Simulating eutrophication in a metacommunity landscape – an aquatic model ecosystem

Abstract

Community ecology has long focused on processes that regulate patterns of species distribution and abundance. Facing an era of anthropogenic global change and biodiversity loss, strategies for conservation biology are increasingly relevant. Our research deals with temporal and spatial aspects of two of the main threats for biodiversity, namely eutrophication and fragmentation. It is known that pulsed nutrient addition increases phytoplankton diversity by allowing higher number of coexisting species1. Furthermore, the benefit of a metacommunity landscape with intermediate connectivity is increasing autotroph diversity2,3. However, it is yet unclear if those two factors are additive in increasing diversity and if these effects can exceed to the consumer level. With the goal of understanding how eutrophication impacts biodiversity in a metacommunity landscape, we hypothesized that pulsed nutrient addition will increase diversity not only among autotrophs, but also in their grazers, and this effect will be even greater in a metacommunity landscape. We simulated eutrophication and fragmentation in a microcosm experiment with three phytoplankton species as primary producers and 8 microzooplankton species as grazers. The nutrients were supplied either continuously, or in a pulsed fashion. In combination with the nutrient factor, two different landscapes were tested: an isolated patch and a metacommunity (interconnected patches). Biodiversity was estimated as Shannon diversity and richness at regional and local scales. Furthermore, betadiversity was performed to investigate the dissimilarity among patches. As expected, nutrient addition had a great effect on phytoplankton diversity, with highest diversity in pulsed treatments, whereas different landscapes did not affect their diversity. The opposite was observed for grazers. Metacommunity landscape was responsible for greater diversity of zooplankton, however, without significant effects of pulsed or continuous nutrient addition. The betadiversity of both trophic levels combined was influenced most by pulsing nutrients. We could confirm that higher diversity of phytoplankton is attained with pulsing nutrient addition, even under grazing pressure. However, was not possible to validate the extension of these effects to the zooplankton diversity, which was mostly influenced by the landscape. References: 1. Sommer U (1985) Comparison between Steady-State and Non-Steady State Competition - Experiments with Natural Phytoplankton. Limnol Oceanogr 30: 335-346. 2. Limberger R, Wickham SA (2012) Disturbance and diversity at two spatial scales. Oecologia 168: 785-795. 3. Steiner CF, Stockwell RD, Kalaimani V, Aqel Z (2013) Population synchrony and stability in environmentally forced metacommunities. Oikos 122: 1195–1206.