Unravelling the determinants of insular body size shifts

McClain, Craig R.; Durst, Paul A. P.; Boyer, Alison G.; Francis, Clinton D.

doi:10.1098/rsbl.2012.0989

Cited by 30 publications

(39 citation statements)

References 25 publications

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“…Although several previous studies examining the island rule have suggested that changes in predation, interspecific competition and population density are responsible for insular body size change (see electronic supplementary material, appendix S1), accurate accounts of island population densities and community composition are not available from primary literature for as broad a sampling of cases as we wished to include. Details on data collection can be found in the electronic supplementary material for McClain et al [11]. As island area and elevation can both be indicators of island terrain heterogeneity [10], we combined measures of the two in a principal components analysis and used PC1 as a measure of island heterogeneity (electronic supplementary material, table S1).…”

Section: Materials and Methods (A) Island Data Collectionmentioning

confidence: 99%

“…Records of insular rodent populations were taken from the database of McClain et al [11,23], which is an expansion of the database from Meiri et al [8]. The size ratio for each population was calculated as the mean island body size (either mass or the cube of linear measurements when mass was unavailable [5,8]) divided by that same measure of body size from the closest mainland population (see [8] for description of original dataset).…”

Section: Materials and Methods (A) Island Data Collectionmentioning

confidence: 99%

“…However, CART methods, especially classification trees, are widely used in other disciplines not only to describe the data used to build the tree, but to build a model to predict values of the response variable for samples independent of those used to construct the tree [29]. Recent work by Lomolino et al [12] provided size ratios and locality data for almost 100 insular rodent populations for which we had island information (obtained earlier for purposes of studying insular mammals other than rodents; [11]) but had not included in our 'model-training' dataset. Of those populations, 39 of them qualified as extreme according to our definition.…”

Section: (D) Comparing Conditions Associated With 'Normal' Versus 'Exmentioning

confidence: 99%

“…Yet despite their morphological coherence, rodents vary widely in body size, habitat and diet. Extant insular populations of rodents exhibit higher variance in and a wider range of size ratios than any other order, and both the direction and the magnitude of size change can vary among different island populations within a single rodent species [8,9,11,13,22].…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Materials and Methods (A) Island Data Collectionmentioning

confidence: 99%

Section: Materials and Methods (A) Island Data Collectionmentioning

confidence: 99%

Section: (D) Comparing Conditions Associated With 'Normal' Versus 'Exmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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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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“…3). Some studies have reported that the bodies and bills of island birds systematically shift in size, reflecting evolution toward a generalist niche in species-poor communities (4)(5)(6)(7)(8). The tendency for island taxa to converge toward intermediate body size after colonizing islands is known as the island rule (4), but this ecogeographic rule has proven to be an inconsistent predictor of evolutionary trends in island bird populations (9)(10)(11)(12).…”

mentioning

confidence: 99%

Predictable evolution toward flightlessness in volant island birds

Wright

Steadman

Witt

2016

Proc. Natl. Acad. Sci. U.S.A.

130

137

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Birds are prolific colonists of islands, where they readily evolve distinct forms. Identifying predictable, directional patterns of evolutionary change in island birds, however, has proved challenging. The "island rule" predicts that island species evolve toward intermediate sizes, but its general applicability to birds is questionable. However, convergent evolution has clearly occurred in the island bird lineages that have undergone transitions to secondary flightlessness, a process involving drastic reduction of the flight muscles and enlargement of the hindlimbs. Here, we investigated whether volant island bird populations tend to change shape in a way that converges subtly on the flightless form. We found that island bird species have evolved smaller flight muscles than their continental relatives. Furthermore, in 366 populations of Caribbean and Pacific birds, smaller flight muscles and longer legs evolved in response to increasing insularity and, strikingly, the scarcity of avian and mammalian predators. On smaller islands with fewer predators, birds exhibited shifts in investment from forelimbs to hindlimbs that were qualitatively similar to anatomical rearrangements observed in flightless birds. These findings suggest that island bird populations tend to evolve on a trajectory toward flightlessness, even if most remain volant. This pattern was consistent across nine families and four orders that vary in lifestyle, foraging behavior, flight style, and body size. These predictable shifts in avian morphology may reduce the physical capacity for escape via flight and diminish the potential for small-island taxa to diversify via dispersal.B irds on islands helped to inspire the theory of evolution by natural selection (1, 2), and they continue to illuminate its mechanisms (e.g., ref.3). Some studies have reported that the bodies and bills of island birds systematically shift in size, reflecting evolution toward a generalist niche in species-poor communities (4-8). The tendency for island taxa to converge toward intermediate body size after colonizing islands is known as the island rule (4), but this ecogeographic rule has proven to be an inconsistent predictor of evolutionary trends in island bird populations (9-12). Detailed studies of island radiations have revealed idiosyncratic patterns of body size and bill size evolution among species, with morphological changes attributable to taxon-specific changes in foraging ecology (e.g., ref. 12). This inconsistency raises the question as to whether there are predictable evolutionary trends that apply generally to island birds.The most striking evolutionary trend among island birds is the loss of flight. Transitions to flightlessness are rapid and irreversible (13,14), with each instance involving the substantial reallocation of mass from the forelimbs to the hindlimbs and near elimination of costly flight muscles (15-18). More than 1,000 independent lineages of island birds have lost flight, including rails, parrots, pigeons, owls, waterfowl, and passerines (13-1...

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