Biosphere 2 Reexamined: Species Composition and Interactions Within a Human-Constructed Ecosystem

Abstract

All ecosystems on the planet today experience some sort of human impact, causing changes in network composition, species diversity, the presence of invasive speices. Understanding how species composition changes in human-disturbed ecosystems has never been more important, and can be studied within research facilities such as Biosphere 2, a structure with several biomes modeled on different ecosystem. This study examines the current arthropod species composition of Biosphere 2 through species surveys, and investigates a mutualism between ants and a mealybug (Hemiptera: Pesudococcidae), in the rainforest biome of Biosphere 2. The species surveys asked how species composition has changed since past surveys and how the species composition of Biosphere 2 compares to the surrounding desert area. Then, to determine the mutualism’s effects on mealybug numbers, four treatments were conducted: A+P+ (where ants and putative predators such as spiders were allowed access to mealybug populations), A-P+ (where ants were excluded but predators were allowed), A+P- (where ants were allowed but predators were excluded), and A-P- (where both ants and predators were excluded). I found species richness to have decreased within Biosphere 2 compared to past recorded invertebrate taxa numbers, as well as high abundances of Paratrechina longicornis, an invasive ant found in past surveys, within Biosphere 2. All genera of ants found within Biosphere 2 were also found in the surrounding desert area, suggesting Biosphere 2 is having an impact on the surrounding native ecosystem. To determine if a mutualism is occurring, and linear mixed models were run to compare differences in mealybug numbers from specific treatments to each other. I conclude the evidence for a mutualism is inconsistent and if one is occurring, the effect is extremely weak. In the future, species surveys and arthropod research within Biosphere 2 should be continued, to aid in further understanding of species composition and interactions in human-disturbed ecosystems.