Tania J. Siemens

MS/PhD student

Department of Natural Resources

Fernow Hall, Cornell University

Ithaca, NY  14853

Phone: (607) 254-7249

Fax: (607) 255-0349

Email: tjs35@cornell.edu

 

 

Research Interests:

 

I am interested in investigating how the presence and spread of invasive plants interacts with and influences ecological patterns and processes.  My Masters research looks at the impact of the rapidly spreading grass, Paspalum vaginatum, on aquatic communities in coastal lagoons in the Galapagos Islands, Ecuador.  P. vaginatum grows along the edges of the lagoons, forming large mats of vegetation and appears to be causing a shift from an aquatic to a terrestrial ecosystem.  Some of the smaller lagoons have already been completely covered by P. vaginatum.

 

I am pursuing my research interests in the Galapagos because islands are particularly vulnerable to invasions and their unique flora and fauna make them an international conservation priority.  In addition, the lagoon ecosystem on the Galapagos, with a growing human community nearby, provides an opportunity to incorporate human dimensions into the dynamic interaction between invasive species and ecological processes.  I hope my work will contribute to an improved understanding of the cumulative effects of human and invasive species on ecosystems and ultimately lead to sustainable and effective conservation management strategies.

 

My work represents a collaboration between Cornell University Ecology and Management of Invasive Plants Program and the Charles Darwin Foundation. 

 

Research Questions: 

 

My Masters research explores:

 

1)     How aquatic invertebrate communities and abundances change across the gradient of vegetation that is formed as P. vaginatum extends from the shoreline toward the open water.

2)     How aquatic invertebrate communities differ in P. vaginatum, mangrove, and open water habitats.  

 

Characterizing shifts in aquatic invertebrate abundance and community composition associated with the presence of P. vaginatum will provide empirical evidence of invasive plant impacts on aquatic ecosystems.  Additionally, it will help refine hypothesis about how P. vaginatum indirectly affects higher trophic levels in the lagoon ecosystem such as fish and birds, thus providing a more holistic view of the impact of invasive plants on ecosystems.

 

Approach:

 

In order to answer the above questions I conducted an observational study in which I established a sampling grid  over a gradient of P. vaginatum and Mangrove habitat.  The grid consisted of 10 rows and 7 columns resulting in 70 sample points.  At each sample point I measured habitat and community characteristics such as water depth, temperature, salinity, dissolved oxygen, P. vaginatum biomass, mangrove cover, and aquatic invertebrates. 

 

Preliminary Results:

 

I am currently in the process of analyzing my results statistically, but my initial data inspection suggests that aquatic invertebrate species richness is higher in both the P. vaginatum and the mangrove and lower in open water habitat.  In the open water species richness is low but there is a higher abundance of the important prey species (Trichcocorixa reticulata) than in P. vaginatum.

 

Implications:

 

My data suggests a P. vaginatum induced shift in invertebrate species abundances and community composition, which implies that P. vaginatum is changing the aquatic food web.  This result indicates that P. vaginatum may be reducing the amount of habitat available for aquatic prey items and thereby reducing prey availability for higher order aquatic predators such as fish and birds. 

 

 

 

Future Research Plans:

 

As I progress in my research, I plan to conduct enclosure experiments to isolate species interactions and removal experiments to test the direct impact of the P. vaginatum.  I also plan to measure and incorporate human impacts on the landscape in order to more fully understand the complex interactions and processes that shape the lagoon ecosystem.