鯨豚生活史策略之比較研究

Abstract

生活史的研究不僅詳細的紀錄生物的生長、生殖及壽命, 是基礎生物學研究的核心, 同使也在生物的保育經營管理中扮演重要的角色。利用多變數統計分析的生活史比較研究, 對生活史的演化提供深入的看法, 同時對於物種的保育管理可以提供整合性的概念。 鯨豚為海洋中的高級消費者, 然而許多種類的鯨豚的永續生存面對極嚴峻的考驗。在鯨豚的保育工作中, 許多困難來自於缺乏詳盡的生活史資料。在本研究中, 我有系統的蒐集並整理超過750篇有關鯨豚生活史的文獻, 涵蓋全部14科83種, 利用general linear model及殘差分析, 探討生活史參數(LHT)間的關係, 並據以發展計算式以估計鯨豚的LHT。在去除共變數的影響後, 鯨豚的壽命可以由其體長(Lx)、成熟年齡(Am)估計: 或 依鯨豚的成熟年齡是否可得決定, 而鯨豚的斷奶體長(Lw)可以利用 或 估計, 依出生體長(Lb)是否得知決定。 除此之外, 本研究也依鯨豚的LHT估計鯨豚一生的生產量( ), 鬚鯨的 介於8~12間而齒鯨的 介於2~6之間, 因此在保育上, 所有的鯨豚均需視為嚴格的K-strategy的生物類型。在對於族群的潛在成長率( )的估計上, 鬚鯨與齒鯨間無顯著差異, 然而在不同科之間有極大的變異。在應用主成分分析及判別分析後, 鯨豚的生活史的差異與其系統分類間的關聯較低, 相對的, 與其潛在生態區位間有高度的關聯性; 依判別分析的結果, 鯨豚的生活史可以分為五個主要的類型(或區位): 類型1為有長程遷移的鬚鯨類, 類型2包含露脊鯨、弓頭鯨、抹香鯨及喙鯨等鯨類, 為對低溫環境的趨同適應, 類型3為高度社會化的海豚, 包含虎鯨、偽虎鯨、長肢及短肢領航鯨, 類型4為大洋生活的中小型齒鯨類, 類型5, 包含侏儒抹香鯨、淡水豚類以及鼠海豚類, 為另一趨同適應的類型, 其共同的生態區位包含淺水、溫暖的環境, 以及獨居的行為。不同類別的鯨類間, 在 及 有顯著的差異, 此結果對於鯨豚的保育政策的制訂, 對於提供有系統的管理方案有巨大的幫助。

Studies of life histories, figuring the detail schedule of growth, reproduction and longevity of life, stand on the central role of biology and provide valuable information for effective resource conservation and management. Many life history traits are not independent of each other and are bound together by three major trade-offs between life span and reproduction, between extant and future reproductive success, and between quantity and quality of offspring. These trade-offs finally form the fast-slow continuum of life history strategy, the r- and K-strategy selection. To find the association between the evolution of life history and ecological-ethological adaptation in different organisms, the comparative analysis by multivariate statistical methods provide an insight into evolution patterns of life history. Cetaceans are top marine predators and many of them face grave conservative challenges in their long-term survival. Some difficulties in making solid conservation policies arise from the deficiency of detailed cetacean life history traits (LHT) that can illustrate the most critical stage in life. The most solid way to obtain the first-hand LHT is to follow the fate of individuals and record the size and age at different status of growth. The alternative method to reliably extrapolate the LHT of undocumented species without any lethally specimen collecting is to use the potential allometric relationships between LHT. At present study, we seek to clearify the LHT interactions in cetaceans. Then we will propose the reliable expressions in the allometry of cetacean LHT. We particularly focus on the estimation of Ax, which has been one of the most difficult one LHT to be obtained by long-lived tracing or massively collecting dead oldest cetaceans. By reviewing published data, we explored the correlation in life history traits by general linear model. After removing confounding and unrelated factors, longevity (Ax) was primarily determined by the asymptotic length (Lx) and age at sexual maturity (Am): Ax = 0.962Lx0.435Am0.463, or Ax = 1.795Lx0.487 when Am is not available. We then calculated the lifetime fecundity as expected daughters per female per lifetime and the intrinsic rate of population increase. In the 47 documented species, most baleen whales deliver less than 10 daughters whereas most toothed cetaceans deliver less than 5 daughters in their whole lives and should be considered as extreme K-species when considering their conservation plans. Even a tiny change in rmax can be sensitive to over-exploitation. The unusual high rmax for migratory Balaenopteridae and Eschritidae may suggest compensation effect to past over-exploitation. The presented estimates of rmax in cetaceans can be used for estimating more precisely the quota of potential biological removal, which has been another critical criterion in management of incidental takes of cetacean. In addition, we proposed a generalized expression to estimate the effective population size, which has been another critical base for conservation management. The comparative study of life history variation reveals the interactions between organisms and their external environment and offers more predictive and quantitative guidance in conservation but quite limited in cetaceans. By principle component analysis, 90.75% life history variation could be explained by the body size and the reproduction factors. By the jackknife correctness from discriminant analysis, cetacean phylogeny itself had only 29.2% correct classification with family. With further ecological implications, 5 major niches of life history patterns in cetaceans are generalized with an average of 95.2% correctness. The Niche 1 concerns the long migratory and interrupted feeding lifestyle; Niche 2 – low ambient temperature waters; Niche 3 - socially cohesive behavior system; Niche 4 – open and pelagic waters; Niche 5 – shallow and warm waters and perhaps high mortality. The differences of fitness among cetaceans were presented on their lifetime fecundity and intrinsic population growth rate with high lifetime reproduction for Niche 1, 4, 5 while low for Niche 2, 3 and highest intrinsic population growth rate for Niche 1, 5 while lowest for Niche 3. The generalization of five life history patterns strongly links the paraphyletic convergence with ecological differentiation and potentially offers more predictive and quantitative guidance for the conservation of cetaceans.