Non-random loss scenarios in a natural phytoplankton community decrease diversity but not ecosystem functioning.

Engel, Friederike Gesine (2013) Non-random loss scenarios in a natural phytoplankton community decrease diversity but not ecosystem functioning. (Master thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 66 pp.

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Abstract

Natural and anthropogenic processes constantly lead to changes on our planet, which cause the loss of species in ecosystems. Mass extinction events have been observed throughout earth's history, but those extinctions were caused by natural processes. In recent years, species have been lost at extremely high rates due to human actions. Among the most severe manmade impacts on the ecosystems are global climate change and habitat destruction. Experiments have shown that communities with higher diversity (meaning higher richness and evenness) have better ecosystem functioning and are overall more resilient to change. Most experiments, however, used random extinction scenarios to come to this conclusion. It is important to know how non-random, realistic, changes in community composition can affect ecosystem functioning and the survival ability of communities, because extinctions are not random. They depend on many factors like population and body size, trophic position, or sensitivity to environmental change. In my experiment, I tested whether non-random removal of species in phytoplankton communities led to changes in diversity and ecosystem functioning. I used natural phytoplankton communities from the Kiel Fjord which were treated in three different ways prior to the experiment (dilution, heat stress, and filtration). I found that even though different species were lost in each of the treatments, which initially decreased species richness and changed community composition, this did not always translate into decreased final diversity or ecosystem functioning. Filtration did not change diversity or ecosystem functioning compared to the Control at all. However, extreme dilution decreased diversity which in turn had no effect on ecosystem functioning. Heat stress also decreased diversity, but increased ecosystem functioning. This shows that in my experiment, decreased richness and diversity did not decrease ecosystem functioning. I also found that due to low initial inoculum densities within-treatment variation was high in the dilution treatments as well as in the fine filtration (20 μm) treatment. This led to more variable responses in these treatments which made comparisons less reliable. The results show that manipulating initial diversity (and biomass) does not necessarily lead to a decrease in ecosystem functioning in a community. The final biomass depends on whether the remaining species can use the competitive release to their advantage to better take up nutrients. In this experiment, the communities could recover from the initial disturbance and the remaining species probably compensated for the loss of ecosystem functions previously performed by other species.

Document Type: Thesis (Master thesis)
Thesis Advisor: Sommer, Ulrich and Matthiessen, Birte
Subjects: Course of study: MSc Biological Oceanography
Research affiliation: OceanRep > GEOMAR > FB3 Marine Ecology > FB3-EOE-N Experimental Ecology - Food Webs
Date Deposited: 13 Dec 2013 09:20
Last Modified: 12 Jan 2022 10:19
URI: https://oceanrep.geomar.de/id/eprint/22630

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