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Optimal foraging and fitness in Columbian ground squirrels

Summary

Optimal diets were determined for each of 109 individual Columbian ground squirrels (Spermophilus columbianus) at two sites in northwestern Montana. Body mass, daily activity time, and vegetation consumption rates for individuals were measured in the field, along with the average water content of vegetation at each ground squirrel colony. I also measured stomach and caecal capacity and turnover rate of plant food through the digestive tract for individuals in the laboratory to construct regressions of digestive capacity as a function of individual body mass. Finally, I obtained literature estimates of average daily energy requirements as a function of body mass and digestible energy content of vegetation. These data were used to construct a linear programming diet model for each individual. The model for each individual was used to predict the proportion of two food types (monocots and dicots) that maximized daily energy intake, given time and digestive constraints on foraging. Individuals were classified as “optimal” or “deviating”, depending on whether their observed diet was significantly different from their predicted optimal diet. I determined the consequences of selecting an optimal diet for energy intake and fitness. As expected, daily energy intake calculated for deviators (based on their observed diet proportion) was less than that for optimal foragers. Deviating foragers do not appear to compensate for their lower calculated energy intake through other factors such as body size or physiological efficiency of processing food. Growth rate, yearly survivorship, and litter size increase with calculated energy intake, and optimal foragers have six times the reproductive success of deviators by age three. Optimal foraging behavior, therefore, appears to confer a considerable fitness advantage.

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References

  • Armitage KB (1977) Social variety in the yellow-bellied marmot: a population — behavioral system. Anim Behav 25:585–593

    Google Scholar 

  • Ayala FJ (1967) Dynamics of populations. II. Factors affecting population growth and population size in Drosophila pseudoobscura and Drosophila melanogaster. Ecology 48:67–78

    Google Scholar 

  • Baker RL, Cox EH, Carter AH (1984) Direct and correlated responses to selection for weaning weight, post-weaning weight gain, and six week weight in mice. Theor Appl Genet 67:113–122

    Google Scholar 

  • Balph DA (1984) Spatial and social behavior in a population of Uinta ground squirrels: interrelations with climate and annual cycle. In: Murie JO, Michener GR (eds) The biology of ground-dwelling squirrels. Univ Nebraska Press, Lincoln pp 326–352

    Google Scholar 

  • Belovsky GE (1978) Diet optimization in a generalist herbivore: the moose. Theor Pop Biol 14:105–134

    Google Scholar 

  • Belovsky GE (1984a) Herbivore optimal foraging: a test of three models. Am Nat 124:97–115

    Google Scholar 

  • Belovsky GE (1984a) Snowshoe hare optimal foraging and its implications for population dynamics. Theor Pop Biol 25:235–264

    Google Scholar 

  • Belovsky GE (1986a) Optimal foraging and community structure: implications for a guild of generalist grassland herbivores. Oecologia 70:35–62

    Google Scholar 

  • Belovsky CE (1986b) Generalist herbivore foraging and its role in competitive interactions. Am Zool 26:51–69

    Google Scholar 

  • Belovsky GE, Ritchie ME (1990) Geographical and seasonal variation in foraging of Columbian ground squirrels. Oecologia (in press)

  • Bintz GL (1984) Water balance, water stress, and the evolution of seasonal torpor in ground-dwelling sciurids. In: Murie JO, Michener GR (eds) The biology of ground-dwelling squirrels. Univ Nebraska Press, London pp 142–166

    Google Scholar 

  • Blake BH (1972) The annual cycle and fat storage in two populations of golden-mantled ground squirrels. J Mamm 53:157–167

    Google Scholar 

  • Boag DA, Murie JO (1981) Population ecology of Columbian ground squirrels in southwestern Alberta. Can J Zool 59:2230–2240

    Google Scholar 

  • Christiansen FB, Bundgaard J, Barker JSF (1977) On the structure of fitness estimates under post-observational selection. Evolution 31:843–853

    Google Scholar 

  • Clutton-Brock TH (ed) (1988) Reproductive success: studies of individual variation in contrasting breeding systems. Univ Chicago Press, Chicago

    Google Scholar 

  • Craighead JJ, Craighead FC (1956) Hawks, owls, and wildlife. Stackpole, Harrisburg, Pennsylvania, USA

    Google Scholar 

  • Davis DE (1976) Hibernation and circannual rhythms of food consumption in marmots and ground squirrels. Q Rev Biol 51:477–514

    Google Scholar 

  • Dobson FS (1983) Agonism and territoriality in the California ground squirrel. J Mamm 64:218–225

    Google Scholar 

  • Dobson FS, Kjelgaard JD (1985a) The influence of food resources on life history in Columbian ground squirrels. Can J Zool 63:2105–2109

    Google Scholar 

  • Dobson FS, Kjelgaard JD (1985b) The influence of food resources on population dynamics in Columbian ground squirrels. Can J Zool 63:2095–2104

    Google Scholar 

  • Elner RW, Hughes RN (1978) Energy maximization in the diet of the shore crab Carcinus maenas. J Anim Ecol 47:103–116

    Google Scholar 

  • Endler JA (1986) Natural selection in the wild. Princeton University Press, Princeton, New Jersey, USA

    Google Scholar 

  • Festa-Bianchet M, King WJ (1984) Behavior and dispersal of yearling Columbian ground squirrels. Can J Zool 62:161–167

    Google Scholar 

  • Garton DW (1984) Relationship between multiple locus heterozygosity and physiological energetics of growth in the estuarine gastropod Thais haematoma. Physiol Zool 57:530–543

    Google Scholar 

  • Goss-Custard JD (1977) Optimal foraging and the size selection of worms by redshank (Tringa totanus), in the field. Anim Behav 25:10–29

    Google Scholar 

  • Hayes JF, Eisen EJ (1979) Environmental maternal influences on body composition in mice selected for body weight. Theor Appl Genet 55:209–223

    Google Scholar 

  • Hixon MA (1982) Energy maximizers and time minimizers: theory and reality. Am Nat 119:596–599

    Google Scholar 

  • Hudson JW, Deavers DR (1973) Metabolism, pulmo-cutaneous water loss, and respiration of eight species of ground squirrels from different environments. Comp Biochem Physiol A 45:69–100

    Google Scholar 

  • Karasov WH (1981) Daily energy expenditure and the cost of activity in a free-living mammal. Oecologia 51:253–259

    Google Scholar 

  • Karasov WH (1982) Energy assimilation, nitrogen requirement, and diet in free-living antelope ground squirrels, Ammospermophilus leucurus. Physiol Zool 55:378–392

    Google Scholar 

  • Karasov WH (1985) Nutrient constraints in the feeding ecology of an omnivore in a seasonal environment. Oecologia 66:280–290

    Google Scholar 

  • Kenagy GJ (1987) Energy allocation for reproduction in the goldenmantled ground squirrel. Symp Zool Soc Lond 57:259–273

    Google Scholar 

  • Kilgore DL, Armitage KB (1978) Energetics of yellow-bellied marmot populations. Ecology 59:78–88

    Google Scholar 

  • Kleiber M (1961) The fire of life. Wiley Press, New York

    Google Scholar 

  • Krebs JR, Erichsen JT, Webber JI, Charnov EL (1977) Optimal prey selection in the great tit (Parus major). Anim Behav 25:30–38

    Google Scholar 

  • Krebs JR, Ryan JC, Charnov EL (1974) Hunting by expectation or optimal foraging? A study of patch use by chickadees. Anim Behav 22:953–964

    Google Scholar 

  • Lack D (1966) Population studies of birds. Clarendon Press, Oxford, UK

    Google Scholar 

  • Leslie PH, Tener TS, Vizuso M, Chitty H (1955) The longevity and fertility of the Orkney vole, Microtus orcadensis, as observed in the laboratory. Proc London Zool Soc 125:115–125

    Google Scholar 

  • Luttich S, Rusch DH, Meslow EC, Keith LB (1970) Ecology of red-tailed hawk predation in Alberta. Ecology 51:190–203

    Google Scholar 

  • Manville RH (1959) The Columbian ground squirrel in northwestern Montana. J Mamm 40:26–45

    Google Scholar 

  • Michener GR (1977) Effect of climatic conditions on the annual activity and hibernation cycle of Richardson's ground squirrels and Columbian ground squirrels. Can J Zool 55:693–703

    Google Scholar 

  • Michener GR (1979a) Spatial relationships and social organization of adult Richardson's ground squirrels. Can J Zool 57:125–139

    Google Scholar 

  • Michener GR (1980) Differential reproduction among female Richardson's ground squirrels and its relation to sex ratio. Behav Ecol Sociobiol 7:173–178

    Google Scholar 

  • Michener GR (1983) Spring emergence schedules and vernal behavior of Richardson's ground squirrels: why do males emerge from hibernation before females? Behav Ecol Sociobiol 14:29–38

    Google Scholar 

  • Miller JM (1975) Tactics of energy partitioning in breeding Peromyscus. Can J Zool 53:967–976

    Google Scholar 

  • Morhardt SS (1975) Use of climatic diagrams to describe microhabitats occupied by Belding ground squirrels and to predict rates of change of body temperature. pp 303–323 in Gates DM, Schmerl RB (eds) Perspectives in biophysical ecology, Springer-Verlag, New York, USA

    Google Scholar 

  • Morhardt SS, Gates DM (1974) Energy-exchange analysis of the Belding ground squirrel and its habitat. Ecol Monogr 44:17–44

    Google Scholar 

  • Morton ML, Sherman PW (1978) Effects of a spring snowstorm on behavior, reproduction, and survival of Belding's ground squirrels. Can J Zool 56:2578–2590

    Google Scholar 

  • Murie JO, Boag DA (1984) The relationship of body weight to overwinter survival in Columbian ground squirrels. J Mamm 65:688–690

    Google Scholar 

  • Murie JO, Harris MA (1978) Territoriality and dominance in male Columbian ground squirrels (Spermophilus columbianus). Can J Zool 56:2402–2412

    Google Scholar 

  • Murie JO, Harris MA (1984) The history of individuals in a population of Columbian ground squirrels: source, settlement and site attachment. In: Murie JO, Michener GR (eds) The biology of ground-dwelling squirrels. Univ Nebraska Press, Lincoln pp 353–374

    Google Scholar 

  • Porter KG, Orcutt JD, Gerritsen J (1983) Functional response and fitness in a generalist filter feeder, Daphnia magna (Cladocera: Crustacea). Ecology 64:735–742

    Google Scholar 

  • Pyke GH (1984) Optimal foraging theory: a critical review. Ann Rev Ecol Syst 15:523–575

    Google Scholar 

  • Rickart EA (1982) Annual cycles of activity and body composition in Spermophilus twonsendii mollis. Can J Zool 60:3298–3306

    Google Scholar 

  • Ritchie ME (1988) Individual variation in the ability of Columbian ground squirrels to select an optimal diet. Evol Ecol 2:232–252

    Google Scholar 

  • Schitoskey F, Woodmansee SR (1978) Energy requirements and the diet of the California ground squirrel. J Wildl Manage 42:373–382

    Google Scholar 

  • Schoener TW (1971) Theory of feeding strategies. Ann Rev Ecol Syst 2:369–404

    Google Scholar 

  • Slade NA, Balph DF (1974) Population ecology of Uinta ground squirrels. Ecology 55:989–1003

    Google Scholar 

  • Smith AD, Shandruk LJ (1979) Comparison of fecal, rumen, and utilization methods for ascertaining pronghorn diets. J Range Manage 32:275–279

    Google Scholar 

  • Sparks DR, Malechek JC (1968) Estimating-percentage dry weight in diets using a microscopic technique. J Range Manage 21:264–265

    Google Scholar 

  • Stephens DW, Krebs JR (1986) Foraging theory. Princeton University Press, Princeton, New Jersey, USA

    Google Scholar 

  • Storr GM (1963) Estimation of dry-matter intake in wild herbivores. Nature 197:307–308

    Google Scholar 

  • Verme LJ (1969) Reproductive patterns of white-tailed deer in relation to nutritional plane. J Wildl Manage 33:881–884

    Google Scholar 

  • Wang LCH (1979) Time patterns and metabolic rates of natural torpor in the Richardson's ground squirrel. Can J Zool 57:149–155

    Google Scholar 

  • Werner EE, Hall DJ (1974) Optimal foraging and the size selection of prey by the bluegill sunfish (Lepomis macrochirus). Ecology 55:1042–1052

    Google Scholar 

  • Westoby M (1974) An analysis of diet selection by large generalist herbivores. Am Nat 108:289–304

    Google Scholar 

  • Zegers DA, Williams OW (1977) Seasonal cycles of body weight and lipids in Richardson's ground squirrel, Spermophilus richardsonii elegans. Acta Theriol 22:380–383

    Google Scholar 

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Ritchie, M.E. Optimal foraging and fitness in Columbian ground squirrels. Oecologia 82, 56–67 (1990). https://doi.org/10.1007/BF00318534

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  • DOI: https://doi.org/10.1007/BF00318534

Key words

  • Optimal foraging
  • Fitness
  • Ground squirrels
  • Energy intake
  • Growth rate