社會行為如何影響兩相鄰同屬物種的競爭與分布

Abstract

合作行為被認為能幫助物種拓展分布範圍。過去研究多專注於不同環境條件下的合作利益，然而鮮少研究測試物種在強烈的種間競爭下合作是否有更好的生存能力。本研究對中國夾金山區沿海拔相鄰分布的兩種同屬埋葬蟲：分布海拔較低的尼泊爾埋葬蟲 ( Nicrophorus nepalensis ) 與分布海拔較高的衿覆葬甲 ( N. schawalleri )。我們測量自然狀態下埋葬蟲的族群密度以及繁殖表現，並且進行合作表型 ( cooperative phenotype ) ( 群體 ) 與無合作表型 ( non-cooperative phenotype ) ( 單對 ) 的操作實驗以及混入他種埋葬蟲的近緣物種競爭操作實驗，檢測沿海拔梯度下合作行為與近緣物種的種間競爭兩者對繁殖適存度 ( reproductive fitness ) 的影響，並與台灣合歡山區沒有高海拔近緣競爭者的尼泊爾埋葬蟲實驗結果比較。結果顯示尼泊爾埋葬蟲的分布上界主要受到衿覆葬甲限制。在夾金山區兩種埋葬蟲分布交界帶，尼泊爾埋葬蟲的合作行為能對抗低溫以及麗蠅的競爭，增加繁殖成功率；然而合作行為對克服近緣物種 ( 衿覆葬甲 ) 的直接競爭沒有幫助。對比夾金山區的尼泊爾埋葬蟲則是在分布上界的環境中群體比單對有更好的繁殖表現，分布下界則群體與單對沒有明顯差異；合歡山區的族群則相反。這可能是由於夾金山區的尼泊爾埋葬蟲在高海拔表現出合作的策略，增加在分布上界的環境適應能力，間接對近緣物種競爭產生優勢，而沒有高海拔近緣競爭者的合歡山區族群，則表現出克服低海拔高溫環境的合作行為。本研究透過操作合作群體，測試不同環境狀態下的合作利益以及種間競爭的影響，更進一步拓展合作行為與適應環境、種間競爭的關係的認知。

Cooperative behavior is considered a trait that could help species extend their distribution range. However, few studies have tested if cooperator has higher fitness than non-cooperator under intensive interspecific competition. This research focuses on two parapatrically distributed burying beetles along elevational gradients in Mt. Jiajin, China, Nicrophorus nepalensis in lower elevation and N. schawalleri in higher elevation. We tested the population density and breeding performance under natural condition of both beetles, manipulated the cooperative phenotype (group) and non-cooperative phenotype (pair) along elevational gradients, and manipulated interspecific competition at two beetles’ contact zone. We also compared the breeding performance of N. nepalensis in Mt. Jiajin (with higher elevation competitor) and Mt. Hehuan (without higher elevation competitior) under natural condition and cooperative phenotype manipulative experiment. Results show that N. nepalensis in Mt. Jiajin had higher probability of breeding success for group than pair, but when group of N. nepalensis meet a pair of N. schawalleri, the group has the probability of breeding success similar to that of pair manipulation. And group of N. nepalensis in Mt. Hehuan has higher probability of breeding success than pair at low elevations, the contradict results of Mt. Jiajin and Mt. Hehuan may indicate the high elevation competitor N. schawalleri in Mt. Jiajin influences N. nepalensis to perform different cooperation strategy. This research extends our view about how the cooperation behavior mediated by environmental condition and interspecific competition.