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Because the escalating loss of species is one of the most serious environmental crises we face, it is vital that students of biology comprehend and can communicate the roles that biodiversity plays in the functioning of ecosystems. Here, we report on a laboratory experiment that has been highly successful in our introductory biology courses at demonstrating the role of biodiversity in the productivity of ecosystems. Students created microcosms consisting of six species of phytoplankton grown separately (monocultures) and in mixtures (polycultures) in 50-mL beakers. On average, monocultures were less productive than three-species polycultures, which in turn were less productive than six-species polycultures. However, the productivity of the polycultures was generally no greater than the productivity of the most productive monocultures--a result that suggests a lack of positive ecological interactions (e.g., facilitation or niche complementarity). In contrast, there was some evidence of negative interactions among species (e.g., predation and allelopathy) that caused some polycultures to be less productive than monocultures of their constituent species. Performing this structured-inquiry experiment provided students with an opportunity to apply aspects of the scientific method in a non-trivial manner to address issues of relevance to both basic ecology principles and applied disciplines with economic significance. [For "Using Algal Microcosms in Introductory Biology Lab. I: The Influence of Nutrient Levels on the Biodiversity of an Ecological Community," see EJ1285501.]

The protection of earth's biodiversity requires a sophisticated understanding of how human activities can affect the relative abundances of species in natural ecological communities. Here, we report on an introductory biology laboratory activity in which students quantified biodiversity while investigating one of the most important controls on the biodiversity of an ecosystem: nutrient availability. Students established microcosms of six species of phytoplankton ("algae") in 50-mL beakers and exposed them to five different levels of inorganic nutrients. After two weeks, students used hemocytometers to count cells and compare the relative abundances of the algal species (i.e., their community composition) at different nutrient levels. The effect of nutrient level on biodiversity (measured by Simpson's reciprocal index) was significantly curvilinear, and best described as "U-shaped." Specifically, the algal community was most diverse at the lowest nutrient level, least diverse with a small amount of added nutrients, and intermediate in diversity at the highest nutrient levels. This convenient, quantitative investigation provided students an opportunity to consider how anthropogenic influxes of nutrients into ecosystems can lead to eutrophication, and how this phenomenon can have negative effects by decreasing the biodiversity of ecological communities. [For "Using Algal Microcosms in Introductory Biology Lab. II: The Influence of Biodiversity on Ecosystem Productivity," see EJ1285505.]

Spatial dynamics can promote persistence of strongly interacting predators and prey. Theory predicts that spatial predator-prey systems are prone to long transients, meaning that the dynamics leading to persistence or extinction manifest over hundreds of generations. Furthermore, the form and duration of transients may be altered by spatial network structure. Few empirical studies have examined the importance of transients in spatial food webs, especially in a network context, due to the difficulty in collecting the large scale and long-term data required. We examined predator-prey dynamics in protist microcosms using three experimental spatial structures: isolated, river-like dendritic networks and regular lattice networks. Densities and patterns of occupancy were followed for both predators and prey over a time scale that equates to >100 predator and >500 prey generations. We found that predators persisted in dendritic and lattice networks whereas they went extinct in the isolated treatment. The dynamics leading to predator persistence played out over long transients with three distinct phases. The transient phases showed differences between dendritic and lattice structures, as did underlying patterns of occupancy. Spatial dynamics differed among organisms in different trophic positions. Predators showed higher local persistence in more connected bottles while prey showed this in more spatially isolated ones. Predictions based on spatial patterns of connectivity derived from metapopulation theory explained predator occupancy, while prey occupancy was better explained by predator occupancy. Our results strongly support the hypothesized role of spatial dynamics in promoting persistence in food webs, but that the dynamics ultimately leading to persistence may occur with long transients which in turn may be influenced by spatial network structure and trophic interactions.