SMALL MAMMAL METAPOPULATION DYNAMICS IN A RECENTLY
ESTABLISHED MITIGATION WETLAND

Christina Kocer and Matthew Watters
Environmental Sciences Program, University of Dubuque, 2000 University
Avenue, Dubuque, Iowa 52001

The reclamation of land for subsequent use in the construction of mitigation
wetlands has increased throughout the Upper Mississippi River Valley. 
Monitoring of the spread of natural populations into previously unoccupied
habitat is an important step in the determination of the success or failure of the
project.  Small mammal populations are key in the establishment of terrestrial
vertebrate ecosystems.  We censussed the small mammal populations and habitat
use in the Schmitt Island Wetland Area, Dubuque, Iowa each fall since 1994, as
well as Spring 1995 and 1997.  Our initial hypothesis was that small mammal
species density would be similar in the two major habitat types, forest and
grassland, and the ecotone area between.  We tested for differences in population
numbers and structure between these habitat types, using a mark-recapture study. 
In 1996, we expanded the project to include the use of PIT tags for detecting
overwintering survival and movement.  We found that the major species using
the area was the northern deer mouse (Peromyscus maniculatus), although
populations of the meadow vole (Microtus pennsylvanicus) increased in late fall. 
We examined the long-term data in light of metapopulation theory.  We
determined that the study area probably represents a source for deer mice
populations (births equal to or greater than deaths) and a sink for voles,
undergoing periodic extinctions.  We were also interested in home range size and
any changes in population structure.  Small mammal habitat use was heaviest in
the ecotone and woods areas.  Little use of the grassland habitat was recorded. 
The primary dispersers into the area initially were subadult males based on
recorded sizes and weights, although pregnant females were captured in Fall
1996.  Females were quite common in 1997.  The small number of recaptures
indicates a large population of deer mice in the area.  Also of interest is the lack
of voles in the grassland area.  This suggests that recolonization has only just
begun for this species following the summer floods of 1993 and the 1997 spring
flood.

Keywords:  small mammals, metapopulations, Peromyscus, Microtus, PIT tags,
succession


Christina Kocer
University of Dubuque
Dubuque, Iowa  52001
(319)589-3598
Fax (319)556-8633
email ckocer@univ.dbq.edu
Poster
Student Author