C. Scott Findlay

Life history studies of the lesser snow goose (Anser caerulescens caerulescens). III: The selective value of plumage polymorphism: net fecundity

Between 1969 and 1977 the frequency of the blue phenotype of the dimorphic Lesser Snow Goose (Anser caerulescens caerulescens) showed a steady increase at the La Pérouse Bay colony near Churchill, Manitoba. Cooch (1961, 1963) suggested the global increase resulted from selection pressures favoring blue individuals. The selection hypothesis was evaluated by examining phenotypic differences in net fecundity. We partitioned the reproductive cycle into a series of stages, each defined by a particular index of fecundity. Despite large samples we were unable to detect any significant differences between the two maternal phenotypes in those indices that could conceivably influence population dynamics. We cannot, however, dismiss selection as the mechanism of population change, nor as a contributor to the maintenance of the polymorphism without assessing potential phenotypic differences in viability, age of maturation, and breeding propensity. These attributes are examined in the following paper (Rockwell et al., 1985).

GENETIC AND ENVIRONMENTAL COMPONENTS OF CLUTCH SIZE VARIANCE IN A WILD POPULATION OF LESSER SNOW GEESE (ANSER CAERULESCENS CAERULESCENS )

Phenotypic variation is present, to varying degrees, in all populations. For some traits this variation is expressed as several discontinuous classes, or morphs. Other characters (e.g., weight and stature) exhibit fine gradations of expression, and are said to show continuous variation. These quantitative characters constitute the bulk of naturally occurring variation (Falconer, 1960). Continuous intrapopulation variation arises from three sources: (1) intra-individual variation in the phenotypic response to varying environmental conditions; (2) inter-individual variation due to differing phenotypic responses to a particular environment; and (3) discontinuous genetic variation arising from genetic segregation, which will translate into continuous phenotypic variation if the trait is determined by a large number of loci, each with relatively small effects (Falconer, 1960; Bulmer, 1980). Since selection results in adaptation only when phenotypic variation reflects underlying genetic variability, theories concerning the evolution of quantitative traits assume the one-time presence of heritable variation (van Noordwijk et al., 1981). Traditionally, the genetic basis of quantitative variation has been inferred from domestic breeding experiments (see Falconer, 1960, for a review), laboratory studies on inbred lines (e.g., Gowen and Johnson, 1946; Giesel, 1979), or wild population stocks under artificial selection (Mukai et al., 1974; Rose and Charlesworth, 1981). Few estimates of the additive component of quantitative variation have been made for wild populations in their natural setting (but see Perrins and Revised September 28, 1982

Life history studies of the Lesser Snow Goose (Anser caerulescens caerulescens)

SummaryWe examined the spatial distribution of nesting cohorts of female Lesser Snow Geese (Anser caerulescens caerulescens) in a small colony located at La Perouse Bay, Manitoba. In general, cohorts show a heterogeneous spatial distribution, which arises from a tendency of females of the same cohort affiliation to cluster together. Further-more these associations are maintained through time, such that cohorts tend to dominate particular regions of the colony over several breeding seasons. These findings provide further evidence for breeding site fidelity among female lesser snow geese.

Life history studies of the lesser snow goose (Anser caerulescens caerulescens). IV: The selective value of plumage polymorphism: net viability, the timing of maturation, and breeding propensity

Cooch (1961, 1963) suggested that changes in the genotypic composition of snow goose colonies comprising the Hudson Bay‐Foxe Basin population could be attributed to selection favoring the blue phenotype. In the preceding paper (Cooke et al., 1985), we examined potential differences in net fecundity between the two phenotypes at La Pérouse Bay in northern Manitoba. No substantial differences in any component of fecundity were detected. In the present paper, we examined potential differences in pre‐reproductive and adult viability, age of maturation, and breeding propensity. Again, no differences associated with the plumage polymorphism were detected in any of these life history characteristics. Thus, despite a thorough analysis of the complete life cycle, we were unable to uncover any evidence supporting a selection hypothesis for the persistence and dynamics of this conspicuous polymorphism. An alternate hypothesis based primarily on gene flow and assortative mating appears more plausible.

Polygenic Variation and Stabilizing Selection in a Wild Population of Lesser Snow Geese (Anser caerulescens caerulescens)

Polygenic Variation and Stabilizing Selection in a Wild Population of Lesser Snow Geese (Anser caerulescens caerulescens) Author(s): Fred Cooke and C. Scott Findlay Reviewed work(s): Source: The American Naturalist, Vol. 120, No. 4 (Oct., 1982), pp. 543-547 Published by: The University of Chicago Press for The American Society of Naturalists Stable URL: http://www.jstor.org/stable/2461077 . Accessed: 21/06/2012 12:44

Concerning the Time-Dependence of Population Vital Rates

Population models come in two flavours: deterministic and stochastic. While deterministic models of population growth have been bandied back and forth for some time, the interest in stochastic models is comparatively recent (e.g. Bartlett 1960, Ludwig 1974, May 1974). The reasons for the historical apathy towards stochastic models are unclear. Of some importance, however, is the fact that the field has traditionally been the domain of the applied mathematician. To these researchers, it is often not only mathematical tractability that counts, but also mathematical elegance. And in this regard, stochastic models are usually far outdistanced by their deterministic counterparts.