Environmental influence on life-history traits: growth, survival, and fecundity in Black Brant

Ecology, Dec, 1995 by James S. Sedinger, Paul L. Flint, Mark S. Lindberg

A positive correlation between juvenile size and survival as well as between adult body size and reproductive investment has been observed in large-bodied mammals (Clutton-Brock et al. 1988). Increased investment by large-bodied mammals may either be expressed as increased fecundity or breeding frequency (Gaillard et al. 1992, Cameron et al. 1993) or increased investment in individual offspring (Clutton-Brock et al. 1988, Kojola 1993). We expect the relationship between body size and reproductive investment to be strongest in large birds and mammals that rely at least partially on nutrient reserves for breeding.

Evolution of life history traits

Numerous studies have detected significant positive heritabilities for life history traits of birds, including body size, egg size, and clutch size (reviewed in Boag and VanNoordwijk 1987, Lessels et al. 1989). James (1983) and Rhymer (1992) showed substantial geographic variation in environmental effects related to growth and clutch size. These studies call into question the ability of fostering studies at the local scale to control for environmental effects completely. Larsson and Forslund (1991) observed substantial variation in growth rate and final adult size for goslings of Barnacle Geese reared on areas only 7 km apart.

Hatch date is an important determinant of gosling size in late summer, not only because earlier hatching goslings are older, but also because earlier hatching goslings grow more rapidly than those hatching later (Sedinger and Flint 1991, Cooch et al. 1991a). A negative correlation between fledging size and hatch date also occurred in small passerines with altricial young (Alatalo and Lundberg 1986, Price 1991), which was attributed to declining food abundance later in the breeding season. In passerines, however, adult size was not negatively correlated with their breeding date (Alatalo and Lundberg 1986, Price 1991); hatch date did not, therefore, contribute substantially to common environment effects in heritability estimates. In geese, however, smaller females tended to nest later (Cooch et al. 1991). Because body size in late summer in turn influences other traits, such as adult body size and clutch size, and mothers and daughters have similar nesting dates (Findlay and Cooke 1982), our data suggest that hatch date is an important component of common environment that must be controlled for to avoid overestimating heritability of life history traits in geese. This may be especially true for clutch size in geese, which is relatively weakly heritable in these birds (Findlay and Cooke 1987).

Larger goslings survived at a higher rate and were larger and more fecund as adults. These fitness advantages accruing to goslings that were larger at fledging, combined with seasonal declines in growth rate (Sedinger and Flint 1991, Cooch et al. 1991a) and the shorter growing season available to later-hatching goslings should favor the earliest possible nesting by Arctic breeding geese. Most populations of geese nest as early as secure nest sites become available (Barry 1962, Ryder 1972, Eisenhauer and Kirkpatrick 1977), and in some colonial species thousands of nests are initiated within a 10-d period (e.g., Findlay and Cooke 1982). Substantial variation in fitness is associated with this apparently minor variation in nesting date, and it is therefore necessary to explain the remaining variation in breeding dates of geese.