Dispersal, migration and management - Ecological Applications: Toward a Sustainable World - page 105

Summary Dispersal and migration

Dispersal, the spreading of individuals away from others, can be passive (e.g. wind-
dispersed seeds) or active (e.g. squirrels dispersing away from their birth site). By
contrast, migration is a mass directional movement of large numbers of a species
from one location to another. The term applies to the classic long-distance migra-
tions of Arctic terns, but also to the to-and-fro movements of shore animals follow-
ing the tidal cycle. Some species migrate not through space but through time. Many
plants (and some animals) spend a period in dormant form, restarting their develop-
ment when favorable conditions return. Plans for conservation areas, for animal
recovery or vegetation restoration, may be doomed to failure in the absence of an
understanding of dispersal and migration behavior.

Species mobility and conservation
Deciding the best place for a nature reserve is especially diffi cult when the species
to be protected moves during its lifetime through a variety of habitats that are more
or less remote from each other. Some species have larval stages that disperse
remotely from their birth place, others migrate among several areas in a geographical
region, some move up and down mountains as the seasons change, and others live
in ephemeral habitats that disappear and reappear elsewhere. In every case, powers
and patterns of movement will infl uence the success of conservation strategies.

Species mobility and restoration
When managers try to restore populations where a species has gone extinct, or to
restore whole communities of plants and animals, they need to take account of
species' mobility. Attempts to restore populations of migratory species must, of
course, take their migratory behavior carefully into account. But when it comes to
plant community restoration, an intimate knowledge of the dispersal ability of seeds
can be equally critical. Some species, because of limited powers of movement, need
to be carried (as seeds, young plants or animals) to their newly created havens.

Predicting the arrival and spread of invaders
The best way to deal with invaders is to prevent their arrival in the fi rst place,
and this involves identifying the novel 'dispersal' pathways opened up by human
travel and commerce. Biosecurity precautions include the screening and cleaning of
cargo at the point of embarkation and on arrival, and inspection of camping gear
and boots of incoming passengers. Once arrived, however, knowledge of dispersal
power is needed to predict patterns of spread - so that suitable precautions can be
taken.

Species mobility and management of production landscapes
Human industry and resource exploitation inevitably have consequences for natural
ecosystems, and managers need to confront the problem of sustaining species in
exploited landscapes; species mobility is again an important consideration. Forestry
management can take account of movement patterns, such as those of fl ying squir-
rels and bats, to minimize adverse effects on biodiversity. Similar considerations
apply to the siting of wind turbines, to minimize risk to migrating and dispersing
birds in their vicinity. And judicious intermingling of native forest habitat with
agricultural production can be managed to maximize the 'free' crop pollination