Community ecology has long focused on processes that regulate patterns of species distribution and abundance. Not only have these processes taken on new significance in an era with significant biodiversity loss, but it has become clear that maintaining biodiversity is essential for maintaining ecosystem functions. Facing an era of anthropogenic global change and biodiversity loss, strategies of conservation biology are increasingly relevant. With this background, our research deals with temporal and spatial aspects of two of the biodiversity threats, namely fragmentation and eutrophication. Fragmentation of continuous habitat can lead to local extinction if there is no connection between newly isolated patches, but if patches are connected to an appropriate degree, building a so-called metacommunity, the regional population can persist longer than a single large patch. With habitat fragmentation becoming the norm, how metacommunities function, and how metacommunity dynamics interact with environmental stressors, are increasingly relevant questions. With the goal of understanding how eutrophication impacts biodiversity in a metacommunity landscape, we experimentally manipulated different ways to load nutrients to an aquatic model system. This eutrophication dissimilarity was created by adding nutrients either continuously with a peristaltic pump, or pulsed, pipetting once a week. In addition, two different landscapes (isolated patches and patchy landscapes) were also compared, resulting in 2X2 factorial treatment combination. The experimental community was composed by phytoplankton, as primary producers, and ciliates and micrometazoans as grazers. The data were analyzed with two-way repeated-measures ANOVA, with local and regional species Shannon diversity being estimated.
The biodiversity was measured for phytoplankton and zooplankton in regional and local scales, with the more relevant responses belonging to the regional scale. This two trophic levels presented different outcomes towards the experimental treatments. According to ANOVA, landscapes do not affect significantly the autotrophs diversity, but the difference in nutrient addition does, with higher diversity under the pulsed treatment. In contrast, grazers were intensely affected by the different landscapes, revealing higher diversity and more stable community under metacommunity landscape in combination of pulsed nutrient addition. Furthermore, grazers diversity was kept higher under continuous treatment when in isolated landscapes. In relation with resource use efficiency, the biomass ratio between prey and predator was higher under pulsed nutrient addition in metacommunities landscapes. These results revels that pulsed nutrient addition can increase or maintain the biodiversity of primary producers and grazers in comparison with continuously nutrient loading, with the proviso of metacommunity landscape condition for grazers.