Honors Program

Project Presenters

Maja Sljivar

Title: “The Plankton Standoff: Algal Digestion Resistance, Algal Growth Trade-off and the Implications for Zooplankton Grazers”

Major: Biology

Faculty Mentor:  Dr. Bill DeMott (Biology)

External Reviewer: Dr. Punya Nachappa (Biology)

Honors Program Council Liaison:  Dr. Timothy Grove (Physics)


Maja Sljivar is an international student from Serbia. She will be graduating in May 2014 with a double major in Biology and Anthropology. During her time at IPFW Maja worked on aquatic ecology research in Dr. Bill DeMott’s lab in the biology department. She is intending to pursue a similar academic path by attending IU Bloomington as a PhD student in Ecology, Evolution and Behavior. When she is not figuring out plankton interactions she hangs out at the local yoga studio, studying to be a yoga teacher.


We can observe two general principles of defense theory in any given food chain. (1) Most animal species are both predators and prey which implies the ability develop defenses against predation while overcoming the defenses of their prey. (2) These defenses have both costs and benefits leading to a trade-off in investment in defenses. We define trade-off as gaining one benefit at the cost of some other benefit. Thus, according to evolutionary theory, investment in defenses against predation leads to cost in other areas, such as slower growth or reduced competitive ability. Phytoplankton with defenses against zooplankton grazing tend to have slower maximal growth rates than undefended taxa. Algae with digestion defenses have an increased probability of surviving gut passage. Daphnia growth can be used as a measure of digestion defenses. Here, I present the results of research done in Dr. DeMott’s lab, working on isolating strains of Oocystis and other digestion resistant algae from local lakes in order to characterize the relationship between algal defenses (measured by Daphnia growth assays) and maximal algal growth rate. According to defense theory, algae with stronger defenses should have lower maximal growth rates.


Agrawal, A. (1998) Algal defense, grazers, and their interactions in aquatic trophic cascades. Acta Oecologica 19.4, 331-337.

DeMott, WR., EN. McKinney, and AJ. Tessier (2012) Ontogeny of digestion in Daphnia: implications for the effectiveness of algal defenses. Ecology 91.2, 540-548

DeMott, WR., and AJ. Tessier. (2002) Stoichiometric constraints vs. algal defenses: testing mechanisms of zooplankton food limitation. Ecology 83. 3412-3426.

DeMott, William R., and Ellen Van Donk. "Strong Interactions between Stoichiometric Constraints and Algal Defenses: Evidence from Population Dynamics of Daphnia and Algae in Phosphorus-limited Microcosms." Oecologia 171 (2013): 174-86.

Tessier, AJ., and P. Woodruff. (2002) Cryptic trophic cascade along a gradient of lake size. Ecology 83.5, 1263.

Yoshida, T., NG. Hairston Jr, and SP. Ellner. (2004) Evolutionary trade-off between defence against grazing and competitive ability in a simple unicellular alga, Chlorella vulgaris. Proc. R. Soc. B. 271, 1947-1953