BEES

1
Invasive Plant Effects on Pollinator Communities
Roxanne Foote University of Montana and Salish
Kootnai College, Project TRAIN
Figure 1 Yellow Pan Trap
Figure 5 Bombus (Apidae)
Introduction Invasive weeds are rapidly spreadi
ng at an alarming rate. For example, two common
weeds found in Montana are Dalmatian toadflax and
Spotted Knapweed (Fig. 3). Many weeds have
developed characteristics that make them
especially hardy. They can upset the natural
balance of the native ecosystem. Invasive plants
are non-native plants that were bought from
foreign places. They do not have natural enemies
here such as insects, fungi or diseases to
control theyre spread. Thus, they crowd out
native plants, increase erosion, and destroy
wildlife habitat, (http//www.mt.blm.gov/education
/weed/intro.html). No one has looked at the effe
cts invasive plants have on pollinator
communities. Pollinators are increasingly
threatened by this loss of habitat. When habitats
are fragmented by invasive weeds it could lead to
a decline the in diversity and abundance of
native pollinators (http//www.desertmuseum.org/
conservation/fp/monitor_threats.html).
To examine this, bees (the most important group
of pollinators) were trapped in three sites that
differed in plant composition,especially weed
abundance.
Abstract Invasive plants may decrease the abunda
nce and the generic level diversity of pollinator
communities. To test this, ten yellow pan traps
were set at three locations simultaneously once a
week for six consecutive weeks. Each field site
differed in plant composition. Across the sites
high percentages of weeds are associated with
lower numbers of bee genera (bee diversity). The
overall diversity of bees is negatively effected
by weed abundance and not the by total number of
plant species. The effect of invasive plants on
pollinator communities should be taken into
account in conservation and restoration efforts.
Vegetation Survey (Mt. Sentinel not shown)
Figure 7 Water Works Hill
Figure 6 Bandy Ranch
Results
Water works Hill was extremely weedy while Bandy
Ranch consisted of few weeds and mostly native
plants (Fig. 9-10), and Mt. Sentinel was
intermediate. Spotted knapweed (Fig. 3) and
yellow toad flax were among the most common weeds
found at the sites. Total number of individuals,
the number of families and number of genera were
recoded for each site (Table 1). Sites with
higher proportions of native plants also had an
increase in number of bee genera. Sites with
high percentage of weeds yielded fewer bee
genera. The total number of plant species appears
to have a less pronounced effect on bee generic
composition (Fig. 4).
Table 1 Bees Totals
Discussion and Conclusions We tested the hypothe
sis that Increased numbers of invasive plants
effect bee communities by (1) decreasing the bee
family and generic diversity and (2) decreasing
the overall abundance of bees. The data show
that Bandy Ranch and Mount Sentinel appear to be
very similar in terms of abundance and diversity
of bees. The site at Water works Hill which had
the most invasive plants had slightly fewer bees
overall and the least diversity of family and
genera. These preliminary results suggest tha
t it is the weeds that negatively effect bee
communities and not the diversity of flowering
plants at the site. However, better data would
be obtained if this experiment were started
earlier in the spring and carried further on into
the fall to account for seasonal differences in
bee species. Additional data analysis is needed
to check the significance of these results. The
issue of how invasive plants influence pollinator
community composition needs further study and is
important in plant conservation and restoration
efforts.
Materials and Methods The study was conducted fr
om June to August of 2001. Field sites were
located near Missoula at Mt. Sentinel, Water
Works Hill, and 50 miles north on the Bandy Ranch
(Fig. 2). Vegetation surveys were conducted at
each site to determine the percentage of invasive
versus native plants. A two meter diameter
circle located 3 meters east of each yellow pan
trap (see below) was examined for percentages of
bare ground, invasive grasses, native grasses,
native forbes, exotic forbes, and number of plant
species (Figs 8-9). Ten yellow pan traps
were set at each site using a GPS (Global
Positioning System) machine to replicate the
locations and the distances among pans. The
vegetation was clipped 20 cm from the center of
each pan to ensure visibility. To better
understand the yellow pan trap method refer to
Deville,1998 and to Fig. 1. The pans were filled
with a mixture of consisting of 4 liters of
water, 6 ml of Dawn dish detergent, and 2 ml
anise extract (to provide a fragrance) and were
set out at 10 AM and collected at 4 PM the same
day. This was done once a week for six
consecutive weeks. All three sites were trapped
on the same day to minimize effects of weather.
The bees were were separated from the
other insects. Female bees (95 of sample) were
pinned, sorted and identified to genus using The
Keys to the Bee Genera (Michener, et al. 1-179),
(Fig 5).
Literature Cited Cane, James H. 2001. Habitat F
ragmentation and Native Bees a Premature
Verdict?11-9. Deville, Naomi and Terry A. Wheele
r. 1998. The Effect of Different Preserving Fluid
on Insect Catches in Yellow Pan Traps.
Proceedings of the Entomological Society of
Ontario Vol 12931-37. Ingrum, Mrill, Gary P. Nab
han, Stephan L. Buchmann. Ten Essential
Reasons to Protect the Birds and the Bees.
11-8. Michener, Charles D., Ronald J. McGinley,
Bryan N. Danforth. 1994. The Bee Genera of
North America and Central America (Hymenoptera
Apoidae). 11-176. http//www.blm/gov//weed/weed
.html

• Acknowledgments
• Penelope Kukuk, University of Montana, Missoula
  MT - Mentor
  
• Pat Hurly and Marianne Luchkiw - Salish Kootnia
  College, Pablo MT - Project TRAIN staff
  
• Special Thanks to Joe Bruster of Bandy Ranch,
  Eric Sweet for plant field work, Jodi Behm and
  Besty Alexander for bee field work.
  
• Funded by The National Science Foundation

Number of Bee Genera
Figure 4 native forbes, weeds, and total
number of forbes versus the total number of bee
genera at each site
Figure 4. Spotted Knapweed (www.blm.gov/educatio
n/weed/photos.html)
Figure 2. Specimen collection at Bandy Ranch.