Dispersal, migration and management - Ecological Applications: Toward a Sustainable World - page 84

Dormancy - migration through time
Habitats are not always favorable and, by moving at the appropriate time, migrant animals can take
advantage of conditions and resources that suit them. This option is not available to plants.
However, many plants (and some animals) achieve the same ends by means of time travel, spending
a period of delay in dormant form, most often as a seed (or an egg). The time travel afforded by
seasonal dormancy is very common, but there are also cases of dormancy for much longer periods,
analogous to long-distance migration in space. You have already come across the phenomenon of
seed-banks in the soil (Box 3.1; Section 3.2.1). The species whose seeds persist for longest in the
soil are often short-lived opportunists waiting for a favorable opening for germination that may
take years or decades to arrive - the same species often lack features that would disperse them
far through space.

4.2 Migration and
dispersal - lessons
for conservation

It is no easy matter deciding the best place for a nature reserve. But the task is doubly
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. Here I describe the cases
of a tropical bird, a charismatic mammal and a diminutive stream insect (Sections
4.2.1-4.2.3) before considering the related matter of how best to design marine
reserves in light of the long-distance dispersal behavior of many marine species
(Section 4.2.4).

4.2.1 For whom the
bell tolls - the
surprising story of a
South American bird

Although the three-wattled bellbird ( Procnias tricarunculata ) is one of Costa Rica's
largest fruit-eating species, little was known about its migratory behavior and
habitat requirements. Costa Rica has an excellent record of setting aside protected
natural areas, but this has not always been done on the basis of detailed ecological
knowledge, and Powell and Bjork (2004) wanted to fi nd out whether the nation's
nature reserves can adequately protect this species. A number of birds were captured
in the Tilaran Mountain Range, close to the Monteverde Nature Reserve (Figure
4.1a), tagged with small radio transmitters and their locations determined succes-
sively through the year.
The birds breed between March and June at mid-elevations (1000-1800 m) in
moist forest on the Atlantic slopes of the mountains before their fi rst migratory move
(step 1) westward over the continental divide to spend several months feeding on
forest fruits at similar elevations but on the mountains' Pacifi c slopes (Figure 4.1a).
These western forest habitats occur mostly in small, isolated fragments on private
farms, and are poorly represented in Costa Rica's system of protected areas. During
September and October the bellbirds migrate eastward (step 2) to lowland Atlantic
forest in Costa Rica and Nicaragua, habitats that are also under threat. Next they
move south (step 3) to heavily modifi ed and fragmented forest, mainly on private
property, along the Pacifi c coast of Costa Rica (Figure 4.1b). In March they return
north (step 4) to their breeding area.
The complex nature of this bird's migratory behavior poses some big challenges
for managers. While breeding habitat seems to be suffi ciently protected, the bell-
bird's situation remains precarious because of habitat decline in three other migra-
tion destinations whose importance was unknown before this study. Perhaps the
species will show some fl exibility in habitat use as prime areas are fragmented and
destroyed, but this cannot be taken for granted. The bellbird is just one among many
species whose ecology links diverse geographical areas that are beyond the scope of