POPULATION ECOLOGY OF SEALS: RETROSPECTIVE and PROSPECTIVE VIEWS

This review focuses on population ecology, with critical accounts of past work and future possibilities in age determination, body growth and condition, estimating abundances, mortality rates and lifespans, reproduction, comparative life histories, population dynamics, population modelling and seals in ecosystems. We suggest ways to reduce errors in age determination and to improve methods of obtaining and presenting growth data. Generalized von Bertalanffy growth equations are promoted as a basis for analysing species differences and intra-population variation in body lengths. Indices other than blubber thickness may be better for following body condition. Catch-effort and survival-index methods of estimating abundances have limited applicability, total counts are only locally useful, and sample counts may only be accurate for scattered, ice-breeding species. Some new techniques for population indices are promising. Pre-adult mortality remains difficult to assess. Although not always recognized, adult mortality rates do increase with age, as well described by Gompertz functions. Existing estimates of lifespans are unreliable, and a new approach is outlined. There are methodological problems in estimating ages of maturity. Corpora albicantia should not be used for back-extrapolation, and more study is needed of use of teeth annuli as indicators of maturity. Age-specific proportions of females parous based on reproductive tracts may disagree with proportions recruited in breeding groups, suggesting that the former may often be in error. Allometric relationships among body sizes and life-history variables need more reliable data, especially since the residuals of such relationships are of greatest interest. Brain size may be a better scalar. Direct evidence of density dependence in population growth of seals is sparse. Early survival has been more widely shown to be density-dependent, but only among polygynous species where crowding on land may be a byproduct of sexual selection; there is as yet no good evidence of trophic restraints. Evidence of density dependence of ages of maturity is generally unconvincing. Predation, especially by sharks, may be critical in some species. Characteristics of equilibrium populations might profitably be sought in mass remains in middens and historic kill sites. More attention should be paid to the search for density-independent influences. Supposed impacts of fisheries and pollutions are not wholly convincing. Natural epidemics may keep some populations below resource or space saturation, and some high-latitude species may show large year-to-year variations in recruitment and abundances. Evidence for such density-independent effects should be sought in residuals of growth curves and in teeth layers. Although surplus yield and production/biomass models have been tried, realistic pinniped models must be completely age-structured and time-dependent. Simple models have questionably assumed stationarity to derive life-history parameters. The best available estimates of density dependence of such parameters give no resolution when extrapolated toward equilibrium, and only limited efforts have been made to introduce stochasticity. Better data, not improved model structures, are needed for better understanding. Recent work has contradicted the assumed voraciousness of seals, but their system impacts and dependencies are not well understood. Extended Lotka-Volterra equations used to model Antarctic food webs, including seals, are merely heuristic. Fixed seal biomasses enter as top-down, driving functions in a Bering Sea model, which accordingly cannot be used to analyse or manage their populations. Some Soviet models are tantalizing but ill-specified. The introduction of harbor seals in well-chosen lakes might give mote insights into system roles than would more elaborate modelling. We wonder if pinniped ecology is well served by too many enthusiasts operating under too many restraints.     

Linking dispersal, immigration and scale in the neutral theory of biodiversity

In the classic spatially implicit formulation of Hubbell's neutral theory of biodiversity a local community receives immigrants from a metacommunity operating on a relatively slow timescale, and dispersal into the local community is governed by an immigration parameter m . A current problem with neutral theory is that m lacks a clear biological interpretation. Here, we derive analytical expressions that relate the immigration parameter m to the geometry of the plot defining the local community and the parameters of a dispersal kernel. Our results facilitate more rigorous and extensive tests of the neutral theory: we conduct a test of neutral theory by comparing estimates of m derived from fits to empirical species abundance distributions to those derived from dispersal kernels and find acceptable correspondence; and we generate a new prediction of neutral theory by investigating how the shapes of species abundance distributions change theoretically as the spatial scale of observation changes. We also discuss how our main analytical results can be used to assess the error in the mean-field approximations associated with spatially implicit formulations of neutral theory.     

A Model of Genome Size Dynamics During Speciation

A model developed for the evolving size of the repetitive part of the eukaryote genome during speciation was subjected to analytical and computer treatment. The basic assumption of the model was that two classes of repetitive DNA contribute mainly to macroevolutionary changes in genome size: arrays of tandem repeats (ATR) changing through unequal crossover and mobile genetic elements (MGE) changing presumably through an integration mechanism of the Tn- and Is-kind operating in bacteria. Within the framework of this model, the macroevolution of the MGE size is formally equivalent to that of the ATR in the particular case when shifts of chromatids have only one repeat out of register. This allowed us to consider genome size as a large set of various ATRs. The results obtained are as follows. If the duplication and deletion of repeats have unequal fixation probabilities during each speciation act, the predicted species distributions of genome size significantly deviate from the real ones; if they have equal fixation probabilities, there is a conformance between calculated and real distributions. In the latter case, the model reproduces the salient features of real distributions upon acceptance of 1) upper selective boundary nonspecifically limiting increase in genome size within the evolving taxonomic group and 2) non-neutrality of variability in genome size with respect to speciation.     

Linear age-dependent population growth with seasonal harvesting

A population growth is modelled by the Von Foerster PDE with accompanying Lotka-Volterra integral equation describing the birth rate; the age specific death and fertility rates are assumed to depend only on age and not time. A harvesting policy where a fraction of the population of age greater than a given age is harvested for a fraction of a given season. This introduces a time dependence, but this difficulty is circumvented by devising approximate timeindependent models whose birthrates bracket the true birthrate-the standard renewal equation theory applies to the approximate models so quantitative results can be obtained.The author wishes to thank Professors J. J. Levin and R. K. Miller for some useful remarks. This research was partially supported by NIH Grant GMO 7661-02.     

Magnetoliposomes

The adsorption of different types of phosphatidylglycerols onto magnetizable solid particles is studied. The super-paramagnetic magnetite spheres used have an average diameter of only 14 nm and are stabilized by lauric acid to keep them in solution. During incubation and dialysis of this water-based magnetic fluid in the presence of preformed sonicated phospholipid vescles, magnetoliposomes are formed which are captured from solution with high efficiency by high-gradient magnetophoresis. Support for the bilayer character of the phospholipid coat is derived from both theoretical calculations and experimental data. Phospholipids which form the inner monolayer are adsorbed very quickly with their charged headgroup orientated towards the iron oxide surface. The high-affinity character of the binding is reflected in the adsorption isotherms and is further illustrated by their non-extractability with high concentrations of Tween 20. The outer layer assembles through interaction with the exposed hydrocarbon chains. As compared to the inner layer, the phospholipids adsorb at a much slower rate and are displaced by Tween 20 concentrations which usually disrupt conventional membranes. The adsorption isotherms for this layer obey the Langmuir expression. The affinity constants, derived from them, progressively increase as the hydrophobic nature of the phosphatidylglycerols is more pronounced.Abbreviations DXPG di-fatty acyl form of phosphatdylglycerol where X=L, Lauroyl - M myristoyl - C _15:0 pentadecanoyl - O oleoyl. TES, 2-((tris(hydroxymethyl)methyl)amino)ethanesulfonic acid     

On a Mixed-Type Randomized Rule for Selecting Superior Binomial Models

We propose a new class of selection rules for selecting superior models from finite Binomial models. This new class of rules extends the classes of classical rules and shows its superiority to the classical selection rules by some Monte Carlo results. This new class of rules is easier and more flexible to apply than these known classical rules.     

Modelling expected trout ranges under current and future water temperature regimes in the Eastern Cape,South Africa

Different values have resulted in conflicts between anglers and conservation lobbies in the management of trout in South Africa. Key to the conflict is the demarcation of boundaries to areas in which brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss currently occur, or are likely to establish following stocking for angling. To provide a longer-term perspective on these areas, we developed models to link salmonid biological thermal thresholds to elevation. These, when applied spatially using a digital elevation model with a probability of occurrence model, provided the basis for estimating potentially available thermal habitat for these two cold water species. Here, we acknowledge that other variables (stocking history; river connectivity) also play a role in understanding trout distributions. Using a simple scenario of an increase in mean daily water temperatures of 2 °C, we demonstrated that both brown and rainbow trout are likely to exhibit considerable range reductions in the future. Because it is possible that these range restrictions will result in an increasing desire to introduce trout into areas above their current distribution limits for the maintenance of angling opportunities, conservation managers should prioritise these areas, with management interventions seeking to understand what will help to limit introductions.     

Plasma Proteome Signature of Sepsis: a Functionally Connected Protein Network

Sepsis is an extreme host response to infection that leads to loss of organ function and cardiovascular integrity. Mortality from sepsis is on the rise. Despite more than three decades of research and clinical trials, specific diagnostic and therapeutic strategies for sepsis are still absent. The use of LFQ‐ and TMT‐based quantitative proteomics is reported here to study the plasma proteome in five mouse models of sepsis. A knowledge‐based interpretation of the data reveals a protein network with extensive connectivity through documented functional or physical interactions. The individual proteins in the network all have a documented role in sepsis and are known to be extracellular. The changes in protein abundance observed in the mouse models of sepsis have for the most part the same directionality (increased or decreased abundance) as reported in the literature for human sepsis. This network has been named the Plasma Proteome Signature of Sepsis (PPSS). The PPSS is a quantifiable molecular readout that can supplant the current symptom‐based approach used to diagnose sepsis. This type of molecular interpretation of sepsis, its progression, and its response to therapeutic intervention are an important step in advancing our understanding of sepsis, and for discovering and evaluating new therapeutic strategies.