title: Ecological implications of reduced forage quality on growth and survival of sympatric geese.
abstract: Allometric constraints associated with digesting leaves require relatively small avian herbivores to consume high-quality forage. How such constraints are overcome during ontogeny when energy and nutrient requirements are relatively high has not been adequately explored. We compared growth trajectories of Canada and lesser snow goose goslings raised on grass-based diets that differed in protein (10%, 14% or 18%) and fibre (30% or 45%) with those of free-living goslings on Akimiski Island, Canada. This common-garden experiment allowed us to test the hypotheses that (i) smaller-bodied geese are more negatively affected by reduced forage quality than larger-bodied geese, and (ii) goslings from subarctic brood-rearing areas have a limited capacity to slow growth in response to reduced forage quality. Canada goose goslings fed low-protein (10%) diets were on average 44% lighter in body mass, had slower growth rates and were delayed >20 days in reaching 90% of asymptotic size compared with Canada goose goslings fed 18% protein. In contrast, snow goose goslings were unable to survive on the low-protein diets, and those fed high- or medium-protein diets grew at a similar rate and achieved similar asymptotic size. Canada and snow goose goslings fed low-protein diets had reduced growth rates of the tarsus and delayed emergence of the 9th primary. Free-ranging Canada goslings on Akimiski Island were similar in mass and structural size to captive-reared goslings fed low-protein diets. In contrast, snow goslings were similar in mass and structural size to the captive-reared goslings fed the high- and medium-protein diets. This suggests that degraded habitats with mostly low-protein forage may be able to support Canada goslings better than snow goslings which require higher-quality forage to survive. Size-related differences in gosling growth and survival in response to diminished diet quality may influence population size when available food reaches a lower threshold in protein content. However, goslings can avoid such density-dependent population regulation if they are able to move their broods and find adequate quality and quantity of forage.
authors.affiliation: Department of Natural Resources Science, University of Rhode Island, 1 Greenhouse Road, Kingston, RI, USA.|Long Point Waterfowl, P.O. Box 160, Port Rowan, ON, N0E 1M0, Canada.
authors.forename: Samantha E
authors.initials: SE
authors.lastname: Richman
authors.affiliation: Environment Canada, Canadian Wildlife Service, 123 Main Street, Suite 150, Winnipeg, MB, R3C 4W2, Canada.
authors.forename: James O
authors.initials: JO
authors.lastname: Leafloor
authors.affiliation: Department of Forest and Wildlife Ecology, 226 Russell Laboratories, University of Wisconsin-Madison, Madison, WI, 53706, USA.
authors.forename: William H
authors.initials: WH
authors.lastname: Karasov
authors.affiliation: Department of Natural Resources Science, University of Rhode Island, 1 Greenhouse Road, Kingston, RI, USA.
authors.forename: Scott R
authors.initials: SR
authors.lastname: McWilliams
mesh_terms: D000821:Animal Feed / Q000032:analysis; D000818:Animals; D004032:Diet; D017753:Ecosystem; D005260:Female; D005777:Geese / Q000254:growth & development / Q000502:physiology*; D008136:Longevity; D008297:Male; D020957:Nunavut; D011897:Random Allocation; D013045:Species Specificity; D061350:Sympatry
keywords: Branta canadensis; Canada goose; Chen caerulescens; arctic geese; forage quality; growth; lesser snow goose; logistic growth curve; survival