臺灣博碩士論文加值系統

本論文利用賽局理論與最適控制理論探討休閒遊憩產業之收益管理，遊客遊憩選擇與遊憩專門化之研究議題。在第二章以生態旅遊為例探討遊客遊憩選擇與其生活型態，當地住民人數與農產品異質程度，對風景區域內之當地住民利益，經營休閒遊憩廠商利潤，以及廠商利潤回饋當地住民比例之影響效果。我們獲得當遊客的互動具有正向的人潮效果，而且遊客是慕名廠商的專屬景點而去風景區域時，廠商所獲得的利潤水準，會高於其在慕名風景區域效果下的利潤水準。第三章則是利用賽局理論建立旅遊經濟模型，探討在觀光旅遊產業中，廠商間實施差異化的小費給予制度對廠商利潤，遊客消費者剩餘，以及社會福利的影響效果。我們得到廠商實施差異化的小費給予制度不但可提高遊客的消費者剩餘，同時也可提高社會福利。第四章利用最適控制理論，分析在休閒遊憩產業中，遊客對遊憩專門化的投入(或投資)，使其體驗或品味遊憩活動時，會有更深入的認知與產生深刻的價值，因而對特定的遊憩活動產生終生的遊憩認知或地方依戀與認同。我們發現當遊客所從事的遊憩體驗投入是相對較辛苦，則遊客有可能會在其遊憩生命週期之前不再進行對遊憩體驗的投入。

This dissertation focuses on the applications of game theory and optimal control theory to the study of tourist’s recreation choices, revenue management, and recreational specialization in a recreation and leisure industry. The applications present the process of model building, the process of transforming an informal description of recreation-related decision issues to a formal game theory and optimal control problems.
There are three essays in the dissertation. The first essay investigates the effects of tourist’s recreation choices and lifestyle, the numbers of local habitant, and agricultural product differentiation upon local habitant benefits, recreational firms’ profits, and the share of firm’s profit with local habitants in a scenic area. It develops a recreation economics model to address the above effects. It shows that when the tourists belong to the positive bandwagon group and choose the firm-specific scenic resort, the firm’s profit is higher as compared to that of under the scenic-specific area effect. The second essay applies the game theory to set up a recreation economics model in which the effects of differentiated tipping systems on firms’ profits, tourist’s consumer surplus, and social welfare are investigated. It demonstrates that firms exert the differentiated tipping systems can increase both consumer surplus and social welfare. The third essay uses an optimal control approach to analyze the case under which a tourist invests his recreation specialization input in pursuing tourism experience and taste to get valuable tourism cognition and the sense of place attachment. It shows that the tourist may not invest recreational experience input in the period of his recreation lifetime as the recreational experience input is relatively harder.

目 次
摘要 i
目次 iii
圖次 v
表次 vi
第一章 緒論 1
第一節 研究背景與動機 1
第二節 研究目的 2
第三節 研究架構 3
第二章 生態旅遊遊客遊憩選擇之效益分析 5
第一節 前言 5
第二節 理論模型 9
第三節 遊客選擇在廠商景點外遊憩 11
第四節 遊客選擇在廠商景點內遊憩 14
第五節 廠商利潤與當地住民利益之比較 15
第六節 利潤回饋比例之決定 19
第七節 小結 25
第三章 小費給予制度差異化與旅遊團費競爭 27
第一節 前言 27
第二節 相關文獻回顧 29
第三節 模型說明 33
第四節 模型分析 37
第五節 遊客消費者剩餘與社會福利 46
第六節 小結 49
第四章 遊憩專門化，場所依戀，與遊憩體驗投入之動態研究 53
第一節 前言 53
第二節 理論模型(一) 56
第三節 分析與討論 58
第四節 理論模型(二) 63
第五節 小結 65
第五章 結論與建議 67
第一節 研究結論 67
第二節 未來研究建議 68
參考文獻 69

圖 次
圖1 與 之比較 18
圖2 在 與 ， 與 之比較 19
圖3 與 之比較 23
圖4 與M之相對值 24
圖5 與 之相對值 24
圖6 小費給予制度之擴展式賽局 46
圖7 遊憩體驗投入 最適路徑圖 61
圖8 遊憩體驗資本 最適路徑圖 61
圖9 遊憩體驗投入 最適路徑圖 62
圖10 遊憩體驗資本 最適路徑圖 62
圖11 遊憩體驗資本與投入相圖 64

表 次
表1 相同小費給予制度之均衡 37
表2 遊客消費者剩餘與會福利 52

王美慧、陳瑞龍、葉陳錦(2006)。民宿旅客之消費行為探討-以花蓮地區為例. 戶外遊憩研究，19(4)，1-30。
王國欽(2006)。銀髮族團體套裝旅遊動機研究，觀光研究學報，12(2)，119-138。
王鑫(2000)。生態旅遊與永續旅遊。推動永續生態觀光研討會論文集。25-35，台中市。
交通部觀光局(2003)。中華民國九十一年國人旅遊狀況調查報告。交通部觀光局，台北市。
吳宗瓊、 劉瓊如(2008)。旅遊紀念品購買行為的解析與探索-記憶在地特色vs旅遊伴手禮。觀光研究學報，14(2)，189-212。
吳忠宏、黃宗成、洪常明(2005)。澎湖居民對生態旅遊知覺與發展生態旅遊態度關係之研究。戶外遊憩研究，18(3)，1-30。
吳欣頤、林晏州、黃文卿(2005)。太魯閣國家公園原住民社區居民對發展生態旅遊之認知與需求，戶外遊憩研究，8(4)，47-67。
吳德晃(2004)。專業表現、服務努力、滿意度與小費之關係。旅遊管理研究，4 (1)，39-58。
呂怡儒(2001)。台北近郊森林地方感之研究。未出版之碩士論文，國立臺灣大學森林學研究所，台北市。
呂適仲(2000)。雪霸國家公家武陵遊憩區發展生態旅遊之遊憩資源效益評估。未出版之碩士論文，東海大學景觀學系碩士論文，台中市。
宋秉明、郭煒琪、彭孟慈、王彬如、蘇佳慧、許鈺青(1995)。玉山國家公園與其原住民之衝突分析。觀光研究學報，1(1)，80-88。
巫喜瑞(2006)。赴國外旅遊團顧客互動事件評價與其影響因素之研究。戶外遊憩研究，19(4)，83-103。
李素馨(1994)。典型相關分析-專業程度、遊憩動機和基地屬性認知關係之探討。戶外遊憩研究，7(3)，39-62。
李素馨、候錦雄(2004)。台休閒農業之體驗付費與觀光商品化現象。觀光研究學報，10(1)，133-145。
李堯賢、呂英瑞、林怡芯、楊琮泰(2007)。競爭性與一致性服務費訂價策略之經濟效率分析：以觀光休閒遊憩產業為例。戶外遊憩研究，21(1)，49-67。
林宗賢、劉佳旻(2007)。溫泉遊客健康生活型態對其心理幸福感的影響。觀光研究學報，13(3)，212-233。
林晏州(2001)。馬公生態園區遊憩系統暨遊程規劃。澎湖：交通部觀光局澎湖國家風景區管理處。
林晏州、陳玉清(2005)。生態旅遊的發展策略與管理：以陽明山國家公園為例。黃宗煌與滕藤合編：生態經濟、生態旅遊與綠色食品產業發展，263-282。
林慧年(2004)。義務解說員的活動涉入、地方依戀和資源知識之相關性-以中華民國荒野保護協會二格山定點自然觀察小組為例。未出版之碩士論文，國立臺灣師範大學環境教育研究所，台北市。
侯錦雄、歐聖榮編(2007)。休閒遊憩與人生發展，休閒遊憩：理論與實務，56-81。前程文化事業，台北市。
柯嘉鈞、歐聖榮(2004)。遊客對生態旅遊經營管理策略之認同度研究-以參山國家風景區為例。中華民國戶外遊憩學會第六屆休閒、遊憩、觀光學術研討會論文集-生態旅遊與衝擊。128-142。台北市：中華民國戶外遊憩學會。
孫雯皓、羅怡如、張國凱、洪盈臻(2002)。太魯閣國家公園設立對鄰近部落經濟、文化之影響暨部落行為之調適。未出版之學士論文，世新大學觀光系，台北市。
曹勝雄(2001)。台灣生態旅遊市場之分析。第一屆永續生態旅遊研討會論文集， 87-98，台南市。
梁英文(2004)。認真性休閒與場所依戀之關係：遊憩專門化之角色。未出版之碩士論文，中國文化大學觀光事業研究所，台北市。
郭岱宜(1999)。生態旅遊：21世紀旅遊新主張。台北市：揚智文化。
陳心怡(2003)。自行車騎乘者專門化程度與場所依戀關係之研究-以台中大度山區騎乘者為例。未出版之碩士論文，逢甲大學建築所，台中市。
陳玉清、林晏州(2003)。生態旅遊地遊客選擇行為之研究。戶外遊憩研究，16(3)，23-40。
陳玟妤(2001)。旅行業領隊之平面廣告效果研究。未出版之碩士論文，中國文化大學觀光事業研究所，台北市。
陳俊男(1995)。出國旅遊旅行社供需行為之研究。未出版之碩士論文，中山大學企業管理研究所，高雄市。
彭逸芝(2004)。遊憩自行車使用者之遊憩涉入與地方依戀關係之研究。未出版之碩士論文，銘傳大學觀光研究所，台北市。
曾梓峰、蔡家秀(2005)。生態旅遊作為區域發展的催化劑？社會經濟觀點下的困境與機會。黃宗煌與滕藤合編：生態經濟、生態旅遊與綠色食品產業發展，119-225。
黃文卿(2002)。台灣地區國家公園永續經營管理指標之研究-以玉山國家公園為例。未出版之博士論文，國立臺灣大學園藝學研究所，台北市。
楊琮泰(2004)。生態旅遊之價格競爭與經營策略分析。未出版之博士論文，中華大學科技管理研究所，新竹市。
廖珮瑜(2003)。旅遊業領隊服務特性對顧客滿意度及忠誠度影響之研究。未出版之碩士論文，淡江大學企業管理學系，台北市。
劉俊志(2004)。居民與遊客對於鯉魚潭風景特定區之地方依戀差異探討。未出版之碩士論文，國立東華大學自然資源管理研究所，花蓮市。
劉瓊如(2007)。生態旅遊地永續發展評估之研究-以阿里山達邦部落為例。觀光研究學報，13(3)，235-264。
歐陽慧真(2002)。賞鳥者專門化程度與場所依戀關係之研究-以七股溼地為例。未出版之碩士論文，東海大學景觀學系，台中市。
歐聖榮、蕭芸殷(1998)。生態旅遊遊客特質之研究。戶外遊憩研究，11(3)，35-58。
歐雙磐(2004)。登山者遊憩專門化程度、情境偏好與場所依戀關係之研究。未出版之碩士論文，東海大學景觀學系，台中市。
鄭明松(1994)。國人出國旅遊行為之研究-以台北市地區居民為例。未出版之碩士論文，中山大學企業管理研究所，台北市。
賴如伶(2002)。南庄蓬萊村居民對原住民觀光發展衝擊認知之研究。未出版之碩士論文，朝陽科技大學休閒事業管理系，台中縣。
賴明洲、薛怡珍(2005)。生態旅遊之實踐：以地景生態學觀點探討生態旅遊之規劃原則。黃宗煌與滕藤合編：生態經濟、生態旅遊與綠色食品產業發展，229-260。
謝宗恆(2003)。文化遊憩涉入與場所依戀關係之研究-以北埔地區遊客為例。未出版之碩士論文，東海大學景觀學系，台中市。
顏家芝(2006)。以地方社會結構為基礎探討居對生態旅遊影響之認知。戶外遊憩研究，19(3)，69-98。
嚴長壽(2008)。做自己與別人生命中的天使。台北市：寶瓶文化事業。
Akerlof, George A (1997). Social distance and social decisions. Econometrica, Econometric Society, 65(5), 1005-1028.
Azar, Ofer H. (2003a). Is future dervice a reason for tipping ? theory and evidence. Working paper.
Azar, Ofer H. (2003b). Optimal monitoring with external incentives: the case of tipping. Journal Southern Economic, 71(1), 171-181.
Azar, Ofer H. (2003c). The implications of tipping for economics and management. International Journal of Social Economics. 3 (10), 1084-1094.
Azar, Ofer H. (2004). The history of tipping-from sixteenth-century England to United States in the 1910s. International Journal of Social Economics. 33(6), 745-764.
Becker, Gary & Murphy, Kevin (1993). A simple theory of advertising as a good or a bad. Quarterly Journal of Economics, 108(4 ), 941-964.
Becker, Gary (1991). A treatise on the Family. Cambridge: Harvard University Press.
Bernheim, B. D. (1994). A theory of conformity, Journal of Political Economy, 102 (5), 841-877.
Bodvarsson, O. & Gibson, W. (1994). Gratuities and customer appraisal of service: evidence from minnesota restaurants. The Journal of Socio-Economics, 23(3), 287-303.
Bookbinder, M. P. Dinerstein E. Rijal A. Cauleyand H. & Rajouria A. (1998). Ecotourism’s Support of Biodiversity Conservation, Conservation Biology, 12(6), 1399-1404.
Brandon, K. (1996). Ecotourism and Conservation: A Review of Key Issues. Global Environment Division, Environment Department, The World Bank.
Bricker, K. S. & Kerstetter, D. L.(2000).”Level of specialization and place attachment: An exploratory study of whitewater recreationists.” Leisure Sciences, 22, 233-257.
Brown, K. (1972). Puzzles & problem, Q773. Journal of Political Economy, 80, 213.
Bryan, H. (1977). “Leisure value systems and recreational specialization: the case of trout fisherman. Journal of Leisure Research, 9(3), 174-187.
Bull, Adrian (1995). The Economics of Travel and Tourism, second edition. Longman.
Caplin, A. & Nalebuff B. (1991). Aggregation and Imperfect Competition: on the Existence of Equilibrium, Econometrica, 59(1), 25-59.
Cheung, S.N.S. (1969). The theory of share tenancy. Chicago: University of Chicago Press.
Chiang, Alpha C. (1992). Elements of Dynamic Optimization, New York : McGraw-Hill.
Chu, W. Gerstner, E. & Hess, J. D. (1995). Cost and benefits of hard-sell, Journal of Marketing Research, 32 (1), 97-103.
Claycomb, C. & Martin, C. L. (2002). Building customer relationships: An inventory of service providers’ objectives and practices. The Journal of Services Marketing, 16(7), 615-635.
Ditton B. Robert, David K. Loomis & Seungdam Choi (1992). Recreation Specialization: Re-conceptualization from a Social Worlds Perspective. Journal of Leisure Research, 24(1), 33-51.
Dixit, A. (1979). A Model of Duopoly Suggesting a Theory of Entry Barriers. The Bell Journal of Economics, 20-33.
Donnelly P. Maureen, Jerry J. Vaske &Alan R. Graefe (1986). Degree and Range of Recreation Specialization: Toward a Typology of Boating Related Activities. Journal of Leisure Research, 18(2), 81-95.
Fennell, D. (1999). Ecotourism: An Introduction. New York : Routledge.
Fullerton, R. A. & Punj, G. (1993). Choosing to misbehave: A structural model of aberrant consumer behavior. Advances in Consumer Research, 24, 340-344.
Gayer A. & Shy O. (2006). Publishers, Artists, and Enforcement. Information Economics & Policy, 18(4), 374-384.
Gerstner, E. Hess, J.D. & Chu, W. (1993). Demarketing as a differentiation strategy. Marketing Letter, 4, 49-57.
Grilo, I., Shy O. & Thisse J. (2001). Price Competition When Consumer Behavior is Characterized by Conformity or Vanity. Journal of Public Economics, 80(3), 385-408.
Hailu, G. Boxall, P.C. & McFarlane, B. L. (2005). The influence of place attachment on recreation demand. Journal of economic Psychology, 26, 581-598.
Harris, K. & Reynolds, K. L. (2003). The consequences of dysfunctional customer behavior. Journal of Service Research, 6(2), 144-161.
Hemenway, D.(1988). Price and choices: Microeconomic Vignettes. second edition, Cambridge:Ballinger Publishing Company.
Honey, M. (1999). Ecotourism and Sustainable Development : Who Owns Paradise? Island Press, Washington D.C..
Hoy, W. K., & Miskel, C. G. (2001). Educational administration: Theory, research, and practice 6th. Boston, MA:McGraw-Hill.
Jacob, N. & Page, A. (1980). Production, information costs and economic organization: The buyer monitoring case. American Economic Review, 70 (June), 476-478.
Kahneman, D. Knetsch, J. & Thaler, R. (1991). The endowment effect, loss aversion, and status quo bias. Journal of Economic Perspectives, 5, 193-206.
Kaltenborn, B. P. (1997). Nature of Place Attachment: A study Among Recreation Homeowners in Southern Norway. Leisure Studies, 19, 175-189.
Kamien, M. & N. Schwartz. (1981). Dynamic Optimization: The Calculus of Variations and Optimal Control in Economics and Management, Amsterdam: North Holland.
Karni, E. & Levin. (1994). Social attributes and strategic equilibrium: a restaurant pricing game. Journal of political Economy, 102, 822-840.
Kotler P. Bowen Joth T. & Makens James C. (2006). Marketing for Hospitality and Tourism. Fourth Edition, Pearson International Edition.
Kuentzel, W. F. & McDonald, C.D. (1992). Different effects of past experience, commitment, and lifestyle dimensions on river use specialization. Journal of Leisure research, 24(3), 269-287.
Leibenstein, Harvey (1950). Bandwagon, snob and veblen effects in the theory of consumers’ demand. Quarterly Journal of Economics, 64, 183-207.
Leibenstein, Harvey (1976). Beyond Economic Man: An New Foundation for Microeconomics. Havard University Press.
Leonard, D. & N. van Long, (1992). Optimal Control Theory and Static Optimization in Economics, Cambridge Umiversity Press: Cambridge.
Lew, A. A. (1998). The Asia-Pacific Ecotourism Industry : Putting Sustainable Tourism Into Practice. In Sustainable Tourism : A Geographical Perspective (eds. C. M. Hall and A. A. Lew), Longman.
Little, B. R. (1976). Specialization and the varieties of environmental experience: Empirical studies within the personality paradigm. In S. Wapner, S. Cohen, & B. Kaplan (Eds.). Experiencing the environment, 81-116. New York: Plenum Press.
Lynn, M. & Graves Jeffrey (1996). Tipping: an incentive reward for service? Hospitality Research Journal, 20 (1), 1-14.
Lynn, M. & B. Latane (1984). The Psychology of Restaurant Tipping. Journal of Applied Social Psychology, 14(6), 549-561.
Lynn, M. & Grassman, A. (1990). Restaurant tipping: an examination of three “rational” explanations. Journal of Economic Psychology, 11, 169-181.
Lynn, M. (2001). Restaurant tipping and service quality. Restaurant Management, 14-20.
Martin, C. L. & Parnter, C. A. (1989). Compatibility management: Customer-to-customer relationships in service environments. Journal of Service Marketing, 3(summer), 6-15.
Martin, C. L. (1996). Customer-to-customer relationships: Satisfaction with other consumers’ public Behavior. Journal of Consumer Affairs, 30(1), 146-169.
McCool, S. F. & Martin, S. R. (1994). Community attachment and attitudes toward tourism development. Journal of Travel Research, 32(3), 29-34.
McIntyre, N. & Pigram, J. J. (1992). Recreation specialization reexamined: The case of vehicle-based campers. Leisure Sciences, 14, 3-15.
Moore, R. L. & Graefe, A. R. (1994). Attachments to recreation settings: The case of rail-trail users. Leisure Sciences, 16, 17-31.
Nitsch, B. & van Straaten, J. (1995). Rural tourism development: Using a sustainable tourism development approach. In Coccossis, H., & Nijkamp, P. (Eds.), Sustainable tourism development, 169-185. Brookfield: Ashgaye Publish.
Parker, C. & Ward, P. (2000). An analysis of role adoptions and scripts during customer-to-customer encounters. European Journal of Marketing, 34(3), 146-169.
Pencavel, J.H. (1977). Work effort, on-the-job screening and alternative methods of remuneration. In R.G. Ehrenberg (Eds.), Research in Labor Economics. 1. Greenwich, CT: JAI Press.
Peters, J. (1998). Sharing National Park Entrance: Forging New Partnerships in Madagascar. Society and Natural Resources, 11(5), 517-531.
Pineau, Pierre Olivier, (2002). An Ethical Behavior Interpretation of Optimal Control, Chapter4 in Optimal Control and Differential Games: Essay in Honor of Steffen Torgensen. Edifed by Georges Zaccour, Kluwer Academic Publishers: Boston.
Rinaldi, (1998). Love Dynamics: The Case of Linear Couples, Applied Mathematics and Computation, 95, 181-192.
Ross, S. & G. Wall (1999a). Ecotourism: Towards Congruence Between Theory and Practice. Tourism Management, 20, 123-133.
Ross, S. & G. Wall (1999b). Evaluating Ecotourism: The Case of North Sulawesi, Indonesians. Tourism Management, 20, 673-683.
Rotemberg, J. J. (1994). Human Relations in the Workplace, Journal of Political Economy, 102(4), 684-717.
Scheyvens, R. (1999). Ecotourism and the Empowerment of Local Communities, Tourism Management, 20, 245-249.
Schreyer, R. & Beaulieu, J. T. (1986). Attribute preferences for wildland recreation settings. Journal of Leisure Research, 18, 231-247.
Schwartz, Zvi. (1997). The economics of tipping: tips, profits and the market’s demand-supply equilibrium. Tourism Economics, 3 (3), 265-279.
Seierstad, Atle & Kunt Sydsaeter, (1987). Optimal Control Theory with Economic Applications, New York :North-Holland.
Sethi, Suresh P. & Gerald L. Thompson, (2000). Optinal Control Theory: Applications to Management Science and Economics, 2nd Edition, Kluwer Academin Publishers: Bostom.
Shapiro, Carl & Hal R. Varian (1999). In formation Rule: A Strategic Guide to the Network Economy. Harvard Business School Press: Boston, Massachusetts.
Shy Oz. & Thisse J. F. (1999). A Strategic Approach to Software Protection. Journal of Economics & Management Strategy, 8(2), 163-190.
Shy, Oz. (2001). The Economics of Network Industries. Cambridge University Press, New York.
Shy, Oz. (2008). How to Price: A Guide to Pricing Techniques and Yield Management. Cambridge University Press .
Shy, Oz. Grilo, I. & Thisse, J. F. (2001). Price competition when consumer behavior is characterized by conformity of vanity. Journal of Public Economics, 80, 385-408.
Sinclair, T. & Stabler, M. (1998). The Economics of Tourism. Routledge.
Sisk, D.E. & Gallick, E.C. (1985). Tips and commissions: A study in economic contraction. FTC Bureau of Economics Working Paper No. 125. Washington, DC: Federal Trade Commission.
Sutton, J. (1997). On Smart Agent. RAND Journal of Economics, 28, 605-628.
Swarbrooke, John & Susan Horner. (2007). Consumer Behavior in Tourism, 2nd Edition, New York :Elsevier.
Symeonidis, George (2002a). The Effects of Competition: Cartel Policy and the Evolution of Strategy and Structure in British industry. The MIT Press.
Symeonidis, George (2008). Downstream Competition, Bargaining, and Welfare. Journal of Economics & Management Strategy, 17(1), 247-270.
Symeonidis, George (2002b). Cartel Stability with Multiproduct Firms. International Journal of Industrial Organization, 20, 339-353.
Tsaur, S. H. Lin, Y. C. & Lin, J. H. (2006). Evaluating ecotourism sustainability from the integrated perspective of resource, community and tourism. Tourism Management, 27(4), 640-653.
Valentine, P. S. (1993). Ecotourism and Nature Conservation: A Definition with Some Recent Developments in Micronesia. Tourism Management, 14(2) 107-115.
Vanhove Norbert (2005). The Economics of Tourism Destinations. Oxford Burlington Elsevier Butterworth-Heinemann.
Varian, H. R. (2003). Intermediate Microeconomics: A Modern Approach, W. W. Norton & Company, New York.
Veblen, Thorstein (1899). The Theory of the Leisure Class: An Economic Study of Institutions. London: Macmillan.
Walpole, M. J. & Goodwin H. J. (2000). Local Economic Impacts of Dragon Tourism in Indonesia. Annals of Tourism Research, 27(3), 559-576.
Wearing, Stephen & Neil J. (1999). Ecotourism: Impacts, Potentials and Possibilities. Butterworth-Heinemann: Oxford.
Wellman, J. D. J.W. Roggembuck, & A.C. Smith, (1982). Recreation Specialization and Norms of Depreciative Behavior Among Canoeists. Journal of Leisure Research, 14(4), 323-340.
Young, E. H. (1999). Balancing Conservation with Development in Small-scale Fisheries: is Ecotourism an Empty Promise? Human Ecology, 27(4), 581-620.