Jiro Kikkawa

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The importance of founder events in promoting evolutionary changes on islands has been a subject of long-running controversy. Resolution of this debate has been hindered by a lack of empirical evidence from naturally founded island populations. Here we undertake a genetic analysis of a series of historically documented, natural colonization events by the(More)
Passerine birds living on islands are usually larger than their mainland counterparts, in terms of both body size and bill size. One explanation for this island rule is that shifts in morphology are an adaptation to facilitate ecological niche expansion. In insular passerines, for instance, increased bill size may facilitate generalist foraging because it(More)
Theory predicts that in small isolated populations random genetic drift can lead to phenotypic divergence; however this prediction has rarely been tested quantitatively in natural populations. Here we utilize natural repeated island colonization events by members of the avian species complex, Zosterops lateralis, to assess whether or not genetic drift alone(More)
Pronounced phenotypic shifts in island populations are typically attributed to natural selection, but reconstructing heterogeneity in long-term selective regimes remains a challenge. We examined a scenario of divergence proposed for species colonizing a new environment, involving directional selection with a rapid shift to a new optimum and subsequent(More)
In Japan the River Law was amended in 1997 to expand the traditional roles of flood control and water supply in river management to include environmental conservation. Two major multidisciplinary research groups were also founded to address the environmental issues arising from the management of rivers and watershed areas in Japan. One called the River(More)
We examined components of agonistic behavior and dominance in parents and offspring of silvereyes on Heron Island, Great Barrier Reef, to discover their determinants. The data were collected over four years on 1,235 juveniles and their parents. Of four behavioral characters used to compare juveniles and their parents, bill clattering was seen significantly(More)
Birds follow the “island rule”, under which small-bodied forms tend to get larger on islands and large-bodied forms tend to get smaller. The traditional explanation for larger island relatives of small-bodied forms is based on ecological release on islands: islands support relatively few species, interspecific competition thus is weak, selection therefore(More)