González-Solís Jacob, Oro Daniel, Jover Lluis, Ruiz Xavier, Pedrocchi Vittorio
Dept. Biologia Animal (Vertebrats), Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain e-mail:
Dept. de Salut Pública i L.S., Universitat de Barcelona, Casanova 143, 08036 Barcelona, Spain, , , , , , ES.
Oecologia. 1997 Sep;112(1):75-80. doi: 10.1007/s004420050285.
The diets of two potential competitor species, Audouin's Larus audouinii and yellow-legged gulls Larus cachinnans, were examined while they bred at the Chafarinas Islands during 1993, 1994, and 1995. Data were collected during two commercial fishing regimes: (1) trawling and purse seine fisheries, and (2) diurnal trawlers only. Since the food supply for the gulls in this area was heavily reliant on the activity of purse seine fisheries, these contrasting situations allowed us to analyze short-term effects, induced by daily changes in food supply, on niche width, dietary shift, and niche overlap between the two species. Overall, both species relied mainly on fish for food, especially Clupeiforms, in the case of Audouin's gull irrespective of the fishing situation, and in the case of the yellow-legged gull, only when purse seine fishing was in operation. When purse seine boats did not operate (food shortage), yellow-legged gulls broadened their niche, consuming equal amounts of all the feeding resources, and they showed a dietary shift toward a greater consumption of prey from refuse tips. In contrast, Audouin's gulls did not change their niche width, but showed a slight dietary shift away from the consumption of epipelagic fish, compensated by an increase in reliance on benthic-mesopelagic resources. Niche overlap was clearly higher on days when both fishing fleets operated, probably because a superabundant food resource facilitates high overlap without affecting coexistence between the two species. Since our study was developed on the basis of daily variations in food supply, and competition effects are to be expected on a longer-term basis, these changes can be seen as the outcome of the coexistence of two species in stable competitive equilibrium.
1993年、1994年和1995年，在查法里纳斯群岛繁殖期间，对两种潜在竞争物种——奥杜邦鸥（Larus audouinii）和黄腿鸥（Larus cachinnans）的饮食进行了研究。数据收集于两种商业捕鱼模式下：（1）拖网和围网渔业，以及（2）仅日间拖网渔船作业。由于该地区鸥类的食物供应严重依赖围网渔业的活动，这些截然不同的情况使我们能够分析食物供应的每日变化对两种鸥类的生态位宽度、饮食转变和生态位重叠的短期影响。总体而言，两种鸥类主要以鱼类为食，对于奥杜邦鸥来说，无论捕鱼情况如何，尤其以鲱形目鱼类为主食；对于黄腿鸥来说，只有在围网捕鱼作业时才以鱼类为主食。当围网渔船不作业时（食物短缺），黄腿鸥会拓宽其生态位，等量消耗所有觅食资源，并且饮食会转向更多地食用垃圾场的猎物。相比之下，奥杜邦鸥的生态位宽度没有变化，但饮食略有转变，减少了对上层鱼类的食用，转而更多地依赖中层和底层水域资源，以此作为补偿。当两个捕鱼船队都作业时，生态位重叠明显更高，这可能是因为丰富的食物资源有利于高重叠度，而不会影响两种鸥类的共存。由于我们的研究是基于食物供应的每日变化开展的，而竞争效应预计会在更长时间内出现，因此这些变化可被视为两种鸥类在稳定竞争平衡中共存的结果。
