Left ordinate: the mean values of the temperature anisotropy of the protons, T_⊥p/T_∥p (red dots), and of the alpha particles, T_⊥α/T_∥α (black diamonds). Right ordinate: mean normalized wave power (blue squares). The bars indicate the uncertainties of the mean values. All quantities are plotted in bins versus the relative ion differential speed, V_αp/V_A. The vertical dotted line separates fast from slow solar wind regimes.