Old house sites in national parks demonstrate the consequences of early horticultural choices. Creatures that require a certain kind of vegetative architecture for forage and shelter find their lives disrupted by changes. Take the example of the California desert's wide-bodied lizard, unable to negotiate dense stands of the invasive Bromus rubens and consequently starving to death. Eucalyptus groves provide habitat for predators like the great horned owl, which preys on other owls. Diminished populations of the smaller saw-whet owl and others might be partly due to the unnatural advantage given to great horned owls by the increase in eucalyptus groves in the area.
Nutritional inferiority can be a subtle factor in the slow diminution of resources.
In a study by Harold W. Avery, captive tortoises were provided either native or non-native food. Those fed the native Camissonia boothii had a greater rate of protein assimilation and remained in positive nitrogen balance throughout the study, whereas those fed Schismus barbatus, a non-native, experienced a significant loss in total body mass. Creatures may be seen eating non-native plants, but their ability to thrive on such fare cannot be inferred. In informal observations of my employees, clients, and neighbors, I've noticed certain developmental steps once the interest in native plants quickens, potential pathways for the back-yard restoration gardener. First, the gardener becomes aware of some part of the native flora, often spring wildflowers, that is visually appealing.