Zooplankton community structure along a pollution gradient at fine geographical scales in river ecosystems: The importance of species sorting over dispersal

Abstract

The release of anthropogenic pollution into freshwater ecosystems has largely transformed biodiversity and its geographical distribution patterns globally. However, for many communities including ecologically crucial ones such as zooplankton, it is largely unknown how different communities respond to environmental pollution. Collectively, dispersal and species sorting are two competing processes in determining the structure and geographical distribution of zooplankton communities in running water ecosystems such as rivers. At fine geographical scales, dispersal is usually considered as the dominant factor; however, the relative role of species sorting has not been evaluated well, mainly because significant environmental gradients rarely exist along continuously flowing rivers. The Chaobai River in northern China represents a rare system, where a significant environmental gradient exists at fine scales. Here, we employed high-throughput sequencing to characterize complex zooplankton communities collected from the Chaobai River, and tested the relative roles of dispersal and species sorting in determining zooplankton community structure along the pollution gradient. Our results showed distinct patterns of zooplankton communities along the environmental gradient, and chemical pollutant-related factors such as total phosphorus and chlorophyll-a were identified as the major drivers for the observed patterns. Further partial redundancy analyses showed that species sorting overrode the effect of dispersal to shape local zooplankton community structure. Thus, our results reject the dispersal hypothesis and support the concept that species sorting caused by local pollution can largely determine the zooplankton community structure when significant environmental gradients exist at fine geographical scales in highly polluted running water ecosystems.

Testing clustering strategies for metabarcoding‐based investigation of community–environment interactions

“…PCR mix and programme were the same as Xiong et al. (). Briefly, PCRs were performed in a 25 μl volume consisting 1 × PCR buffer, 2 mM of Mg 2+ , 0.2 mM of dNTP, 0.4 μM of each primer, 2 U of Taq DNA polymerase (LA Taq , Takara Inc., Japan) and approximately 100 ng of genomic DNA.…”

“…In the DADA2 workflow, sequence reads were filtered using the standard filtering parameters (i.e., maxN = 0, truncQ = 2, rm.phix = TRUE and maxEE = 2) in the online pipeline suggested by Callahan et al. () and trimmed to 225 bp as suggested by our previous study (Xiong et al., ). Then error model parameter learning was carried out on the sequences passing the filtering step.…”

“…The increasing release of chemical pollutants into freshwater ecosystems has become a global ecological and environmental problem (Cai, Varis, & Yin, ; Nyenje, Foppen, Uhlenbrook, Kulabako, & Muwanga, ; Vörösmarty et al., ), causing a series of negative impacts such as biodiversity loss and consequent compromised provision of goods and services (Arthington, Naiman, Mcclain, & Nilsson, ; Chapin et al., ; Loreau et al., ). Such negative influence is particularly severe in highly exploited ecosystems, such as rivers and streams flowing through megacities (Sala et al., ; Xiong, Li, Chen, et al., ; Xiong, Ni, Chen, et al, ). Deep understanding of complex interactions between biological communities and environmental pollution, as well as mechanisms responsible for resulted patterns of communities, is essential for diagnosing causes and consequences of chemical pollutants and restoring impaired ecosystems in management programs (Geist, ).…”

“…Using a pollution gradient along the Chaobai River in the Haihe River Basin in Northern China (see more details in Xiong et al., ), we aimed to test potential influence of different clustering strategies (nonclustering and clustering with varied thresholds for OTU generation) on results in studying community–environment interactions. Particularly, we tested (a) to which degree did different clustering methods (nonclustering vs. clustering) influence the geographical distribution patterns of zooplankton communities along a pollution gradient?…”

Geographical distribution of zooplankton biodiversity in highly polluted running water ecosystems: Validation of fine‐scale species sorting hypothesis

“…Such a challenge is attributed to several aspects. First, the relative importance of these two processes is largely scale‐ and gradient‐ dependent (Heino, Melo, Siqueira, et al., ; Soininen, Korhonen, Karhu, & Vetterli, ; Xiong et al., ). At large geographical scales such as across basins, species sorting tends to be more important, as environmental gradients often exist at relatively large geographical scales (Heino, Melo, Bini, et al., ; Heino, Melo, Siqueira, et al., ).…”