Hanno Sandvik

Tree thinking cannot taken for granted: challenges for teaching phylogenetics

Tree thinking is an integral part of modern evolutionary biology, and a necessary precondition for phylogenetics and comparative analyses. Tree thinking has during the 20th century largely replaced group thinking, developmental thinking and anthropocentricism in biology. Unfortunately, however, this does not imply that tree thinking can be taken for granted. The findings reported here indicate that tree thinking is very much an acquired ability which needs extensive training. I tested a sample of undergraduate and graduate students of biology by means of questionnaires. Not a single student was able to correctly interpret a simple tree drawing. Several other findings demonstrate that tree thinking is virtually absent in students unless they are explicitly taught how to read evolutionary trees. Possible causes and implications of this mental bias are discussed. It seems that biological textbooks can be an important source of confusion for students. While group and developmental thinking have disappeared from most textual representations of evolution, they have survived in the evolutionary tree drawings of many textbooks. It is quite common for students to encounter anthropocentric trees and even trees containing stem groups and paraphyla. While these biases originate from the unconscious philosophical assumptions made by authors, the findings suggest that presenting unbiased evolutionary trees in biological publications is not merely a philosophical virtue but has also clear practical implications.

Short- and long-term consequences of reproductive decisions: an experimental study in the puffin

The purpose of the present study was to inspect the response of the Atlantic Puffin (Fratercula arctica) to an experimental manipulation of the investment needed to successfully raise an offspring. We achieved this by replacing an old offspring with a younger chick, and vice versa, thereby prolonging and shortening the chick-rearing period. To examine any costs of reproduction we then followed the breeding success, the recruitment of young to the population, and the survival of parents for 11 years following the manipulation. Parents in the prolonged and shortened category had a lower breeding success than controls mainly because parents deserted their chick shortly after swapping. Among those that raised their chick, the age and body mass of foster chicks at fledging were the same in all three categories even though the parents had raised chicks for different lengths of time. The recruitment of young to the breeding population was high and independent of treatment. Likewise, the survival of adults was independent of treatment. For the 11 years after the experiment, however, the resighting rate of those that deserted their chick was clearly lower than among those that accepted their foster chick. For parents that raised their foster chick, the survival to the following year was positively related to their body mass. The results support the hypothesis that puffins have a highly flexible parental investment, which they adjust according to their own individual quality and the survival prospects of the chick.

EFFECT OF INVESTIGATOR DISTURBANCE ON THE BREEDING SUCCESS OF THE BLACK-LEGGED KITTIWAKE

Abstract The effect of investigator activity on Black-legged Kittiwakes (Rissa tridactyla) was assessed using the disturbance caused by an ongoing intensive study investigating chick growth and adult mass loss. Though the effects were small, investigator disturbance decreased adult nest attendance and increased daily chick loss rates. Whereas overall chick survival until day 18 post-hatch was significantly lower in the high-disturbance plot in the first year of the study, it was substantially higher in the second year. We hypothesize that changes in predator activity as an indirect consequence of disturbance were responsible for this pattern. Herring Gulls (Larus argentatus) which nested near the high-disturbance plot and are the main predator of kittiwakes in our study area may have been more susceptible to the effect of disturbance than the kittiwakes themselves. There was otherwise no statistically significant impact of disturbance on chick growth, or on adult kittiwakes extending into the following year. Biases in studies of kittiwakes due to investigator disturbance may thus be negligible when the study is carefully designed. Future studies investigating effects of disturbance on birds should, however, include data concerning potential predators of the focal species and include more than one low-disturbance plot, and should be carried out over two or more years.

High Survival of Immatures in a Long-Lived Seabird: Insights from a Long-Term Study of the Atlantic Puffin (Fratercula Arctica)

Abstract Survival from fledging to maturity is an important life-history parameter in long-lived species such as seabirds. However, because of the long period of unobservability following fledging, few studies have reported reliable estimates of survival rates for immatures. We estimated survival to maturity of two cohorts of Atlantic Puffin (Fratercula arctica) fledglings from Hornøya in northern Norway using capture–mark–recapture methodology. By considering only juveniles that actually left their nest burrows, we arrived at unbiased estimates of survival rates for immatures. Contrary to many previous studies, annual survival of immatures was not depressed in relation to adult survival. By the age of five years, more than two-thirds of all fledglings are still estimated to be alive. Averaged over this period, annual survival of immatures is estimated as 0.933 (95% confidence interval: 0.806–0.993). This compares to an annual adult survival of 0.943 (0.909–0.965) during the same period. The survival estimates also imply that the cohorts studied are overwhelmingly philopatric. Dispersal of immatures must be extremely rare or absent. The annual estimates of resighting reveal a clear age-related pattern, including a peak at three years of age and a subsequent minimum at six years of age. Possible biological explanations for this behavior are given.

Persistent organic pollution in a high-Arctic top predator: sex-dependent thresholds in adult survival

In long-lived species, any negative effect of pollution on adult survival may pose serious hazards to breeding populations. In this study, we measured concentrations of various organochlorines (OCs) (polychlorinated biphenyl and OC pesticides) in the blood of a large number of adult glaucous gulls (Larus hyperboreus) breeding on Bjørnøya (Bear Island) in the Norwegian Arctic, and modelled their local survival using capture–recapture analysis. Survival was negatively associated with concentrations of OCs in the blood. The effect of OCs was nonlinear and evident only among birds with the highest concentrations (the uppermost deciles of contamination). The threshold for depressed survival differed between the sexes, with females being more sensitive to contamination. For birds with lower OC concentration, survival was very high, i.e. at the upper range of survival rates reported from glaucous and other large gull species in other, presumably less contaminated populations. We propose two non-exclusive explanations. First, at some threshold of OC concentration, parents (especially males) may abandon reproduction to maximize their own survival. Second, high contamination of OC may eliminate the most sensitive individuals from the population (especially among females), inducing a strong selection towards high-quality and less sensitive phenotypes.

Generic ecological impact assessments of alien species in Norway: a semi-quantitative set of criteria

The ecological impact assessment scheme that has been developed to classify alien species in Norway is presented. The underlying set of criteria enables a generic and semi-quantitative impact assessment of alien species. The criteria produce a classification of alien species that is testable, transparent and easily adjustable to novel evidence or environmental change. This gives a high scientific and political legitimacy to the end product and enables an effective prioritization of management efforts, while at the same time paying attention to the precautionary principle. The criteria chosen are applicable to all species regardless of taxonomic position. This makes the assessment scheme comparable to the Red List criteria used to classify threatened species. The impact of alien species is expressed along two independent axes, one measuring invasion potential, the other ecological effects. Using this two-dimensional approach, the categorization captures the ecological impact of alien species, which is the product rather than the sum of spread and effect. Invasion potential is assessed using three criteria, including expected population lifetime and expansion rate. Ecological effects are evaluated using six criteria, including interactions with native species, changes in landscape types, and the potential to transmit genes or parasites. Effects on threatened species or landscape types receive greater weightings.

Climate-Driven Ichthyoplankton Drift Model Predicts Growth of Top Predator Young

Climate variability influences seabird population dynamics in several ways including access to prey near colonies during the critical chick-rearing period. This study addresses breeding success in a Barents Sea colony of common guillemots Uria aalge where trophic conditions vary according to changes in the northward transport of warm Atlantic Water. A drift model was used to simulate interannual variations in transport of cod Gadus morhua larvae along the Norwegian coast towards their nursery grounds in the Barents Sea. The results showed that the arrival of cod larvae from southern spawning grounds had a major effect on the size of common guillemot chicks at fledging. Furthermore, the fraction of larvae from the south was positively correlated to the inflow of Atlantic Water into the Barents Sea thus clearly demonstrating the mechanisms by which climate-driven bottom-up processes influence interannual variations in reproductive success in a marine top predator.

The stress hormone corticosterone in a marine top predator reflects short‐term changes in food availability

In many seabird studies, single annual proxies of prey abundance have been used to explain variability in breeding performance, but much more important is probably the timing of prey availability relative to the breeding season when energy demand is at a maximum. Until now, intraseasonal variation in prey availability has been difficult to quantify in seabirds. Using a state-of-the-art ocean drift model of larval cod Gadus morhua, an important constituent of the diet of common guillemots Uria aalge in the southwestern Barents Sea, we were able to show clear, short-term correlations between food availability and measurements of the stress hormone corticosterone (CORT) in parental guillemots over a 3-year period (2009–2011). The model allowed the extraction of abundance and size of cod larvae with very high spatial (4 km) and temporal resolutions (1 day) and showed that cod larvae from adjacent northern spawning grounds in Norway were always available near the guillemot breeding colony while those from more distant southerly spawning grounds were less frequent, but larger. The latter arrived in waves whose magnitude and timing, and thus overlap with the guillemot breeding season, varied between years. CORT levels in adult guillemots were lower in birds caught after a week with high frequencies of southern cod larvae. This pattern was restricted to the two years (2009 and 2010) in which southern larvae arrived before the end of the guillemot breeding season. Any such pattern was masked in 2011 by already exceptionally high numbers of cod larvae in the region throughout chick-rearing period. The findings suggest that CORT levels in breeding birds increase when the arrival of southern sizable larvae does not match the period of peak energy requirements during breeding.

Anthropocentricisms in cladograms

Both written and graphic accounts of history can be biased by the perspective of the historian. O’Hara (Biol Philos 7:135–160, 1992) has demonstrated that this also applies to evolutionary history and its historians, and identified four narrative devices that introduce anthropocentricisms into accounts of phylogeny. In the current paper, I identify a fifth such narrative device, viz. the left–right ordering of the taxa at the tips of cladograms. I define two measures that make it possible to quantify the degree of anthropocentricism of cladograms, the human attention score and human rightness score. I then carry out an analysis of the presence of the different distorting mechanisms in phylogenetic textbooks. I deliberately chose two textbooks that adopted a cladistic perspective, since their authors can be assumed to be more conscious about the aim of avoiding anthropocentricisms. Three of the narrative devices are thus absent from cladistic works. However, there is a weak tendency that the resolution of cladogram branches is biased in favour of Homo sapiens. Furthermore, the human perspective is clear and highly significant in the positioning of taxa along the left–right axis of cladograms. I discuss the reasons for and implications of these biased presentations.

Climate fluctuations and differential survival of bridled and non‐bridled Common Guillemots Uria aalge

Climate fluctuations and its effects on ecological processes are evident in most areas worldwide but whether such climatic effects are induced phenotypic plasticity or whether animals adapt to the new environment through micro-evolutionary processes is poorly known. In this study we have analyzed long-term data (22 years) on the relationship between climatic fluctuations and the adult survival of two distinct genetic morphs of the Common Guillemot (Uria aalge) breeding in a colony in the southern Barents Sea. In the North Atlantic, the Common Guillemot is a genetic color dimorphic species, with a non-bridled morph, with an entirely black or dark brown head, and a bridled morph having a white eye ring and auricular groove sloping back from the eye. Our results show that the two morphs responded differently to variation in the Barents Sea winter sea-surface temperature (SST). The survival rate of the bridled morph was negatively correlated to the winter SST in the Barents Sea, while that of the non-bridled morph was slightly positively correlated to the same parameter. Over the whole study period, SSTs fluctuated between warm and cold winters and the overall mean survival rates of the two morphs remained similar (96.2% and 95.9% for the bridled and non-bridled morph, respectively). This suggests a balanced selection and a stable dimorphism of the two morphs over this time period. The contrasting trends in the survival of the two morphs with respect to temperature suggest that further warming of the sea may induce directional changes and alter the frequency of the two morphs.