Brittany Huntington San Francisco State University, California

Biodiversity and Complexity: Niche Differentiation in an African Lake Overview Importance Findings Lake Tanganyika is an ideal system to test Increasing impacts from overfishing and My results suggest that habitat complexity plays the theory that complex support deforestation make it crucial that we an important role in structuring . greater . This lake has: understand the factors supporting the These trends warrant further research into niche • A highly diverse extraordinary biodiversity of this lake so that differentiation in this system. • Numerous endemic species, including littoral snails we can better protect this ecosystem.

• Distribution and diversity patterns that are poorly vs. Algal 1.8 Gastropod diversity vs. Algal Biomass Species Richness vs. GPP 12 10 e 2 2 1.4 = 0.4042 2 understood R = 0.3315 R 9 R = 0.6524 10 P = 0.0491 8 Scientific Approach 1 8 7 6 6 0.6

Species Richness Species 5 Species Richness 4 Ind H Diversity Shannon 0.2 4 Hypothesis 0.00 5.00 10.00 15.00 20.00 0.00 5.00 10.00 15.00 20.00 0.00 50.00 100.00 150.00 Sites with high benthic primary productivity (snail food supply) Benthic Algal Biomass (ug/cm2) Benthic Algal Biomass (ug/cm2) GPP (mg C / m2-h) and high habitat complexity (high niche complementarity) Fig 1Fig 2Fig 3 support greater diversity of snails. Fig 1 & 2 Increased primary productivity is correlated to decreased Observed snail distributions on rocky substrate species richness and diversity. Competitive exclusion may be Questions Measurements occurring in sites with greater food supply, allowing better • Is niche differentiation a potential explanation for • Benthic primary productivity using chlorophyll a competitors to dominate at the expense of poor competitors. concentrations and dissolved oxygen fixation. snail diversity and distributions? Fig 3 ‘Unimodal productivity pattern’ of species richness across a productivity gradient. Several animal communities have shown this • Are there any correlations between environmental • Habitat complexity using grain size variation (a), pattern, including marine snails (Rosenzweig, 1995)! factors and biodiversity? shoreline angle, and benthic structural complexity (b) Habitat Complexity • Diversity and distribution of snails using species richness,

Measures of Snail Diversity & Distribution 1 Structural Complexity vs. Diversity density and biomass (c, d) 1Structural Complexity vs. Evenness Species Richness 0.8 0.8 Density 0.6 0.6 0.4 0.4 Biomass 2 2 0.2 R = 0.6138 Evenness 0.2 = 0.7499 Simpson's 1-D Simpson's P = 0.0025R P = 0.0003 0 0 1 1.11.21.31.41.51.6 1 1.1 1.2 1.3 1.4 1.5 1.6 Rugosity Rugosity Measures of Productivity Measures of Habitat Complexity Fig 4 Fig 5 Benthic Algal Biomass Grain Size Variation Benthic Algal Biomass Grain Size Variation Fig 4 & 5 Structural complexity correlates positively with diversity. Gross Primary Productivity Shoreline Angle Gross Primary Productivity Shoreline Angle abc dEvenness (a component of the diversity measurement) accounts for (GPP) Structural Complexity Citations: Rosenzweig, M.L. 1995. Species Diversity in Space and Time. Cambridge Univ Press. 436 pgs. Research made possible by Dr. Ellinor Michel, Nyanza Project 2004 and the NSF (ATM#-0223920) this correlation.