Alien Species.vp - IUCN

Motivations and consequences of the human
dispersal of plants
Richard N. Mack
Abstract
In attempting to colonize new areas, humans proceed in a deliberate manner that arises
from deep-seated motives based on a compelling need for security. Aside from immediate
concerns about personal safety, humans strive for security in the amount, reliability, and
sustainability of their food, fuel, forage, and medicine. Historic trans-oceanic voyages of
colonization epitomize the preparation to meet these concerns because return to, or even
timely resupply from, the homeland was problematical. As a result, colonists bound for
distant locales have always carried living plants. Further incentive for immigrants to
transport plants arises from the need for plants that are not only reliable but also
familiar. Adoption of newly encountered plants, especially as food or medicine, proceeds
reluctantly and often through dire necessity. Familiar food also serves as a tangible
reminder of the homeland, thereby contributing to a sense of security. Perception among
immigrants that the homeland remains a source of solutions is also common. Even centuries
after the initial immigrants arrived, their descendants readily import plants as solutions
to perceived deficiencies or newly detected problems in their colonized land. All
people share a common allure for diversity in their surroundings, including the diversity
provided by ornamental plants. This incentive or preference for floristic diversity in
people’s immediate vicinity has long driven the enormous effort to gather species from
afar. The composite consequence of these expressions of human necessity and choice has
been the dispersal of tens of thousands of species into distant new ranges. Some species
transported as the result of these expressions of human behaviour have become invasive;
the number of such species belies their immense environmental and economic impact. In
effect, deep-seated aspects of human behavior continue to determine the character,
extent, and rate of the human-mediated transformation of the earth’s vegetation.
Introduction
Even if humans were not anthropocentric, human behaviour would be a worthy subject for
study. We are, after all, members of a fascinating species. Among aspects of our behaviour, we
express strong motives or motivations (sensu Mook, 1987) for which the evolutionary
explanations seem apparent. For example, the motivations to attain personal security, including
a secure supply of food and shelter, protection from hazards, and avoidance of disease, all relate
directly to reproductive fitness (Ridley, 1993). The means by which people in any culture
attempt to attain this security is rapidly taught and learned within that group (Ornstein, 1985).
We also display other strong behaviours that do not necessarily enhance fitness but certainly
contribute to our perception of well being. These behaviours include our extraordinarily varied
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