Impacts of parasitic plants on natural communities

Summary Parasitic plants have profound effects on the ecosystems in which they occur. They are represented by some 4000 species and can be found in most major biomes. They acquire some or all of their water, carbon and nutrients via the vascular tissue of the host's roots or shoots. Parasitism has major impacts on host growth, allometry and reproduction, which lead to changes in competitive balances between host and nonhost species and therefore affect community structure, vegetation zonation and population dynamics. Impacts on hosts may further affect herbivores, pollinators and seed vectors, and the behaviour and diversity of these is often closely linked to the presence and abundance of parasitic plants. Parasitic plants can therefore be considered as keystone species. Community impacts are mediated by the host range of the parasite (the diversity of species that can potentially act as hosts) and by their preference and selection of particular host species. Parasitic plants can also alter the physical environment around them – including soil water and nutrients, atmospheric CO 2 and temperature – and so may also be considered as ecosystem engineers. Such impacts can have further consequences in altering the resource supply to and behaviour of other organisms within parasitic plant communities.ContentsSummary 737 I. Introduction 738 II. Parasitism: direct consequences 738 III. Dynamics of parasite–host interactions: host range, preference and selection 738 IV. Impacts of parasitic plants on the plant community 739 V. Impacts of the plant community on parasite populations 741 VI. Impacts of the parasite on other trophic levels 742 VII. Impacts of the parasite on the abiotic environment 747 VIII. Concluding remarks 748References 748