The
introduction of non-indigenous species can have lasting impacts on
ecosystem structure, including shifts in food web dynamics, species
composition, and biodiversity. The Great Lakes and St. Lawrence
River in North America are host to 185 non-native species, as of
2007 (Great Lakes United,2009). While not all non-native
species cause disruptions to ecosystem
functioning, multiple species in the Great Lakes basin have
proven to be "invasive," establishing themselves in communities and negatively affecting
indigenous species through competition for food and space
resources, by preying on them, or through the indirect effects
of altered ecosystem dynamics.
The problem of invasive
species in the Great Lakes area has been
widely addressed with research and multiple preventative and
reparative efforts. The most effective and economical way to deal
with invasive species is considered to be focusing on their
prevention (Leung et al., 2002
), as control measures are not always
effective once a population has become established. Prevention
requires knowing about the species' current disrtibution, mechanisms
that enable spread, and their potential dispersal. For that reason,
surveying and monitoring are a key component to management as they enable
understanding of a species' current distribution.
There exists an ample
amount
of spatial data for the Lake Michigan Basin,
including the locations of recorded sightings for several invasive
species. Collaborative surveying efforts have allowed compilation of
this data, made
available by the Great Lakes Information Network. The distributions
of sea lampreys, quagga mussels, and zebra mussels in particular
have been documented in the waters inland of Lake
Michigan.
Sea lampreys are parasitic predators to many desirable fish
species (Fetterolf, 1980) and have been
known to have deterimental effects on their hosts, e.g. lake trout
in Lake Michigan (Lawrie, 1970).
Zebra Mussels
and
qu
agga mussels have been
shown to have significant impacts on ecosystem food webs as they are
filter feeders and therefore graze plankton (Nalepa,
2008). Zebra mussels
that adhere to in-water infrastructure such as water intake
pipes have been a nuissance and resulted in high costs associated
with their removal (O'Neill, 1997). Quagga mussels
have replaced some zebra mussels in nearshore areas and are able to
colonize deeper areas that limit survival of zebra mussels
(Nalepa, 2008).
The impact of having more than just one of these species present in
a community may be different from what is expected if only one
of them were present. That is because invaders may
directly or indirectly interact with one another, influencing
the way each of them interacts with the indigenous community.
Additionally, having more than one invasive species present may be
indicative of an "invasional meltdown," where the presence of
an invasive species makes it easier for others to join (Ricciardi,
2001).
Surveying for invasive species is
selective in nature. In addition to Lake Michigan, there are many
inland waterways that could serve as potential habitats, but
it is not always feasible
to devote resources
to actively monitor every single site all
of the time. When records are based on involvement by community members, success
depends on the participation and ability of individuals to identify
species.
Another important consideration is that Lake
Michigan is bordered by four
different
states (Michigan, Wisconsin, Indiana, and Illinois), separated into
numerous counties. Political and social differences between areas have
the potential to influence institutional and community willingness to
document sightings of these species. Since counties are
relatively small units but with administrative cohesiveness, they
can be targeted areas for fostering community participation. Explicitly identifying which counties are
currently the most affected and have
the potential to be affected can help promote monitoring efforts
where they are most needed based on likeliness of species
occurrence.
Using point data
showing the occurrence of sea lamprey, quagga mussels, and
zebra mussels; these species' relative abundances in each
surrounding county were mapped. The potential inland distributions of
these species were determined, and areas were identified where potential distributions for more
than one species overlapped. These areas
were mapped by county to highlight where monitoring should be particularly
emphasized, to enable maintenance of these valuable data
sets.