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

INTRODUCTION

Environmental (James 1983, Cooch et al. 1991a, b, Larsson and Forslund 1991, Sedinger and Flint 1991, Rhymer 1992, Saether and Heim 1993) and maternal factors (Ricklefs and Peters 1981, Sinervo 1990, Kojola 1993) strongly influence growth in numerous vertebrates. Difficulty in estimating survivorship and future fecundity of individual juveniles in most vertebrate populations has generally precluded measuring fitness consequences of such variation in growth (but see Clutton-Brock et al. 1988).

Understanding the relationship between growth and future fitness is essential to understanding the fitness consequences of reproductive "decisions" in many populations. For example, timing of reproduction influences survival of offspring (Cooke et al. 1984, Daan et al. 1990). Arctic geese are especially good subjects for examining fitness consequences of early growth because females return to their natal areas to breed (Rohwer and Anderson 1988), thereby increasing the feasibility of monitoring fitness in the same individuals whose growth histories are known. Furthermore, mechanisms by which early growth might influence fitness by affecting adult body size have been proposed and studied (Ankney and MacInnes 1978).

Female geese rely heavily on stored protein and lipid reserves to produce eggs (Ankney and MacIness 1978, Raveling 1979a, Ankney 1984) because insufficient nutrients are available in the nesting environment in late spring, when geese begin breeding, for females to meet their maintenance requirements and produce eggs (Ryder 1972, Raveling 1979b). Large body size should enable females to store larger reserves, because a given mass of reserve comprises a smaller proportion of mass of larger compared to smaller females. Furthermore, lower mass-specific metabolic rate and greater fasting endurance of large individuals (Calder 1984) may enable them to store absolutely larger lipid reserves. Ankney and MacInnes (1978) detected a significant positive relationship between culmen length and nutrient reserve size in Lesser Snow Geese (Anser caerulescens caerulescens), (hereafter snow geese) on a breeding area, and Alisauskas (1988) observed a correlation between size of nutrient reserves and body size in snow geese late in spring migration. These findings imply that body size should be positively correlated with clutch size in snow geese. Studies at La Perouse Bay (58 [degrees] N, 94 [degrees] W) on the west coast of Hudson Bay, have not detected a relationship between body size and clutch size in a more southerly population of snow geese (Cooch et al. 1992). Therefore, the relationship between body size and fecundity in snow geese remains somewhat controversial (Alisauskas and Ankney 1990, Cooch et al. 1992.).

Geese are nearly strictly herbivorous during the growth period (Owen 1980, Sedinger and Raveling 1984), in contrast to herbivorous mammals that rely on nutrient-rich milk for growth. Plant foods are relatively low in protein and metabolizable energy (Cargill and Jefferies 1984, Sedinger and Raveling 1984, 1986, Sedinger et al. 1989) and processing time in the gut restricts food intake (Sedinger and Raveling 1988), limiting the ability of goslings to compensate for low dietary nutrient concentrations by increasing food intake. Growth of goslings, therefore, responds to nutritional content of their diet (Lieff 1973, Wurdinger 1975). Because diet quality varies both spatially (Larsson and Forslund 1991, Cooch et al. 1993) and temporally (Sedinger and Raveling 1986, Manseau and Gauthier 1993), gosling size late in their first summer is strongly influenced by environmental factors (Cooch et al. 1991a, b, Larsson and Forslund 1991, Sedinger and Flint 1991). Genetic, environmental, and maternal effects shared by brood mates explained an insignificant (5%) proportion of total variation in gosling size in Black Brant (Branta bernicla nigricans) (hereafter brant) after hatch date and egg size were accounted for (Sedinger and Flint 1991). Adult size in snow geese (Cooch et al. 1991a) and Barnacle Geese (Branta leucopsis) (Larsson and Forslund 1991) is correlated with body size of the same individuals as goslings. Therefore, a substantial portion of within-population variation in adult body size of Arctic nesting geese is likely of environmental origin.

Because of the potential for adult body size to determine size of nutrient reserves and, consequently, clutch size in Arctic geese, early environment during the growth period may play an important role in expression of life history traits. In this paper, we examine the relationship between size of brant goslings late in their first summer and adult body size, breeding propensity, and fecundity. In snow geese (Cooch et al. 1993), Barnacle Geese (Owen and Black 1989), and Emperor Geese (Anser canagicus) (Schmutz 1993), first-year survival was correlated with gosling size in late summer. Therefore, we also examine the relationship between gosling size and first-year survival in brant.