Positive interactions are traditionally defined as interactions in which one species benefits from the presence of another species, without harm (and, potentially, with benefit) to the latter.

Common examples include mutualisms--both species benefit, commensalism--one species benefits with no measurable effect on another species, and facilitation--one species makes conditions more favorable for another species.

 mutualisms：    互惠作用，对作用的双方都有利！

commensalism：偏利共生或共栖，一方受益，一方无害也无利。

facilitation：           一物种通过对周边生存环境的改善，从而使他种受益。通常这种作用的相互的，只是它们作用的媒介是周围环境。这也是我实验的重点。我们在高寒草甸的实验结果证实了，至少对部分物种来说来自邻体的正效应对其生活周期是至关重要的。