Abundance, reproduction, and seed predation of an alpine plant decrease from the center toward the range limit

Area of Science:

• Ecology
• Evolutionary Biology
• Biogeography

Background:

• Biogeographic models predict declining population size, density, and reproduction at range edges due to environmental stress.
• Previous empirical tests often lacked comprehensive assessments of population and fitness traits.

Purpose of the Study:

• To empirically test biogeographic models by examining population size, density, and fitness-related traits of Carduus defloratus across its range.
• To investigate the factors contributing to reduced reproductive success at the northern range limit.

Main Methods:

• Studied 66 populations of Carduus defloratus along latitudinal and altitudinal gradients.
• Assessed population size, plant density, plant size, seed production, seed abortion, and insect parasitization.
• Analyzed fluctuating asymmetry as an indicator of developmental instability.

Main Results:

• Population size and density decreased, while plant size increased towards the range margin.
• Seed production significantly declined at the range margin, primarily due to increased seed abortion.
• Despite lower insect parasitization at the margin, viable seed production was substantially reduced.
• Fluctuating asymmetry was consistent across the range and unrelated to population size.

Conclusions:

• Findings partially support biogeographic models but highlight complex interactions affecting range limits.
• Increased seed abortion, not parasitization, is a key factor limiting reproduction at the range edge.
• Population size influences reproductive components, with larger populations exhibiting higher reproductive output.