The global increase in anthropogenic disturbances has introduced patterns of heterogeneity across many landscapes. Local disturbances are often studied from the perspective of the local habitat patch, where their direct effects on local community composition are more evident. However, local disturbances can have regional implications when connected to other patches within a metacommunity. Invasive species provide a unique opportunity for studying the influence of biologically induced disturbances on metacommunity dynamics, because invasive species are influential in structuring local communities and have a propensity for dispersing across landscapes, producing gradients in disturbance intensity. The invasive zebra mussel, Dreissena polymorpha, is widespread throughout the eastern USA and is having negative impacts on native communities. Using zebra mussels to induce disturbances in mesocosm zooplankton communities, we tested how the relative abundance of disturbed and undisturbed habitat patches within a metacommunity influenced community and metacommunity biodiversity and composition. The zebra mussels negatively affected pelagic zooplankton species richness, while facilitating the population growth of littoral species. Undisturbed communities mitigated disturbance‐induced local and regional pelagic species loss in heterogeneous metacommunities, while the fully disturbed metacommunity experienced significant losses of pelagic zooplankton at local and regional scales. Disturbed communities influenced undisturbed communities in heterogeneous metacommunities by increasing the densities of littoral zooplankton species. Overall, these results highlight the important effects that undisturbed habitat patches can have on mitigating species loss in locally disturbed patches and maintaining regional biodiversity in heterogeneous metacommunities.
Harmful algal blooms (HABs) diminish the utility of reservoirs for drinking water supply, irrigation, recreation, and ecosystem service provision. HABs decrease water quality and are a significant health concern in surface water bodies. Near real‐time monitoring of HABs in reservoirs and small water bodies is essential to understand the dynamics of turbidity and HAB formation. This study uses satellite imagery to remotely sense chlorophyll‐a concentrations (chl‐a), phycocyanin concentrations, and turbidity in two reservoirs, the Grand Lake O′ the Cherokees and Hudson Reservoir, OK, USA, to develop a tool for near real‐time monitoring of HABs. Landsat‐8 and Sentinel‐2 imagery from 2013 to 2017 and from 2015 to 2020 were used to train and test three different models that include multiple regression, support vector regression (SVR), and random forest regression (RFR). Performance was assessed by comparing the three models to estimate chl‐a, phycocyanin, and turbidity. The results showed that RFR achieved the best performance, with R2 values of 0.75, 0.82, and 0.79 for chl‐a, turbidity, and phycocyanin, while multiple regression had R2 values of 0.29, 0.51, and 0.46 and SVR had R2 values of 0.58, 0.62, and 0.61 on the testing datasets, respectively. This paper examines the potential of the developed open‐source satellite remote sensing tool for monitoring reservoirs in Oklahoma to assess spatial and temporal variations in surface water quality.
1. Aquatic ecosystems are biodiversity hot spots across many landscapes; therefore, the degradation of these habitats can lead to decreases in biodiversity across multiple scales. Salinisation is a global issue that threatens freshwater ecosystems by reducing water quality and local biodiversity. The effects of salinity on local processes have been studied extensively; however, the effects of salinisation or similar environmental stressors within a metacommunity (a dispersal network of several distinct communities) have not been explored.2. We tested how the spatial heterogeneity and the environmental contrast between freshwater and saline habitat patches influenced cladoceran biodiversity and species composition at local and regional scales in a metacommunity mesocosm experiment. We defined spatial heterogeneity as the proportion of freshwater to saltwater patches within the metacommunity, ranging from a freshwater-dominated metacommunity to a saltwater-dominated metacommunity. Environmental contrast was defined as the environmental distance between habitat patches along the salinity gradient in which low-contrast metacommunities consisted of freshwater and low-salinity patches and high-contrast metacommunities consisted of freshwater and high-salinity patches.3. We hypothesised that the α-richness of freshwater patches and metacommunity γ-richness would decrease as freshwater patches became less abundant along the spatial heterogeneity gradient in both low-and high-contrast metacommunities, because there would be fewer freshwater patches that could serve as source populations for declining populations. We hypothesised that low-contrast metacommunities would support more species across the spatial heterogeneity gradient than high-contrast metacommunities, because, via dispersal, low-salinity patches can support halotolerant freshwater species that can mitigate population declines in neighbouring freshwater patches, whereas` high-salinity patches will mostly support halophilic species, providing fewer potential colonisers to freshwater patches.4. We found that α-richness of freshwater mesocosms and metacommunity γ-richness declined in saline-dominated metacommunities regardless of the environmental contrast between the freshwater and saline mesocosms. We found that environmental contrast influenced freshwater and saline community composition | 593 MAUSBACH And dZIALOWSKI
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