The Island Rule in Large Mammals: Paleontology Meets Ecology

Raia, Pasquale; Meiri, Shai

doi:10.1111/j.0014-3820.2006.tb00516.x

Cited by 173 publications

(125 citation statements)

References 76 publications

(114 reference statements)

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“…Although much study is needed to fully understand patterns of trait evolution and covariation in insular vertebrates, we hope to have shed some light on this complex issue, by showing how disparate factors must be taken into account in order to gain a meaningful depiction of the evolution of life on islands [94]. …”

Section: Discussionmentioning

confidence: 99%

The blue lizard spandrel and the island syndrome

et al. 2010

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BackgroundMany small vertebrates on islands grow larger, mature later, lay smaller clutches/litters, and are less sexually dimorphic and aggressive than their mainland relatives. This set of observations is referred to as the 'Island Syndrome'. The syndrome is linked to high population density on islands. We predicted that when population density is low and/or fluctuating insular vertebrates may evolve correlated trait shifts running opposite to the Island Syndrome, which we collectively refer to as the 'reversed island syndrome' (RIS) hypothesis. On the proximate level, we hypothesized that RIS is caused by increased activity levels in melanocortin receptors. Melanocortins are postranslational products of the proopiomelanocortin gene, which controls pleiotropically pigmentation, aggressiveness, sexual activity, and food intake in vertebrates.ResultsWe tested the RIS hypothesis performing a number of behavioral, genetic, and ontogenetic tests on a blue colored insular variant of the Italian Wall lizard Podarcis sicula, living on a small island off the Southern Italian coast. The population density of this blue-colored variant was generally low and highly fluctuating from one year to the next.In keeping with our predictions, insular lizards were more aggressive and sexually dimorphic than their mainland relatives. Insular males had wide, peramorphic heads. The growth rate of insular females was slower than growth rates of mainland individuals of both sexes, and of insular males. Consequently, size and shape dimorphism are higher on the Island. As predicted, melanocortin receptors were much more active in individuals of the insular population. Insular lizards have a higher food intake rate than mainland individuals, which is consistent with the increased activity of melanocortin receptors. This may be adaptive in an unpredictable environment such as Licosa Island. Insular lizards of both sexes spent less time basking than their mainland relatives. We suspect this is a by-product (spandrel) of the positive selection for increased activity of melanocortins receptors.ConclusionsWe contend that when population density is either low or fluctuating annually as a result of environmental unpredictability, it may be advantageous to individuals to behave more aggressively, to raise their rate of food intake, and allocate more energy into reproduction.

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Section: Discussionmentioning

confidence: 99%

The blue lizard spandrel and the island syndrome

et al. 2010

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“…The simple scenario that Foster [4] described, in which size increase or decrease predominates within a given order of mammals, has been replaced with the description of a generally monotonic trend of decrease in size ratio with increasing body size across species [5]. This, in turn, has been refined and replaced by models of size change that apply differently in different cases and are contingent both on the phylogenetic affinity of the population and on an array of ecological, environmental, geographical and species-specific attributes of the island þ population pair ( [6 -12]; for more thorough treatments of island rule literature and theory, see [7,13,14]). …”

Section: Introductionmentioning

confidence: 99%

Mainland size variation informs predictive models of exceptional insular body size change in rodents

Durst

Roth

2015

Proc. R. Soc. B.

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The tendency for island populations of mammalian taxa to diverge in body size from their mainland counterparts consistently in particular directions is both impressive for its regularity and, especially among rodents, troublesome for its exceptions. However, previous studies have largely ignored mainland body size variation, treating size differences of any magnitude as equally noteworthy. Here, we use distributions of mainland population body sizes to identify island populations as 'extremely' big or small, and we compare traits of extreme populations and their islands with those of island populations more typical in body size. We find that although insular rodents vary in the directions of body size change, 'extreme' populations tend towards gigantism. With classification tree methods, we develop a predictive model, which points to resource limitations as major drivers in the few cases of insular dwarfism. Highly successful in classifying our dataset, our model also successfully predicts change in untested cases.

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“…Explanations of this kind need to be employed with great care [44], and to explain the island rule, it must be demonstrated that individual selection tends towards the same outcome, or that differential extinction has indeed played an important role. Furthermore, it is not clear that total resource availability is limiting in some well-studied cases [7], [45].…”

Section: Discussionmentioning

confidence: 99%

The “Island Rule” and Deep-Sea Gastropods: Re-Examining the Evidence

Welch

2010

PLoS ONE

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BackgroundOne of the most intriguing patterns in mammalian biogeography is the “island rule”, which states that colonising species have a tendency to converge in body size, with larger species evolving decreased sizes and smaller species increased sizes. It has recently been suggested that an analogous pattern holds for the colonisation of the deep-sea benthos by marine Gastropoda. In particular, a pioneering study showed that gastropods from the Western Atlantic showed the same graded trend from dwarfism to gigantism that is evident in island endemic mammals. However, subsequent to the publication of the gastropod study, the standard tests of the island rule have been shown to yield false positives at a very high rate, leaving the result open to doubt.Methodology/Principal FindingsThe evolution of gastropod body size in the deep sea is reexamined. Using an extended and updated data set, and improved statistical methods, it is shown that some results of the previous study may have been artifactual, but that its central conclusion is robust. It is further shown that the effect is not restricted to a single gastropod clade, that its strength increases markedly with depth, but that it applies even in the mesopelagic zone.Conclusions/SignificanceThe replication of the island rule in a distant taxonomic group and a partially analogous ecological situation could help to uncover the causes of the patterns observed—which are currently much disputed. The gastropod pattern is evident at intermediate depths, and so cannot be attributed to the unique features of abyssal ecology.

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The Island Rule in Large Mammals: Paleontology Meets Ecology

Cited by 173 publications

References 76 publications

The blue lizard spandrel and the island syndrome

The blue lizard spandrel and the island syndrome

Mainland size variation informs predictive models of exceptional insular body size change in rodents

The “Island Rule” and Deep-Sea Gastropods: Re-Examining the Evidence

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