Connectivity, passability and heterogeneity interact to determine fish population persistence in river networks

Area of Science:

• Ecology
• Conservation Biology
• Population Dynamics

Background:

• Human-made structures like dams impede fish migration in watersheds.
• This lack of connectivity between fish subpopulations is linked to population declines.
• Existing connectivity indices may not fully capture population-level impacts of barriers.

Purpose of the Study:

• To model the impact of a single migration barrier on fish population growth rate.
• To investigate how barrier location and characteristics influence population dynamics.
• To compare demographic model results with existing connectivity indices.

Main Methods:

• Formulation of a matrix model for a spatially distributed fish population.
• Analysis of how barrier introduction and characteristics affect asymptotic population growth rate.
• Comparison of model outputs with the dendritic connectivity index.

Main Results:

• Barrier introduction can decrease population growth but may also increase it via a 'retention effect'.
• Obstacle-induced mortality significantly impacts population growth rate.
• The dendritic connectivity index fails to account for retention effects and obstacle mortality.

Conclusions:

• Structural connectivity indices are insufficient for predicting population persistence and extinction.
• Demographic models provide a more nuanced understanding of barrier impacts.
• Development of novel functional indices is needed for accurate conservation assessments.