The island rule: An assessment of biases and research trends

Aim

The island rule has been widely applied to a range of taxonomic groups, with some studies reporting supporting evidence but others questioning this hypothesis. To bring more clarity to this debate, we conducted a comparative analysis of the available literature, focussing on potential biases.

Location

Worldwide.

Methods

We performed a systematic review to identify studies testing the island rule and translated these studies’ outcomes, so that they follow a consistent approach. The studies were assessed for differences in their analysis of the island rule. We created an authorship network showing who published studies with whom on the topic and weighted the data based on co‐authorship and number of publications.

Results

We identified 143 relevant studies, finding a significantly lower frequency of supporting studies according to our consistent approach (50%) than the authors’ own statements (59%). Two core‐author groups could be identified with a strong publication record on the island rule. The first group has predominately published studies supporting the rule, whereas the other group has mainly published studies questioning it. According to a subsequent analysis excluding studies with a high risk of HARKing (hypothesizing after the results are known), the frequency of studies supporting the rule further dropped to 42%.

Main conclusions

Empirical support for the island rule is low, especially for non‐mammalian taxa and when using a consistent evaluation approach. Differences among studies in supporting versus questioning this hypothesis seem to be partly due to author‐related biases. Methods to address potential biases in studying ecological hypotheses are urgently needed. We offer such a method here.     

Hierarchy establishment among potentially similar buds

A plant has a great excess of buds each with the potential of developing an entire shoot system. The general question tackled was to what extent shoot size and time of bud development are important for bud hierarchy. Pea seedlings with two shoots, which were either equal or unequal in size, were obtained by the early removal of the seminal shoot. When these two shoots were also removed, one of the two cotyledon buds next to the bases of the shoots developed into the new shoot system. The determination of which of the buds became dominant was studied as a function of the relative sizes of the two primary cotyledonary shoots, of differences in the timing of the removal of these shoots and of the size of the buds. The bud that became dominant was not necessarily the larger one, nor did it always emerge from the axil of the larger shoot. Instead, it was usually the bud that was inhibited for a shorter period by the shoot next to it. It is suggested that the fate of a bud is predominantly determined by developmental parameters, for example lime of release, which are correlated with its developmental status and not necessarily with its physical size or with the past development of its shoot.     

State-dependent feed acquisition among two strains of hatchery-reared Arctic charr

The effects of genetic and environmental factors on aggression and feeding hierarchies were studied using X-radiography to measure food intake by hatchery-reared individuals of two strains (Hammerfest and Svalbard) of Arctic charr Salvelinus alpinus . A reduction in food rations and/or water current speed increased intraspecific aggression, and both factors led to increased interindividual variability in food intake, increasing the coefficient of variation (CV). Following a return to pre-manipulation conditions, CVs decreased to their original level. In control groups, CVs and share of group meals were stable throughout the experiment. The increase in CVs following manipulation was the result of a small number of dominant individuals obtaining a high share of the meal. Restriction in food ration affected share of meals, specific growth rates and the frequencies of non-feeding fish, while reductions in water current speed affected only share of meals. Feeding hierarchies were size-dependent in the control groups. In contrast, no relationships between body weight and feeding rank were evident in groups in which food ration or water current speed were reduced. A small, but consistent, difference was revealed in feeding hierarchy responses between the two strains.     

The feeding response of diploid and triploid Atlantic salmon and brook trout

Pair and group experiments were conducted to determine whether differences exist in feeding success between juvenile diploid and triploid salmonids in a competitive situation. In the pair experiments, 22 pairs (one diploid and one triploid) of size-matched Quebec-strain brook trout Salvelinus fontinalis (7·2–46·3 g) were fed an unlimited number of pellets three times a day for 5 days. Dominance was assigned to the fish which ate the most pellets within each pair. In the group experiments, groups of three diploid and three triploid size-matched fish were fed a restricted ration three times a day for 5 days. Hierarchical rank within the group was assigned based on the number of pellets consumed by each fish. The group experiment was repeated 10 times with Atlantic salmon Salmo salar (5·1–62·7 g), Quebec-strain brook trout (11·8-110·8 g), and large UNB-strain brook trout (18·2–33·0 g), and 12 times with smaller UNB-strain brook trout (0·6–2·0 g). A statistically significant difference in rank between ploidies was found only for the smaller UNB-strain brook trout in the group experiments, with diploids dominant over triploids. This suggests that there may be a difference in competitive feeding success between diploid and triploid brook trout early in development, but that this difference diminishes as the fish grow.     

Developing an ethics-based approach to indicators of sustainable agriculture using analytic hierarchy process (AHP)

This study was conducted to determine the strategies and ethics of sustainability in agriculture and food systems in Iran. To represent the points of view of 57 agricultural stockholders, including an ago-ecologist specialist, agricultural extension and development experts, farmers, and the Iranian Scientific Society of Agroecology (ISSA) members, the analytic hierarchy process (AHP) was employed. A hierarchical network was developed at two levels for selection from among the three ethical approaches, which were developed based on the general tenets of utilitarian, rights, and virtue models. The findings indicated that criteria, i.e. resilience of agricultural systems, supportive policies and self-reliance, and equity, are the most important criteria for sustainable agriculture (SA) in Iran. A sensitivity analysis was carried out to determine the critical factors affecting the priority of alternatives. The results indicated that virtue, rights, and utilitarian models have successive levels of priority as the theoretical base of sustainable agricultural development in Iran. Finally, we outline two strategies for developing a macroethics approach: informational strategies to consider the priorities of virtue model, and structural strategies to highlight the reinforcing nature of right model and utilitarian model.     

Does education ‘trump’ nationality? Boundary-drawing practices among highly educated migrants from Turkey

Inspired by a super-diversity approach, this paper seeks to explore the influence of the ‘ethnic hierarchy’ of ‘old’ minority groups over the way ‘new’ migrants from Turkey negotiate their interaction in the daily life in three settings: Amsterdam, London and Barcelona. By focusing on highly educated migrants from Turkey who by virtue of their country of origin or religion are positioned at the bottom of ‘ethnic hierarchies’, it strives to understand the significance of these different sources of diversity in daily interaction. Applying boundary-drawing strategies developed for ethnic boundaries, this paper argues that education does not necessarily ‘trump’ nationality, but allows for substantial claims of difference. New migrants from Turkey carve out a space for themselves by on the one hand homogenizing Turkish or other Muslim communities through attributing ‘unwanted’ behaviours and on the other re-defining the boundaries of their individual identity with emphasis on different sources of diversity.     

Ethnic minorities and brothers in arms: competition and homophily in the military

Although the solidarity of brothers in arms is an important feature of the military, when it comes to ethnic minorities there is a pivotal paradox. On the one hand the military aims at drawing boundaries between soldiers and civilians by blurring existing ethnic and racial divisions inside the military. On the other hand the military is a highly national institution which prides itself on conservative values. Can these contradictions work? And how soldiers understand them? This paper examines the construction of ethnic boundaries in inter-group relations by focusing on the tension between ethnic hierarchy and competition versus homophily – the preference for maintaining ties with persons who are similar. Through participant observation and in-depth interviews with Dutch soldiers before and during deployment in Bosnia and Kosovo I ask when each strategy is put into work and why.     

The evolution of inequality

Understanding how systems of political and economic inequality evolved from relatively egalitarian origins has long been a focus of anthropological inquiry. Many hypotheses have been suggested to link socio‐ecological features with the rise and spread of inequality, and empirical tests of these hypotheses in prehistoric and extant societies are increasing. In this review, we synthesize several streams of theory relevant to understanding the evolutionary origins, spread, and adaptive significance of inequality. We argue that while inequality may be produced by a variety of localized processes, its evolution is fundamentally dependent on the economic defensibility and transmissibility of wealth. Furthermore, these properties of wealth could become persistent drivers of inequality only following a shift to a more stable climate in the Holocene. We conclude by noting several key areas for future empirical research, emphasizing the need for more analyses of contemporary shifts toward institutionalized inequality as well as prehistoric cases.