Using algal microcosms in introductory biology lab - II - The influence of biodiversity on ecosystem productivity

Oct 15, 2026

Uploaded by Mary Man

Because accelerating species loss is a major environmental crisis, biology students must understand and communicate how biodiversity affects ecosystem functioning. This laboratory experiment demonstrates, in introductory courses, how biodiversity shapes productivity using algal microcosms. Students grow six phytoplankton species either as monocultures or in polycultures, comparing productivity patterns. Three-species polycultures outperform monocultures, and six-species polycultures outperform three-species, while polyculture gains often match best monocultures, indicating limited positive interactions and occasional negative effects.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages10

Reading Time25 min

AccessFree to download

Abstract

Introduction

Species richness and ecosystem productivity

Niche requirements and species interactions

Complementarity and niche complementarity

Facilitation and allelopathy

Sampling (selection) effects

Transgressive overyielding and interpretation

Using algal microcosms in introductory biology lab. II: The influence of biodiversity on ecosystem productivity Michael J. Wise1,2* and Rachel Collins2 1 Environmental Studies Program, Roanoke College, Salem, VA 24153 2 Department of Biology, Roanoke College, Salem, VA 24153 *[Corresponding author:](Corresponding author: wise@roanoke.edu)[ ](Corresponding author: wise@roanoke.edu)[wise@roanoke.edu](Corresponding author: wise@roanoke.edu) Abstract 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. Keywords: biodiversity, microcosms, niche complementarity, phytoplankton, productivity, species richness, structured inquiry, transgressive overyielding. Introduction The number of species present in an ecosystem (i.e., its species “richness”) is important from both a basic science and an applied perspective. Specifically, species richness can influence the stability and productivity of an ecosystem, which in turn affect the goods and services that ecosystems provide to benefit humans (Balvanera et al., 2006; Cardinale, 2011; Cardinale et al., 2011; Hooper et al., 2012; Gross et al., 2014; Liu, 2016) . A basic question is whether ecosystems composed of many species tend to be more productive than ecosystems composed of fewer species (Duffy, 2009; Willig, 2011; Stockenreiter et al., 2012; Yuan et al., 2015) . For managed ecosystems, a common question is which combinations of species should be propagated in order to maximize biomass production for food or fuel. The alteration of species richness can have a range of effects on the productivity of an ecosystem, depending on the niche requirements of the species and how the species interact. If two species in an environment use the same resources in the same manner, then their combined productivity when grown together (in a polyculture) is likely to be the average of their productivities when grown separately (in monocultures) . However, biological interactions may lead to a phenomenon called“complementarity,” such that the total productivity ina polyculture is greater than the productivities of any of the component species in monoculture (Cardinaleet al., 2007; Nalley et al., 2014; Brooker et al., 2015; Wendling et al., 2017) . For instance, if the two species do not use the same resources in the same manner, then the two species in a polyculture may use of the resources in an ecosystem more completely—a phenomenon known as “niche complementarity.” In addition, if one species is able to acquire a resource in abundance that the other species cannot (e.g., one species can fix nitrogen) or otherwise improves

FAQs

What is the main goal of this introductory biology lab experiment?

To help students understand and communicate how biodiversity influences ecosystem productivity by using a structured inquiry laboratory experiment with algal microcosms.

How were the microcosms designed in the experiment?

Students created microcosms containing six phytoplankton species grown separately as monocultures or together as polycultures in 50-mL beakers.

Why can polycultures be less productive than monocultures?

Negative interspecific interactions such as predation and allelopathy can reduce polyculture productivity below that of constituent monocultures.

Oct 15, 2026

Uploaded by Mary Man