Environmental flow assessment in estuaries taking into consideration species dispersal in fragmented potential habitats

Abstract

Here, we propose an approach to environmental flow assessment that pays attention to species dispersal among fragmented potential habitat patches affected by river inflow and tidal currents in estuaries. The approach consists of three steps. In step one, potential suitable habitats were mapped and the Habitat Aggregation Index (HAI) was determined to understand the fragmentation of potential suitable habitats by integrating the requirements for critical environmental factors that have temporal and spatial variability. In the second step, an individual-based model was developed to simulate the dispersal of target species among potential habitat patches. The model provided the species distributions for altered hydrological processes. In the third step, environmental flows were defined by comparing the occupancy of suitable habitat patches by individual organisms and habitat aggregation for varying freshwater inflows. This approach was tested using a case study in the Yangtze River Estuary. We stressed the ecological importance of flood pulse, rather than average discharge, and recommend a Gaussian-type flood pulse, as provides a win-win point for both the numbers of individuals that could occupy suitable habitat and the HAI. We also demonstrated the importance of the peak flow and flood pulse duration in terms of affecting species distribution. Based on the results presented here, the proposed approach offers a flexible assessment of environmental flow for aquatic ecosystems.

Density‐dependent dispersal strategy of pollinator moderates the adverse effect of habitat loss on plant reproduction: An integrated model based on pollinators' behavioural response

“…The status of any given cell at time ( t ) depended on both its original status and the status of its neighbourhood at time ( t − 1). Cells with different statuses were transformed following the same rules regardless of differences in space and time (Zhang et al, 2017). An individual pollinator could move between plant patches according to its dispersal rate, dispersal direction and dispersal quantity.…”

“…Cells with different statuses were transformed following the same rules regardless of differences in space and time (Zhang et al, 2017).…”

“…Specifically, high-quality habitats with a suitable environment and sufficient resources are capable of supporting more pollinators than do low-quality habitats. Nevertheless, a higher conspecific density of pollinators can intensify intraspecific interactions and increase dispersal rate (Kun & Scheuring, 2006;Zhang et al, 2017). By promoting individual migration, the DDD strategy partly improves habitat utilization for dispersers and so can be viewed as an adaptive strategy for responding to intraspecific interactions (Bocedi et al, 2014;Zhang et al, 2018) To clarify the impact of pollinator dispersal strategy on plant reproduction, based on our previous field observations, we developed strategy alleviates the negative effect of habitat loss on plant production, and maintain plant population persistence.…”