What Is the Island Rule
Comparative phylogenetic analyses do not support predictions of island dominance, neither for all mammals nor within clades. When species are instead considered as independent points, small mammals have a small but significant tendency to grow on islands, while large mammals develop a smaller size on islands (R2 = 0.03). The significance of the trend, however, may be influenced by large sample sizes, the likely non-independence of many data points, and the statistical tendency to negatively correlate ratios with their denominators (Smith, 1999; Brett, 2004). Some clades show a tendency towards gigantism (murid rodents) or dwarfism (artiodactyls, heteromyids and some carnivores), consistent with the conclusions of Foster (1964), suggesting that the small versus large dichotomy in earlier work (e.g., Van Valen, 1973) may be an artifact of contrasting groups exhibiting specific responses to clothing (rather than size) to insularity. Brasileiro, C. A., Haddad, C. F., Sawaya, R. J. & Sazima, I. A new threatened island species of Cycloramphus (Anura: Cycloramphidae) from southeastern Brazil. Herpetologica 63, 501-510 (2007). Yusefi, G.
H., Kiabi, B. H., Khalatbari, L., Faizolahi, K. & Monteiro, N. M. The morphological analysis of Brandt`s hedgehog (Paraechinus hypomelas) reflects the history of the isolation of the islands of the Persian Gulf and has implications for taxonomy. Biol. J. Linn. 119, 497-510 (2016). Keehn, J.
E., Nieto, N. C., Tracy, C. R., Gienger, C. M. & Feldman, C. R. Evolution on a desert island: Body size divergence between the reptiles of Nevada`s Anaho Island and the mainland around Pyramid Lake. J.
Zool. 291, 269-278 (2013). For each island-continent comparison, we calculated the ratio of body size (RS) of the island to the mainland. Where data were available for both sexes, we averaged the SRs of men and women. In species-level analyses, we used the median RS for each species because the median is less affected by abnormal measurements than the mean when population numbers are small. Overall, there is no tendency for island populations to be larger or smaller than mainland populations, either in the dataset as a whole (matched t-test: t274 = −0.04, p = 0.97) or only in well-sampled species (t145 = 1.21, p = 0.23). However, some taxa have shown significant trends (Table 1). Artiodactyls and carnivores (especially herpestids and viverrides) tend to shrink on islands, while island animals (especially murids) tend to be larger than their counterparts on the mainland. Only the increase in murid size remains significant when only well-sampled species (see above) have been used, and heteromyoid rodents tend to decrease in size, suggesting that data quality may be an issue.
Lyon, M. W. Mammals collected by Dr. W. W. Abbott across the chain of islands off the west coast of Sumatra, with descriptions of twenty-eight new species and subspecies. 52, 437,462 (1916). Changes in island size are often assumed to be closely related to the characteristics of islands and their mammalian fauna, such as island size, isolation, and the presence or absence of carnivores (Healey 1978; Michaux et al., 2002). We found little evidence that these factors have a consistent influence on the development of body size.
Admittedly, it is difficult to estimate which index best reflects isolation (e.g., Distance to the nearest continental land, to the next larger island, to the next, species-rich island). Similarly, the effects of carnivores on different mammalian species are probably complex: predation pressure is probably more related to the abundance and identity of predators than to their richness. With the indices commonly used for these variables, we find no evidence that they have a consistent effect on size change. Although we use different subsets of our database, we find few significant factors influencing changes in island size, regardless of the analysis method used. Therefore, insularity does not lead to simple patterns of waist development that manifest along individual axes such as body size. More coherent detailed clade studies that explicitly model the biotic composition of different islands and the biology of focal species (e.g., Lawlor, 1982; Angerbjörn, 1985; Smith, 1992; Raia & Meiri 2006) may shed more light on the mechanisms influencing size change than a general macroecological study of all mammals. The islands can be quite impressive places. From the volcanic islands of Hawaii and the Galapagos to the mangrove islands of the Florida Keys, to the sandy beaches of the Caribbean and even the deserted rocky islands off the coast of California, islands represent many types of ecosystems. As different as the islands may be, their natural inhabitants can be incredibly unique themselves.
KlÃ1/4tsch, C., Misof, B., Grosse, W. R. & Moritz, R. Genetic and morphometric differentiation between island populations of two Norops lizards (Reptilia: Sauria: Polychrotidae) on colonized islands independent of the islands of Bahia (Honduras). J. Biogeogr. 34, 1124-1135 (2007). If more than one height index was reported for a population pair, we preferred indices based on mass, then body length, then skull and tooth length (Lomolino 2005). Bat wing length was not used because island bats` wing lengths have been shown to vary in terms of wind speed and feeding strategies (Iliopoulou-Georgudaki 1986; Jacobs, 1996).