Abstract

Understanding how plant fitness varies along natural gradients is critical for predicting responses to environmental change. However, individual vital rates are often used as fitness proxies without knowing how other vital rates vary. To address this gap, we investigated how water availability, plant-plant interactions and heterogeneity in shade and soil influenced emergence, survival, seed production, and population growth rates of nine annual plant species in semi-arid Western Australia. We sowed plots of seeds across a reserve, removed all neighbouring plants from half of the interaction neighbourhoods and altered precipitation using rainout shelters. We found high consistency among species' responses to abiotic and biotic factors. Most species exhibited opposing responses of different vital rates along a natural abiotic gradient which translated to neutral trends in population growth rates across the gradient. This research demonstrates the importance of demographic trade-offs and pitfalls of measuring a single vital rate as a fitness proxy.