A model of ecological and evolutionary consequences of color polymorphism

We summarize direct and indirect effects on fitness components of animal color pattern and present a synthesis of theories concerning the ecological and evolutionary dynamics of chromatic multiple niche polymorphisms. Previous endeavors have aimed primarily at identifying conditions that promote the evolution and maintenance of polymorphisms. We consider in a conceptual model also the reciprocal influence of color polymorphism on population processes and propose that polymorphism entails selective advantages that may promote the ecological success of polymorphic species. The model begins with an evolutionary branching event from mono- to polymorphic condition that, under the influence of correlational selection, is predicted to promote the evolution of physical integration of coloration and other traits (cf. multi-trait coevolution and complex phenotypes). We propose that the coexistence within a population of alternative ecomorphs with coadapted gene complexes promotes utilization of diverse environmental resources, population stability and persistence, colonization success, and range expansions, and enhances the evolutionary potential and speciation. Conversely, we predict polymorphic populations to be less vulnerable to environmental change and at lower risk of range contractions and extinctions compared with monomorphic populations. We offer brief suggestions as to how these falsifiable predictions may be tested.     

New approaches to modelling fish-habitat relationships

Ecologists often develop models that describe the relationship between faunal communities and their habitat. Coral reef fishes have been the focus of numerous such studies, which have used a wide range of statistical tools to answer an equally wide range of questions. Here, we apply a series of both conventional statistical techniques (linear and generalized additive regression models) and novel machine-learning techniques (the support vector machine and three ensemble techniques used with regression trees) to predict fish species richness, biomass, and diversity from a range of habitat variables. We compare the techniques in terms of their predictive performance, and we compare a subset of the models in terms of the influence each habitat variable has for the predictions. Prediction errors are estimated by cross-validation, and variable importance is assessed using permutations of individual variable values. For predictions of species richness and diversity the tree-based models generally and the random forest model specifically are superior (produce the lowest errors). These model types are all able to model both nonlinear and interaction effects. The linear model, unable to model either effect type, performs the worst (produces the highest errors). For predictions of biomass, the generalized additive model is superior, and the support vector machine performs the worst. Depth range, the difference between maximum and minimum water depth at a given site, is identified as the most important variable in the majority of models predicting the three fish community variables. However, variable importance is highly dependent upon model type, which leads to questions regarding the interpretation of variable importance and its proper use as an indicator of causality. The representation of ecological relationships by tree-based ensemble learners will improve predictive performance, and provide a new avenue for exploring ecological relationships, both statistical and causal.     

Small-scale genetic structure in a marine population in relation to water circulation and egg characteristics

Until the last decade it was assumed that most marine species have pronounced gene flow over vast areas, largely because of their potential for dispersal during early life stages. However, recent genetic, modeling, and field studies have shown that marine populations may be structured at scales that are inconsistent with extensive dispersal of eggs and larvae. Such findings have stimulated the birth of new studies explaining the mechanisms that promote population structure and isolation in the oceans, in the face of high potential for dispersal. Here we study the vertical and horizontal distribution of cod (Gadus morhua) eggs in relation to small-scale circulation and water column hydrography in a coastal location of southern Norway. Previous studies conducted in this region have shown that cod populations inhabiting fjord locations, which are on average 30 km apart, are genetically differentiated, a remarkable outcome considering that Atlantic cod have pelagic egg stages and long pelagic larval duration. We document that cod eggs are found in greater abundance in shallow water layers, which on average are flowing up the fjord (away from the open ocean), and in the inner portion of the fjord, which is subject to lower current speeds compared to the outer or mouth of the fjord. Eggs were found to be neutrally buoyant at shallow depths, a trait that also favors local retention, given the local circulation. The same patterns held during two environmentally contrasting years. These results strongly suggest that population structure of Atlantic cod is favored and maintained by a balance between water circulation and egg characteristics.     

Dynamics of de novo vitellogenesis in fish with indeterminate fecundity: an application of oocyte packing density theory to European anchovy, <Emphasis Type="Italic">Engraulis encrasicolus</Emphasis>

De novo vitellogenesis is common among teleosts; however, its dynamics and the timing of batch recruitment are poorly understood. In this study, we combine a suite of methods and theories in fish reproductive biology (oocyte packing density, stereology, ovarian allometry, oocyte size frequencies and postovulatory follicle [POF] ageing) to reconstruct the steps and timing of batch recruitment in European anchovy. Using general linear modelling to standardize oocyte numbers, we demonstrate that the fractions of primary growth, cortical alveoli and vitellogenic oocytes in the ovary are relatively stable in females with migratory nucleus oocytes (MN) or with POFs 1 and 2 days old (POF-1 and POF-2), but they change abruptly at hydration. These results imply that batch recruitment in European anchovy occurs in pulses of very short duration (less than a day). The standing crop of vitellogenic oocytes in MN, POF-1 and POF-2 females equals the number of eggs contained in two mature batches.     

Effects of small-scale habitat fragmentation on predator–prey interactions in a temperate sea grass system

During the last decades, fragmentation has become an important issue in ecological research. Habitat fragmentation operates on spatial scales ranging over several magnitudes from patches to landscapes. We focus on small-scale fragmentation effects relevant to animal foraging decision making that could ultimately generate distribution patterns. In a controlled experimental environment, we tested small-scale fragmentation effects in artificial sea grass on the feeding behaviour of juvenile cod (Gadus morhua). Moreover, we examined the influence of fragmentation on the distribution of one of the juvenile cod’s main prey resources, the grass shrimp (Palaemon elegans), in association with three levels of risk provided by cod (no cod, cod chemical cues and actively foraging cod). Time spent by cod within sea grass was lower in fragmented landscapes, but total shrimp consumption was not affected. Shrimp utilised vegetation to a greater extent in fragmented treatments in combination with active predation. We suggest that shrimp choose between sand and vegetation habitats to minimize risk of predation according to cod habitat-specific foraging capacities, while cod aim to maximize prey-dependent foraging rates, generating a habitat-choice game between predator and prey. Moreover, aggregating behaviour in grass shrimp was only found in treatments with active predation. Hence, we argue that both aggregation and vegetation use are anti-predator defence strategies applied by shrimp. We therefore stress the importance of considering small-scale behavioural mechanisms when evaluating consequences from habitat fragmentation on trophic processes in coastal environments.     

Influence of wing and tail morphology on the duration of song flight in skylarks

Summary Song flight, which is an aerial song display especially used by many open country bird species, is expected to be energetically very costly. Any morphological adaptation reducing the magnitude of this cost thus would be favored by selection. Male skylarks Alauda arvensis perform frequent song flights during a period of nearly half the year. Skylarks are sexually size dimorphic in most body traits, but particularly in wing area and wing span, which is absolutely and relatively larger in males than in females. Wing loadings, aspect ratios, and flight costs therefore are smaller in males than in females. I investigated the effect of wing area and aspect ratio on the duration of the song flights of individual birds by timing their duration before and after an experimental manipulation of wing area. Male skylarks were caught, ringed, and released (control I), had the tips of their wing feathers cut (control II), or had the tips of their wing feathers reduced by approximately 10 mm. There were no statistically significant differences in morphology or duration of songs between treatment groups before experimental treatments. However, males having the tips of their wing feathers reduced by ca. 10 mm performed only greatly abbreviated song flights. Original wing loading and aspect ratio also affected the duration of song flights, since male skylarks with low wing loadings and high aspect ratios performed longer song flights than did males with high wing loadings and low aspect ratios. This was the case both before and after experimental treatment. Wing area is suggested to reflect the ability of individual skylarks to invest in morphological structures allowing an increased song output.     

A method of hazard assessment of a gaseous substance with respect to formation of toxic photodecomposition products. Application to CCl4, CCl3F and CCl2F2

CCl₄, CCl₃F and CCl₂F₂ decompose in ambient air forming highly toxic carbonyl halides etc. when exposed to sources of intense uv-emission, e.g. welding arcs. The resulting health hazard is assessed using a mathematical model.     

Evaluation of different CHP options for refinery integration in the context of a low carbon future

This study presents a comparison of different concepts for delivering combined heat and power (CHP) to a refinery in Norway. A reference case of producing high pressure steam from natural gas in boilers and electricity in a combined cycle power plant, is compared to a: (1) natural gas fueled CHP without any CO₂ capture; (2) hydrogen fueled CHP with hydrogen produced from steam methane reforming (SMR); (3) hydrogen fueled CHP with hydrogen produced from autothermal reforming (ATR); and finally (4) natural gas fueled CHP with postcombustion CO₂ removal. The options are compared on the basis of first law efficiency, emissions of CO₂ and a simplified cash flow evaluation. Results show that in terms of efficiency the standard natural gas fueled CHP performs better than the reference case as well as the options with carbon capture. The low carbon options in turn offer lower emissions of greenhouse gases while maintaining the same efficiency as the reference case. The cash flow analysis shows that for any option, a certain mix of prices is required to produce a positive cash flow. As expected, the relationship between natural gas price and electricity price affects all options. Also the value of heat and CO₂ emissions plays an important role.