptive selection where generalist are out-competed due trade-offs in foraging efficiency for different prey. In order to study resource polymorphism, I have used fish as the animal group in focus and the methods I have used range over laboratory experiments, field experiments, literature surveys and theoretical modelling. In my work, I have showed that different resource use induces different body shapes and that the rate of change is dependent of the encounter rate of different resources. The induced body changes partly led to increased foraging efficiency but surprisingly I did not find any trade-offs due to specialization. However, when studying predation risk in relation to resource polymorphism, my studies point towards that resource use and predation risk may act as balancing factors in such a way that disruptive selection can take place. My work also shows that population feedbacks have to be explored when considering the evolution of resource polymorphism. In pond and field experiments, I found that changes in resource densities affected the actual resource use despite previous adaptations to certain resources. By performing a literature survey, I found that cannibalism indirectly by its effect on population dynamics seems to facilitate the evolution of resource polymorphism. Modelling a size-structured population, I found that resource dynamics were stabilized, and the relative availability of different resources was levelled out due to cannibalism. Taken together, my studies strongly suggest that to understand the development of resource polymorphism in consumer populations, future studies have to include the effect of a dynamic environment both with respect to resources and predators.

The Holocene spread of Picea abies in Scandinavia provides an excellent opportunity for detailed study of the dynamics of tree spread and population expansion. Early- and mid-Holocene macrofossil evidence for the presence of Picea abies in Scandinavia has questioned traditional interpretations of the timing and direction of its spread. This study aims to determine the pattern of the spread of Picea abies in Scandinavia from pollen and other data, to evaluate the significance of possible early outpost populations and to deduce possible factors that influenced the spread and population expansion of Picea abies in Scandinavia. Palaeoecological investigations were carried out on the sediments of four small lakes in central Sweden to gain detailed insight into the dynamics of the spread. Holocene pollen diagrams with independent dating control were collected from Fennoscandia and adjacent areas to compare the timing of selected features of the Picea abies pollen curve. Computer models were used to test possible scenarios for the spread and Picea abies population expansion. Picea abies entered the Scandinavian peninsula from the east at different times and by different pathways. Early-Holocene outposts can be discerned in pollen records from northwest Russia, eastern and northeastern Finland for the time before 9000 cal. BP. Pollen records from Sweden and Norway indicate small Picea abies populations after 8000 cal. BP. The mid to late-Holocene spread, which superficially resembles a front-like pattern, may in fact represent a wave of expanding populations. Disturbance through fire and human activity did not significantly influence the pattern of the spread. Changing climate parameters, slow adaptation and gene flow through seeds and pollen have to be considered as possible explanations for the late spread of the tree. Population dynamics and propagule pressure are likely to be important factors that shaped the spread of Picea abies.

Effective conservation strategies for imperiled species require an understanding of processes that influence fitness throughout the organism's life cycle and across the range of habitats needed to complete that cycle. I evaluated factors that affect population viability of bull trout Salvelinus confluentus, a threatened freshwater char species, throughout individual life stages and over the entire life cycle. I assessed the relationship between bull trout egg incubation success and environmental variables. Egg survival was negatively related to the percent of fine sediment in redds and positively related to hydraulic conductivity and the strength of downwelling. Next, I quantified juvenile bull trout survival rates and described movement patterns for this life stage. Juvenile bull trout emigrated from natal headwaters into larger rivers throughout the entire year and across a range of sizes. Estimates of juvenile survival rates improved dramatically when emigration was incorporated into the analysis. I integrated my observations of bull trout survival, growth, and movement to create a life-cycle model, which I used to better understand how populations respond to changes in specific demographic rates. Bull trout populations were particularly sensitive to changes in juvenile growth and survival. The relative effect of changes to fertility rates and adult survival varied depending upon whether a population was composed primarily of large, migratory, or smaller, resident individuals. Dispersal helped to lower the probability of extinction for small or declining populations when neighboring populations were stable. My research demonstrates that bull trout require access to habitats throughout entire watersheds to maintain population viability. My results suggest that limiting anthropogenic sources of fine sediment and maintaining areas of channel complexity that promote downwelling can be important for bull trout embryo survival. Management decisions should also consider the diverse behavior of juvenile bull trout and the wide range of habitat they use. Additionally, connectivity between populations is likely to be important for declining populations to persist. The diversity of life-history strategies expressed by bull trout helps maintain demographic stability within and among populations. As such, preservation of habitat integrity and full life-history diversity is imperative for conservation and recovery of bull trout populations range-wide.

Although semi-natural grasslands in Europe are declining there is often a time delay in the local extinction of grassland species due to development of remnant populations, i.e., populations with an extended persistence despite a negative growth rate. The objectives of this study were to examine the occurrence of remnant populations after abandonment of semi-natural grasslands and to examine functional traits of plants associated with the development of remnant populations. We surveyed six managed semi-natural grasslands and 20 former semi-natural grasslands where management ceased 60-100 years ago, and assessed species response to abandonment, assuming a space-for-time substitution. The response of species was related to nine traits representing life cycle, clonality, leaf traits, seed dispersal and seed mass. Of the 67 species for which data allowed analysis, 44 species declined after grassland abandonment but still occurred at the sites, probably as remnant populations. Five traits were associated with the response to abandonment. The declining but still occurring species were characterized by high plant height, a perennial life form, possession of a perennial bud bank, high clonal ability, and lack of dispersal attributes promoting long-distance dispersal. Traits allowing plants to maintain populations by utilizing only a part of their life cycle, such as clonal propagation, are most important for the capacity to develop remnant populations and delay local extinction. A considerable fraction of the species inhabiting semi-natural grasslands maintain what is most likely remnant populations after more than 60 years of spontaneous succession from managed semi-natural grasslands to forest. / <p>authorCount :3</p>

Northern environments are often characterised by large seasonal and annual fluctuations in food abundance. In this thesis, I examined how arctic foxes (</i>Alopex lagopus</i>) used seasonally superabundant foods (geese and their eggs) and how access to these foods influenced population dynamics of arctic foxes. I addressed this against a backdrop of variation in lemming and vole abundance (small mammals hereafter) the main foods of arctic foxes throughout most of their range. Field work was done at the large goose colony at Karrak Lake and surrounding areas in the Queen Maud Gulf Bird Sanctuary in Nunavut, Canada, in the spring and summers of 2000 to 2004. <p> Behavioural observations of individually-marked arctic foxes showed that they took and cached 2,000-3,000 eggs per fox each year and that the rate at which they took eggs was largely unrelated to individual attributes of foxes (e.g. sex, size, and breeding status) and nesting distribution of geese. Further, the rate at which foxes took eggs varied considerably within individuals in that foxes were efficient at taking eggs at times and inefficient at other times. This may have resulted from foxes switching between foraging actively and taking eggs opportunistically while performing other demands such as territorial behaviours. <p>Comparison of stable isotope ratios (13C and 15N) of fox tissues and those of their foods showed that the contribution of cached eggs to arctic fox diets was inversely related to collared lemming (<i>Dicrostonyx torquatus</i>) abundance. In fact, the contribution of cached eggs to overall fox diets increased from <28% in years when collared lemmings were abundant to 30-74% in years when collared lemmings were scarce. Furthermore, arctic foxes used cached eggs well into the following spring (almost 1 year after eggs were acquired) a pattern which differs from that of carnivores generally storing foods for only a few days before consumption. <p>A field-study of experimental caches showed that survival rate of these caches was related to age of cache sites in the first year of the study (e.g. 0.80 and 0.56 per 18-day period for caches from new and 1 month old cache sites, respectively) and departure by geese after hatch in the second year of the study (e.g. 0.98 and 0.74 per 18-day period during and after goose nesting, respectively). Food abundance and deterioration of cache sites (e.g. loss of soil cover and partial exposure of caches) were, thus, important factors affecting cache loss at Karrak Lake. Further, annual variation in the importance of these factors suggests that strategies to prevent cache loss are not fixed in time but vary with existing conditions. Evolution of caching behaviours by arctic foxes may, thus, have been shaped by multiple selective pressures. <p>Comparisons of reproductive output and abundance of arctic foxes inside and outside the goose colony at Karrak Lake showed that (i) breeding density and fox abundance were 2-3 times higher inside the colony than they were outside the colony and (ii) litter size, breeding density, and annual variation in fox abundance followed that of small mammal abundance. Small mammal abundance was, thus, the main governor of population dynamics of arctic foxes whereas geese and their eggs elevated fox abundance and breeding density above that which small mammals could support. These results highlight both the influence of seasonal and annual variation on population dynamics of consumers and the linkage between arctic environments and wintering areas by geese thousands of kilometres to the south.

No description available.

Northern environments are often characterised by large seasonal and annual fluctuations in food abundance. In this thesis, I examined how arctic foxes (</i>Alopex lagopus</i>) used seasonally superabundant foods (geese and their eggs) and how access to these foods influenced population dynamics of arctic foxes. I addressed this against a backdrop of variation in lemming and vole abundance (small mammals hereafter) the main foods of arctic foxes throughout most of their range. Field work was done at the large goose colony at Karrak Lake and surrounding areas in the Queen Maud Gulf Bird Sanctuary in Nunavut, Canada, in the spring and summers of 2000 to 2004. <p> Behavioural observations of individually-marked arctic foxes showed that they took and cached 2,000-3,000 eggs per fox each year and that the rate at which they took eggs was largely unrelated to individual attributes of foxes (e.g. sex, size, and breeding status) and nesting distribution of geese. Further, the rate at which foxes took eggs varied considerably within individuals in that foxes were efficient at taking eggs at times and inefficient at other times. This may have resulted from foxes switching between foraging actively and taking eggs opportunistically while performing other demands such as territorial behaviours. <p>Comparison of stable isotope ratios (13C and 15N) of fox tissues and those of their foods showed that the contribution of cached eggs to arctic fox diets was inversely related to collared lemming (<i>Dicrostonyx torquatus</i>) abundance. In fact, the contribution of cached eggs to overall fox diets increased from <28% in years when collared lemmings were abundant to 30-74% in years when collared lemmings were scarce. Furthermore, arctic foxes used cached eggs well into the following spring (almost 1 year after eggs were acquired) a pattern which differs from that of carnivores generally storing foods for only a few days before consumption. <p>A field-study of experimental caches showed that survival rate of these caches was related to age of cache sites in the first year of the study (e.g. 0.80 and 0.56 per 18-day period for caches from new and 1 month old cache sites, respectively) and departure by geese after hatch in the second year of the study (e.g. 0.98 and 0.74 per 18-day period during and after goose nesting, respectively). Food abundance and deterioration of cache sites (e.g. loss of soil cover and partial exposure of caches) were, thus, important factors affecting cache loss at Karrak Lake. Further, annual variation in the importance of these factors suggests that strategies to prevent cache loss are not fixed in time but vary with existing conditions. Evolution of caching behaviours by arctic foxes may, thus, have been shaped by multiple selective pressures. <p>Comparisons of reproductive output and abundance of arctic foxes inside and outside the goose colony at Karrak Lake showed that (i) breeding density and fox abundance were 2-3 times higher inside the colony than they were outside the colony and (ii) litter size, breeding density, and annual variation in fox abundance followed that of small mammal abundance. Small mammal abundance was, thus, the main governor of population dynamics of arctic foxes whereas geese and their eggs elevated fox abundance and breeding density above that which small mammals could support. These results highlight both the influence of seasonal and annual variation on population dynamics of consumers and the linkage between arctic environments and wintering areas by geese thousands of kilometres to the south.