Article

Holoparasites in primary habitats mostly have a limited distribution. They grow in some sort of equilibrium with the flora of their natural ecosystem, due to particular adaptive habits like limited dispersal and restrained infestability. Their survival depends on a combination of biological and demographic characters of their hosts, their own ecological demands, and environmental conditions that affect their development. Significant change of any of these factors may result in severe reduction of the parasite's population and eventually in its elimination. Such changes can be caused by human interferences, by catastrophes, or by natural succession; they may affect the parasite direCtly, or its host's population, or the whole vegetation. The higher the specificity of the parasite, the higher are the chances of its going extinct. Parasites in secondary habitats, many of which have become cosmopolitan in distribution, are less prone to extinction than those in primary habitats, owing to their weed-like adaptations; only if hostspecific they may become rare or extinct when culture of their particular host crop is abandoned. Parasitic higher plants in both habitat types do not endanger the existence of their host species. Examples from the Cuscutaceae are briefly discussed.