Direct and indirect effects: estimating the contributions along individual pathways during transient dynamics

All species in a community directly and indirectly affect each other, often through many causal pathways. The effects along each pathway can vary in magnitude as densities fluctuate during transient dynamics. Quantifying the changes in these pathway-specific effects is important for understanding the drivers of population-level dynamics. I present two computational methods that decomposes the total effect of one species on another into contributions along individual pathways during transient dynamics. These methods yield insight into which processes and species interactions are the primary drivers of transient population-level dynamics and how the effects of individual pathways scale with the number of intermediary species, time length, and interspecific interaction strength. I apply the method to two parameterized models, answering questions about the magnitudes of top-down effects in an intraguild predation system and the mechanisms driving disease reduction in a host-parasite system, and how the answers change through time.