Assemblage organization over time prevents invasion success in phytoplankton

Invasion plays a central role in long-term species coexistence, sometimes rejuvenating and, at other times, collapsing diversity. Community resistance to invasions depends partly on the community’s species richness and structure, both of which change with community organization over time. Here, we study the resistance of phytoplankton assemblages to invasions based on varied initial species richness and structure, as well as assemblage organization over time. We hypothesize that invasion success will be greater in less organized assemblages and lower in more organized assemblages. To test this, we first experimentally constructed phytoplankton assemblages by mixing natural assemblages from regional lakes and manipulated richness along with a dilutional gradient as part of a large-scale mesocosm experiment. Phytoplankton assemblages from these mesocosms of varying dilution rate were selected and mixed to create unorganized assemblages of  high and low richness. We considered these c..., Invasion experiments were initiated at different times using water samples collected from an ongoing mesocosm experiment. That mesocosm experiment had manipulated initial species pool richness from natural phytoplankton assemblages. Those constructed assemblages then organized over time, allowing for these invasion experiments (Figure 1). In the sections below, this is described in detail.
Collection of phytoplankton assemblages
Integrated water column samples were gathered from the euphotic zones of three sub-Alpine lakes in Lower Austria during August 2022. The euphotic zones were estimated using 2.5 times the Secchi depth (Nõges et al. 2010). The lakes included Lake Lunz (N 47°85’37”, E 15°05’23”, dimictic, maximum depth 32 meters), Lake Erlaufsee (N 47°79’30”, E 15°27’08”, dimictic, maximum depth 30 meters), and Lake Purgstall (N 48°09’61”, E 15°13’62”, polymictic, maximum depth 3.5 meters). Samples were sieved through a 100 µm mesh in the field to remove large zooplankton and were ..., # Assemblage organization over time prevents invasion success in phytoplankton

Dataset DOI: [10.5061/dryad.73n5tb3bw](https://doi.org/10.5061/dryad.73n5tb3bw)

**Description of the data and file structure**

The data are from mesocosm experiments in which artificially assembled phytoplankton communities were allowed to organize over time. Two communities were used, one that started with low diversity and another that started with high diversity. During this period of organization, invasion experiments were conducted using aliquots from these mesocosms. The data is in a workbook. The first worksheet shows the cell count data of the invader from the start and end of the invasion experiment. Four invasion experiments were performed one after the other. The second worksheet shows the species composition of the phytoplankton communities as they organized over time.

**File: BEFree_Invasion_Exp_raw_data_plus_comm_data_2_(post_to_Dryad).xlsx**

In the first worksheet called 'counts of invader...,