生活史特徵、氣候變遷與漁撈壓力對魚類族群的空間變異之影響

Abstract

空間同步效應是指同一物種分散在不同區域的族群會有相似的豐度變化情形，是一種常見的族群時空動態特徵。空間同步效應的強度會受到內在(例如: 個體散布、密度調節及生活史特徵)和外在因素影響(例如: 環境因子和漁撈)而有所不同。了解這些內外在因素對於空間同步效應所造成的影響至關重要，因為空間同步效應的改變會影響重要生態過程及功能，例如物種滅絕危機、疾病傳播和食物生產。在這篇研究當中，我探討氣候變遷和漁撈作用對於魚類族群的空間同步效應之影響，並將魚種的生活史特徵納入考量。我分析加州沿近海16種受捕撈影響和13種沒有受捕撈影響的魚種、海表溫(SST)和風速的空間同步效應之情形(1951-2007)，資料取自 California Cooperative Oceanic Fisheries Investigations (CalCOFI)。我估算出各物種在空間距離為零之空間同步效應，在跨物種分析上發現，隨著特定生活史數值(性成熟年齡、性成熟體長、最大體長及食物階層)的增加，空間同步效應會有下降的情形，意味著 K 策略性的物種具有較低程度的空間同步效應。更重要的是，在考慮物種生活史特徵下，受捕撈影響物種相較於沒有受捕撈影響物種，具有較高的空間同步效應值，顯示漁撈會對物種的空間同步效應造成影響。另一方面，氣候變遷也改變環境因子和魚種的空間同步效應。在分析中發現，海表溫、風速及六種中的四種呈現完整的同步效應隨距離衰減之魚種，在氣候暖期顯現出較高程度的空間同步效應，因此環境因子空間同步效應的上升可能是導致魚群空間同步效應上升的主因。這些結果顯示外部因素(例如，氣候變遷及漁撈)會導致物種空間同步效應增加，進而使物種產生不穩定的族群動態，可能導致滅絕危機的提升。結論顯示避免空間同步效應上升具有一定的必要性，這是維持族群動態穩定性及生物資源永續利用的關鍵因素。

Spatial synchrony, which refers to the simultaneous change of abundance in spatially separated subpopulations of a species, is a common feature in spatio-temporal population dynamics. The degree of spatial synchrony can be influenced by various intrinsic (e.g., dispersal, density regulation, and life-history traits) and extrinsic (e.g., environmental forcing and fishing) processes. Understanding the underlying mechanisms that drive such changes in spatial synchrony is essential because it can impact crucial ecological processes and functionings such as extinction risk, disease outbreak, and food production. In this study, I focus on investigating the response of spatial synchrony to climate transitions and fishing, with consideration of life-history traits of fish species. I extracted data from the California Cooperative Oceanic Fisheries Investigations (CalCOFI) spanning the years from 1951-2007. I analyzed data of 16 exploited and 13 unexploited fish species, as well as sea surface temperature (SST) and wind speed of the CalCOFI region. My findings revealed that, in general, spatial synchrony at distance approaching zero decreases with certain increasing life-history traits (including age at maturation, length at maturation, maximum length, and trophic level). This finding indicates that species with traits associated with K-strategy tend to exhibit lower synchrony in nearby regions. Interestingly, exploited species demonstrated higher spatial synchrony at distance approaching zero values compared to unexploited species, after accounting for their life-history variation, suggesting that fishing has altered the spatial synchrony patterns of species. In addition, climate transitions have a modifying effect on the spatial synchrony of both environmental variables and some fish species. Specifically, during warm climate period, I observed an increase in synchrony for SST, wind speed, and four out of six species with the complete synchrony decay patterns. Thus, the increasing synchrony of environmental variables may be the underlying reason for the increasing synchrony observed among those fish species. My results emphasize that extrinsic factors such as climate transitions and fishing can enhance the spatial synchrony of fish, consequently leading to unstable population dynamics and an elevated risk of extinction. In order to maintain the stability of population dynamics and promote sustainable resource utilization, it is crucial to prevent the occurrence of strong spatial synchrony among subpopulation for a species.