CHARACTER DISPLACEMENT AND RELEASE IN THE SMALL INDIAN MONGOOSE,HERPESTES JAVANICUS

Abstract

In western parts of its native range, the small Indian mongoose (Herpestes javanicus) is sympatric with one or both of two slightly larger congeners. In the eastern part of its range, these species are absent. The small Indian mongoose was introduced, about a century ago, to the West Indies, the Hawaiian islands, Mauritius, the Fijian islands, and Okinawa. All introductions except possibly that to Mauritius were from the region of Calcutta and Bangladesh, where it is sympatric with both congeners. No other mongoose is present on any of these islands. In each instance, the introduced population derived from a small propagule. We examined size variation in the maximum diameter of the upper canine tooth (the prey‐killing organ) and skull length. In the eastern (allopatric) part of its native range, males of the small Indian mongoose are much larger in both traits than in the western (sympatric) regions, approaching the size of the smaller of its absent two congeners, Herpestes edwardsii. Females from the allopatric part of the range are also larger than those of the source region. The species is more sexually dimorphic in the region of allopatry. On all islands to which it has been introduced, in 100–200 generations the small Indian mongoose has increased in male size and in sexual dimorphism; changes in female size have been slight and inconsistent. In general, sizes of island individuals are approximately intermediate in size between those in the region of origin (where they are sympatric and small) and those in the region of allopatry. Sexual dimorphism is greatest for canine diameter. Thus, H. javanicus shows variation consistent with ecological release from competition with its congeners. There is no evidence on whether this variation is genetic, nor on what dietary items might be partitioned between species and between sexes. However, morphological variation is consistently smaller for both traits and both sexes on the islands of introduction than in any part of the native range, consistent with idea of a genetic bottleneck imposed by the small propagule size. Neither of the two congeneric mongooses shows morphological variation consistent with ecological release from competition with H. javanicus in the southern part of their ranges, where the latter species is absent.

Indo-Pacific lionfish are larger and more abundant on invaded reefs: a comparison of Kenyan and Bahamian lionfish populations

“…Similar comparisons of animal species in their indigenous and introduced ranges are rarer, but those we have found show a similar pattern (e.g. Indian mongoose: Simberloff et al 2000;coypu: Guichón et al 2003). There are several non-mutually exclusive explanations.…”

“…However, the rapidity and magnitude of the shift in body size suggest a phenotypic rather than genetic response. Ecological release from congeneric competitors (Simberloff et al 2000), as well as introduction into areas that are more productive (perhaps exacerbated by prey naivety) could also account for the larger size of Bahamian lionfish. As a result of both higher abundance and larger body size, the total biomass of lionfish on Bahamian reefs was 13 times higher than the biomass of P. miles on Kenyan reefs, and more than six times higher than the biomass of all lionfish species on Kenyan reefs.…”

Contrasting growth strategies of pond versus marine populations of nine-spined stickleback (Pungitius pungitius): a combined effect of predation and competition?

“…Interspecific competition, by constraining individuals' possibilities for utilizing critical resources, can counteract selection favouring large body size (Wilson 1975;Lomolino 1985;Simberloff et al 2000). Pond sticklebacks are facing negligible interspecific competition as they are the only fish species present, and thus have the possibility to break out from their 'size niche'.…”

Analyzing the process of domestication: Hagoshrim as a case study

“…Viewing domestication as an evolutionary process, two sources of information are especially useful in shedding light on this process [3,8,65,77,89]: modern experiments in evolution and domestication, and the study of species that dispersed (or were introduced) to islands. These phenomena are characterized by the isolation of a relatively small number of individuals that are transferred to a new environment.…”