張 強(qiáng),馬克明,李金亞,張育新

中國(guó)科學(xué)院生態(tài)環(huán)境研究中心,城市與區(qū)域生態(tài)國(guó)家重點(diǎn)實(shí)驗(yàn)室,北京 100085

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不同尺度下停歇點(diǎn)濕地對(duì)遷徙水鳥的影響研究綜述

張 強(qiáng),馬克明*,李金亞,張育新

中國(guó)科學(xué)院生態(tài)環(huán)境研究中心,城市與區(qū)域生態(tài)國(guó)家重點(diǎn)實(shí)驗(yàn)室,北京 100085

停歇點(diǎn)濕地是遷徙水鳥重要的能量補(bǔ)給地,在水鳥每年的往返遷徙過程中具有十分重要的生態(tài)意義。近年來隨著全球變化和人類活動(dòng)增加,遷飛路線上的停歇點(diǎn)濕地正發(fā)生劇烈變化。各個(gè)停歇點(diǎn)濕地的生境變化及周圍環(huán)境不僅是影響水鳥棲息地適宜性的重要因素,還改變了各路線上遷徙水鳥的種群大小和群落多樣性。分析不同尺度下停歇點(diǎn)濕地影響遷徙水鳥種群變化的主要生態(tài)因子和環(huán)境因素,不僅有助于理解各停歇點(diǎn)景觀變化的生態(tài)效應(yīng),也可為遷徙水鳥種群保護(hù)提供理論支持。首先分析了在棲息地斑塊尺度上停歇點(diǎn)濕地內(nèi)的水、食物、棲息地格局和人類干擾等生態(tài)要素對(duì)水鳥覓食和棲息活動(dòng)的影響；其次,分析了景觀尺度上濕地周圍的氣候變化、土地利用和外來生物等環(huán)境條件在各停歇點(diǎn)對(duì)水鳥棲息地質(zhì)量的改變；最后,基于多尺度條件下濕地影響因素的耦合效應(yīng),分析了當(dāng)前濕地生境與水鳥種群關(guān)系研究中存在的主要問題,并總結(jié)了對(duì)濕地和水鳥保護(hù)的啟示。

停歇點(diǎn)；濕地；水鳥；棲息地；遷飛路線

濕地生境對(duì)水鳥遷徙具有重要的生態(tài)意義,尤其是遷飛路線上分布的各類濕地是水鳥遷徙過程中重要的能量補(bǔ)給來源,為不同種群提供食物和棲息地[1]。全球依賴濕地生存的水鳥有870多種,多數(shù)濕地水鳥是季節(jié)性遷徙鳥類[2]。沿遷徙路線分布的一系列可用停歇點(diǎn)濕地是保證水鳥遷徙成功的基礎(chǔ),在整個(gè)遷飛網(wǎng)絡(luò)中起到中繼站和食物補(bǔ)給地的作用,但往往也是眾多水鳥種群遷徙過程中的瓶頸[3]。濕地棲息地的變化尤其是具有國(guó)際意義的重要中途停歇點(diǎn)濕地的生境變化,對(duì)遷徙過程中水鳥種群的數(shù)量產(chǎn)生強(qiáng)烈影響[4]。

近幾十年來隨著氣候變化和人類活動(dòng)的加劇,自然濕地發(fā)生大規(guī)模喪失,尤其是位于東亞-澳大利西亞遷徙路線上的沿海濕地發(fā)生了巨大變化[5]。截至20世紀(jì)末,全球已有超過50%的濕地消失,而中國(guó)則在1978—2008年間喪失了約33%的濕地,剩余部分在人類活動(dòng)干擾下也發(fā)生了不同程度的退化[6]。位于遷飛路線上的眾多水鳥棲息地喪失或生境質(zhì)量下降,已對(duì)遷徙種群造成了嚴(yán)重威脅[7]。如果現(xiàn)存濕地生態(tài)系統(tǒng)進(jìn)一步遭到破壞,水鳥種群將在遷徙過程中失去合適的濕地作為停歇地或越冬地,無法完成遷飛循環(huán)而最終滅絕。

濕地對(duì)遷徙水鳥影響的研究很早就引起了人們的重視[8]。近年來相關(guān)研究逐漸從現(xiàn)象描述發(fā)展為機(jī)制分析,研究?jī)?nèi)容多關(guān)注濕地景觀變化的模擬預(yù)測(cè)和水鳥種群對(duì)棲息地變化的響應(yīng)等方面,且更加重視大尺度環(huán)境變化對(duì)整個(gè)水鳥遷徙過程的影響[9- 11]。隨著越來越多新技術(shù)的應(yīng)用和國(guó)際合作的逐步展開,人們開始研究不同尺度效應(yīng)下濕地對(duì)水鳥的影響[12-13]。針對(duì)濕地生境變化與水鳥種群波動(dòng)間的關(guān)系,研究范圍開始面向探討影響水鳥群落多樣性和遷徙策略的主要因素等內(nèi)容,而且研究方向也逐步從現(xiàn)象和數(shù)量的描述向濕地生態(tài)功能和遷徙水鳥的種群反饋機(jī)制的分析等方向深入[14-15]。

雖然當(dāng)前有關(guān)繁殖地和越冬地生境變化對(duì)候鳥的影響研究較多,但在中途停歇點(diǎn)濕地對(duì)遷徙水鳥的影響方面還較為缺乏[16-17],已有研究也主要是關(guān)注單個(gè)濕地生態(tài)系統(tǒng)的變化或單一水鳥物種的遷徙[18]。對(duì)于整個(gè)遷飛路線上的水鳥種群來說,各遷徙種群的需求各異,不同停歇點(diǎn)濕地內(nèi)的生境要素對(duì)水鳥的生態(tài)意義也不相同[19-20]。研究發(fā)現(xiàn),棲息地適宜性是決定各中途停歇點(diǎn)水鳥數(shù)量的主要因素,也是影響濕地內(nèi)種群分布和多樣性變化的重要原因[21-22]。因此在研究停歇點(diǎn)濕地的影響機(jī)制時(shí),需要根據(jù)水鳥種群在遷徙過程中對(duì)主要生態(tài)因子的需求,找出影響水鳥種群棲息地適宜性的共同因素。

1 棲息地斑塊尺度濕地生境要素的影響

沿遷徙路線分布的濕地作為水鳥遷徙過程中的重要節(jié)點(diǎn),濕地面積的多少和棲息地質(zhì)量的高低決定了其生態(tài)承載能力的大小。各停歇點(diǎn)濕地內(nèi)的適宜生境面積是影響棲息水鳥種群大小的決定性因素,生境要素的配置變化則對(duì)水鳥的物種多樣性有顯著影響[23-24]。水鳥對(duì)停歇點(diǎn)生境的利用程度受濕地內(nèi)景觀結(jié)構(gòu)和多生境要素綜合作用的影響,濕地內(nèi)的水位變化、水質(zhì)、食物資源、棲息地結(jié)構(gòu)以及人類干擾等生境特征的變化都強(qiáng)烈影響水鳥的覓食和棲息,是水鳥遷徙過程中選擇棲息地的主要依據(jù)。

1.1 水位變化的影響

停歇點(diǎn)濕地水量影響水鳥棲息地的適宜性主要體現(xiàn)在水位高低、水位變化和水面面積3個(gè)方面[25]。首先,水位是決定濕地水鳥選擇適宜生境的重要因素。不同水鳥對(duì)水位要求不同,濕地鳥類的分布與水位高低關(guān)系密切,低水位濕地是鸻鷸類水鳥重要的覓食地和棲息地,而高水位則對(duì)雁鴨類有利[26-27]。水位還影響水鳥棲息地面積的大小,如You等[28]的研究表明,鄱陽(yáng)湖濕地水位在10.22 m至19 m之間時(shí),可以提供的水鳥棲息地面積最大。其次,濕地水位的變化規(guī)律影響水鳥對(duì)棲息地的選擇[29]。水位的波動(dòng)能夠營(yíng)造多樣化生境,對(duì)于提高水鳥多樣性具有重要意義；能夠調(diào)節(jié)濕地動(dòng)植物種類和生物量,引起水鳥多度的變化；濕地水位的季節(jié)性升降還會(huì)影響水鳥棲息地的面積和質(zhì)量等[30]。最后,濕地水面面積的比例也是決定水鳥分布的重要因素。一般大的水面可以包含更多的生境類型,使水鳥可利用的覓食與棲息空間擴(kuò)大,水鳥的種類和數(shù)量也隨水面面積的擴(kuò)大而增加[31-32]。

1.2 水質(zhì)的影響

濕地水質(zhì)與水鳥的多度相關(guān),對(duì)其影響多是間接和隱性的。水質(zhì)變化一般直接影響水生生態(tài)系統(tǒng),然后反映在水鳥適宜棲息地?cái)?shù)量的波動(dòng)上。如在不同的pH值、鹽度和水體富營(yíng)養(yǎng)化狀態(tài)下,濕地水生生物的數(shù)量也將發(fā)生變化,最終引起水鳥食物和棲息地面積的改變[33]。此外,水鳥對(duì)污染引起的水質(zhì)變化也十分敏感,如排入濕地內(nèi)的工農(nóng)業(yè)污染物可能導(dǎo)致水鳥抵抗力減弱[34],對(duì)其飛行和健康造成影響；濕地內(nèi)的重金屬和持久性污染物還會(huì)隨著食物鏈進(jìn)入鳥類體內(nèi)累積,損害其羽毛和器官機(jī)能[35]；濕地水體因石油泄漏被嚴(yán)重污染,導(dǎo)致水鳥大量死亡等[36]。

1.3 食物資源的影響

水鳥對(duì)停歇點(diǎn)食物資源需求不同于繁殖地和越冬地,其豐富度不僅決定了棲息地的適宜程度,也是影響水鳥遷徙過程的最重要因素[37]。無論是遷飛時(shí)間的選擇還是停歇點(diǎn)的確定,均受食物資源的限制[38-39]。食物資源的數(shù)量、質(zhì)量和獲取難易是水鳥是否能夠獲取足夠能量的決定性因素,也是影響水鳥對(duì)停歇地的選擇的直接原因[40]。如由于停歇點(diǎn)濕地與越冬地在食物類型和質(zhì)量上的不同,黑腹濱鷸(Calidrisalpine)在遷徙過程中將采取不同的覓食策略,以保證能量的攝入[41]。遷徙路線上食物資源豐富的濕地能夠提供更多食物,也吸引更多水鳥棲息,因而維持濕地棲息地較高的生產(chǎn)力對(duì)于水鳥種群保護(hù)具有重要意義[42]。

食物資源的可利用性和覓食對(duì)策共同決定了在湖泊灘涂和淺水區(qū)域覓食的水鳥群落的結(jié)構(gòu),而食物的獲取難易是評(píng)價(jià)食物資源數(shù)量和質(zhì)量時(shí)的主要依據(jù),也是影響水鳥豐富度的重要因素[43]。如底棲動(dòng)物的分布是決定鸻鷸類覓食地選擇的重要因子,當(dāng)一定范圍內(nèi)易于獲取的底棲動(dòng)物密度增加時(shí),鳥類的密度和取食效率都會(huì)隨之增加[44]。取食難易程度決定了水鳥遷徙過程中的覓食效率,不僅影響水鳥對(duì)棲息地的選擇偏好,而且能夠?qū)崿F(xiàn)具有不同取食方式的種群共存,降低種間競(jìng)爭(zhēng)壓力[45]。增加食物資源是水鳥生境恢復(fù)的重要目標(biāo)之一,某些情況下可獲取的食物資源的比例將直接影響濕地水鳥保護(hù)的效果[46]。

1.4 棲息地結(jié)構(gòu)的影響

各停歇點(diǎn)濕地內(nèi)不同生境需求的水鳥多度與濕地的類型有關(guān),種群在濕地內(nèi)的分布不僅有微生境質(zhì)量的要求,還會(huì)對(duì)棲息地斑塊特征的變化做出響應(yīng)[47]。適宜棲息地斑塊的面積和分布是決定水鳥種群遷徙策略的主要因素,濕地斑塊的多樣性和完整性能在不同的時(shí)空尺度上影響水鳥種群的大小,所以多種類型棲息地的喪失和斑塊破碎化是導(dǎo)致水鳥種群下降的重要原因[48]。

水鳥對(duì)棲息地的利用受到多重景觀格局因素的影響,其中棲息地的斑塊多樣性是影響濕地鳥類群落結(jié)構(gòu)的重要因素[49]。在景觀尺度上,多樣化的濕地生境更有利于不同需求的鳥類棲息,水鳥多樣性與斑塊多樣性顯著相關(guān)[50]。有研究在分析水鳥群落與濕地棲息地特征間的關(guān)系時(shí)發(fā)現(xiàn),在較大和異質(zhì)性較高的濕地中,物種豐富度、鳥類的多度和多樣性均更高[51]。此外,對(duì)有些海岸帶鹽沼水鳥物種來說,斑塊異質(zhì)性甚至比其大小更重要[52]。與之對(duì)應(yīng),盡管濕地內(nèi)的人類活動(dòng)也能夠增加斑塊多樣性,并使部分邊緣生境鳥類的多樣性增加,但濕地開墾所造成的天然濕地減少和生境均質(zhì)化,將導(dǎo)致濕地內(nèi)水鳥的種類和數(shù)量總體呈現(xiàn)下降趨勢(shì)[53]。

1.5 人類干擾的影響

除了食物、水深等因素外,干擾來源及分布對(duì)濕地水鳥的分布、密度和多樣性均有不同程度的影響。濕地內(nèi)的各種人類活動(dòng)是水鳥遷徙和棲息過程中面臨的主要干擾,食物的豐富程度和應(yīng)對(duì)干擾風(fēng)險(xiǎn)的成本共同決定了水鳥對(duì)覓食區(qū)域的選擇[54]。水鳥種群對(duì)不同類型的干擾的響應(yīng)不一樣,而且不同水鳥對(duì)干擾的敏感程度也有差別[55]。干擾除影響水鳥在停歇過程中對(duì)棲息地的選擇和濕地內(nèi)的活動(dòng)范圍外,還會(huì)降低棲息地質(zhì)量和改變水鳥遷徙策略。

不同強(qiáng)度的干擾對(duì)水鳥的影響主要體現(xiàn)在對(duì)棲息地生境和鳥類活動(dòng)的改變上。首先,干擾的存在影響水鳥對(duì)濕地棲息地的選擇。如河口濕地中的涉禽即使在同等食物條件下,相比鹽田,也更傾向于選擇干擾較少潮間帶泥灘棲息[56]。在不同干擾強(qiáng)度下的生境類型中,則分別對(duì)應(yīng)不同的水鳥生態(tài)類群,干擾越強(qiáng),種類越少[57]。其次,干擾還影響水鳥在棲息地內(nèi)的能量補(bǔ)給和種群行為,其影響程度也與水鳥的覓食策略、生境需求以及干擾類型有關(guān)。如Burger[58]的研究發(fā)現(xiàn),笛鸻在人類活動(dòng)較少的區(qū)域?qū)?0%的活動(dòng)時(shí)間用于覓食,而在人類活動(dòng)較多區(qū)域,用于覓食的時(shí)間則不足50%。最后,各種類型的干擾還影響水鳥在濕地停歇點(diǎn)間的飛行狀態(tài)。近年來在遷飛過程中針對(duì)水鳥的捕殺、投毒及偷獵等現(xiàn)象不僅干擾其遷徙,更是直接威脅種群的生存；遷徙路徑上越來越多的風(fēng)電場(chǎng)、高壓線等人工設(shè)施引發(fā)碰撞,影響種群的順利通過[59]；濕地內(nèi)日益增加的建設(shè)開發(fā)還使得噪音、煙霧等強(qiáng)烈干擾頻繁,導(dǎo)致水鳥個(gè)體離群或迷路等現(xiàn)象增多[60]。

2 景觀尺度濕地環(huán)境背景的影響

除了棲息地斑塊尺度的濕地生境因素,景觀尺度的環(huán)境背景也是導(dǎo)致水鳥遷徙過程中種群變化的重要因素[61]。盡管在不同尺度上環(huán)境因素影響停歇點(diǎn)濕地內(nèi)水鳥種群的主導(dǎo)因子不同,但都將直接或間接改變棲息地的各類生境要素[62]。在棲息地斑塊尺度,濕地對(duì)水鳥的影響主要體現(xiàn)在各生境要素對(duì)停歇點(diǎn)覓食和棲息條件的改變上,而景觀尺度對(duì)水鳥的影響則主要表現(xiàn)為對(duì)水鳥遷徙過程中不同停歇點(diǎn)棲息地適宜性的改變上。在引起水鳥停歇點(diǎn)濕地生境變化的眾多環(huán)境因素中,氣候變化、土地利用和外來生物入侵等對(duì)遷徙水鳥種群的影響最為顯著。

2.1 氣候變化的影響

氣候變化對(duì)濕地水鳥的影響包括氣候變暖導(dǎo)致遷徙時(shí)間和遷徙距離發(fā)生變化,以及改變停歇點(diǎn)濕地食物和棲息資源的提供等[63]。氣候變化不僅需要遷徙水鳥在權(quán)衡能量消耗和飛行時(shí)間時(shí)做出改變,而且需要中途棲息地的食物、植被等因素變化與遷徙時(shí)機(jī)相一致。此外,氣候?qū)⒌胤植嫉母淖兒蜆O端天氣的增加也會(huì)影響水鳥棲息地的選擇和食物補(bǔ)給。

2.1.1 棲息地分布的變化

近年來隨著氣溫升高和棲息環(huán)境變化,海平面上升,沿海和高緯度濕地區(qū)域的極端天氣頻繁發(fā)生,停歇點(diǎn)濕地的變化對(duì)水鳥地理分布和遷徙策略的影響也越來越重。在過去30年間,當(dāng)初冬氣溫上升后,沿西北歐遷飛的3種水鳥停歇點(diǎn)的分布重心向東北方向發(fā)生明顯偏移[64]。氣候變化還直接影響水鳥的停歇和飛行,遷徙距離增加迫使水鳥的停歇點(diǎn)選擇和飛行路徑發(fā)生改變,一些小型鳥類每年在飛行途中將面臨更大的生存風(fēng)險(xiǎn),而且停歇點(diǎn)棲息地分布的變化也將使得對(duì)生境要求較高的水鳥種群數(shù)量急劇下降[65]。氣候變暖還使得單位面積濕地上的水鳥數(shù)量減少,相同數(shù)量的種群將需要更大面積的濕地棲息地,將迫使那些競(jìng)爭(zhēng)力較弱的物種尋找其它替代生境[66]。

2.1.2 物候的變化

氣候變暖、降水減少、水位異常波動(dòng),不僅影響會(huì)各停歇點(diǎn)濕地的棲息地適宜性,也影響水鳥的多樣性[67]。首先,氣候變暖加速了濕地景觀格局演變的進(jìn)程,間接增加了水鳥種群的環(huán)境壓力。研究表明,洞庭湖濕地水鳥的遷徙規(guī)律與洪枯水位季節(jié)性交替變化的環(huán)境相適應(yīng),若氣候異常導(dǎo)致低水位提前或推后,都會(huì)對(duì)鳥類的適宜棲息地面積產(chǎn)生影響[68]。其次,氣候變化在改變濕地棲息地適宜性同時(shí),也影響了水鳥的種群結(jié)構(gòu)和數(shù)量。如Steen等[69]發(fā)現(xiàn)美國(guó)大草原的小型濕地在氣溫和降水變化影響下面臨干涸,近1/2的水鳥適宜棲息地將消失,但不同物種之間的響應(yīng)差異顯著,因而水鳥群落結(jié)構(gòu)也將隨之變化。

2.2 土地利用的影響

隨著社會(huì)經(jīng)濟(jì)發(fā)展和人類活動(dòng)范圍的不斷擴(kuò)大,各類生產(chǎn)建設(shè)活動(dòng)的對(duì)濕地生境的影響日益顯著。與具體干擾因素作用于濕地內(nèi)的水鳥種群不同,土地利用對(duì)遷徙水鳥種群的影響主要作用于景觀尺度上,包括對(duì)中途停歇點(diǎn)適宜生境斑塊的類型和數(shù)量的改變,因而對(duì)依賴濕地遷徙的水鳥種群的影響常是整體性和破壞性的[70]。土地利用對(duì)土地類型和微地形的改變,影響了棲息地周邊的水文、水質(zhì)、生物多樣性和地表生態(tài)過程等,引起植被的退化和動(dòng)物的遷移,導(dǎo)致濕地內(nèi)停歇的水鳥種群多度和多樣性下降[71]。

2.2.1 棲息地的類型

土地利用往往改變濕地生境要素的分布,破壞濕地生態(tài)系統(tǒng)完整性,造成水鳥棲息地類型的變化和分布的不均[72]。土地利用對(duì)濕地棲息地類型的影響具體體現(xiàn)在以下兩個(gè)方面：1)造成生境單一,如濱海養(yǎng)殖塘的修建不僅導(dǎo)致生境同質(zhì)化嚴(yán)重,而且引起濕地富營(yíng)養(yǎng)化以及食物和棲息資源的分布集中,加劇不同覓食種群間的競(jìng)爭(zhēng)[73]；2)改變水文格局。如流域內(nèi)各類開發(fā)建設(shè)活動(dòng)影響了濕地的水文過程,不僅造成污染,還將改變濕地植被結(jié)構(gòu),間接影響水鳥的群落組成和多度[74]。

2.2.2 棲息地的面積

停歇點(diǎn)濕地的景觀變化直接決定了水鳥棲息地的多少,而周邊開墾活動(dòng)的增加和土地類型的轉(zhuǎn)換在不斷改變濕地內(nèi)適宜棲息地的面積,并影響水鳥種群的大小。研究發(fā)現(xiàn),人為活動(dòng)驅(qū)動(dòng)下的濕地土地利用變化是造成遷徙水鳥棲息地喪失和種群變化的重要原因,近80%的水鳥物種所受威脅來自于農(nóng)業(yè)生產(chǎn)引起的棲息地?cái)?shù)量變化[75]。濕地周邊越來越多的道路、堤壩等人工設(shè)施不僅改變了水文條件和棲息地?cái)?shù)量,而且影響鳥類的覓食和活動(dòng)范圍。如作為水鳥重要停歇點(diǎn)和越冬地的東洞庭湖濕地,近年來由于周圍水田和低洼坑塘逐漸被開墾為旱地,在濕地暖干化趨勢(shì)下,水鳥適宜棲息地大幅減少[76]。

2.2.3 棲息地景觀格局

棲息地格局的變化也會(huì)影響鳥類群落變化[77],破碎化是引起不同鳥類棲息地適宜性變化的主要原因[78]。由于殘存生境斑塊之間的距離增加,使得水鳥賴以生存的水文條件、覓食區(qū)域、棲息環(huán)境等均發(fā)生變化[79]。在此過程中,那些對(duì)斑塊面積、景觀連通性要求較高的鳥類種群數(shù)量迅速降低,而那些生境要求較低、適應(yīng)能力較強(qiáng)的鳥類種群波動(dòng)則較小。如海岸帶濕地破碎化可能為蝦蟹等小型動(dòng)物提供適宜環(huán)境,對(duì)以之為食的鳥類種群也更為有利,但其對(duì)于生境連續(xù)性有較高要求的多數(shù)鳥類則不利[80]。因此,棲息地破碎化既會(huì)導(dǎo)致水鳥物種數(shù)量的下降,也會(huì)使得群落組成的時(shí)空格局發(fā)生變化。

2.3 外來生物入侵的影響

外來生物入侵不僅影響本地動(dòng)植物群落的生存,而且改變了水鳥棲息和種群覓食生境。外來生物入侵對(duì)濕地生態(tài)系統(tǒng)造成的破壞使得大多數(shù)鳥類的適宜棲息地發(fā)生變化和生態(tài)承載力下降[81]。入侵生物的定居對(duì)棲息植被和水鳥食物的影響,導(dǎo)致多數(shù)水鳥在遷徙過程中因無法適應(yīng)入侵生境而不得不尋找其它停歇點(diǎn)濕地[82]。

2.3.1 本土植被群落

外來物種尤其是植物還改變了水鳥棲息地的群落類型,影響其活動(dòng)和停歇空間[83]。以互花米草群落為例,因其植株較密,阻礙鳥類視線和在斑塊內(nèi)的活動(dòng),無法提供有效的棲息空間,所以互花米草群落內(nèi)鳥類的物種數(shù)和密度都顯著低于本地植物群落。在崇明東灘河口鹽沼濕地,由于互花米草的入侵,造成土著植被面積銳減,鳥類適宜棲息地大面積喪失,原生境斑塊內(nèi)的各類水鳥也逐漸消失[84]。

2.3.2 底棲生物群落

外來物種的大量繁殖取代本地濕地物種,影響水鳥遷徙中的能量補(bǔ)充。首先,外來生物在濕地內(nèi)的擴(kuò)散定居將造成底棲生物多樣性降低,原有物種的快速減少將使部分水鳥無法在停歇點(diǎn)濕地內(nèi)獲得足夠的食物[85]。其次,盡管目前對(duì)于外來動(dòng)植物的定居過程對(duì)不同濕地生態(tài)系統(tǒng)和遷徙水鳥種群的影響大小缺少定量數(shù)據(jù),但已有研究表明外來植物的擴(kuò)散影響濕地分解速率和養(yǎng)分循環(huán),造成生態(tài)系統(tǒng)生產(chǎn)力降低,食物質(zhì)量下降,使得水鳥無法在短期內(nèi)補(bǔ)充飛行所需能量[86]。

雖然外來生物對(duì)水鳥的影響多是負(fù)面的,但濕地外來物種并非必然使?jié)竦伉B類的棲息地質(zhì)量降低。如千屈菜作為濕地外來物種有利于某些鳥類棲息,并增加物種多樣性[87]；水葫蘆等對(duì)水生動(dòng)植物群落的影響隨群落組成和食物網(wǎng)結(jié)構(gòu)而不同,若加以適當(dāng)控制則可能對(duì)水鳥群落有利[88]。目前有關(guān)外來動(dòng)植物對(duì)水鳥的影響因物種的不同而存在不確定性,其影響還有待進(jìn)一步深入分析。因此,對(duì)外來入侵物種的控制還需要根據(jù)保護(hù)目標(biāo)制定相應(yīng)策略。

3 對(duì)停歇點(diǎn)濕地和水鳥保護(hù)的啟示

圖1 停歇點(diǎn)濕地影響遷徙水鳥種群的主要因素示意圖 Fig.1 Main factors impact on waterbird populations in their annual cycle

遷徙水鳥種群多度和多樣性的變化是局域和區(qū)域環(huán)境因子以及氣候變化共同作用的結(jié)果(圖 1),對(duì)棲息地影響因素的研究方法也需要遵循由各點(diǎn)調(diào)查到沿線跟蹤,再到過程模擬和生態(tài)效應(yīng)分析的過程。當(dāng)前濕地對(duì)遷徙水鳥的影響機(jī)制研究還在以下幾個(gè)方面存在不足：(1)水鳥對(duì)生境要素的需求會(huì)隨著不同的生長(zhǎng)階段、氣候條件、競(jìng)爭(zhēng)強(qiáng)弱和適應(yīng)能力而變化,在進(jìn)行濕地棲息地適宜性評(píng)價(jià)時(shí)未與水鳥遷徙途中的具體需求相結(jié)合；(2)傳統(tǒng)的濕地保護(hù)管理措施多側(cè)重于面向固定的濕地單元,未從景觀尺度或區(qū)域尺度上來充分考慮濕地自身的生態(tài)過程、功能和生產(chǎn)力特征對(duì)遷徙水鳥的影響；(3)在不同尺度下影響水鳥棲息地選擇的主要因素也不同,而當(dāng)前濕地景觀格局變化的量化指標(biāo)對(duì)水鳥棲息地適宜性的生態(tài)意義還不清楚；(4)沿水鳥遷飛路線上多個(gè)停歇點(diǎn)棲息地之間的生境分析尚未建立聯(lián)系,缺乏多時(shí)空尺度上濕地累積效應(yīng)方面的研究。

基于不同尺度條件下停歇點(diǎn)濕地的主要生態(tài)功能及作用機(jī)制,建議在濕地單元水平上,加強(qiáng)濕地水文與土壤環(huán)境對(duì)濕地生物群落和水鳥的協(xié)同響應(yīng)機(jī)制研究；在景觀層面上,重點(diǎn)開展?jié)竦馗窬肿兓瘜?duì)遷徙水鳥棲息地適應(yīng)性與連通性的影響機(jī)制研究,進(jìn)而從景觀配置角度提出不同水鳥棲息地及其種群的保護(hù)管理對(duì)策。

3.1 不同水鳥生境限制因子的識(shí)別及其響應(yīng)機(jī)制研究

濕地生境對(duì)遷徙水鳥的影響不僅包括多個(gè)尺度上的生境要素,其影響程度還與地形和季節(jié)等條件密切相關(guān)。鳥類數(shù)量和生境條件等統(tǒng)計(jì)指標(biāo)雖能夠反映棲息地質(zhì)量,但濕地對(duì)多種水鳥可能存在不同的限制因子,所以在未來的研究中,需要我們?nèi)嬖u(píng)估整個(gè)濕地內(nèi)鳥類群落結(jié)構(gòu)的多年變化情況,建立水鳥種群突變與濕地生境間的耦合關(guān)系。通過對(duì)主要保護(hù)對(duì)象的生境需求分析,將濕地生境要素、環(huán)境基質(zhì)等因子根據(jù)影響權(quán)重納入衡量生態(tài)承載能力的指標(biāo)體系中,建立種群響應(yīng)模型,來分析預(yù)測(cè)水鳥群落的變化,為將來監(jiān)測(cè)水鳥遷徙策略的變化和遷飛路線上重要停歇點(diǎn)濕地的保護(hù)提供支持。

3.2 景觀尺度的濕地生態(tài)過程與功能分析

盡管目前在斑塊尺度上針對(duì)固定濕地生態(tài)系統(tǒng)恢復(fù)或生物多樣性保護(hù)的措施能夠?qū)w徙水鳥的覓食和棲息起到積極作用,但在景觀尺度上,棲息地斑塊與周邊景觀類型存在密切的物質(zhì)和能量交換關(guān)系,濕地區(qū)域景觀格局對(duì)水鳥棲息地的選擇具有重要影響。因此,濕地生態(tài)功能的發(fā)揮也與周圍環(huán)境背景密切相關(guān)。在較大時(shí)空尺度上分析濕地景觀格局變化的驅(qū)動(dòng)因子及其生態(tài)過程,不僅有利于對(duì)濕地水鳥棲息地的分布和適宜性變化趨勢(shì)進(jìn)行預(yù)測(cè),還有助于區(qū)域發(fā)展與濕地保護(hù)策略的制訂。此外,隨濕地周邊城鎮(zhèn)化進(jìn)程加快,霧霾天氣、熱島效應(yīng)等大概率事件對(duì)遷徙水鳥的影響也需要在景觀尺度上展開研究。

3.3 濕地斑塊破碎化的量化分析及景觀變化的生態(tài)效應(yīng)研究

濕地景觀格局變化在不同尺度上影響因素和作用范圍不同,所以在探討影響遷徙水鳥棲息地選擇的主要因素時(shí),還需要探究引起濕地景觀變化的多尺度因素。盡管棲息地斑塊結(jié)構(gòu)特征和濕地景觀格局特征分別在各個(gè)尺度上影響水鳥棲息地的類型和面積,但目前相應(yīng)格局指數(shù)變化所代表的生態(tài)學(xué)意義還不清楚,而且濕地景觀變化及其驅(qū)動(dòng)因素引起的生態(tài)效應(yīng)也有待進(jìn)一步分析。未來通過對(duì)不同鳥類物種景觀破碎化的敏感性分析,建立濕地景觀連通性等指數(shù)與水鳥適宜棲息地之間的對(duì)應(yīng)關(guān)系,識(shí)別引起棲息地適宜性變化的景觀指數(shù)閾值,將有助于指導(dǎo)濕地生態(tài)系統(tǒng)的恢復(fù)和景觀格局的構(gòu)建。

3.4 停歇點(diǎn)濕地間的對(duì)比分析與遷飛保護(hù)網(wǎng)絡(luò)的建立

水鳥種群的波動(dòng)是遷徙路徑上一系列濕地景觀變化共同作用的后果,需要在多個(gè)時(shí)空尺度分析各停歇點(diǎn)濕地景觀變化與水鳥種群的相關(guān)關(guān)系,以確定每年引起遷徙水鳥種群變化的決定性因素是位于濕地內(nèi)還是飛行途中。未來不僅需要加強(qiáng)對(duì)位于水鳥遷飛路線上的一系列停歇點(diǎn)濕地的生態(tài)承載能力的對(duì)比分析,確定不同水鳥種群的瓶頸棲息地和生境變化驅(qū)動(dòng)因素,還需要分析遷徙過程中水鳥對(duì)不同停歇點(diǎn)的選擇機(jī)制和策略變化,以便通過連接國(guó)際重點(diǎn)鳥區(qū)(Important Bird Areas, IBA)建設(shè)遷飛保護(hù)網(wǎng)絡(luò)。

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The effect of stopover wetlands on migratory waterbirds at different scales: a review

ZHANG Qiang, MA Keming*, LI Jinya, ZHANG Yuxin

StateKeyLaboratoryofUrbanandRegionalEcology,ResearchCenterforEco-EnvironmentalSciences,ChineseAcademyofSciences,Beijing100085,China

Abstract: Stopover wetlands are important refueling stations for numerous migratory waterbird species, and are ecologically significant in the annual cycle of birds. Recently, stopover wetlands located on flyways were faced with dramatic changes owing to global warming and increasing human activities. Previous studies have suggested that both habitat and environmental factors of these wetlands contributed to the habitat suitability of various species, and the key factors affecting the abundance and diversity of waterbird communities. Therefore, it would be helpful to understand the ecological effects of landscape changes at each stopover by analyzing the diverse habitats and environmental factors that affect various waterbird populations during migration. Furthermore, it would provide theoretical support necessary to formulate effective conservation strategies. In this review, we systematically analyzed how habitat factors such as water body, food resources, habitat configuration, and human disturbance affect the foraging and resting of waterbirds at a local scale. Then, we discussed various environmental contexts, including global warming, land use, and exotic species, that indirectly affect habitat suitability and bird migration at the landscape scale. Finally, on the basis of the coupling effects of various influencing factors that were related to stopover wetlands at different scales, we summarized some shortages based on the research of the present relationships between wetlands and waterbirds, and suggested some priorities for future studies and environmental conservation.

stopover; wetland; waterbird; habitat; flyway

國(guó)家“十二五”科技支撐計(jì)劃項(xiàng)目課題(2012BAC07B04)

2015- 10- 26;

2016- 07- 11

10.5846/stxb201510262158

*通訊作者Corresponding author.E-mail: mkm@rcees.ac.cn

張強(qiáng),馬克明,李金亞,張育新.不同尺度下停歇點(diǎn)濕地對(duì)遷徙水鳥的影響研究綜述.生態(tài)學(xué)報(bào),2017,37(8):2520- 2529.

Zhang Q, Ma K M Li J Y, Zhang Y X.The effect of stopover wetlands on migratory waterbirds at different scales: a review.Acta Ecologica Sinica,2017,37(8):2520- 2529.