Figure 18.7 Interdependence of species under extreme environmental conditions. In alpine tundra biomes around the world, researchers measured how plants at low and high elevations responded to having neighboring plants removed in terms of (a) survival and (b) the percentage of plants that produced flowers. At low elevations, the removal of neighbors caused plants to survive better and produce more flowers or fruit, which suggests that the plants are competing. At high elevations, removal of neighbors caused the plants to experience lower survival and produce fewer flowers, which suggests the plants in the community facilitate each other. Error bars are standard errors.

Data from R. M. Callaway et al., Positive interactions among alpine plants increase with stress, Nature 417 (2002): 844–848.