A Colonization Strategy in Field Voles (Microtus Agrestis): Reproductive Traits and Body Size

Abstract

Populations of the field vole (Microtus agrestis) in the Stockholm Archipelago in the Baltic (southern Sweden) are highly dynamic, with frequent extinctions and recolonizations of islands. In order to investigate the demography of such a successful island colonizer, I studied reproductive traits in two breeding colonies of Swedish field voles, one mainland and one from the archipelago, which I kept in a laboratory for 3 yr. Insular voles, as compared to mainland voles, were characterized by a larger adult body size, more rapid growth, larger and heavier litters, and a larger reproductive effort relative to body size. The two colonies were similar in gestation time, litter mortality, and age at sexual maturation. A large body size in combination with a high reproductive investment can be predicted neither from large—scale interspecific allometric relationships, nor from r—K—selection in its wider sense. It is instead argued that both the large body size and the reproductive traits are coevolved components of an island colonization strategy.

Phenotypic evolution of dispersal-enhancing traits in insular voles

“…Local extinctions and recolonizations from neighbouring islands are frequent in insular populations of field voles [11 -13], and breeding experiments have demonstrated that insular voles have evolved different life-history characteristics (i.e. produce more and larger young that grow faster, and make a larger reproductive effort) than mainland voles [10]. The larger body size with increasing distance from the mainland and increasing inter-island fragmentation may thus represent a correlated response to selection for traits that enhance reproductive performance in dynamic metapopulation systems [11,13,42,43].…”

“…(b) Laboratory common garden experiment We used wild-caught voles from the mainland site U and from the insular localities A þ R þ H (figure 1) as breeding nuclei for one mainland and one insular colony kept in the laboratory for a period of three years. Detailed information on the breeding schedule and housing conditions are given elsewhere [10]. A total of 463 litters were produced by 100 females and 101 males.…”

“…Populations of field voles, Microtus agrestis, on groups of islands in the Stockholm archipelago provide a good model system to test this prediction. These islands emerged from the sea approximately 500-1000 years ago [9] as a result of land elevation following the termination of the latest glaciations, and were colonized by field voles from the mainland [10]. These insular populations are characterized by drastic fluctuations in numbers of individuals and high turnover rates; extinctions and recolonizations from neighbouring islands are frequent [11 -13].…”

Adaptive variation in head size in Vipera berus L. populations

“…Sexual dimorphism in morphological characters as well as in foraging behaviour and diets has been demonstrated in birds (Selander, 1966(Selander, , 1972 and mammals (Erlinge, 1981;Moors, 1980). For species with indeterminate growth such a difference is harder to imagine since the sexes will be overlapping in adult body size.…”

Evolução das estratégias reprodutivas de Bothrops jararaca (Serpentes: Viperidae)

“…Segundo, o tamanho do corpo pode diferir por modificação genética local (possivelmente por adaptação) ou mesmo devido a um efeito fenotípico direto da disponibilidade de alimento nas taxas de crescimento . Características ecológicas como diversidade de espécies, competição interespecífica e dimensões de nicho variam geograficamente e podem afetar a disponibilidade de alimento em populações diferentes (BERRY et al, 1987;EBENHARD, 1990).…”